All species are embedded in complex networks of interactions. ~ English ecologist Michael Pocock
There are 2 primary drivers of evolution: tolerance to environmental conditions and the ability to procure metabolic energy. Adaptation to the environment is expressed in myriad ways; likewise, energy procurement.
For those that can’t live off water and sunshine, meeting trophic needs is multifaceted, but boils down to what’s around to put on the menu. Animals adapt to consume others.
Plants play a vital role in the flow of energy through all ecological cycles. The whole system of life rests solidly on their industry, without which the evolution of many other organisms could not have occurred. ~ English biologists Martin Ingrouille & Bill Eddie
One way in which biota are categorized is by their consumptive role in an ecosystem: as giver or taker. Producers are primarily plants, along with marine algae. These are self-nourishing life: autotrophs requiring only what the Sun and inorganic elements provide.
Almost all other life are consumers: unable to fix for themselves the carbon needed to sustain their lives; so they consume other organisms. Consumers (heterotrophs) are generally recognized by primary feeding preference: herbivore, omnivore, or predator.
Preference is not always immediate necessity. Grizzly bears are considered carnivores, but can subsist on grass, at least for a while. A grizzly won’t last the winter if not fattened by eating much richer.
As consumers all eat other life, heterotrophs form food chains: hierarchies of consumption based upon who eats whom. Herbivores eat producers. Omnivores willingly eat producer or consumer.
At the top of the food chain are carnivorous predators, which eat other animals regardless of its prey’s food preference. Predators live off the flesh of others. Top predators are at the apex of the food chain.
Saprovores (aka detrivores), notably bacteria and fungi, delight in decaying organic matter, regardless of its origin as producer or consumer.
Saprovores are often first on the scene for a meal of carrion, but last in the trophic chain: the final consumer. Microbial saprovores are also known as decomposers.
Hierarchical food chains are aggregately stratified into trophic levels: a trophic pyramid.
The only things chewing into top predators are parasites and pathogenic microbes, in a process termed disease. By altering the interactions that occur between organisms at every level of the trophic pyramid, parasites and pathogens play an invisible but important role in food web dynamics.
The map of consumption among a biome’s biota is a food web, ranging in trophic flow from producer to consumer to decomposer. The food web is an intricate gyre. Diminishment of one biotic element in a food web can have rippling cascade effects, especially if the loss occurs lower on the food chain.
The turbulence of seawater affects how well marine bacteria are able to absorb nutrition. This stir can spill over onto the trophic abundance for animals that live further up the food chain.
Of all species living in and beside the river, the salmon is the most beautiful. ~ Canadian author Bruce Hutchison
The temperate coastal rainforest of British Columbia has some of the oldest and largest trees on Earth: up to 90 meters and 1,500 years old. The trees are watered by a network of rivers and tributaries and fertilized by the fish in them.
Pinkish pearls placidly float under gravel in a Pacific Northwest cold-water stream; the peaceful beginning of an otherwise tremendously turbulent life. Eggs are laid in the fall, and incubate over the winter, typically protected under a layer of snow and ice.
In late winter, the eggs hatch into alevins: tiny aquatic beings with enormous eyes, secured to bright orange sacs which are their food supply, which is a perfectly balanced diet. A good flow of pure water is essential to alevin survival.
Having eaten their sacs away, alevins emerge as fry in May and June. Free-swimming fry, some 2.5 cm long, are a tasty treat for larger fish. Mortality is at its highest at this stage.
Fry stay briefly where they hatched. They then travel downstream to the river, or upstream to a lake, depending upon the species; lingering from a few days to a year or more, as fingerlings that grow to 10 cm.
In a process called smolting fingerlings undergo physiological changes that enable them to survive in salt water. During the season of freshets – in the spring, with the rising of the river from snowmelt – smolt head to the sea.
Salmon savor their maturity in the ocean, growing rapidly by eating greedily on plankton and smaller fish, such as krill, herring, and pelagic amphipods (small crustaceans). Some species spend up to 8 years at sea, traveling in schools for thousands of kilometers throughout the north Pacific.
There are 5 known Pacific salmon species: chinook, chum, coho, pink, and sockeye.
Pink are the smallest adults (1–2.5 kg), and the most abundant. Their life cycle is but 2 years.
Coho are bigger than pink (2–4.5 kg average, though up to 9 kg may occur), and much more powerful swimmers. Coho can negotiate their way up waterfalls that pink could not dream of surmounting. Coho stay at sea 2 or 3 years before returning to spawn.
Chum have the widest distribution, and the 2nd-largest size (20 kg). Chum fry migrate directly to the sea soon after winning their fins. Their return to spawn varies from 2 to 7 years.
Sockeye are the most varied species by both look and lifestyle. The small kokanee (35 cm) live their lives in freshwater, never going to sea. Anadromous (migrating) sockeye spend a year in a freshwater lake after emergence, then 1 to 4 years at sea before returning to spawn.
Chinook adults can reach 45 kg. Chinook migrate to sea in their 1st year, typically within 3 months after becoming fry, but then spend much of the adulthood – 2 to 5 years – in coastal waters. They return to their natal river in the autumn to spawn.
Salmon are gregarious, with social ranking roughly corresponding to size. Top-drawer salmon are first to grab choice food morsels and are less likely to be preyed upon. Socially dominant chum salmon tend to have pronounced vertical markings, whereas subordinate chums are predominantly marked by horizontal patterns.
Migrating salmon are particularly susceptible to predation, so, while normally swimming at shallow depths, they prefer having a deep-water retreat in case of attack. The flashy sides of salmon can act as an illusion to confuse a predator, which may mistake a salmon for a much larger predator.
Ultimately, after years in coastal waters, if not out in the open sea, the biological clock goes off with the urge to spawn. Sexual maturity is typically felt at the onset of summer, though the time of year varies by species.
In preparation for their journey home, salmon separate into groups by native stream.
To facilitate their migration, Pacific salmon are born with an inherited magnetic map that allows them to knowledgeably navigate via geomagnetism.
Salmon sight is excellent, but nearsighted: 1 meter max in front of them. Perception of details is sharp. Salmon can see a full spectrum of colors: red, green, blue, and ultraviolet.
Salmon also have a terrific sense of smell. They can detect a drop of their home stream among 760,000 liters of sea water: 1 part in 100 million. In migrating to spawn, salmon hone in on their natal home by its smell.
Salmon also have sensitive tastes; but then, taste is an adjunct to smell.
Salmon hearing – via tiny inner ear bones termed otoliths – is attuned to high frequencies. Salmon also have the lateral line common to fish; especially apt for detection of nearby movement at the side, and for lower frequencies. The 2 perceptions mentally converge to provide senses of balance and depth.
Fish use the lateral line to localize the source of sudden sounds, and, more generally, to detect flows of water like we sense slight air flows. Fishes’ sense of their watery surroundings is analogous to land animals with an atmospheric environment. Evolution has respectively honed perceptiveness for both fluid mediums.
Salmon possess a well-developed sense of touch. They are quite sensitive to tactile sensation.
In the brackish waters before reentering freshwater, salmon go through profound physiological changes once again. The bodies of both sexes metamorphize for the trip home: toughening up, as well as transforming. Salmon skin thickens significantly to survive the upcoming battering on the rocks.
Some changes give females an advantage. Males grow a humped back, particularly noticeable in pink salmon – a handle that makes them more likely to be snatched up by predators. Males also turn a bright red; alluring to females, but also raising the risk of being easily spotted by predators.
Males widen into sumo form, making them more difficult for other males to wrestle with in the upcoming mating contests. Female abdomens swell, while their gums recede to expose their teeth.
Pacific salmon may travel up to 3,000 km to reach the same spot where they spawned. Arduous is an understatement for what the trip takes – “astounding stamina” a restraint of expression.
Salmon must swim upstream against a strong current, and repeatedly jump waterfalls of impressive heights: what to a human would be equivalent to leaping a 4-story building. Salmon may clock up to 32 kilometers per day in upstream travel.
They do this on little food. Many eat nothing on the trip home. Salmon may use up to 96% of their body fat in their marathon swim to their birthplace.
Salmon do take shortcuts, though the term is a laughable euphemism here. Salmon sometimes swim in tight schools upstream, the ones behind drafting on the wake of the chargers ahead. Lingering behind larger fish can reduce water drag by 50%.
Sockeye salmon may struggle upstream for a dozen days before taking a break; slipping into a side stream for a snooze. Many rest before leaping rapids.
The need for salmon to reach their birthplace to spawn is legend. But some salmon will settle for less.
Pink salmon seem less attached to their birth stream than other species. They have been seen spawning some 560 km from their natal nursery.
The way home is treacherous. Hungry bears, subsisting on grasses and greens before the arrival of salmon, wait in the streams to snatch salmon on the fly, or step on them in shallow waters as salmon take a siesta, before grabbing them up for dinner. Salmon are safe from bears in deeper water, as bears don’t like to get their ears wet.
Bears’ demand for salmon is ravenous. A single bear may kill 1,000 salmon or more during spawning season to fatten itself for winter. Bears depend upon the salmon run to survive the winter’s cold.
Other mammals and birds also make a feast of salmon on the run. Bald eagles snatch salmon out of streams from the skies. Salmon are a mainstay of the river otter diet, but run-time is an especial time of easy pickings.
Many species rely upon bear leftovers. Secondary scavenging feeds a host of animals: wolves, raccoons, shrews, and other small mammals, as well as numerous birds, less adept than eagles in their ability to order salmon takeout.
Mottled and tattered, nearly depleted to sinewy swimming skins, the remaining salmon reach their natal nook. The males compete for the haggard females with threat displays, jostles, and fights.
Females require courtship before committing to digging a nest. A male dances in the water nearby, then slides over a female’s back in a caress. A male’s change to bright coloration before the swim upstream, whatever the enhanced risk of predation, now pays off in female appreciation.
Fights between the females for prime nesting sites is common. They will bite at each other: at the gills or tearing at the tail to win an appealing nesting spot.
Salmon are fussy about where they mate. The water must be clear, cool, fast-flowing, and devoid of predators. The gravel must be pebbles rather than smallish stone bits.
A female prepares a nest in the streambed gravel by sweeping digs with her tail. The task may take days. By the time she is done, her tail is typically frayed and torn.
Meanwhile, as a tension reliever, some nerve-racked males may dig nests of their own. These never get used for eggs, but this displacement behavior takes the edge off the wait.
When ready, a female bends her body into a U, dropping her anal fin into the nest as a tempt. This positioning excites the male. He hovers close by. Upon his approach, she dips her back fin in again.
Often both of the mating salmons’ mouths open from the tension release. With a delicate quiver, the female lays her eggs, which a male duly fertilizes with a cloud of sperm (milt). Salmon sex per se may take less than 20 seconds.
Depending upon the species and size, each female has 4–5 nests, laying 500–5,200 eggs per nest. Each male milt is loaded with 50 million sperm.
The female then carefully covers the eggs by fanning nearby gravel with her tail. She then builds her next nest a bit upstream. This routine is repeated until she is exhausted. The set of nests, a female’s redd, are her legacy.
A mother-to-be may have enough energy to guard her redd for a few days, adding gravel and chasing off other females that might disturb her nests, to try to replace them with their own. Eventually she joins others rocking in the wake of the river, awaiting her last breath.
Males that outlast their mates will try for another mate: another ticket in life’s lottery. Only 1 in 2,000 eggs that hatch survive to spawn. That’s after the 85–90% of eggs that die before hatching.
The urge to live is strong, even as the life force is waning. Some exhausted salmon struggle to the center of the stream, where the water flow is strongest, and life-giving oxygen rushing over their failing gills the richest.
All these moments will be lost, in time, like tears in rain. Time to die. ~ Roy Batty in the movie Blade Runner (1982)
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Pacific salmon live a much more dramatic life than their Atlantic cousins, which face a relative jaunt upstream to spawn. Some 6% of Atlantic salmon survive spawning and return to the sea.
In the Pacific, some steelhead salmon may live to return to the sea. Some 6–30% of those that do may make one more spawning trip home to freshwater.
Gulls, bears, and other animals rely upon the short summer buffet of salmon to survive the rest of the year. Salmon predators move from stream to stream, following the slightly warming water temperatures that trigger spawning at different locations.
This hydrological diversity in the network of spawning streams affords a tripling of the time that salmon eaters enjoy: from a few weeks to 3 months or more. This is possible because the streams are but a kilometer or 2 apart.
Courtesy of bears, salmon play an outsized role in growing the gigantic coniferous forests that filter the snowmelt into the pure water that flows past their eggs. Having snagged a snack, bears casually haul their salmon into the woods. Facing overwhelming abundance, bears are sloppy eaters: consuming less than 25% of the biomass they have caught. Large chunks are left uneaten.
Rich in bio-nutrients, caught salmon fertilize the firs and pines after feeding the insects that swarm on the carcasses. Salmon discards by bears are equivalent to 4,000 km per hectare of commercial fertilizer, though much more valuable in readily accessible nitrogen.
20% of the streamside nitrogen in the soil comes directly from the decayed salmon; 20–30% from the insect consumers of the bears’ leftovers.
Kneeling angelica are 1- to 2-meter plants that reside near salmon streams. They produce clusters of tiny white blossoms, but quite late in the season, long after most pollinating insects are gone.
Blow flies lay their eggs on salmon carcasses. Before laying their eggs, the blowflies feast on nectar and spread pollen from the only flower about: kneeling angelica.
Dead salmon left in the stream provide food for emerging alevin. Juvenile salmon grow twice as fast in streams rich with salmon carcasses.
Part of the growth effect is indirect. Solvent salmon are savored by plankton, thus providing a food source for the fry of the next generation.
Salmon are prey in freshwater. They are predators only in the ocean.
In the finale, salmon returning from the sea to spawn inland represents a substantial transfer of nutrients from the ocean to terrestrial life. In life and death, salmon are a keystone species.
The oceans are diverse but sparsely populated; altogether holding only half of the planet’s biota.
Of the 33 animal phyla, 30 are ocean residents; 15 exclusively so. Only 16 phyla are on land or freshwater, and only one is exclusively terrestrial.
The land is a more competitive biome. Thus, while oceanic phyla diversity is considerable, species diversity is sparse.
5 to 50 million macroscopic terrestrial species exist, mostly vascular plants and insects, which are the land’s earliest large inhabitants. In the oceans, an estimated 450,000 species are extant; a figure unlikely to break 1 million at most, microbes excluded.
The air and ocean as much different media go a long way to explaining how life differs between the two. Seawater is 800 times as dense as air, and vastly more viscous.
Sunlight does not penetrate the deep, and so most marine organisms are found in the upper waters, feeding on the plankton and those that feed on the plankton.
Phytoplankton are crucial oceanic producers. Their density varies by region, as they depend on certain nutrients, notably B vitamins. Without enough vitamins in the water a local food web is never spun.
The large algae and aquatic plants that dwell on the bottom do so only in shallow coastal waters, and so contribute little to overall bioproductivity.
The ocean lacks much plant life because it lacks vital nutrients. Nitrogen and phosphorus are only 1/10,000th of that found in fertile soil. Whence the happy evolution of land plants. The more abundant and relatively long-lived terrestrial producer base explains the grater fecundity of animal life on land.
Unlike terrestrial trees that may survive for centuries, plant life turnover in the ocean is rapid. Dead oceanic organic matter, mostly phytoplankton and zooplankton, drop into the deep and dissolve. This marine snow is part of the food web.
Before heading into the deep, let’s first glance a life near the surface of the seas.
Coral Reef Gardeners
Coral reefs are the rainforests of the sea; forming some of the most diverse ecosystems on Earth. Though they occupy less than 0.1% of the world’s ocean surface, coral reefs are home to 25% of all marine species. Coral is one of the most important keystone species on the planet.
Paradoxically, coral reefs flourish even when surrounded by otherwise nutrient-poor water. They can do so because of their little friends. Coral have beneficial viruses, bacteria, algae, and fungi as microbial symbionts (microbiome).
Colorful damselfish live in tropical coral reefs. They eat small crustaceans, plankton, and algae. But not just any algae. Damselfish lack the digestive enzymes to consume many kinds of algae. But red alga is scrumptious. So damselfish cultivate gardens of red alga on the reefs. They pluck unwanted algae varieties from their territories and dispose of them at a distance. They weed out invasive plants. They chase away troublesome invaders, such as sea urchins, which would trample their fields. Protected red alga turfs thrive, affording damselfish abundant dining on one of their favorite foods.
Punishment can help to sustain cooperation where it would otherwise fail. ~ English zoologist Nichola Raihani
Cosmopolitan coral reefs make an irresistible place for ectoparasites to feed. Fortunately, blighted fish can get cleaned free of charge. Cleaner fish, such as the cleaner wrasse, work hard at keeping their clients unsullied.
Cleaning is competitive. Cleaner fish provide a higher-quality cleaning service when competitors are around.
An individual wrasse inspects as many as 2,300 fish a day, consuming up to 1,200 parasites from clientele. This sums to 7% of a wrasse’s body weight.
Each male cleaner wrasse holds a territory which encompasses several female breeding partners. For cleaning services, cleaner wrasse often work in pairs: a male and a female.
Although the service that cleaner wrasse provide is removing skin ectoparasites, they prefer to feed on client tissue. A client won’t sit still for that.
In order to receive a good cleaning service, clients require cleaners to cooperate by feeding against their preference. Clients achieve this either by avoiding cleaners they observe cheating other clients, avoiding cleaning stations where they have received a poor service in the past, or aggressively punishing cheating cleaners. ~ Nichola Raihani
Male wrasse keep their ladies in line; punishing them for cheating by aggressively chasing after them. The larger the client, the more esteemed. To females who cheat, male cleaners mete out a level of punishment commensurate with how valuable the client was.
Female wrasse may switch sex if they become as big as their partner. This is the real incentive for male wrasse to keep females in line, beyond the immediate problem of losing clients. A female that eats too well becomes a competitor.
In contrast to wrasse, Caribbean cleaner gobies do not change sex. Male gobies do not punish females that cheat.
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The service provided by cleaner fish is invaluable to clients. Fish that fail to go to the cleaners have 5 times as many ectoparasites as those that do.
Fish cleaning is not without hazard, and not just from snappy clients or greedy workmates. Cleaner shrimp form monogamous pairs that claim exclusive service areas. Competitors are eliminated, typically during the night while shedding old skin, when they are momentarily more vulnerable.
There’s still a lot we don’t know. ~ Australian marine biologist Julie McInnes in 2018
The marine food web is little understood. Biologists long ignored the abundant jellyfish, as the gelatinous animals are 95% water and provide scant calories.
Jellyfish are ubiquitous in the world’s oceans and can occur in very high densities. Yet they have long been considered trophic dead ends that are ignored by most predators because of their low nutritional content. ~ Australian marine biologist Graeme Hays
Many sea creatures, from tuna to turtles to penguins, seek jellyfish to eat.
The more we look, the more animals are feeding on jellyfish. They’re absolutely, really important. ~ Irish marine biologist Thomas Doyle
There’s a lot more to jellyfish than jelly. Our perception has switched hugely. It’s almost a reboot of jellyfish ecology as a central part of the ocean system. ~ Irish marine biologist Jonathan Houghton in 2018
The ocean is temperature-stratified (thermoclines). The uppermost shell is warmed by the Sun, at least in the tropics.
Just below is a mixed surface layer. Winds and tides mix the water, but the biota there also do their part, including the copious congregations of jellyfish. Even zooplankton are substantial contributors to the mixing. All told, life in the near-surface layer contributes as much to mixing as the wind and waves. This mixing provides for both oxygenation and distribution of warmth to a greater depth.
Below the thermally mixed layer is a narrow thermocline that separates the warm surface water from the colder and heavier water beneath. At the poles, much of the ocean is equally cold.
Though life concentrates near the surface, it is the cold, heavy water in the deep that revitalizes the food web. The marine snow of organic detritus drops down in prodigious volumes. Most marine snow is consumed within the top 1,000 meters, but a considerable quantity reaches the deep. Upwelling cold-water currents return that nutrient-rich supply toward the surface.
The richest concentrations of sea life occur where these cold currents come up. Near the coast, where steady winds sweep warm surface waters offshore, deep-water rises to fill the displacement. In temperate regions, winter storms churn the water, delivering cold comfort to life there.
In the tropics, the separation of warmth at the surface and cold at depth is so great the even hurricanes and typhoons cannot thoroughly mix the two. Tropical seas stay crystal clear, bereft of the microscopic clouds that bring fine dining from below.
On land, oxygen is available at a fairly constant level: 210 milliliters per liter. At sea, usable oxygen enters only at the surface.
Because most of the water in the deep ocean originated on the surface, in or near the polar regions where it sank, it holds the most dissolved oxygen. These down-welled water masses may spend centuries in the deep before rising again. As life is sparse there, oxygen is rarely depleted.
The intermediate depths are where oxygen is at a minimum. In the Pacific Ocean, the oxygen minimum zone (OMZ) is between 500 and 1,000 meters down. Oxygen may be only 1/30th of its concentration on the surface.
Only a few organisms are adapted to living in this band of oxygen-poor water. The vampire squid is one; the only cephalopod to tolerate the OMZ.
The vampire squid is something of a hybrid of squid and octopus; a living relic; the only modern representative of cephalopods before they split into 2 groups: one with 8 limbs, the other 10.
A vampire squid has 8 arms that are webbed together. It propels itself through the water by flapping 2 small fins, 1 on each side of the mantle.
Inside webbed limbs are 2 tactile filaments, which can extend well past their arms. These filaments let vampire squid forage.
Vampire squid are saprovores: feeding on marine snow and other detrital matter that comes around.
This relic is admirably adapted. Vampire squid can breathe normally when oxygen is just 3%. Their metabolic rate is the lowest of all deep-sea cephalopods. Their gills cover an especially large surface area. Their blue blood’s hemocyanin binds and transports oxygen most efficiently.
To help minimize physical requirements, the gelatinous tissues of vampire squid closely match the density of the surrounding seawater. Vampire squid have weak musculature but are able to stay agile and maintain buoyancy with minimal effort, thanks to balancing organs (statocysts) which are similar to the human inner ear.
Life in the slow lane has its advantages. Whereas all other soft-bodied creatures like it (coleoids) have a single reproductive cycle, vampire squid have multiple reproductive cycles.
Vampire squid are covered in photophores: tiny light-producing organs. They can exercise exquisite control over this multitude of luminescent spots: able to produce disorienting flashes of light for up to several minutes.
If threatened, the vampire squid releases a dazzling luminescent mucus from its arm tips that lets it disappear into the blackness without having to swim far.
This self-limited lifestyle has a large payoff. The only predators that vampire squid have are those transiently passing through the OMZ.
Pressure is another challenge in the deep, though less than lacking oxygen. Many invertebrates and some fish can tolerate trips between the surface and a kilometer down.
In the deep sea, life’s diversity is high, but density is quite low. Marine snow can only feed so many. The food pyramid is small.
Those creatures that live in deep waters have adapted in various ways. They tend to be sluggish, and often gelatinous.
Calcium carbonate is hard to come by, and so skeletons are lightweight if they exist at all. Fish that live midwater tend to be small; typically, no more than 20 centimeters.
Invertebrates are not so restricted. Comb jellies become the size of basketballs. Giant squid may reach 20 meters. Siphonophores can be twice that. With a body length of up to 50 meters, the giant siphonophore is the longest sea life.
These marine invertebrates that resemble jellyfish are colonial. Each is comprised of innumerable, tiny, connected individuals – zooids – each with a specific function (feeding, defense, et cetera), energetically and communicatively coordinated into an acting organism.
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The dark is the final frontier of the deep, and so 90% of midwater creatures provide their own light. Bioluminescence offers several advantages beyond being able to see, including communicating to one’s own kind, luring prey, and startling predators. Some can even put an “eat me” sign on an advancing predator by releasing a sticky, glowing tissue that coats the attacker, making it more vulnerable to its predator.
At a few hundred meters depth, dim sunlight still penetrates. A bit of bioluminescence lets a creature blend in so as to be invisible from below.
Although able to flash light, fishes tend to be black, crustaceans red. Large comb jellies and jellyfish prefer purple or red as well. Long wavelength red light does not penetrate the deep, and so reddish hues are effective camouflage.
Top carnivores have no need to hide, and so seldom take such solemn tones of appearance. Tuna, seals, sea lions, dolphins, and whales come and go as they please.
Almost nothing is known of predation in the deep ocean – such as how a sperm whale can dive a kilometer and snag a giant squid.
The assortment of life on Earth is almost unimaginable: in size, shape, look, function, metabolism, and reproduction. Yet all life is locked into biochemical cycles of energy production that sustains trophic webs.
Sunlight is transformed by plant photosynthesis into usable energy, giving animals oxygen to breath, and the plants themselves become fodder for animals.
Interactions among species are the ties that bind communities together. ~ American ecological zoologist Mariano Rodriguez-Cabal et al
Organisms constantly interact with each other in a wide variety of ways. Meaningful relations most often involve food; sometimes shelter or other protection which amounts to not becoming food.
The ecological networks that emerge from these interactions strongly influence the population dynamics of species. In times of a relative environment equanimity, the gyres of these networks tend to stabilize into patterns of population activity.
Symbiosis is one of the fundamental mechanisms by which ecosystems become productive and robust. ~ Dutch evolutionary biologist Geerat Vermeij
Many plants get essential nutrients, notably nitrogen, by intimate association with bacteria and fungi. Fungi even provide health care to plants.
Sophisticated chemo-communication creates and maintains relationships. When first rooting, plants put out a chemical advertisement that bacteria and fungi respond to.
Microbes ubiquitously have symbiotic relationships with large organisms – macrobes – in every way: mutualistic, commensal, and parasitic. For multicellular eukaryotes, some microbial relations are vital.
Macrobes are cellular colonies, living symbiotically with microbes as a symbiorg. Every plant and every animal comprise a community: a macrobial host relying upon its microbiome for most every aspect of living, including metabolism, bodily defense (immune system), intelligence, reproduction, and many other functions. From a microbial perspective, multicellular organisms increase the number of venues in which they may thrive.
Beyond the microbiome, microbes are the foundation of a balanced ecosystem; the living framework of intricate, interdependent relationships among larger life and the environment.
Marine Microbe Synchrony
We usually think of the ocean as a big stew, but now we see a coordination that could involve ‘talking’ between microbes, timing with the day, and responding to the environment. ~ American microbiologist Elizabeth Ottesen
Marine microbes bifurcate into phytoplankton that photosynthesize to feed themselves and heterotrophs that live off others. As the open ocean is a nutritional desert, the heterotrophs are hard-pressed.
Cyanobacteria rise to the surface during the day to collect sunlight and sink at night in respite. They naturally time their gene expression cycles to match their diurnal activity.
Heterotrophic bacterioplankton in the community do likewise. This concurrent choreography helps the heterotrophs get enough to eat.
Such synchrony is universal. Marine microbe communities throughout the world display strikingly similar rhythms in their metabolic patterns.
Extremely different ecosystems exhibit very similar diel cycles, driven largely by sunlight and interspecies microbial interactions. ~ American marine microbiologist Frank Aylward
While some relations among organisms are readily appar-ent, most are not easily observed.
The distribution of plants has long bemused botanists. Certain plants live in widely separated places. The same plant may live in the upper reaches of North America and the tip of South America, but nowhere in-between.
Migratory birds may trap and carry in their feathers small plant parts with them on their journeys. Mosses, which are especially rugged, are common passengers. After a bird cleans itself from the trek, deposited stowa-ways establish a new population in a new land.
Witches’ broom is a woody plant disease that provokes bushy tumors, caused by phytoplasma, which are parasitic bacteria that live in plant phloem tissue.
Phytoplasma tweak the molecular switches inside an infected plant so that flowers develop like leaves. This bacterial interference creates more soft tissue that leafhoppers like to suck sap from. Phytoplasma thus create an advertisement for their transport.
A leafhopper comes and sucks a plant’s phloem juices, infecting itself with phytoplasma. On succeeding stops, the leafhopper passes the disease on to other plants.
Phytoplasma hijack a plant’s developmental machinery and make it work to their advantage and the plant’s detriment, since leaf-like flowers are sterile. The leafhopper acts as a middleman, unharmed by the commensal relationship with phytoplasma, which alter their gene expression depending upon their current host.
Mutualism is sometimes termed true symbiosis – each interdependent party gains. Mutualism is a product of coevolution: a process of evolving mutual dependency.
Symbioses are pervasive throughout the tree of life. ~ Canadian evolutionary biologist Jeffrey Joy
Most people think symbiosis means there is an evolution toward harmony, a perfect balance of the two partners. ~ Italian evolutionary biologist Vittorio Boscaro
Endosymbiosis allows hosts to acquire new functional traits, such that the combined host and endosymbiont can exploit vacant ecological niches and occupy novel environments; consequently, endosymbiosis affects the structure and function of ecosystems. However, for many endosymbioses, it is unknown whether their evolutionary basis is mutualism or exploitation. ~ English ecologist Christopher Lowe
Eukaryotes arose through coevolution between an archaeal host and a bacterial endosymbiont. The original nature of the association between the two is unclear. It may not have been mutually beneficial.
What we have always thought of as mutualism, where species gain mutual benefit from interacting with each other, might actually be based on exploitation, where one species gains by capturing and then taking resources from another. ~ Christopher Lowe
Euplotes is a single-celled, ciliate protozoan that incorporates a freshwater bacterium as an endosymbiont: Polynucleobacter. These bacteria live within Euplotes for a time, but the relationship does not last.
They’re being replaced, just like you change your clothes. You take advantage of your symbiont until it’s no longer useful, and then you get a new one. The relationship is more like death row than cooperation; sure, the symbiont is kept safe and well-fed in the short term, but ultimately it’s not a good place to be. ~ Canadian microbiologist Patrick Keeling
Microbes are major mutualists. A ubiquitous mutualism is between digestive bacteria and their animal hosts. The mutual relations between plants and nutrient-providing soil microbes are analogous.
Among themselves, numerous plants and animals have mutually beneficial relations. Plant pollination by insects or birds is exemplary.
Mutualistic networks such as plant-pollinator communities are “nested.” Specialist pollinator species visit plant species that are subsets of those visited by more generalist pollinators. Nestedness prevails because it stabilizes mutualistic networks. ~ Indian biologist Samraat Pawar
Hydrothermal vents are a likely location for life on Earth having got its start. These steaming fissures in the seabed are chemically rich.
Early evolved prokaryotes dined there on the finest high-energy molecules: double-shot hydrogen (H2), methane (CH4) and high-octane hydrogen sulfide gas (H2S). Channeling cosmic power, these microbes suckled the favored fuel of stars: hydrogen.
Later-evolved life gets by in this horridly hot habitat by relying upon the descendants of early residents. Many, including tubeworms and mussels, shelter the wee hydrogen-fueled powerhouses within, feeding off their leftovers. For these animals, foraging is as simple as funneling water into themselves and letting their microbiome do the rest.
Bean Bugs & Burkholderia
The most intimate mutualism is the relationship between multicellular organisms and their microbiomes. The little ones look after their host.
The bean bug is an agricultural pest. Its prospects in a field sprayed with insecticide would be dim without a friend on the inside.
Bean bugs invariably ingest Burkholderia bacteria, which live in the dirt. Burkholderia have the happy knack of being able digest and disarm a commonly applied insecticide, thus saving the bean bug from terminal indigestion.
The Nematode & Its Killer Bacteria
Microbial populations stochastically generate variants with strikingly different properties, such as virulence or avirulence and antibiotic tolerance or sensitivity. ~ Indian bacteriologist Vishal Somvanshi et al
Heterorhabditis bacteriophora is a nematode that infects insects. Nestled inside it is Photorhabdus luminescens, a bioluminescent bacterium that is an accomplice to its host in eating insects from the inside out.
A juvenile nematode penetrates an insect victim, whereupon it vomits its intestinal symbionts into the insect’s body cavity (hemocoel).
Once outside the worm and inside the insect, the bacteria grow exponentially and secrete potent insecticidal toxins. P. luminescens prepares the insect for nematode reproduction by producing helpful proteins, as well as antimicrobials that defend the insect cadaver from its own competitors.
The bacteria transform from tiny benign mutualist inside the nematode into an engorged pathogenic insect slayer by flipping a genetic switch.
Ants in Fiji farm plants. They carry the seeds of the Squamellaria plant and insert them into cracks in trees, where the seeds germinate. The ants fertilize the seedlings with their wastes. When the plants sufficiently mature, the ants take up residence in the cavities that the plants provide. This potted homebuilding has been going on for 3 million years.
Pseudomyrmex is a genus of wasp-like, stinging ants. Certain Neotropical Pseudomyrmex – tree ants – diligently defend the trees in which they reside. Triplaris, the ant tree, provides room and board for the tree ants, which prune any foreign seedlings they find near the tree. The tree ant is a protector of and gardener for its ant tree.
These ants are very protective of their host tree. It doesn’t matter if it’s an animal or another plant species – they’re going to attack it. ~ biologist Jorge Vivanco
An arboreal ant lives in the leaf pockets of the Amazonian ant-plant. The ants protect the plants from leaf-eating insects.
On the host plant’s stems, worker ants build galleried structures which they employ as traps to capture larger insects. First, they cut plant hairs (trichomes) along the stem construction site to clear a path. Next, using uncut trichomes as pillars, the ants build a gallery by binding the cut plant hairs together using a sappy regurgitated compound. They leave enough room to maneuver between the stem and the surface of the structure, creating a vault.
This gallery is reinforced with a black, sooty mold of mycelia that the ants cultivate. The mold grows on the goop. The ants cut numerous holes in the structure, just large enough that they can stick their heads through from the vault.
Workers hide in the vault, their heads just under the holes, waiting for prey. The trap is set.
When a large insect lands on the structure, it is temporarily stuck. The workers grab the victim’s body – legs, antennae, wings – and pull on it until the prey is progressively stretched out against the gallery.
Swarms of workers then sting the insect to death. Next, moving in and out of the holes, they slide the banquet-to-be to their leaf pouch where they carve it up.
The ants sometimes get uppity on their host, by destroying its flower buds, to skew the plant’s growth-reproduction ratio to favor more leaves and stems. Plants whose buds have been devastated grow more quickly.
When such exploitation happens, a plant can sanction the ants by producing leaf pockets too small for the ants to use. This teaches miscreant ants respect.
Coral reefs are constantly assaulted by algae which wish to steal prime sunlit locations for themselves. To gain control, many of these seaweeds pack toxins that take a toll on coral metabolism.
Left unchecked, seaweed can smother coral and take over a reef; an often-irreversible demise.
Gobies and other herbivorous fish live among the coral, which produces mucus to feed them. When coral is being damaged by seaweed, it lets loose a chemical cry for help. Sensing distress at home, gobies gobble the algae.
For a goby and others, seaweed may be a fine snack, but it does not provide a reliable food source and a place to live like a coral reef. Herbivorous fish are critical in keeping the algae on reefs in check; hence, coral provide for police protection.
Clownfish & Anemone
A sea anemone is a predatory sessile polyp which attaches itself to a surface with an adhesive foot (basal disc). Its mouth/anus is in the middle of an oral disc surrounded by tentacles armed with cnidocytes, which help capture prey and ward off predators. A cnidocyte is a hair-trigger explosive cell that delivers a harpoon of paralyzing toxin.
Anemones are related to corals, jellyfish, and hydra. Anemones often live on their cousin’s coral reef.
Clownfish are warm water, shallow sea dwellers of the Indian and Pacific Oceans. Clownfish shun the Atlantic Ocean.
Clownfish are omnivores that might otherwise consider anemone dinner potential, as the potent poison of the anemone is tolerable to a clownfish. Instead, the two keep close company.
An anemone provides a tentacle-guarded keep while its clownfish drives off predators and parasites which would chew its homestead. The clownfish feeds off the offal of anemone kills and the occasional dead tentacle, while the anemone picks up nutrients from clownfish excrement. The anemone also appreciates a clownfish prowling about at night.
Oxygen levels on a coral reef often plummet when the Sun goes down, as photosynthesis shuts down. Some symbiotic fish fan their coral home at night to keep it oxygenated. Clownfish perform the same favor for their anemone nest.
Clownfish themselves keep close company. A group of clownfish practice a strict dominance hierarchy, with the largest and most aggressive female at the apex. Only 2 clownfish in a group reproduce: a male and a female, via external fertilization.
Clownfish are sequential hermaphrodites: they develop as males before maturing into females. When a female clownfish dies, one of the largest/most dominant males becomes a female, and the remaining males move up a notch in the social hierarchy.
Seagrass & Clams
Seagrasses are flowering plants. With their long and narrow leaves, these marine plants resemble grass from which they descended. Seagrass grows in shallow, sheltered coastal waters, anchored to a sand or mud bottom.
Seagrass leaves slow water current and increase sedimentation. Seagrass roots and rhizomes stabilize the seabed while recycling nutrients. Seagrasses are 35 times more efficient at sequestering carbon than rainforests.
As such, seagrass fosters a productive and diverse ecosystem. A seagrass meadow acts as a nursery for fish, and a home to sea turtles, manatees, sea birds, and other marine creatures; providing both nourishment and protective cover.
Being a stick in the mud has its limitations. In buffering the shoreline, seagrass captures organic debris that turns the seabed into muck. Decaying plant matter produces sulfides that are unhealthy for plant roots on the grow.
Oxidization is the solution. But seagrass roots alone are not enough.
Seagrass gets help via a 3-way symbiotic relationship with sulfide-swallowing bacteria. The bacteria come with a buddy: lucinid clams.
The clams host bacteria in their gills that oxidize sulfides, converting it into mollusk-sustaining energy. Seagrass roots provide ready access to extra oxygen. Altogether, seagrass and clams make a happy seaside home, thanks to a bacterial broker.
Accelerating loss of seagrasses across the globe threatens coastal ecosystems. ~ Australian marine biologist Michelle Waycott et al
Apex predators that have largely disappeared from so many ecosystems may play vitally important functions. ~ American ecologist and evolutionary biologist Brent Hughes
Fertilizer runoff in coastal waterways spurs the growth of algae on seagrass leaves which starves the seagrass of sunlight. Sea slugs and small crustaceans in the genus Idotea graze on the algae, but these are gobbled up by crabs. Sea otters consume enormous amounts of crab.
In a trophic cascade, sea otters are seminal in seagrass comeback: consuming the crabs that eat algae grazers which free the seagrass to access sufficient sunlight.
The prospects are not bright. By the early 20th century sea otters had been hunted to the brink of extinction for their thick fur. A hunting ban ensued, but sea otter recovery was spotty.
By the end of the 20th century, sea otters were again struggling, thanks to pollution, especially oil spills, and competition for sea otter food – abalone, clams, and crabs – by humans. Sea otters are unlikely to survive to mid-century.
Strong interactions exerted by sea otters on their invertebrate prey can have cascading effects, leading to profound changes at the base of the food web. ~ Brent Hughes
Sloths & Moths et cetera
It’s almost as if people don’t want to know the truth about sloths. There’s something charming about thinking of them as lazy and stupid. ~ English zoologist Becky Cliffe
Sloths come by their name honestly. Besides sleeping 9.5 hours a day, they do a lot of nothing. When a sloth does move, it does so slowly. Top speed in the trees, trying to escape a predator, clocks at 4 meters a minute. On the ground, half that at best.
A sloth spends its life hanging from a tree in a tropical rainforest. Sloths eat and sleep in the trees. They even give birth in a tree. Too lazy to hit the ground upon their demise, some even remain hanging from a branch when dead.
2-toed sloths forage for leaves widely across the treetops, albeit at a leisurely pace. Its 3-toed relative cannot be bothered with that much exertion.
3-toed sloths have 1/4th the muscle tissue of comparably sized mammals; another disincentive to a vigorous life. They have the slowest metabolic rate of any mammal, and a low body temperature even when allegedly active.
Leaves are a poor source of nutrition. Animals that depend upon them, such as gorillas, typically have a large gut to accommodate their digestion. Living in the trees, sloths cannot afford such tummy luxury.
About the only time a sloth is on the ground is to literally lay waste. It digs a hole to urinate and defecate, then covers it up afterwards, to avoid giving away its location. Digestion is so slow that a sloth only needs to go once a week. The 2-toed sloth lets loose from the trees, while the 3-toed sloth climbs down to the ground.
Considering their speed, sloths are at greatest risk when on terra firma. Being caught on the ground is the leading cause of sloth death. Dropping waste from the trees is also a hazard, as it allows predators to more easily locate them, especially considering how little they move. The only time that 3-toed sloths dump from the trees is during a rainstorm, when waste readily washes away.
Despite staying in one place, sloths attract little attention. Sloths’ only predators are Jaguars and harpy eagles. Jaguars can climb trees but can’t reach sloths on the branches that sloths prefer, as these limbs are too slight to support a jaguar’s weight. Harpy eagles, which diet on monkeys and opossums, can see and snag a sloth only if it carelessly exposes itself on an ill-chosen branch.
Everything in the forest can eat them. So they have to be careful to go undetected, and one of the best ways to do that is to be very slow and very quiet. ~ American zoologist Sam Trull
Thanks to their long, curved claws, sloths hang upside-down for hours on end. The constant grip is possible because of a lattice of tendons in the hands and feet that draw their digits closed while at rest. That, and sloths are surprising strong, and their muscles resist fatigue.
Sloth muscles employ unique enzymes that confer tolerance to heavy accumulations of lactic acid, which wear muscle strength down. The sloth’s protein profile (proteome) is like fast-running cats such as cheetahs.
Sprinting is all about anaerobic power for short durations. So it is odd that a sloth that hangs for extended periods of time matches that metabolic profile. ~ American zoologist Michael Butcher
Moths that live within the sloth’s fur plant their eggs in sloth excrement, which their caterpillars consume before becoming adults, whereupon they fly up to become part of the sloth ecosystem.
When a moth dies on a sloth, its body is decomposed by fungi that live there. That releases nitrogen and other nutrients to feed the copious algae that live on the sloth. The strands of a sloth’s fur are grooved to trap rainwater and provide an ideal environment for the algae.
A sloth grooms itself so slowly that the moths within have no trouble escaping before getting raked. Grooming harvests the algae, which provides essential nutrition to the 3-toed sloth.
The algae are highly digestible, and far richer in fat than the leaves which are so slowly chewed. The leaves are a supplement, as a 3-toed sloth expends more energy than it takes in from eating leaves.
The 2-toed sloth has a similar system, but its symbiotic colonies are less fulsome, and so its reliance upon leaves greater. By living in the trees lower down, and taking the trouble to poop on the ground, the 3-toed sloth minimizes its exertions and maximizes its ease, while its colonial friends do as they please.
They are very economical animals and they make the most of every single thing they have available to them. ~ Becky Cliffe
The greatest mystery surrounding sloths is their near invincibility.
Of all animals, this poor, ill-formed creature is most tenacious to life. It exists long after it has received wounds which would have destroyed any other animal. ~ English naturalist Charles Waterton in 1828
Why and how sloths are capable of bouncing back after horrible injuries is still a mystery. ~ Becky Cliffe
Take A Load Off
Carnivorous plants made a wily evolutionary move: able to compensate for living in lousy soils by literally taking in animals. Directly or indirectly, the animals are a meal ticket.
Pitcher plants are carnivorous. They lure insects to the top of their specialized leaf traps with sweet nectar, where many lose their grip on the slippery rim, falling into a fluid-filled trap below.
The victims desperately try to climb out, only to discover with their last breaths that their prison is filled with stretchy fibers. The more an insect struggles, the more entangled it becomes.
Digestive enzymes in pitcher fluid break down the sunken prey, harvesting the hardest nutrient to get enough of: nitrogen. Pitcher fluid is itself a microbial ecosystem.
In the instance of the North American purple pitcher plant, the pitcher is an expansive ecosystem: a self-contained food web, home to an array of mosquito larvae, midges, rotifers, protozoa, and bacteria, many of which can survive only in this unique habitat. The little pitcher animals shred prey that fall in, with the microbiome feeding on the remainders. Finally, the pitcher plant absorbs the leftover bits.
Having the animals creates a processing chain that speeds up all the reactions. Then the plant dumps oxygen back into the pitcher for the insects. It’s a tight feedback loop. ~ American biologist Nicholas Gotelli
The rim of the southeast-Asian-native Raffles’ pitcher plant is not always slippery, letting some insects escape. It is a loss-leader strategy.
Individual scout ants search for profitable food sources. Finding a pitcher full of sweet nectar, they report back at the colony and recruit many more foragers.
By turning off their traps for part of the day on ‘dry’ days, these pitcher plants increase their overall capture. (Raffles’ pitcher plants have selective dry days where they keep their lips dry for up to 8 hours.) If the trap was always slippery, ant scouts would be in the pitcher rather than recruiting pitcher-plant food.
What looks like a disadvantage at first sight turns out to be a clever strategy to exploit the recruitment behavior of social insects. ~ German botanist Ulrike Bauer
Insect-trapping pitcher plants are small-timers compared to their cousins: the giant pitchers in the misty mountains of Borneo. These plants lure tree shrews, small rats, and bats – not to their deaths, but for their defecations. The plants are precisely sized for their clientele.
Tree shrews are enticed by the sweet nectar placed on the inside lid at the top of a giant pitcher plant. The pitcher is arranged so it can support the weight of these animals, and to situate clients so that they must crouch to take their treat.
The posturing puts a shrew or similarly sized rat so that it may easily defecate while dining, dropping nitrogen and other nutrients into the pool below. These pitcher plants get most, if not all, of their nitrogen needs met by their clientele. Swapping easily made sweets for hard-to-get fertilizer is a bargain.
Pitching for shrews is a smart strategy. There are fewer ants on the mountainsides where these plants grow.
Tree shrew droppings are especially nitrogen rich, as they have short guts that do not extract all the nutrients from their food. Plus, the speedy throughput means frequent deposits.
Taking a different tack, the Borneo pitcher Nepenthes hemsleyana provides a cozy lodging for woolly bats without the need of providing sweets. The pitcher’s orifice has an extended concave surface which distinctively reflects bat echolocation calls, making the plant easy for bats to locate amid the cluttered forest.
Pitcher walls have a girdle of thick tissue that lets the bats snugly wedge themselves in. To accommodate multiple bats, there is less fluid. What fluid there is maintains a comfortable humidity, preventing dehydration of its guests. The temperature is stable, providing a respite during the heat of midday; altogether a restful place to unload – which is exactly what the host has in mind.
Bats that lodge in pitchers are generally healthier than those that have to rough it. And the plants benefit: they economize by producing less sweets than those that attract insects. Breaking down the bodies of victims is time-consuming. Feces provides a readier source of nitrogen and other nutrients than tough, scrawny insects.
Birds & Alligators
Egg-eating racoons and opossums are the bane of nesting birds in the Florida Everglades. So, these birds site their nests above resident alligators.
The alligators provide protection from predation, and benefit when a bird lays more eggs than it can raise. Chicks that fall from a nest are like manna from heaven to an alligator wanting a snack.
Symbiotic microbes can benefit their animal hosts by enhancing the diversity of communication signals available to them. ~ Kevin Theis
Microbes also facilitate their hosts’ communications. Many animals mark spots in their habitat to convey various messages: whether a claim of territoriality or notes to friends or potential partners.
Host-resident microbes, or their work products, are on the spot to convey the communiqué. Besides aforementioned hyenas, badgers and bats are known to employ microbial compatriots to yarn for them.
Mutualisms develop in an environment where cooperation is beneficial to both parties. If the environment changes, the costs and benefits of cooperating can change as well.
In one experiment, researchers studied a microbial cross-feeding mutualism, in which each yeast strain supplied an essential amino acid to its partner strain. Depending upon the amount of freely available amino acid in the environment, the yeast strains shifted between mutualism and competition.
Commensalism is a relationship between organisms where one benefits another without being harmed. In larger organisms, this typically involves nutrition.
Microbes are often more intimate, sharing with each other genic bits that provide rapid adaptability. The littlest ones live a lifestyle of genetic literacy.
Bromeliads are a family of 3,170 different flowering plants. The pineapple is a bromeliad.
Numerous bromeliads are epiphytic. An epiphyte is a plant that grows upon another plant, albeit non-parasitically. Lichen, moss, and orchids are exemplary epiphytes. The smallest bromeliad is Spanish moss.
Tank plants are a species of rainforest bromeliad that cling to trees with their small roots. A tank bromeliad’s broad leaves press together at the base, forming a container that holds water; anywhere from 0.24 liters to 45 liters, depending upon the species.
This pond-among-the-trees creates an ecosystem. Microbes make a home, as do small animals.
A food web forms. The bacteria and protozoa feed insect larvae and tiny crustaceans, who make a meal for spiders, larger insects, salamanders, and tree frogs. These are in turn prey to larger animals, including snakes and birds.
Thus, by providing a watering hole, tank plants are a keystone species, facilitating a habitat for worms, insects, snails, crabs, frogs, rodents, and many others. The bromeliad benefits by feeding on the droppings that the animals leave behind – a nutrient-rich soil substitute.
Many bromeliads bloom conspicuous flowers that are pollinated by nectar-gathering birds. The inflorescence (flower clusters) of bromeliads are the most diverse of any plant family.
Sardine Tongue Trap
In the Indian Ocean off South Africa, the southern winter brings a spectacle of consumption. Billions of silvery sardines (aka pilchard) follow cold water that is rich in the phytoplankton that feed them. In doing so, the sardines become fodder themselves.
The Benguela Current is a counter-clockwise oceanic gyre in the Atlantic Ocean; a carrier of cool water. The fast Agulhas Current is an Indian Ocean equivalent, carrying warm water clockwise.
When the 2 currents meet at the southern tip of Africa at the beginning of the southern winter, the Agulhas Current has weakened somewhat. The Benguela gyre pushes a tongue of cold water from the Southern Ocean off Antarctica up along the coast of southwest South Africa.
An upwelling brings nutrients from the depth to the euphotic zone: the layer of water with enough sunlight for photosynthesis. Phytoplankton proliferate there.
In contrast, there is little mixing of surface and deeper waters in tropical oceans. Phytoplankton are relatively scarce in the tropics.
Massive schools of sardines, slaves to cool current because of its food supply, follow the tongue. The tongue will eventually flag into a return gyre of warmer water.
The pilchard run on the tongue is a trap. Other animals know this. Hordes of copper sharks follow in the wake of sardine shoals.
Bryde’s whale is a smallish whale with notably small flippers for its size. They typically feed on small fish and squid at depth but are opportunists that take advantage of herding done by another species.
Cape gannets, a large seabird, tirelessly patrol the skies at the right time of year, waiting for the shimmering slick of surface oil that the sardine shoals produce on the run. On their own, the gannets cannot harvest the sardines, nor can the sharks. So they wait.
The pilchard maestro of menace is the common dolphin, which normally feeds on a staple diet of squid in the depths. For the sardine run they come up for a feast.
A dolphin scout spots indications that the pilchard run is on – the signal may be the sardines, or groups of gannets or sharks. Great dolphin pods congregate, fanning out in a line. Once set, dolphin groups break off in a coordinated attack, breaking off sardine schools and driving them to the surface.
The sardines naturally form a tight ball as a defensive measure, concentrating in the classic stratagem of “safety in numbers confuses an enemy,” which backfires horribly in this instance. Individual dolphins take turns swooping in while others continue to herd the school ball.
The sharks too take bites from the surface balls, as do Bryde’s whales. As schools come to the surface, the gannets dive bomb for dinner. Other species, such as seals, join in.
Predators ignore each other, all focused on filching the pilchards. Dolphins host a dinner party that lasts for weeks.
Sometimes the commensal is incidental to the provider. Orchids and mosses grow on the trunks or branches of trees, getting the light they need, along with nutritional runoff from the tree. The tree is unharmed.
Birds follow army ant raids on the forest floor. The ferocious ant colony stirs up various flying insects who flee from the onslaught on the ground. The birds following the ants snag the fleeing fliers.
Cattle egrets forage alongside bovine who stir up insects as they graze; a meal for the egrets.
In the Pacific Ocean, a titan triggerfish improves foraging prospects for smaller fish by shifting rocks too large for the littler ones to move.
The flip side of the coin of commensalism is amensalism: an organism negatively impacts another while immediately gaining nothing or being harmed. Amensalism arises from the struggle for limited resources creating an evolutionary impetus to thwart others.
One plant slows the growth of another by putting it in the shade. The forest canopy is a competitive exercise, as trees reach for the sky for sunlight exposure.
Various bacteria, algae, fungi, coral, and plants practice allelopathy: biochemical secretions that influence another organism’s prospects. Bread mold secretes penicillin to kill bacteria that would otherwise compete for its food.
Plants, the most sophisticated producer of biochemicals, are eager allelopaths. Many invasive plant species gain their competitive edge by interfering with the natives through allelopathy.
Black walnuts release naphthalene glucoside from their roots. In the soil, the compound converts to juglone, which inhibits seed germination and seedling growth of other species competing for light and space. Black walnuts can dramatically retard the growth of apple and pine trees, rhododendrons, and even otherwise competitive walnut relatives.
Eucalyptus trees root exudates and leaf litter kill certain soil bacteria that are beneficial to other plants species, as well as directly affecting plants.
Allelopathy has an evolutionary race element. The pace of allelochemical production has accelerated in higher plants.
Amensalism in general, and especially allelopathy, necessitates a feedback loop, as well as intelligence operating upon hidden information. (The attribution hidden information refers to data beyond empirical investigation. Human understanding of the energy patterns and coherence which compose Nature is scant. This is most apparent in evolutionary biology.) While such dynamics are evolutionary outgrowths – adaptations through time – there can be no dismissing intelligence behind it.
However bread mold managed to discover how to kill bacteria, and effect penicillin production, it was not a product of trial and error. The biochemical permutations are too prolific. Mold learned via horizontal gene exchange. Bread mold applied cunning in learning how to put down its competition.
Eukaryotic horizontal gene transfer is real. ~ American geneticist Chris Hittinger
While amensalism offers particularly striking examples of intelligence based upon hidden information, such coherence proliferates throughout Nature, albeit often in subtle ways that have gone unappreciated.
You had no right to be born; for you make no use of life. Instead of living for, in, and with yourself, as a reasonable being ought, you seek only to fasten your feebleness on some other person’s strength. ~ English novelist Charlotte Brontë in Jane Eyre (1847)
Parasitism is a symbiotic relationship of an inveterate taker inflicting itself upon a host, which is typically a much larger life form than the parasite. Pathogens go a step further and cause disease.
Parasites may actively seek and invade their hosts or passively await entry. Most arthropods are proactive, whereas viruses, bacteria, and protists typically enter passively via some vector, such as water, food, or a hemophagic arthropod. Host-seeking is a complex endeavor, involving chemical, visual, and even auditory cues.
Ectoparasites live on the surface of a host. Mites and ticks are exemplary ectoparasites. Endoparasites, such as parasitic worms, live inside.
Most obligate parasites are parasitic as adults. Their larvae are not necessarily so.
A facultative parasite is opportunistically parasitic. Such parasitism in plants is called hemiparasitism.
Just as some viruses can themselves suffer viral infection, hyperparasites prey upon parasites. Hyperparasites are usually microbes, typically bacteria or viruses, though some protozoa, cestodes (tapeworms), and crustaceans parasitize other parasites.
Injuries by parasites occur in several ways. Parasites growing or moving through tissue damage by mechanical insult. Others, such as bloodsucking hookworms, feed on a host.
The harm caused by the parasite may in many cases vary with the host or with the time since infection. In some situations, parasites may even be beneficial. ~ American biologist Janice Moore
Parasites are pervasive. Their diversity matches that of self-standing life. More than half of all animal species are parasitic. The proportion of parasitic plants is much less, as the power of photosynthesis takes the edge off the urge to sap another’s life.
The frog lung fluke illustrates how parasites may make their way through various hosts at different stages of their life cycle. This parasitic flatworm (trematode) lives in the lungs of frogs as an adult. The fluke’s eggs are swallowed by the frog and pass through its digestive system, where they are excreted with feces.
A ramshorn snail consumes fluke eggs, which hatch inside it. Hatchling flukes (miracidia) settle into the digestive gland, asexually reproducing into sporocysts (elongated sacs), which produce cercaria (larvae).
The cercaria leave the snail. They enter the gills of a dragonfly nymph and encyst in its tissues. Encysted trematode larvae are termed metacercariae.
Once an infected dragonfly nymph or adult is eaten by a frog, metacercariae become adults. The life cycle is complete.
~4,000 plant species prey on their distant relations as parasites. Parasitic plants vary widely in their dependencies and techniques. Many have lost the capacity for photosynthesis and so are no better than animals in their predations. Others, such as mistletoe, can photosynthesize, but have no roots. They latch on by a haustorium and suck water and minerals out of their host. A haustorium is a hook used by parasitic fungi and plants to attach and draw nutrients.
In the plant world, the meanest bitch is the weed that is a witch: witchweed, which feeds from the roots of many plant species.
It’s like root radar. ~ American botanist David Nelson
Witchweed seeds near the roots of potential victims germinate upon catching the scent of strigolactone hormones that the soon-to-be victimized root exudes. Witchweed then grow toward the host to rudely introduce themselves. Once in touch, a witchweed root swells with a haustorium, poking the host to suck it dry.
Witchweed parasitizes a wide range of commercial grass and legume crops, including corn, sugarcane, and rice. It is so witchy that it can wipe out an entire crop.
Haustoria do more than suction nutrients. Parasitic plants input specific genic bits to shut down host defense responses and gain more information about their host.
The Cape region of South Africa is a hotspot of plant biodiversity: with over 9,000 plant species, nearly 70% of which are endemic, within an area of only 90,000 km2. In contrast, Germany, which is 4 times the size, has 1/3rd the number of native plant species.
Among the South Africa plethora is Cape sumach, a woody hemiparasitic plant in the Sandalwood family. Cape sumach is tough and adaptable: able to withstand heat, frost, and winds. It grows fast and can survive in sandy soils, even coastal dunes.
Cape sumach is prone to supplement its diet via haustoria that tap into the roots of nearby plants and suck their sap. Although it can make it on its own, Cape sumach grows best with a parasitic boost, especially in dry conditions or poor soil.
Unlike predators, parasites do not kill their prey. In-stead, parasites very much want their host alive, at least for a spell. Parasites are looking for free rent and board, along with steady meals, at host expense.
Social parasites take advantage of ecological interac-tions in other social animals. Ant slavery is an example of social parasitism, as is brood parasitism.
Parasitoids contrast to other parasites in their debili-tating effect on their hosts. Parasitoids spend much of their life attached to or within a single host, which they ultimately sterilize or kill, and sometimes consume.
Some parasitic organisms induce changes in the behaviour of their hosts that favour the reproduction of the parasite rather than that of the host. ~ American ethologist William Eberhard
Some parasites alter host immune response, physiology, and/or behaviors.
Parasites evolved the ability to manipulate host behaviour in order to advance their own reproductive success. ~ English parasite epidemiologist Joanne Webster & Canadian invertebrate behavioral physiologist Shelley Anne Adamo
Host pathological symptoms evolved to assist the parasite in completing its life cycle. Changes in host behavior typically improve the probability of issuing a next generation of parasite, at host expense. Similarly, parasite-induced host immunosuppression permits longer residency, increasing the opportunity for transmission.
Parasites do not selectively attack discrete brain areas. Parasites typically induce a variety of effects in several parts of the brain. Parasitic manipulation of host behaviour evolved within the context of the manipulation of other host physiological systems (especially the immune system) that was required for a parasite’s survival. This starting point, coupled with the fortuitous nature of evolutionary innovation and evolutionary pressures to minimize the costs of parasitic manipulation, likely contributed to the complex and indirect nature of the mechanisms involved in host behavioural control. ~ Shelley Anne Adamo
Animals have bidirectional communication between immune and intelligence systems. The immune system biochemically reports – via cytokines – that it is struggling with an infection, inducing sickness behavior that alters motivational state. The nervous system has receptors for cytokines, which are small cell signaling proteins.
A parasite coopts the same communication factors that the body uses to interfere with host immune function, and to promote physiological functions and psychological behaviors that favor the parasite’s survival and reproduction. Parasites that make zombies of their hosts may also fiddle with neurotransmitters to have the hosts do their bidding. Ultimately, such parasitic manipulation is of the mind, of which brains and nerves are merely correspondent artifacts.
If the mind is a machine, then anything can control it that understands the code and has access to the machinery. ~ Shelley Anne Adamo
Fish Eye Flukes
Diplostomum pseudospathaceum is parasitic fluke that infects snails, fish, and birds. Adult flukes mate in a bird’s digestive tract, shedding their eggs in its feces. The eggs hatch into larvae in the water, then seek out freshwater snails to infect. Fluke larvae grow and asexually multiply inside snails, eating their hosts’ bodily reserves before being released into the water, ready to track down their next victim: fish.
Upon finding a fish, flukes make their way into the fish’s eye lenses, which lack blood vessels, and so are protected from attack by the fish’s immune system. From this remote post Diplostomum energetically alters the fish’s behavior. While the larvae in the eye mature, the host fish is less active than usual, making itself less visible to predators, and so more likely to survive. Immature flukes are too young to infect their next (avian) host, so they protect the fish they are in.
Once the fluke larvae are fully grown, they have their host swim more actively near the surface, making the fish more conspicuous to piscivorous birds. The flukes repress the normal evasive responses the fish would otherwise have when feeling threatened (such as a shadow over it). By this time the fish is likely mostly blind, its sight having suffered the ravages of hosting growing flukes. The fluke completes its life cycle once the fish has been caught and eaten by a bird.
Tangle Web Spider
The tangle web spider of South America normally builds a perfectly round orb web. Its moniker appears a misnomer. Alas, when infected by the parasitoid wasp Polysphincta gutfreundi, the spider lives up to its name.
A Polysphincta wasp attacks the spider, temporarily paralyzes it, and lays an egg on the tip of its abdomen, where the egg is out of harm’s way. The egg hatches, and the wasp larva attaches itself to the spider.
For 2 weeks thereafter, the spider spins its web and snags insects every day as if nothing were amiss, except that there is a growing larva clinging to its belly, sucking juices that drip through small punctures the larva makes in the spider’s body.
The night before the larva kills the spider, it induces the spider to spin a very different web: one that provides a durable platform upon which the wasp larva spins its cocoon, safe from predatory ants that patrol the ground below.
Parasites can modify characteristics of arthropod hosts in diverse ways to facilitate their transmission to subsequent hosts. These modifications often are behavioral. However, frequently the altered behaviors are accompanied by physical changes that make the host more conspicuous.
Whereas increasing the conspicuousness of familiar palatable prey may be a common and effective parasite transmission strategy, there are few cases of parasite-induced mimicry, whereby the appearance of an intermediate host is transformed to the extent that it resembles a completely different organism. ~ American biologist Steven Yanoviak et al
Cephalotes atratus is an arboreal ant native to the Neotropics, able to glide from a tree and steer its fall to land back on a tree rather than hitting the ground.
Myrmeconema neotropicum is an endoparasitic nematode. It has 2 hosts in its life cycle: the gliding ant and fruit-eating birds.
Parasitic worm eggs are passed to ants via bird feces, which is collected by foraging ants and fed to ant larvae in the nest. The eggs hatch.
Nematode larvae migrate to the abdomen of ant pupae, where they mature and mate. Male worms die after mating.
Nematode females incubate their eggs inside the ant, stunting the ant’s growth somewhat. As the nematode eggs mature, the young adult ant’s abdomen turns from black to bright red.
An infected ant, which had been tending brood within the nest, starts foraging outside. But the ant is dysfunctional, as it feels compelled to stand stationary, holding its berry-red bum in the air. The scene is set for frugivorous birds to be duped into eating an ant they would normally avoid.
The nematode lives its life in the ant. Birds act solely as a transmission vector, to spread parasitic worm eggs afar.
Due to modification of brain dopamine signaling, the ants were just mad for the caterpillars. ~ Japanese ecologist Masaru Hojo
The Japanese Oakblue is a butterfly native to east Asia. Its caterpillars hire protection.
When ants encounter an Oakblue larva, they crawl over the caterpillar (as ants are wont to do to all sorts of things). This ambulatory encounter prompts an Oakblue caterpillar to secrete a sweet, sticky liquid that ants greedily lap up. The secretion addicts ants, enslaving them to the caterpillar. Within 3 days of first nipping Oakblue juice, an ant forsakes its responsibilities to the colony and devotes itself to the caterpillar.
Caterpillars are subject to attacks by spiders, parasitoid wasps, and other dangers. A caterpillar raises its tentacle organs near its rump as a ruse, to divert attacker attention toward its less-vulnerable rear. This rouses a doped ant, which grows aggressive when the caterpillar reacts to a perceived threat. Ants are formidable fighters; able to tackle predators that caterpillars can’t.
Toxoplasma is an especially promiscuous parasite. It infects nearly all warm-blooded species, most nucleated cell types, and much of the human population. Although it lives in vital brain and muscle tissues, it usually causes no obvious reaction. Infection can seriously harm people with weak immune systems, yet most hosts experience no overt symptoms because Toxoplasma has found a way to coerce cooperation. ~ American immunologist Eric Denkers
Toxoplasma gondii is a protozoan parasite of endotherms that causes toxoplasmosis: a disease producing both physical and mental disabilities.
Cats are T. gondii‘s primary host, but over half of the world’s human population carries the little protozoan.
Toxoplasma also infects rodents and makes them foolishly reckless; increasing the odds of their becoming prey, and so infect a feline predator. Rats have an innate fear of cat odors. T. gondii abolishes that.
T. gondii alters the behavior of infected rats by abolishing innate fear, creating instead a ‘fatal attraction’. The behavioral effects of T. gondii infection are fairly specific to innate fear, leaving many other related or energetically costly behaviors intact. ~ Singaporean biologist Ajai Vyas
Toxoplasma is sexually transmitted. The protozoan alters rodent mating preference, making infected males more alluring to females, contrary to their natural instincts.
There is a bit of evolutionary depravity in these events. In general, females tend to detect and avoid males infected with an array of bacteria, protozoan, lice, and nematodes. The odor of parasitized males is stressful for females. Toxoplasma gondii infection results in inversion of this innate aversion of females, instead instituting an attraction to parasitized males. ~ Ajai Vyas
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In humans, latent Toxoplasma infection slows reaction time. It also stimulates schizophrenia. In suppressing the immune system and altering testosterone production, T. gondii raises the odds of a mother birthing a boy with Down’s syndrome.
Men infected with Toxoplasma have a higher tendency to disregard rules, are more suspicious and jealous. Infected women are the opposite: more warm-hearted, gregarious, and easy-going. While T. gondii-infected men are less altruistic, women are more so. Both infected sexes become more complacent and extraverted, while losing confidence in their ability to be diplomatic or appropriately socially assertive.
The ubiquitous protozoan Toxoplasma gondii can cause permanent behavioral changes in its host, even as a consequence of adult-acquired latent infection. ~ Joanne Webster
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The parasite actively releases messages into cells that change cell behavior. ~ Eric Denkers
To stabilize their environment, Toxoplasma suppress-es inflammation warnings from cells, preventing an early immune system response.
Toxoplasma hijacks immune cells to enforce a mutually beneficial balance. ~ Eric Denkers
Twisted-wing parasites are insects in the order Strepsiptera, with 9 extant families of some 600 species, so-named for the look of the wings on short-lived adult males. Their lives are largely spent as endoparasites inside other insects, including cockroaches, bees, wasps, leafhoppers, and silverfish.
With rare exceptions, females never leave their host. Virgins release a pheromone to attract males, which, as adults, live only enough hours to find and inseminate females. The males superficially look like flies, but their mouthparts are merely sensory, as they do not feed.
Newly hatched larvae bust a move to find a new host before exhausting their limited food reserves. Once inside a host, a larva metamorphizes into legless, less-mobile larval form.
The larva induces its host to produce an isolating bag, inside of which it feeds and grows. Made from host tissue, the bag protects from host immune defenses.
Some strepsipterans practice mind control and alter host behavior. Myrmecolacids cause their ant hosts to climb up to the tips of grass leaves, thereby improving the wafting of female pheromones, to up the odds of being located by males.
Some myrmecolacids have the curious power to extend the lives of their hosts by a third or more.
Myrmecolacid males and females infest separate species. Females of Caenocholax fenyesi – a myrmecolacid – plague grasshoppers, crickets, and mantises. Meanwhile, males only parasitize ants. Fire ants are a favorite. The 2 myrmecolacids manage to stay nearby, as females prey upon insects that fire ants feed on.
The ability of parasites to alter host cognition and behav-iour captivates the interest partly because it questions the existence of free will. ~ Joanne Webster
An obligate parasite is totally dependent on its host throughout its life cycle. This is what is commonly thought of as parasitism, but there are other types.
A facultative parasite takes advantage of its chosen host but may get by if its victim dies.
Honey fungus lives on woody shrubs and trees. Its host’s demise is no cause for distress, as a honey fungus continues to digest wood without further ado. The simple nutritional requirements of honey fungus give it a long life, with the potential to be one of the largest organisms in the world. Parasitic life can be a simple pleasure.
Kleptoparasites are fond of theft. While many can forage or hunt on their own, they prefer saving time and effort by stealing. Kleptoparasitism may be of others in the same species (intraspecific) or of another species (interspecific).
Interspecific parasites are commonly close relatives of the organisms they parasitize; a phenomenon known as Emery’s Rule, after Carlo Emery, who made the observation about insects in 1909.
Oystercatchers are a group of waders found on sea coasts around the world. They are fond of mussels and have the unusual ability to crack open bivalve shells. Juvenile oystercatchers readily nip food from adults, as they are not yet strong or skilled enough to open mollusk shells themselves.
A good-looking nest is critical to a chinstrap penguin male in securing a mate. There are always more than a few in a penguin breeding colony that pilfer rocks and other nest materials from neighbors.
Seagulls are noted for aggressive opportunism. They happily snatch the retrievals of diving birds, as gulls are unable to fetch fish from the sea floor themselves.
Freeloader flies visit spider webs, where they scavenge half-eaten stink bugs. Blow flies in the Bengalia genus lurk near ant-foraging trails and steal food and pupae portaged by ants.
Cuckoo bees and cuckoo wasps lay their eggs in the nests of other bees and wasps respectively. Cuckoo hatchlings dine on the food provided for the larvae of the host. This kleptoparasitism differs from brood parasitism, which involves parental care of offspring.
These parasites are literally infection machines. ~ Patrick Keeling
Many microbes prefer an inside job but are disinclined to working for a living. Some even wreck the joint.
Microparasites are often, though not necessarily, pathogenic. They may be intercellular – living in body cavities or organs – or intracellular.
Some parasitic protozoa and filarial worms employ vectors to reach their hosts. The mosquito that carries the malaria protozoan Plasmodium is exemplary.
Intracellular parasites tend to have a carrier to their host. The vector is typically a small predator or parasite.
Microparasitism often involves close-range combat, as the host immune system attempts to oust the invader. Such continual antagonism provokes an evolutionary arms race, as microparasites attempt to anticipate and counter elimination measures by their hosts. To this end, microparasites often steal host genetic material to gain the upper hand in infestation and prolonged residence. Microparasites may also introduce new genes to their hosts. This countermeasure does not necessarily prevent host evolution to oust the interloper.
The genetic wiles of microparasites are sometimes expressed by altering host behavior to the parasite’s advantage. The little rascals can be quite manipulative.
Intracellular parasitism results in extreme adaptations. ~ Swiss zoologist Karen Haag et al
Microsporidia are a phylum of unicellular, spore-forming, intracellular fungal parasites. There may be a million species. ~1,500 have been named.
Microsporidia are restricted to animal hosts. All animal phyla host microsporidia. Most infect insects, but they are also responsible for common diseases of crustaceans and fish. Only 10% are vertebrate parasites.
Known species of microsporidia are usually restricted to a specific host or closely related species. Some of the most opportunistic infect humans.
Microsporidia influence their hosts in various ways. All organs and tissues may be invaded, though generally by different microsporidia species.
Microsporidia use a specialized harpoon – polar tube – to insert themselves into the cells of their host.
Once infected, a microsporidian restructures the host cell, with the parasite seeking control of metabolism to survive and facilitate reproduction. The host cell provides protection from the host’s immune system. The cytoplasm is largely replaced with machinery that does the microsporidian’s bidding.
In extremity, a microsporidian rules its host cell completely, controlling metabolism and reproduction, forcing formation of an aberrant tissue growth termed a xenoma. Microsporidia are known to produce xenomas in earthworms, insects, crustaceans, and fish.
In dropping all but the absolute necessities, microsporidia are essentially eukaryotic viruses; an instance of convergent evolution in this regard. Microsporidia have the smallest known genome of all eukaryotes. They have no mitochondria. Their molecular evolution rate is viral in its rapidity. Like viruses, microsporidian reliance upon the molecular machinery of their hosts is as complete as can be.
An epiparasite (aka hyperparasite) is a parasite of a parasite. A parasitic protozoan that resides in a flea’s digestive tract is an epiparasite. Hyperparasites are typically far less restricted in host selection than the parasites upon which they rely.
Epiparasites are commonly ectoparasites. Many are insects preying on other insects.
Attack by an epiparasite usually spells the slow death of the host. Thus, hyperparasites are typically parasitoids.
Some flowering plants attacked by caterpillars call for help by emitting airborne volatile chemicals that attract wasps which attack the caterpillars. The wasp parasitoids are themselves preyed upon by smaller epiparasites, also attracted by plant volatiles that signify where the action is.
Plants often release volatiles in response to damage by herbivores (e.g., by caterpillars), and these can indirectly help defend the plants. Volatiles can recruit the natural enemies of herbivores, such as predators and parasitoid wasps, whose offspring feed on and develop within their caterpillar hosts.
Such induced plant odours can also be detected by other organisms. Hyperparasitoid wasps also take advantage of the odours that plants produce in response to the feeding by caterpillars.
The larvae of parasitic wasps developing inside the caterpillar alter the composition of the oral secretions of their herbivorous host and thereby affect the cocktail of volatiles the plant produces. The hyperparasitoids on the lookout for their parasitoid prey can preferentially detect infected caterpillars, although not all parasitoid wasps gave away their presence through this host–plant interaction. ~ Dutch entomologist Erik Poelman et al
A meal for a diatom is a smidgen of CO2 and a few rays of sunshine. Overall, the trophic efficiency of photosynthetic primary producers is low. Only 1% of the energy in sunlight is converted into chemical energy. But the ingredients are abundant, and their capture energetically cheap.
When a copepod consumes a diatom, 90% of the energy spent – in the diatom’s capture, digestion, excretion, and synthesis – is generated as heat; of no further use to the copepod or any other organism. Trophic efficiency is a measly 10%.
The copepod is eaten by a small fish. 10% trophic efficiency again. On up the chain of ingestion.
Trophic inefficiency is why food chains rarely extend beyond 5 or 6 levels. Food chains are a compounding of energy inefficiency. A tertiary consumer in a chain originating from incident sunlight has employed only 0.001% of the total energy involved.
There are primary producers that work without sunlight, consuming inorganic chemicals. The earliest life arose by this route. Capturing sunshine was an acquired art.
Even now, benthic sentiment teems with life. Mud-bound microbes feast on the chemical leftovers of atoms in their last gasp. The chow comes via radiolysis: natural radioactivity that decays elements in the mud and rocks, bombarding water, splitting H2O into its constituents, providing a near-endless supply of food.
This food chain is further fed from a finale from another food chain, as marine snow from the ocean above showers down into the seafloor mud. For hundreds of meters below the ocean floor, archaea, bacteria, and fungi thrive, all of them host to an audacious array of viruses. And the pace is relaxed. Oxygen is low, so buried microbes breath slowly. Life is fine where the Sun doesn’t shine.
Back to the diatom, though not the one eaten by the copepod. This different diatom had the misfortune to die of a viral infection; its contents scattered into the watery world.
This diatom DOM is at the origin of another food chain. Dead diatoms are not the only source of dissolved organic material. Alive and kicking phytoplankton philanthropically rain marine snow. Depending upon nutrient availability, phytoplankton release a substantial fraction of their photosynthetic production as DOM.
This phytoplankton largesse arises over lack of nitrogen. Light and CO2 are all they need to cobble up carbohydrates, but proteins and nucleic acids need nitrogen. Excess carbohydrates are released, rather than stored, pending sufficient nitrogen.
As long as this snow is in solution, it cannot be passed up the food chain. Up to 50% of solar energy used by phytoplankton to fix carbon is spent from the start for lack of nitrogen.
Some marine snow descends to a watery grave, to enjoy an afterlife as a carbon store, or a snack for microbes in the mud. A large fraction of these carbs on the loose are ingested by bacteria.
This microbial loop puts photosynthetic particulate product back into the trophic flow. DOM-fattened bacteria are voraciously hunted by ciliates and flagellates, themselves preyed upon by copious copepods. Here we have another marine food chain.
The average milliliter of seawater contains a million heterotrophic bacteria that play an essential role in remineralizing dissolved organic matter (DOM) by decomposing 35 to 80% of net primary production and converting it into particulate form, available for consumption by larger organisms. ~ English physicist John Taylor & Roman Stocker
Bacterial recovery of DOM is an important aspect of marine ecology. The trophic significance of this microbial loop is augmented by the efficiencies involved.
In contrast to the meager trophic efficiencies of multicellular animals, typically 10%, bacteria eat at 50% trophic efficiency, sometimes as high as 90%. Their tiny predators – flagellates, and ciliates – may consume at a 70% efficiency. As a result of the microbial loop, high efficiencies afford support for a vast population of consumers.
Other organisms chow down on DOM, such as marine invertebrate larvae, but bacteria have an inherent advantage: size.
For little ones in the deep sea, DOM is absorbed through cellular membranes. The rate at which food can be absorbed is proportional to surface area. But a microorganism’s need for energy is a function of its volume, not its surface area. The bigger, the hungrier.
The ratio of surface area to volume is nonlinear. Surface area to volume progressively grows as the size of an organism shrinks. A 2 µm long bacterium has 50 times the surface area per volume of a ciliate 100 µm long.
Hence, a bacterium is better at dining on DOM. Bacteria are also more trophically efficient in other ways, by virtue of evolutionary adaptation to better access the energy from absorbed nutrients.
Then there is a viral loop within the microbial loop. Half of the bacteria at sea are infected by bacteriophages: viruses that specialize in preying on bacteria. 20–40% of infected bacteria die each day via lysis: cell wall rupture. A bacterium bursts, releasing DOM – the same fate as the diseased diatom.
The microbial loop reintroduces DOM into the food chain. The viral loop short-circuits that, dumping marine snow once again.
The viral loop is significant. There are 4×1030 viruses in the sea – 800 tonnes – equal to 20 days’ worth of carbon fixed by the entire ocean in 20 days.
Death for Life
A tree falls in the forest. Thus begins a feast for beetles, fungi, and other death-loving detrivores.
If the tree falls into water, fish are better fed, thanks to decomposers that put nutrients in the drink. Other trees may use a rotting log as a base for their growth.
In the trophic gyre, every death sires life. A corpse is but a seed to a new cycle of animation.
In marine food webs, fish are typically thought of as predators. They have an often-overlooked role. Their excretions recycle nutrients, fertilizing sea grass and algae: feces as food.
The population of primary producers sets the stage for the carrying capacities of downstream consumers. Carrying capacity is the maximum population size of a species given the constraints imposed by the environment.
The carrying capacity of primary producers, particularly plants, is determined by trophic upstream availability of raw materials: light, nitrogen, carbon, other key elements, and water if the producer is not already afloat. There is a downstream limiting factor to producers as well: herbivores.
Herbivore energy is had at the expense of the producer population. Herbivores are not just eating the producer’s profit – they are eating the producer.
Hence, carrying capacity is controlled by trophic conditions both upstream and downstream. This dynamic regulation occurs regardless of trophic level. Carrying capacity is a gyral calculation.
Apex predators are considered as having no predators of their own; a definition by which biologists exclude parasites and microbes, which are exactly what preys upon them. Pay no attention to the pathogens behind the curtain: the microparasitic Wizards of Oz that more than carry their weight in affecting carrying capacity.
Sanitation affects carrying capacity, especially for animals, as it alters the supply of clean water. Unclean water is a hazard by ill-virtue of nasty little wizards or toxins which overcome cells’ capacity to clear them.
Similarly, pollution lessens carrying capacity, as pollution is a force that saps trophic energy in organisms to combat its effects, as well as limiting nutrient supply. Pollution takes a thick slice of trophic energy away from all but the hardiest in a food web.
The food web has far-reaching implications, many indirect. There is a relationship between species diversity and the topology of predator-prey linkages. The concept of trophic cascade encapsulates the dynamic of predators preventing overgrazing, and thus increasing plant growth by chewing away at herbivore populations.
As humans settled the US west, predators of all sorts were wantonly slaughtered to protect livestock.
An 1872 law established Yellowstone National Park. Despite Federal statute protecting wildlife, wolves were eliminated there in the 1920s. By the mid-20th century, wolves were almost wiped out of the continental 48 states.
Through remorse, wolves were reintroduced into Yellowstone in 1996. Their predation reduced browsing pressure by herbivores. Instead of eating greenery to the nub, elk and deer only take a bite or 2 before for checking for threats and moving on.
The increased vegetation improved the park’s degraded streams. Beavers, despite being on the wolf’s menu, benefited. The extra lumber provides food and shelter. Beavers in turn create dams that help keep rivers clean and lessen the effects of drought.
In altering water flow in the lakes where they live, beavers provide accommodations for other lives. Insects, fish, amphibians, birds, and small mammals all gain from beaver efforts. The improved vivacity in the ecosystem helps feed the wolves.
The food web is but one facet of the biotic web between species. Widely varying in significance, a vast variety of interactions between species take place, ranging from incidentally indirect to studiously conscientious.
There no apportioning consequence. However ancillary an interaction may seem, its import may ripple throughout an ecosystem. We simply cannot know the impact of disturbing Nature until long after the damage is done, perhaps irreversibly so (via self-organized criticality).
Living things exist in a fine balance. ~ English microbiologist John Postgate
Ecological networks are both fragile and robust in their facets and dynamics. That dichotomy spans an emerging understanding about the intricate workings of ecosystems.
A keystone species is one that has a disproportionately large effect on the health of a biome. Keystone species play a vital role in creating and maintaining an ecological community. The contributions of keystone species are not always obvious.
Plants are commonly creators of ecosystems. A few animals shape their habitat to the benefit of other species. Even parasites can sprinkle ecological benefits where they would not otherwise appear.
Seed-dispersing animals are integral to the health of the forest ecosystems where they live. Large herbivores, such as elephants and rhinos, are especially essential.
Smaller herbivores are less productive to plants, as seeds either are spit out in the same place or do not survive chewing or digestion. Tapirs defecate 8% of the seeds they eat, while elephants drop 75%, along with copious fertilizer. 65% of elephant-deposited seeds germinate.
Megaherbivores act as the ‘gardeners’ of humid tropical forests. They are vital to forest regeneration and maintain its structure and biodiversity. ~ ecologist Ahimsa Campos-Arceiz
Microbes, plants, and animals affect the lives of others in a variety of ways. Ecological interactions of all kinds form an interdependent web.
The addition or loss of particular species and the alteration of key interactions can lead to the disassembly of the entire interaction web. ~ Mariano Rodriguez-Cabal et al
The production of organic matter in tropical rainforests is prodigious. Living and dying creates tonnes of debris. It has to be cleaned up or the forest would suffer.
Thanks to ants, the rainforest floor is kept in good condition. Ants account for over half of debris removal in the rainforest. Collectively, ants are crucial ecosystem engineers.
The movement, consumption, and recycling of dead organic material in ecosystems is important because it facilitates nutrient redistribution and decomposition. Because ants collect waste products and take them to their nests, they create hotspots of nutrients where plants and microbes thrive. This maintains a diverse and healthy soil. ~ English ecologist Catherine Parr
In the western United Sates, sagebrush is often the dominant vegetation over vast areas. It is a highly digestible forage: high in protein and other nutrients. Sage grouse and ungulates migrate long distances for it. Sagebrush offers thermal and security cover for animals. In sum, sagebrush is a keystone species in a sparsely populated landscape.
Herbicide applications, mechanical treatments, and prescribed burning are commonly applied to large areas in big sagebrush communities, often with the goal to improve wildlife habitats. Managers should refrain. ~ American ecologist Jeffrey Beck et al
Acre for acre, salt marshes are among the most valuable ecosystems on the planet. ~ American ecologist Mark Bertness
Marshes form a transition zone between aquatic and terrestrial ecosystems. Marshes are found worldwide.
3 types of marshes are delineated by water quality: salt, freshwater tidal, and freshwater. Each type is home to different communities.
Salt marshes are the most challenging for plants in having to accommodate high salinity. Nonetheless, salt marshes are important to aquatic and terrestrial food webs, and in delivery of nutrients to coastal waters.
Unsurprisingly, plants form the foundation of marsh ecosystems. Grasses, reeds, and rushes dominate marsh vegetation; establishing habitats for many invertebrates, fish, amphibians, waterfowl, and mammals. The bioproductivity of marshes is among the highest of all biomes.
Marshes are a mosaic of extensive unvarying vegetation in patches of uniform composition, with sharp transitions over tiny topographic gradients. Different plants have specific preferences for elevation based upon soil aeration and salinity.
It was long thought that plant distribution within a marsh was a passive adaptation. Instead, plants adjust their elevations by producing different volumes of organic soil, and by trapping and accumulating inorganic sediments. Each single-species community builds up the elevation of its substrate to a favorable range, much the way that corals do in the ocean.
Plants make a trade-off when colonizing within their preferential range: locating themselves slightly above the elevation of maximum biomass productivity. This gives the plants a safety margin of compensation for environmental fluctuations. A community hedges its bet by paying with a bit of productivity for greater long-term stability.
Predators are key to the health of marshes. If their presence is diminished, such as by overfishing or excessive crabbing, populations of prey are left unchecked. Overabundant herbivores then eat up the plants that are the foundation of marsh ecosystem health. Disruption at the top of the food chain cascades to unbalance the entire ecosystem.
River dredging and damming starve marshlands of sediment, creating erosion vulnerability. More directly, wetlands are drained to create agricultural land or expand urban sprawl. Man has consistently been a wantonly destructive creature.
Populated areas of the world have already lost 90% of their wetlands, including marshes. Coastal development has been the major cause for the loss of salt marshes.
Canary Islands Trees
The Canary Islands are an archipelago only 70 kilometers west of the Sahara Desert. The islands receive virtually no rainfall.
But the Canary Islands long had rich forests. Moisture-rich fog drifted in from the Atlantic Ocean and anointed the trees with plentiful water. These trees were key to a viable biome.
When humans populated the islands, they chopped down enough trees to deforest entire islands. When the number of trees went past the point of self-organized criticality, there was not enough water to sustain any population. Drying out the land destroyed the ecosystem.
Restoration has not been possible. The islands’ water supplies are inadequate to keep newly planted trees from drying out.
In shaping their habitats by their constructions and other efforts, beavers and hippopotamuses are ecosystem creators. Both craft the effect by altering aquatic features on the terrain.
In flooding African plains, hippos bulldoze paths that create water channels, diverting swamp flow. These hippo waterways are used by many other animals, including grazing herds and crocodiles, who treat the channels as lanes to the diner.
The 40 kilograms of grass that hippos eat each night recycle nutrients, providing loads of dung for insects and smaller life near the bottom of the animal food chain.
Elephants are messy eaters: ripping trees and other vegetation apart. Their voluminous scraps provide ready-to-eat meals for a bevy of other herbivores, including rhinos, geckos, frogs, and an array of invertebrates.
As ecosystem service-providers of a different sort, pollinators are something of a keystone. In that they typify the bottom of the terrestrial food chain, plants are a root keystone in every terrestrial ecosystem.
The oceanic realms also ultimately rely upon producers and the most prolific in the lower rungs of the food chain, such as sardines. As constructors, the beavers of the sea are coral reefs and their northern cousins: kelp beds, which create environs for others to flourish.
In ecological systems, most species are rare – that is, represented by only a few individuals or restricted to particular habitats. Around the world, the human-induced collapses of populations and species have triggered a mass extinction crisis, with rare species often being the first to disappear. ~ French ecologist David Mouillot et al
Biodiverse environments are characterized by large numbers of rare species. These rarities uniquely contribute to ecological vitality in ways that common species cannot.
Pyramidal saxifrage is a long-lived European alpine plant with thick, dense leaves, adapted to stressful environments. This rare cliff dweller is important in the species-poor lands where it resides.
Pouteria trees in the Guyana rainforest grow to over 40 meters high. They have thick, plate-like bark and low-density wood. These rare trees are particularly resilient to drought and fire, and so act as a buffer in helping maintain forest structure during stressful times.
Batfish are a rare fish that keep algae growth in check around and on coral reefs, while common parrotfishes and rabbitfishes, with similar diets, fail do so. On the Great Barrier reef, batfish eat seaweed that more common fish will not touch. Seaweed inhibits coral.
Manipulative parasites modify energy flow among organisms, and consequently affect the structure, dynamics, and functioning of food webs. ~ Japanese zoologist Takuya Sato
The power of parasites paints the trophic pyramid a parody. Unlike top predators, whose feasting is largely self-serving, parasites are often biome keystones; admittedly an irony, considering their lifestyle.
Hairworms are a cricket’s worst nightmare. A cricket with this worm inside is fine until the parasite reaches maturity and feels the urge to escape into the water. Then the worm forces its cricket host to stumble into a stream, where it becomes fish fodder. In some watersheds, fast-food delivery of crickets accounts for more than half the dietary intake of trout living there.
The mudflats on the coast of New Zealand are rich with the New Zealand cockle. This clam is subject to infection by a parasitic fluke (Curtuteria australis) that embeds itself in the mollusk’s foot muscle. As parasites accumulate, the clam loses the use of its foot muscle, so it can no longer dig its way to safety. Stranded on the mudflat, the clam becomes easy pickings for shorebirds. This suits the fluke. Infected birds complete its life cycle. The fluke’s handiwork paves the mudflat with clam shells, enriching the environment and raising biodiversity.
Mistletoes provide structural and nutritional resources within canopies. ~ Australian ecologists David Watson & Matthew Herring
Essentially tree leeches, mistletoe represent a successful business model. There are over 1,300 species, found in forests around the world, both boreal and tropical.
Mistletoe is a hemiparasitic plant that can damage or even kill its host tree. Birds snack on the berries, but only the aptly named mistletoebird makes the mistletoe its main meal ticket.
Many animals drink mistletoe nectar or eat the leaves or berries. Some birds use the leaves for nest lining, or nest in mistletoe clumps.
To keep to the trees, mistletoe berries are a sticky, viscous goop with a sturdy seed inside. After eating the berries, birds often regurgitate the seeds. They then wipe their bills on tree twigs to clean them off, leaving the sticky seeds attached to their new home.
For birds that swallow seeds, such as the silky flycatcher, the stickiness persists through digestion. To clean up after a berry dump, they wipe their butts on branches, pasting seeds as they go. There is evidence that the term mistletoe is old Anglo-Saxon for “dung on a twig.”
Mistletoe matters. Without mistletoe, bird populations drop by over 25%, and woodland-dependent residents decline by 35% or more. Species richness goes poor sans mistletoe.
Weakening and killing trees is good business for wood-boring bugs, and bugs are good business for birds.
What’s more, mistletoe shed a lot of their leaves: 3–4 times the rate of host trees. This adds depth to the leaf litter pile in the woods, upon which insects may thrive.
Nonparasitic plants suck all the nutrients out of their own leaves before they let them fall, sending dry containers to the ground. In contrast, as mistletoe draw water and nutrients from their host, they are more nonchalant about leaving nutrition in their falling leaves. Thus, mistletoe leaf litter is unusually high-quality.
As evergreens, mistletoe grow all year, even when trees are dormant. Their berries are valuable sustenance to birds as winter fruit. To the leaf-eaters below, it is a perennial mistletoe banquet.
Hence, mistletoe act as a keystone species by providing tasty leaf fodder, and by increasing the velocity of turnover in a biome; an instigator in a biotic butterfly-effect vortex.
Invasive species are a worldwide scourge – a nasty side effect of modern transportation technology and economic globalization. ~ The Week
An invasive species is a plant or animal introduced into an ecosystem which then has a disruptive effect by establishing itself as dominant, to the diminishment or exclusion of native species.
An introduced species may establish itself by using resources unavailable or untapped by natives, such as plants tolerating low-nutrient soils, or outcompeting indigenous animals that feed on the same food sources.
An invasive species tends to be successful when introduced into a habitat like the one in which it evolved. Amphibian introductions are particularly successful. When frogs and salamanders come into an area where a similar species exists, they are more, not less, likely to establish themselves. Darwin staunchly predicted otherwise.
Generalist species may rapidly adapt to their adopted home. Their tolerance for temperature and other variables gives them a head start.
The purple loosestrife is a flowering plant native to northwest Africa, Europe, Asia, and southeastern Australia. When it was inadvertently cut loose in eastern North America, the loosestrife did so well as to earn condemnation as “one of the world’s most serious wetland invaders.” The loosestrife managed its notoriety by quickly adapting to the local climate.
The creeping daisy, native to Central America and the Caribbean, received a different reception upon its prolific invasion of Fiji via rapid climate acclimation. The daisy was welcomed by the local pollinators, and by crop growers concerned about a decline in pollinating insects. They thought it harsh that the daisy was damned a “nuisance weed.”
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Many plant species can persist at low population densities. Propagation prospects improve with more favorable resource abundance, fewer competitors, or herbivores. This is true for either native or introduced species.
Oftentimes, exotic and native plants live together relatively peaceably. Such instances seldom inspire the derogation invasive among judgmental onlookers.
Exotics often face a circumstance that sets them back: previously unencountered herbivores. Insects are particularly fond of new plant species that have yet learned how to cope with them.
An introduced species may occupy a new habitat at low density, biding its time until conditions ripen for rapid expansion. Decades may pass before an exotic plant pushes a population surge, outcompeting the natives and becoming the dominant plant in the community. Only then is the invasive label pinned on it.
Kudzu is a hardy perennial vine, originally native to the Japan. Kudzu was introduced to China and Korea centuries ago. In those countries, winter weather induces an aboveground die back, keeping the vine from becoming a nuisance.
Kudzu was introduced to the United States in 1876, at an exposition in Philadelphia. Its debut in the south was at a New Orleans exposition, in 1883.
From then, the vine was widely marketed in the southeast as an ornamental plant, to shade porches. During the first of the 20th century, kudzu was distributed as a high-protein fodder for cattle and employed as a cover plant to prevent soil erosion, especially during the Dust Bowl years, in the 1930s.
During the 1930s and 1940s, the federal government grew and subsidized planting kudzu. By 1946, 1.2 million hectares of kudzu had been planted.
Kudzu thrived in the subtropical southeast; so much so that the US Department of Agriculture (USDA) removed kudzu from its list of suggested cover plants in 1953. In 1970, the USDA decreed kudzu a weed, whereupon kudzu became accursed as an invasive species.
All the while, in Japan and Korea, kudzu root is cooked and eaten, and used in herbal medicines. Kudzu is fed to sick animals to abet their recovery. The Chinese also use kudzu as a natural medicine, including as a treatment for alcoholism.
Wind, water, and animals, notably humans, commonly act as transport for species introduction. Changing climate can remove one or more obstacles that keeps a biome isolated.
King Crabs Under Antarctica
Antarctica separated from South America 40 MYA. From the divorce emerged a circumpolar ocean current, which isolated Antarctica from warmer air and water masses farther north. This plunged the new continent into perpetual winter.
Falling temperatures brought a bloom of soft-bodied echinoderms on the sea floor. These invertebrates – sea cucumbers, brittle stars, sea spiders, sea stars, and sea lilies – date back to the early Cambrian.
Echinoderms flourished because their predators were being excluded with the creeping cold. The water got too frigid for sharks and carnivorous crustaceans.
At less than 0 °C, crabs and lobsters cannot regulate the magnesium in their body fluids. This leads to clumsiness, breathing paralysis, and narcosis.
The fish under the Antarctica ice shelf evolved antifreeze proteins to keep blood flowing. Unlike their cousins in balmier seas, these ~100 species lack powerful jaws, and so pose no threat to the unprotected echinoderms.
The water directly under Antarctica’s ice shelf is slightly warmer than the ocean water at its edges. The cold, salty water in the Southern Ocean sinks below the less dense water directly under the ice shelf.
The polar regions early on showed the effects of global warming caused by human pollution, most notably glacier loss and increasing sea ice melt during the summer. That, and a hole in the ozone layer over Antarctica, have resulted in westerly winds strengthening and the circumpolar current intensifying.
These changes have lifted warmer water over the lip of the continental shelf. The temperature difference is only 1.8 °C, but it has been enough to allow passage back for crusty carnivores. Long excluded by a barrier of cold, king crabs invaded Antarctica in 2011. Their incursion is causing a major reduction in seafloor biodiversity.
More generally, global warming is opening new habitats to many species, both flora and fauna, in a diverse variety of ecosystems. From a geologic time-frame perspective, the mix of biota worldwide is rapidly changing.
Islands and other environments where species competition has been minimized favor invasive species. Disruptive ecological events, such as wildfire, can improve prospects for invasive species.
Successful plant and animal migrated species typically have at least some the following traits: generalist capacities, such as being able to eat a variety of foods, and/or tolerate a wide variety of environmental conditions; good dispersal ability; fast growth; rapid reproduction; and phenotypic plasticity: the ability to alter themselves to suit current conditions. For all that, invaders are almost always no more successful in their new habitat than they were in their old.
An exotic species invariably carries with it its own microbiome, and frequently parasites. Hence a migrant may pose less of a threat to its new habitat than its passengers.
Often the label invasive represents a snapshot impression. Many introduced species are considered native by the natives.