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The nature of a creature, its predators, and its habitat, present adaptive pressures that affect sociality and other facets of life. A lack of resources – food or mates – creates territorial instincts, or, conversely, may spur greater sociality. The great tit is alternately territorial or gregarious depending upon the season: territorial during mating season but wintering in large flocks with their own and other species.
Mating seasons often spur competitive and/or territorial behaviors, or alternately, may foster breeding colonies. Defending territory is energy expensive.
Social Dominance
Male elephant seals and red dear spend much of the breeding season in battle: fighting for paternity of the next generation. The winner, either by aggressive negotiation or bloody fight, takes the spoils; at great cost.
Male elephant seal mortality is high. Few achieve the strength and size to hold a harem on a breeding beach.
A male lion may hold onto a pride of lions for very few years before being displaced by a younger and stronger rival. The reproductive life of a female red deer may be 20 years, but a stag’s breeding years are considerably fewer, as holding onto the privilege of paternity takes a heavy toll.
Conflicts arise in all social animals. The fiercest are often over mating rights and prime breeding spots. Yet few mating contests are so taxing as to be terminal to the loser. Such fighting in most species is ritualized.
A male mantis shrimp could easily kill a vanquished opponent. It seldom happens. A beaten combatant can signal his opponent that he has had enough. Specific submission gestures vary by species, though they typically involve putting oneself in a vulnerable position.
African wild dogs show an open-mouthed grimace, lower and turn the head, and even go belly up in a groveling motion. The winner permits the defeated to leave the field without further harm.
The Occam’s-razor explanation for letting an opponent live another day is that evolution generally favors success of a population, not just individuals. Nature does not intend to create murderous brutes as a norm.
Gall Aphids
A petiole is the stalk attaching the leaf blade to the stem of a plant. With the coming of spring, aphid eggs hatch on the petioles of cottonwood and poplar trees. The emerging aphids amble to leaves on the branches.
Of tens of thousands per tree, each female settles at the petiole of a selected leaf. There she chemically induces a hollow ball of leaf tissue – a gall – for her homestead, where she will bear offspring parthenogentically. Parthenogenesis is asexual reproduction without fertilization.
Once her daughters have matured, they either fly off to another host or stake a claim on the natal tree. Staking a claim to a choice leaf is not easy. Prize petioles can be hard to come by. There may be 20 aphids for every large leaf on the tree. Females may spend hours kicking each other for a preferred leaf, or a superior leaf site. They may fight for 2 days, to the death, for the right to grow a gall in a great location.
Lovely leaves are worth fighting for. Defeated females, and those disinclined to aggressive negotiation to death, are forced to accept inferior lodgings. The choices are a smaller unoccupied leaf or taking a secondary spot on a larger leaf: midrib, where the juices are not as nutritious. Both are equivalent in worth, but a significant step down in quality from a prime petiole.
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Dominance and deference are common components of presocial societies. There are many situations where social dominance enters in. First or best access to a meal is exemplary.
Territory is commonly critical. A dominant individual or pair take the choice spot, for whatever reason or whim. Might makes right in the animal world.
Chickens are unusual in develop a specific pecking order. In other species, particularly primates, the social hierarchy is much more complex, including alliances. 2 chimpanzee males may cooperate to share a top spot in their troop.
Conflicts recede when a social hierarchy has been achieved. Animals learn of other individuals’ capabilities and defer when appropriate to avoid losing a fight. Chickens are less aggressive once they get to know each other, as are other species.
Social stability lasts only as long as abilities remain static. A young male chimp or baboon that grows stronger may challenge the existing hierarchy. Other relationships in the group may change in that wake.
Some animal groups are too large for all to know each other. Such species use status badges to maintain hierarchy and avoid unnecessary conflict.
Male house sparrows have black bibs, which distinguish dominant birds from subordinates by size. Harris’ sparrows have black head feathers to the same effect: the blackest heads are the top birds.
Male African red-shouldered widowbirds wear epaulets. Territory holders have larger and redder shoulder patches than territory floaters, who are loiterers in other birds’ territories. These 2nd-place birds immediately concede defeat when challenged but are ready to assume a territory should a resident vacate.
Cheating is prevented because weak mimics would face constant challenges that they would lose. Deception would come with a heavy social cost. While status badges are more reliable than they may first appear, they are used primarily in species that constantly encounter large numbers of other individuals, such as sparrows and great tits.
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For most species social organization and individual interactions are too various to easily categorize. Many factors are in play. Changing seasons often alter social organization.
Male chaffinches tend to dominate females in winter flocks, displacing them at feeding sites. This is reversed in spring, when females displace males, as male flocks disperse to establish territories.
Feral chickens on an island off Queensland, Australia alternate between a hierarchical flock during the winter and a territorial regime in the breeding season.
The social structures of some mammals may shift by season. Red deer are a dramatic example. Other than the breeding season, red deer bucks and doe live apart. Red deer males live in loose bachelor herds, with a dominance hierarchy by body size. A higher-ranking stag may displace lower-ranked stags at a choice food patch by lowering his head and displaying his antlers.
Females (hinds) live in their own herds with the young of both sexes. Hinds seldom threaten or displace each other, even in winter, when food is scarcer.
Come April, stags shed their antlers. Male aggression takes a new form: rearing up on their hind legs and boxing with their hooves. As new antlers grow, the males become ever more aggressive: fighting head-to-head.
With a hierarchy established, male red deer herds break up in September. Each male heads to a favored display area, where he roars to gather hinds coming into estrous. So goes rutting season. Males defend the females they attract rather than any territory. Rutting season is but a few weeks, whereupon the different sexes return to their respective herds for the winter.
Sociality is commonly consistent for many mammals. Wolves hunt in packs, with a stable hierarchy based on their extended family group. Lion prides are similar in their social permanence.
Compared to wolves, elephant social order is more extended and complex. Females maintain immediate family groups of 5 to 15, which may also include young elephants of either sex. When a group gets too big, elder daughters form their own group, though the different herds remain aware of their family ties. Male adults are more solitary, though they do occasionally form friendships with other males, as well as establish dominance hierarchies for breeding rank.
Many primates maintain a uniform social organization regardless of season, characterized by complexity and subtlety in individual affections. Even lemurs have intricate mixed-sex social groups, with each troop maintaining a stable-boundary territory. Relationships are mostly friendly, except for males during the short breeding season, when dominance hierarchies play out. There are strong mother-offspring bonds. Play and mutual grooming are ubiquitous.
Each animal that lives in a complex social assemblage is critically dependent on cooperative interactions with others. This necessitates mental models of behaviors toward other individuals according to intimacy, biological relation, and social hierarchy.
A rhesus macaque mother may hold her own infant along with another of similar age. The other being held is most often the offspring of a dominant female.
The hope is for a social head start: to engender future association between one’s own offspring and high-ranking youngsters. Other primates behave similarly.
The social norms of different primate species vary, but monogamy is rare. Gibbons are a near-perfect exception to that rule. They have lifelong pair bonds between male and female, and a strict territoriality that is maintained by elaborate singing, especially at dawn. There are parallels between gibbons and songbirds in facets of their lifestyles.
