Dispersal & Adaptation
Dispersal and local adaptation are major drivers of population structure. In general, their respective roles are not independent. The two may often be at odds with one another evolutionarily, each one exhibiting negative feedback on the evolution of the other. ~ American evolutionary biologist Simon Levin et al
Scattering or adapting are the evolutionary strategies. The two are not mutually exclusive. Context matters.
A main factor influencing the evolution of dispersal is the spread of risk in unpredictable environments. ~ Finnish evolutionary biologist Éva Kisdi
In a homogeneous habitat, such as a desert, dispersal typically occurs, as offspring are likely to encounter a similar environment wherever they go. Conversely, a highly diverse habitat favors specialization, as dispersal offers a lower probability of finding an already-suitable habitat; mountains are exemplary.
A highly dispersing generalist species will continue to scatter even as environmental heterogeneity increases, but only to a point. At a certain threshold, populations shift to specialist lineages, each adapted to a specific habitat. This shift can be highly discontinuous.
Once local adaptation has taken place, dispersal is disadvantageous because individuals move away from a habitat that they are adapted to and land in other habitats where they are selectively inferior. ~ Éva Kisdi
Once a generalist population starts to specialize, the resulting drop in dispersal induces further specialization. This positive feedback loop between reduced dispersal and local adaptation triggers a dramatic shift in evolution strategy: forgoing the possibility of returning to generalization.
There is ample empirical evidence that habitat specialization promotes adaptive diversification in, for example, bacteria, plants, insects, and vertebrates. ~ Éva Kisdi
Evolution appears to practice localized risk minimization.
Several locally evolutionarily stable attractors may exist simultaneously, but generally, only one of them is a global evolutionarily stable strategy. ~ Éva Kisdi
Global Microbes
It challenges the imagination to think of nearly identical microbes 16,000 kilometers apart in the cracks of hard rock. ~ American geomicrobiologist Matt Schrenk
Probing mineshafts, wells, and drilling rigs that run kilometers deep, in locations ranging from the Arctic Circle to Antarctica, including the benthos in between the poles, has repeatedly revealed the same 19 species of microbes all around the world.
There seems to be a core group of microbes that appears again and again in all of these environments. ~ American microbiologist Rick Colwell
Many of the “everywhere” microbes have been found in serpentine minerals, which form under the geophysical conditions that may have prevailed when life on Earth originated. These hardly primordials may have been transported around the globe by plate tectonics, or perhaps they convergently evolved, or a bit of both among them all.
There seems to be a commonality of colonisation of the subsurface of the planet. ~ Canadian geologist Barbara Sherwood-Lollar
