This quote brings home the critical importance of not letting populations fall into the extinction abyss. We need to rescue species from that fate. But how to do it? Often their habitat is a fraction the size it once was, and likely degraded and polluted, too. In the time required to restore habitats, species can go extinct.
We need tools to give us time. My coauthors and I demonstrate in our new paper in PNAS (!!) that migration can be that tool. Apologies for the paywall, email me for a copy.
But what kinds of migrants? When populations are small, they can go extinct just by chance. Increasing their size might help. But when populations find themselves in a degraded environment, they need to adapt to survive. Also, those same populations, being small, become inbred. Just a few migrants can increase genetic variation and reduce inbreeding.
So do we want a lot of migrants to overcome demographic stochasticity, or just a few migrants with the right genes to rescue our populations?
One good way to answer this question is by using a model experimental system. We used Tribolium flour beetles, and gave struggling populations either lots of extra individuals to increase size, or just a few genetically distinct individuals to reduce inbreeding and enhance adaptive potential.
Which works best? Just adding individuals with the right genes is more effective than lots of individuals that don't necessarily have the right genes. The good news is that even without efforts to rescue populations with migration they evolved higher fitness.
This last is somewhat surprising. Much research thus far on what has been called "evolutionary rescue" (essentially adaptive evolution that enables a population to avoid extinction) has focused on large populations of organisms that aren't obligately sexual. Our work shows that even obligately sexual diploids with small populations can adapt quickly enough to avoid extinction, at least under some conditions.