Small population size? It doesn't have to mean that species can't adapt to environmental change

A study recently published in Evolutionary Applications by a group of Concordia biologists shows that small populations of species can still adapt and respond to natural selection.

"Our research shows that, just because an animal or plant is few in numbers, that doesn't necessarily mean that they can't be brought back from the brink of extinction -- they might still possess enough genetic diversity to respond to changing conditions through natural selection," says biology professor Dylan Fraser, one of the study's authors.

But, he warns, "I wouldn't advocate that we can hammer down every species. There are a number of concerns always, but from a genetic standpoint, small population size may not be as bad as we initially thought."

For the study, Fraser and his co-authors -- Jacquelyn Wood, the senior author who recently graduated from Concordia with her PhD and now works for the Ontario Ministry of Natural Resources and Forestry, and current PhD candidate Matthew Yates -- combed through empirical studies produced between 1980 and 2014. They produced an extremely thorough database that maps the extent of natural selectiin and amount of genetic diversity underlying traits needed to adapt to environmental change of 146 separate population groups across 83 different species ranging from simple plants to large mammals.

"We found little evidence for consistent differences in genetic variance, or the extent of natural selection across a wide gradient of population size in nature. These are notable results given the large size of the data set and the general lack of research investigating patterns of selection in relation to population size in wild species," says Fraser.

"Our results don't jibe with the widespread view that small populations should have lower amounts of genetic variation. We observed no significant effects of population size on genetic variance in our analysis."

This finding has important implications for conservation efforts, which should consider that the evolutionary trajectories of some small populations appear to be very much affected by natural selection, and different small and large populations of the same species may contain variation that is adaptive in a wide range of circumstances. What's more, minimum viable population sizes for some species may not need to be as high as previously thought.

While this is cause for hope, Fraser recommends we proceed with cautious optimism.

"Our findings don't mean that all species are robust and can handle depletion, but it generally hints that there must be situations in nature that allow small populations to adapt to environmental change. If we can pinpoint which species can handle small population size, and even specific populations within species, it will influence conservation efforts."