When a species’ population declines, it seems logical to assume that that species will get closer to extinction. With a smaller population, after all, problems that occur naturally within the species or the environment should have a bigger effect.
For example, if you have $100 and spend half of it, you will still have $50 left over—a reasonable amount of spending money. If you start with $10, on the other hand, spending half your money leaves you nearly broke.
But what if this logic is flawed? A group of Concordia scientists recently published a paper in Evolutionary Applications suggesting just that: that small populations have a better chance at survival than we think.
The argument for small populations
Using information gleaned from previous papers dating back to 1980, the Concordia study compares population sizes to the amount of genetic variance that can be passed from parent to offspring. It also tests to see if the number of individuals in a species has any effect on the population’s strength of natural selection.
This comparison was applied to a wide variety of species, in hopes that the findings of the study would be proven universal—which appears to be the case. Selection strength and genetic adaptive potential stayed consistent throughout all population sizes. This outcome implies that those issues have no special effect on declining populations.
Problems with the argument
It’s possible that the results obtained by the Concordia study were due to something other than strength in declining populations. Other possibilities include methodical errors, inaccuracy in measurements, insufficient research time and over-speculation.
First, studying such a wide variety of organisms can make it difficult to properly identify a single clear pattern. Harmony Dalgleish, a biology professor at the College of William and Mary, states that because the researchers are “lumping in all these different types of species with different life history traits, I’m not sure you would even expect to find a pattern.”
Second, evolution takes an incredibly long time. Biology professor Helen Murphy explains: “These are probably, on some level, on an evolutionary scale at least, recently fragmented populations, so these are long lived birds who, even if it was 20 years ago that their habitat fragmented, there’s still going to be a ton of genetic – come back in 300 years and see what you find.”
In short: a population will not genetically respond to a change in size unless many, many generations have passed. The Concordia paper, unfortunately, did not have information for such a lengthy time span.
So, what concrete information can this paper offer conservationists? If nothing else, it reinforces the idea that variation within a species should not be our top concern.
Dalgleish explains that there are “a lot of dangers related to small population sizes that aren’t necessarily genetic […] so they were comparing the dangers of inbreeding essentially versus just the dangers of living in a small population demographically.”
Murphy does say “the one thing that would be a disaster is if the wrong organization took this and went to a congressman and said ‘look, small population sizes don’t matter at all.’”
Essentially, people could take advantage of this study and misinterpret it in very dangerous ways. If people try to argue that small populations can “fight back” on their own, we could end up forcing a lot more species into extinction. Even now, some proposed actions are threatening 111 endangered species and 108 species of migratory birds.