14 DAY TRIAL // Naturalists have been finally able to understand one of the most puzzling aspects of species' evolution, namely why rare traits seem to persist in the general population over a long time. According to recent investigations, this happens because the natural predators of those species have the tendency to avoid catching prey they are unfamiliar with, at least as far as the exterior aspect goes. A new study, conducted on birds and reptiles, shows that birds tend to capture salamanders that look common, rather than going for the more rare varieties, which have different shapes, or are colored differently than the majority.
“Maintenance of variation is a classic paradox in evolution because both selection and drift tend to remove variation from populations. If one form has an advantage, such as being harder to spot, it should replace all others. Likewise, random drift alone will eventually result in loss of all but one form when there are no fitness differences. There must therefore be some advantage that allows unusual traits to persist,” University of Tennessee expert Benjamin Fitzpatrick says. He has collaborated with colleagues Kim Shook and Reuben for the new study, which appears in a recent issue of the journal BMC Ecology, ScienceDaily reports.
During the experiments, the experts monitored the hunting behavior of a flock of Blue Jays. They created an enclosure in which they placed salamanders for seven days at a time. During one experiment cycle, they filled the enclosure with 90 percent stripped salamanders, while in the others they did it with 90 percent unstripped salamanders. In the weeks between the cycles, equal numbers of stripped and unstripped creatures were placed in the test space. When looking at the way Blue Jays hunted, the researchers noticed that the birds tended, in the weeks between the cycles, to attack the type of salamanders that was present in larger numbers the week before.
“We believe that the different color forms represent different ways of blending in on the forest floor. Looking for something cryptic takes both concentration and practice. Predators concentrating on finding striped salamanders might not notice unstripped ones. Thus, the maintenance of color variation in terrestrial salamanders might be explained by the oldest and most obvious hypothesis – rare form advantage arises because predators tend to overlook rare prey,” Fitzpatrick argues.