Humans' ever spreading presence around the globe influences patterns of biological evolution in ways that we are just beginning to explore. On the Galápagos Islands, a body of evidence shows that the effect of our presence is increasing.
Luis F. De Leon from the University of Massachusetts Boston, together with other 6 scientists spent two years observing Darwin's finches (雀科小鸟) to evaluate our effects on their behavior. They started by conducting feeding observations on coexisting finch species at sites that ranged from non-urban areas to urban areas. They also employed finch-human interaction experiments to test whether and how finches respond to human presence. To measure whether finch feeding preferences varied with the degree of urbanization, "cafeteria" experiments were carried out — finches were presented with a selection of human and native food items.
The scientists found that Darwin's finches fed almost on human foods like rice and cookies or introduced garden species at urban locations. In contrast, at non-urban sites, finches fed mainly on native plant species and insects. Interaction tests suggest that urban birds get more accustomed to the presence of humans. Finally, at all sites of regular human presence, finches preferred human foods to natural foods.
The researchers warn that exploiting urban environments might present challenges for organisms (有机体), including shorter lifespans brought by the consumption of highly processed foods. Furthermore, the year-round availability of abundant human foods in urban environments might affect ecological and evolutionary processes that promoted species diversity. While the results clearly show a shift to human foods at urban sites, the adaptive significance of that shift is still an open question.
These findings also suggest that human behavior is the main driver of finch preference for human foods. The researchers propose a possibility that the effect of human behavior is facilitated by our tendency to feed birds, directly or inadvertently via food dropping or littering.
