Human land use with cascading ecological effects: An examination of hunting mode switching in Podarcis erhardii and associated effects on insect populations

Background/Question/Methods

Human land use can be a pervasive driver of population decline, but species’ capacity to adapt can also make ecosystems more resilient than previously appreciated. Adaptations to anthropogenic changes may result in functional trait changes that alter the role a species plays in the ecosystem. Understanding the functional implications of a species’ behavioral, morphological, and physiological responses to coexisting with humans is a relatively unexplored but critical component of predicting the effects of land use on ecological systems. I tested whether the presence of built stone walls and subsequent colonization of those structures by the lizard Podarcis erhardiihas resulted in behavioral, morphological, and performance differences relative to populations naïve to human-built infrastructure. I then tested whether observed differences in those traits have affected the broader ecological community.

I conducted my study at nine sites on the island of Naxos in the Greek Archipelago, five with built stone structures and four without. At each site, I caught P. erhardii lizards; flushed the lizard’s stomachs; measured a suite of body, head, and limb morphological characteristics; calculated maximum bite force; and assessed locomotion capacity. I also videotaped lizard behavior in-situand collected trap data on insect diversity and abundance.

Results/Conclusions

I found significant behavioral differences between lizards living at sites with and without walls. “Wall” lizards usually perched, waiting for prey, while “no-wall” lizards foraged for food more actively. I also found morphological differences between these populations: body size was larger, and head width and foot length were proportionally longer, among wall populations. Head differences corresponded to proportional differences in bite force, and longer hind feet enabled wall lizards to accelerate more quickly over rocky substrates relative to no-wall populations. Finally, I found that these behavioral and morphological responses to habitat context resulted in differences in diet. The sit-and-wait wall lizards ate a higher proportion of fast-moving insects, while the actively foraging no-wall lizards consumed more slow-moving insects. These diet preferences are consistent with theory on predator foraging mode, which predicts that more active predators should be able to find and eat less active prey.

Some species’ capacity to rapidly adapt may enhance their resilience to anthropogenic land use; however, functional trait changes in novel contexts may have cascading consequences for the ecosystem as a whole. This study uniquely demonstrates such behavioral, morphological, and performance change due to human land use and traces those changes to the ecological community.