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Timothy Thurman

McGill University
Phenotypic change in response to introduced predators and competitors: a field experiment with Anolis lizards

Timothy J Thurman, Robert M Pringle, Rowan D H Barrett

Whether due to climate change induced range expansion or human-mediated dispersal, the sudden arrival of a new species can wreak havoc on native food webs and ecosystems. In particular, new competitor or predator species could impose strong natural selection on natives, and native species’ persistence may depend on their ability to meet these selective challenges. We present results from a large-scale, replicated field experiment studying the response of brown anoles (Anolis sagrei) to introduced predators and competitors. Over six years and across 16 islands, we manipulated the presence of a competitor species (the green anole) and a predator species (the curly-tailed lizard) in a replicated, factorial design. With a combination of demographic, behavioral, and phenotypic data, we examine how novel ecological interactions affect the native A. sagrei. We show that predators impose strong demographic pressure on A. sagrei, leading to reduced population densities. A. sagrei displayed a rapid response in predator-avoidance behavior, perching higher in vegetation. However, this behavioral shift did not lead to phenotypic selection on traits associated with locomotor performance: phenotypic change was limited to sex-specific changes in body size. Together, behavioral and phenotypic changes allowed A. sagrei to mitigate the negative impacts of invaders and persist in their natural habitat. Our results provide insights into the ways in which native species might respond to invasive species, while our replicated design allows us to examine the extent to which such responses are parallel, repeatable, and predictable.