Close encounters of the urban kind: predators influence prey body size variation in an urban landscape

Abstract

Body size is a key trait linked to many aspects of an organism’s life history, physiology, and behavior. Variation in body size can thus have important fitness consequences across a broad range of ecological contexts. We utilized the variation in multiple abiotic and biotic factors found among urban habitats to test simultaneously their relative effects on body size variation in urban populations of brown anole lizards (Anolis sagrei). These factors represent major hypotheses regarding body size variation in ectotherms and other animal groups: temperature, food availability, conspecific abundance and predator abundance. We also performed a tethered intruder experiment to determine whether the attack behavior of predatory curly-tailed lizards (Leiocephalus carinatus) depends on the body size of their brown anole prey. Lastly, we conducted a common garden experiment to assess whether brown anole body size differences between sites with and without curly-tailed lizard predators are genetically based. Predator abundance was the primary predictor of brown anole body size for both males and females. No other hypotheses were consistently supported. Brown anole body size increased along with increasing predator abundance, and predator abundance was negatively related to body size variation. Additionally, predators approached larger brown anoles less often and at longer latencies compared to smaller ones. Finally, male brown anoles from sites with predators had faster growth rates compared to those from sites without predators under common conditions in the lab. Brown anole body size differences among populations may result from higher survival of larger lizards during predatory confrontations, and this trait is at least partially heritable in males. Therefore, our results suggest that curly-tailed lizard predators may be important agents of evolution by natural selection for brown anole populations in urban habitats. To further investigate the ecological and evolutionary consequences of predator–prey interactions in urban habitats, future research should focus on measuring predator-induced selection in these novel environments.