The effects of predation risk, shelter, and food availability on the reproduction of Aegean Wall lizards (Podarcis erhardii) in the Greek islands

Abstract

Reproductive investment, including the average number of offspring produced by an organism, is one of the fundamental characteristics of a species. Among other things, it predicts a species’ resilience to environmental disruption: taxa that produce more offspring are able to recover more quickly from environmental perturbations and survive long-term environmental change. Despite the clear importance of this trait, ecologists do not have a good understanding of the primary drivers shaping the reproductive investment of each species. To answer this question, I compare the reproductive efforts of numerous island populations of the Aegean Wall Lizard (Podarcis erhardii), which differ in multiple key environmental characteristics. I test three hypotheses, namely that reproductive investment (measured as clutch size, clutch volume and egg volume) is: 1) positively associated with predation risk [‘Predation Risk Hypothesis’]; 2) positively associated with the presence of reliable vegetation cover that provides shelter [‘Gravid Female Protection Hypothesis’], and 3) limited by (and hence positively correlated with) food availability [‘Food Limitation Hypothesis’]. Although field data are consistent with all three hypotheses, statistical analysis shows strong support for the Predation Risk Hypothesis. The result not only shed light on which fundamental forces shape reproductive investment in island vertebrates, but can also help set conservation priorities by identifying the most sensitive populations because reduced reproductive ability can be predicted based on easily quantifiable island characteristics (number of sympatric predator species).