The effects of reptiles as top predators on the ecology of small island systems

Background/Question/Methods

In mainland ecosystems top trophic positions are typically inhabited by mammalian and avian predators, the presence of which then affects trophic levels below. In contrast, on smaller islands, reptiles - which by virtue of their reduced energetic demands require less area to maintain a sustainable population – frequently inhabit the same position. Recent research has suggested that reptile populations can have similarly strong effects on island food webs, although these ideas have rarely been tested in a rigorous manner. Here we report on the ecological impacts of replicated experimental lizard introductions onto a set of Mediterranean landbridge islands. The Aegean Wall lizard (Podarcis erhardii, Lacertidae) is a widespread species in the islands of the Aegean Sea (Greece) where it forms multiple ecotypes. As part of a 5-year experimental evolution experiment we evaluated the effects of these lizards on the food webs of 10 Cyclades islands (5 introduction, 5 control islands).

Results/Conclusions

We found that establishment of lizards on an island resulted in broad reductions of resident arthropod populations and in pronounced shifts towards chemically or mechanically defended taxa. In addition, we observed trophic cascade effects with clear benefits of lizard presence to resident plant communities. The results demonstrate that lizards have the ability to shape island species communities and to bestow important benefits to local plant communities via reduced rates of herbivory.