Shade or shun? Effects of plant invasions on native ectotherms under a warming climate

Shade or shun? Effects of plant invasions on native ectotherms under a warming climate
Raquel A. GARCIA, Susana Clusella-Trullas
Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Matieland 7602, South Africa

Ectothermic species, such as amphibians and reptiles, tend to follow environmental temperatures closely and are thus seen as particularly vulnerable to climate change. Changing climates translate into altered air temperature, but it is the interplay between air temperature and habitat structure that ultimately determines the range of microclimatic environments available to individuals. Alien plants modify vegetation structure and shade availability, thus affecting the thermal landscapes experienced by ectotherms and the options available to behavioural thermoregulators for shuttling between microclimates. Despite widespread concern about ongoing climatic changes and plant invasions, the synergistic effects of the two threats have hitherto received insufficient attention. In a warming world, are ectotherms likely to avoid invasive vegetation or seek their shade?

We start by reviewing the current state of knowledge about thermal effects of alien vegetation on native herpetofauna, and then illustrate potential hotspots of synergistic effects with climate change at a national scale. Using South Africa as illustration, we show the overlap between plant invasions, projected temperature changes, and diversity of reptiles and amphibians.  We apply a biophysical approach to explore the effects of invasion-induced changes in shade availability on the operative temperatures of reptiles and amphibians, and discuss the potential implications for groups of species with different traits. Increasingly, prioritisation of conservation efforts needs to rely on knowledge of the spatial distribution of multiple threats such as shown here, and on an understanding of the mechanisms underlying potential synergistic effects between threats.