Do climate envelope models transfer? A manipulative test using dung beetle introductions.

Richard P Duncan,Tim M Blackburn,Phillip Cassey

doi:10.1098/rspb.2008.1801

Abstract

Climate envelope models (CEMs) are widely used to forecast future shifts in species ranges under climate change, but these models are rarely validated against independent data, and their fundamental assumption that climate limits species distributions is rarely tested. Here, we use the data on the introduction of five South African dung beetle species to Australia to test whether CEMs developed in the native range can predict distribution in the introduced range, where the confounding effects of dispersal limitation, resource limitation and the impact of natural enemies have been removed, leaving climate as the dominant constraint. For two of the five species, models developed in the native range predict distribution in the introduced range about as well as models developed in the introduced range where we know climate limits distribution. For the remaining three species, models developed in the native range perform poorly, implying that non-climatic factors limit the native distribution of these species and need to be accounted for in species distribution models. Quantifying relevant non-climatic factors and their likely interactions with climatic variables for forecasting range shifts under climate change remains a challenging task.

Highlights

Climatic constraints are a potentially key factor limiting species’ distributions (Gaston 2003)
The distribution of successful dung beetle releases in Australia was highly predictable from Australian Climate envelope models (CEMs) constructed using boosted regression trees (BRT), with predictive performance, as measured by area under the receiver operating curve (AUC) applied to independent data, much closer to 1 than 0.5 for all model runs across all species
BRTs account for nonlinear relationships and we included up to three-way interactions in the model, so the most likely reason for the lack of fit is that the distribution of O. alexis in Australia is influenced by other non-climatic variables

Summary

INTRODUCTION

Climatic constraints are a potentially key factor limiting species’ distributions (Gaston 2003). Dispersal limitations may mean that current distributions have not reached equilibrium (Svening & Skov 2004) or result in past distributional shifts lagging behind climate changes (Green et al 2008) Because they are slow to spread, introduced species may not yet have reached their potential distribution in an invaded range (Peterson 2003). Blackburn 2008, unpublished data), unlike other studies where substantial variation in introduction effort typically leads to this being a primary determinant of success (Lockwood et al 2005; Colautti et al 2006; Hayes & Barry 2008) This ensured that the absence of a species at a release location was not due to dispersal limitation. Australia no. of release locations where species persisted no. of release locations where species failed to persist

Onthophagus binodis

RESULTS

DISCUSSION

South African distribution