Disentangling climate change effects on species interactions: Body size mediates interaction of temperature and phenological shifts

Background/Question/Methods

Predicting the impact of climate change on species and communities is a central challenge in ecology and conservation. Increasing evidence suggests that some of the most profound effects of climate change on the structure and functioning of natural ecosystems are likely to be driven by changes in the interaction between species. Phenological shifts have been among the best documented and obvious responses of natural communities to climate change. Climate-mediated shifts in species’ phenologies are expected to alter species interactions, but predicting the consequences is difficult because climate change typically alters multiple abiotic and biotic factors concurrently. At a mechanistic level, climate change can alter the phenology of species interactions by i) altering the relative timing of appearance of species in a community (e.g. hatching of larvae ) and ii) changing relative developmental rates. However, both factors may be driven by different abiotic aspects of climate change (e.g. rainfall pattern vs. temperature) that may or may not be correlated. Recent theory suggests that shifts in relative body size could determine how these climate mediated shifts in species’ phenologies affect interacting species. Here we test this theory by independently manipulating temperature and the relative hatching phenologies of two competing tadpole species.

Results/Conclusions

Results show that relative shifts in hatching time generally altered the strength of species interaction, but the presence and magnitude of this effect was temperature dependent and joint effects of both factors were non-linear. Species that hatched relatively early or late performed significantly better or worse respectively, but only at increased temperatures and not at lower temperatures. As a consequence, climate mediated shifts in appearance-phenology or developmental rates resulted in stronger or weaker effects than expected when both factors acted in concert. However, consistent with theory, these differences were correlated with relative changes in body size. In general, these results emphasize the need to account for interactions between different aspects of climate change and indicate that size-structured interactions can mediate the impact of climate change on natural communities.