The strength and type of interactions that occur between species generally depends on the relative ontogeny of the interacting species, including their appearance phenology and their individual developmental rates. There is now ample evidence that climate change affects the phenology of many animals and plants, though species often respond differently. As a consequence, climate change is likely to alter the phenology of many species interactions, changing which ontogenetic stages and size-classes interact. While increasing attention has been paid to changes in phenology, most previous work has focused on the “mismatch” between peak consumer abundances and peak resource abundances.  However, little is known about when and how such phenological changes are likely to affect the character of species interactions, and the consequences of these changing interactions for populations and individuals. Here, we propose a conceptual framework to examine changes in the phenology of species interactions and their effects on fitness.

Results/Conclusions

Using this framework, we show that predicting the consequences of phenological mismatch requires a detailed mechanistic understanding of how interactions between different ontogenetic stages and/or size classes affect the fitness of individuals. We propose that this can be measured with an ontogeny-phenology fitness landscape that can be derived empirically from size-structured interactions. On this fitness landscape, changes in the relative phenologies of two interacting species can be used to predict changes in the nature of species interactions and the fitness of individuals. Consistent with this conceptual framework, an analysis of the current literature showed that the impacts of phenological changes depend not only on the direction of the shift but more importantly on the specific type of interaction affected (e.g. competition, predation, or mutualism) and the relative ontogenies of the interacting species. In general, our study suggests that simply measuring the changes in timing of abundance peaks is not sufficient to reliably predict the consequences of climate change. Instead, we need to understand how this phenological change is likely to alter the nature of species interactions over the ontogenies of the interacting species.