Linking variation in the timing of species interactions to dynamics of species interactions and community assembly

Background/Question/Methods

The timing of seasonal life-history events, such as germination, hatching, flowering, or migration, determine when and at what stage (size) individuals “appear” in the environment and interact with other members of the community. Consequently, most species interactions strongly depend on the relative timing of life-history events (i.e. phenologies) of species within a community. Phenologies of species, however, naturally vary among years with changes in weather conditions. Furthermore, ample evidence indicates that climate change is shifting the phenologies of species worldwide. Given that species typically differ in what environmental cues influence their phenology, these changes in environmental conditions inevitably lead to shifts in relative phenologies and thus alter timing of species interactions. Although shifts in phenologies of species interactions are ubiquitous in natural communities, they are typically neglected when studying the dynamics and structure of natural communities. Yet, understanding how phenological shifts affect species interactions is not only critical for our ability to predict the dynamics and functioning of natural communities, but also essential to predict how future climate change will affect natural ecosystems. Here I propose a mechanistic framework aimed to integrate seasonal variation in the timing of species into basic community ecology using data form experiments in amphibian pond communities as an example.

Results/Conclusions

Experiments demonstrate that shifts in the relative timing of species interactions lead to concurrent shifts in the per-capita strength of inter-specific interactions. However, the direction and magnitude of these shifts were depended on the specific environmental conditions, like ambient temperature and resource productivity. Moreover, the relationship between phenological shifts and change in per-capita interactions were frequently non-linear. While these context-dependent effects of phenological shifts may seem idiosyncratic, I suggest that these patterns can be explained and predicted by shifts in the relative size of interacting species and positive feedbacks between relative size and performance.  Finally, I show that these context dependent outcomes of inter-specific interactions also lead to concurrent changes in community structure and ecosystem processes. Together, these results demonstrate that shifts in the relative timing of species interactions can dramatically alter the relative fitness of species, the dynamics of communities, and even ecosystem processes, emphasizing the importance of a temporally explicit approach to community ecology.