Diversity is maintained by seasonal variation in species abundance

Background

Some of the most marked temporal fluctuations in species abundances are linked to seasons. In theory, multi-species assemblages can persist if species use shared resources at different times, thereby minimizing inter-specific competition. However, there is scant empirical evidence supporting these predictions and, to our knowledge, seasonal variation has never been explored in the context of fluctuation-mediated coexistence.
Results

Using an exceptionally well-documented estuarine fish assemblage, sampled monthly for over 30 years, we show that temporal shifts in species abundances underpin species coexistence. Species fall into distinct seasonal groups, within which spatial resource use is more heterogeneous than would be expected by chance at those times when competition for food is most intense. We also detect seasonal variation in the richness and evenness of the community, again linked to shifts in resource availability.
Conclusion

These results reveal that spatio-temporal shifts in community composition minimize competitive interactions and help stabilize total abundance.