On the Seasonal Stability of Zooplankton in a Large Temperate Lake

Background/Question/Methods

Differential responses of diverse species to environmental variation can generate stability at higher levels of organization (i.e., portfolio effects, PEs). But much of this work has focused on spatial and interannual variation. As global change continues to alter seasonality and ecosystem functioning, understanding the underlying food web structures that help maintain stability at multiple spatial and temporal scales is critical to managing ecological systems. Here, we employed a spatially and temporally extensive long-term data set of zooplankton abundance from a large temperate lake to investigate temporal (seasonal) and spatial PEs (e.g., stability, diversity, and asynchrony) of zooplankton across organizational scales (local community, metapopulation, cross-community) within Lake Simcoe, ON, Canada. We seek to answer three questions: i) which scales contribute the most to the seasonal stabilization of zooplankton, ii) what roles do diversity and asynchrony (PEs) play in the seasonal stabilization of this lower trophic level, and iii) how are global changes influencing diversity and the seasonal stabilizing structures within this zooplankton metacommunity. To explore these questions, we use classical metrics and a recent across-scale PE framework to quantify seasonal zooplankton diversity, asynchrony, and variability (CV2) across organizational scales within Lake Simcoe.

Results/Conclusions

We found that seasonal asynchrony (PEs) of different species within local communities and across communities (i.e., cross-community) generated the vast majority of stabilization (20% & 75%, respectively) of zooplankton, while spatial PEs (i.e., metapopulation), were more synchronous and contributed relatively little (5%). Of particular note, our results show that the more classical portfolio effects, which concentrate either on species PEs (e.g., temporal asynchrony of species within local communities) or spatial PEs (e.g., spatial asynchrony of metapopulations), operate along a stronger seasonal axis, rather than due to spatial differences within and between species at the whole lake scale. Furthermore, significant positive diversity-asynchrony relationships at the total, local- and cross-community scales were found as asynchrony was positively correlated with Shannon diversity. These results suggest that diversity plays a role to varying degrees in contributing to the amount of asynchrony and thus stabilization at some scales. Finally, an investigation into the impact of global changes (i.e., climate warming, ice cover) suggested that stabilizing structures (PEs) maybe eroding, as increasing synchronous dynamics at all scales and declining diversity in recent years have led to a rise in seasonal zooplankton metacommunity variability (CV2).