Seasonal strengths of the abiotic and biotic drivers of a zooplankton community

1. Multiple factors operate simultaneously and interact in complex ways to shape community assembly. Understanding the organisation of communities including species interactions and the importance of driving factors (food, temperature, nutrients, oxygen concentration, etc.) is a central topic in ecology. Intra-annual variation in zooplankton and the factors that drive them are described in the Plankton Ecology Group (PEG) conceptual model. However, there has been little empirical evidence quantifying the relative contribution of abiotic and physical factors to plankton seasonality in zooplankton communities. 2. Using a long-term time series of zooplankton abundances and environmental conditions, we investigated which physical, chemical, and biotic factors structure zooplankton communities. We quantified their importance in seasonal changes in species composition by exploring networks of interacting species in the Rimov Reservoir (Czech Republic). We investigated how these factors were associated with seasonal and intra-annual (across all seasons) patterns of temporal variation in zooplankton. 3. We predicted that: (1) the zooplankton community in the Rimov Reservoir follows the general seasonal PEG pattern; (2) abiotic factors play an important role in the temporal distribution of zooplankton at the intra-annual scale, but their influence on the community declines at the seasonal scale; and (3) the network of interacting species is more complex at the seasonal scale than at intra-annual scale, so biotic drivers most strongly influence zooplankton patterns at seasonal scales. 4. The intra-annual pattern of zooplankton abundance was mainly determined by the physical environment. As expected, the roles of abiotic drivers of community assembly changed between seasons. There were more interactions between abiotic factors and species structuring the community at the intra-annual scale than at the seasonal scale. Additionally, these interactions were weaker at the seasonal scale than the intra-annual scale. The intra-annual zooplankton community of the Rimov Reservoir was the most stable, while the summer zooplankton community was the most variable. 5. Our results provide evidence that the network of interacting zooplankton taxa is composed of positive and negative relationships, which suggests facilitative, competitive, and predator-prey interactions. Although zooplankton species interactions have an influence year-round, the network of interacting species is more complex during the vegetative period and especially in summer, when species richness and abundance are high. Our results suggest that the zooplankton community is structured by both the biotic network at the seasonal scale and by the physical environment at the intra-annual scale. 6. Seasonal succession in zooplankton communities of temperate lakes is a well-known pattern. However, the influence of interspecific interactions within seasons on this pattern has not been clearly shown until this study. Exploring the community in only one season may provide incomplete knowledge of the factors and species interactions driving the whole community.