Community assembly within ponds: the roles of space, time, and environmental gradients

Abstract

Environmental and spatial–temporal processes are proposed as important mechanisms regulating permanent pond communities, but comprehensive research of these factors at fine scales (i.e. patches or microhabitats) is still lacking. Here, we investigated environmental, spatial, and temporal variables influencing community structure and diversity (α, β, γ) in pond microhabitats over one annual cycle (i.e. four seasons). Standardized surveys were conducted monthly for one year, and a suite of biotic and abiotic variables were recorded at each microhabitat to test which assembly processes are important in structuring pond communities. As expected, spatial and environmental variables influenced local species organization at both the annual and seasonal scale. The high β diversity among pond microhabitats was mainly attributed to species turnover from one microhabitat to another rather than richness differences. Habitat heterogeneity largely explained the variation on α and β diversity among pond microhabitats. Overall, our results suggest that multiple ecological processes affect community assembly dynamics in permanent ponds. First, the temporal variation on the distribution of species across pond microhabitats that was associated with environmental fluctuations (mainly temperature, dissolved oxygen, substrate composition, and emergent vegetation) inferred that species sorting (i.e. niche-based processes) is an important driver of the observed community patterns, while the spatiotemporal turnover in species composition and density can be explained by colonization and dispersal events occurring within microhabitats. Our study emphasizes the need to include time, space and environmental variables in studies assessing communities in permanent pond systems, as they appear to be related to distinct processes regulating communities at fine scales.