Contrasting Compositional and Abundance Patterns in Zooplankton Communities Between Mountain and Lowland Ponds

Understanding the patterns and mechanisms underlying community structure and composition along altitudinal gradients is key for modern ecology and biogeography; indeed, this research agenda can provide a useful toolbox to forecast the consequences of climate change on present-day ecosystems. However, spatial variation of zooplankton communities at different elevations has rarely been addressed, and most available research on aquatic systems has focused on species richness only. Here, we aim to study the effect of elevation on zooplankton communities, both in terms of species composition and abundance. NMDS analysis was performed to examine community-level patterns in the ordination space between plateau and mountain ponds. In addition, we used SIMPER to assess whether these ponds differed in the composition of zooplankton communities and identify species groups that contributed to biotic dissimilarities between mountain and lowland regions. Mann–Whitney’s tests were run to verify the existence of statistical differences in the total abundance and relative abundances of constant, rare and accessory species between plateau and mountain ponds. Our findings illustrate a clear patterning in zooplankton community composition and abundance between mountain and lowland ponds in a geographically extensive area of the Iberian Peninsula. These contrasting patterns were correlated with a set of environmental features that vary concomitantly along altitudinal gradients (e.g., mean annual temperature, ionic content, nutrient concentration and the development of dense aquatic plant stands). Accessory species contributed most to total abundance at increasingly lower elevations, although small-sized rotifers were the dominant component of zooplankton communities in both pond types. These results should bring certainty to predictions about the effects of future climate on freshwaters, especially in the context of the potential consequences of altitudinal migrations on the spatial variation of community composition and abundance of these small planktonic animals.