Metacommunity structures of dormant and active zooplankton in two distant mediterranean regions

Abstract

Temporary ponds are small-sized limnic systems that dry periodically. The length of the wet phase defines the hydroregime and determines community assembly in temporary ponds. Zooplankton species have adapted to desiccation by adopting some dormant strategies, such as the formation of resting stages. Hatching from resting stages is a source of recolonization after drought events and the composition of hatching taxa is also influenced by hydroregime. We compared metacommunity structure and composition of the dormant sub-community (resting stages); the pioneer active sub-community (fauna present immediately after inundation of ponds); and the cumulative active sub-community (fauna present at the initial, middle and final phases of hydroperiod) in a set of temporary ponds with semipermanent and seasonal hydroregimes in two areas with mediterranean climate: central Chile and eastern Spain. We aimed to determine the influence of hydroregime and identify whether metacommunity patterns are consistent between regions sharing a mediterranean climate. We selected five semipermanent and five seasonal ponds in each region to sample sediments and active zooplankton sub-communities. By combining hatching experiments from the sediments with direct counts of active zooplankton from the field samples, we gathered data on both dormant and active sub-communities to build unweighted bipartite networks of species occurrences in each pond. The obtained networks were analysed to determine seasonal trends in structural features of the metacommunities (diversity, nestedness and modularity) and their relation to hydroregime (semipermanent and seasonal) and geographical location (Chile and Spain). We observed consistent differences in community structure when comparing sub-communities at different successional stages (dormant, pioneer active and cumulative active) and with different hydroregimes (semipermanent vs. seasonal). Both α- and γ-diversity showed a consistent trend, being highest in cumulative active sub-communities and lowest in dormant ones, and were consistently higher in seasonal ponds, regardless of the region. In addition, β-diversity was higher in the pioneer active sub-community in both regions, with no significant differences between hydroregimes. The species composition of cumulative active sub-communities were less heterogeneous than that of the pioneer and dormant ones. No consistent patterns were found in modularity and nestedness values across sub-communities and hydroregimes. In agreement with our hypotheses, we observed a gradual accumulation of taxa as well as community homogenization over time in both regions. Contrary to our expectations, hydroregime did not affect these patterns and, surprisingly, shorter hydroperiods exhibited higher regional diversity. Our results suggest that hydroregime as a single variable does not have a strong explanatory power for metacommunity assembly of temporary ponds. Therefore, a more comprehensive theory is needed to anticipate the effects of the upcoming hydroperiod shortening