Print PageCompared to tropical and temperate environments, life for the zooplankton in aridlands seems precarious: vast tracts of dryness separate these waters and the risk of drought is continual, even in permanent habitats (e.g., springs, rivers, reservoirs). However, in temporary waters (e.g., playas, rock pools) probability of drought is certain. Thus, life is adapted to a dual existence—wet or dry, but mostly dry—and organisms living in ephemeral habitats must endure a protracted dormancy to persist. We posit that zooplankton communities in aridlands have reduced hydrochory and zoochory, and that anemochory is likely restricted to seasonal, but stochastic dust events. Here we investigate the role of anemochory and sediment egg banks in determining rotifer community composition comparing species composition of live samples from Chihuahuan Desert waters to those hatching from rehydrated pond sediments and captured blowing dust. Our analysis included calculating a variety of species richness metrics, as well as nestedness analysis, and taxonomic and phylogenetic distinctness.
Results/Conclusions
Almost 13% (ca. 255 species) of all known monogonont rotifer species were found in our survey of active aquatic >200 sites in the US and México. In addition, rotifer community composition varied dramatically among even geographically proximate sites with an average Species Turnover Index = 84.6%±9.0. Comparing these sites we found that as richness increases, congeneric and confamilial species become proportionately more common. In addition, 5 sites showed high degrees of taxonomic distinctness. Further, nestedness analyses of sites across the Chihuahuan Desert demonstrated that rotifer species are not randomly distributed, but occur as spatially ordered subsets (supported by 4 null models; p<0.001), with more permanent sites possessing richer assemblages. Rotifer communities of 3 ponds with varying hydroperiod exhibited phylogenetic overdispersion having negative net relatedness index and nearest taxon index scores. Rehydrated sediments comprise a subset of the local active community. Several rotifers hatched from dust samples that were not commonly found in surveyed sites. Barriers to dispersal and colonization are reflected in species compositions among these highly disconnected sites. We propose a simple conceptual model that illustrates the important elements that order rotifer and other micro-metazoans that inhabit the desert aquatic systems.
