Wetland pulse amplitude better predicts aquatic species richness than static wetland size

Pond drying is integral to the structuring of aquatic faunal assemblages by filtering species by larval development time and via the identity of top predators. The effects of seasonal habitat size fluctuations on aquatic community assemblages, however, are not well known. As such, few studies have quantitatively investigated the role of seasonal habitat expansion on wetland community structure in natural settings. In this study, we examine a series of naturally occurring fishless ponds across a size and permanence gradient to assess the importance of hydrological expansion on aquatic faunal diversity. We measured the extent of the shift in the aquatic terrestrial transition zone throughout the year by mapping pond perimeters, thus quantifying the area of periodically flooded riparian zones. Aquatic fauna (insects, larval anurans, and decapods) was surveyed by dipnet and identified to species. Relative primary productivity was estimated using periphyton accumulation rates. Primary productivity rates were positively influenced by the size of the aquatic habitat expansion area. Aquatic habitat pulse amplitude was a better predictor of species richness than median size estimates in our regression models. These results emphasize the need to better understand the mechanisms driven by annual cycles of expansion and contraction that shape wetland community structure.