Pond permanence is a key determinant of aquatic macroinvertebrate community structure in wetlands

Globally, many aquatic ecosystems experience periodic desiccation that imposes stress on biota. The Northern Prairie Pothole Region (NPPR) in Alberta, Canada, contains abundant wetlands that fill with spring snowmelt and then draw down throughout the summer. They are often assigned a pond-permanence class based on the duration of ponded water. These dynamic wetlands are home to diverse and productive communities of macroinvertebrates. We expected that pond permanence structures macroinvertebrate communities in NPPR wetlands. In addition to exploring the taxonomic composition of macroinvertebrate communities, we aimed to characterise these communities by functional groups to test for associations between pond permanence and desiccation strategies, feeding groups or behavioural guilds. We sampled aquatic macroinvertebrates from 87 wetlands in the NPPR that spanned a range of pond-permanence classes. We identified macroinvertebrates to the lowest practical taxonomic level, usually family. We then performed multivariate analyses (multiresponse permutation procedures, non-metric multidimensional scaling) to identify differences in community composition and functional groups among permanence classes. Community composition of macroinvertebrates was statistically distinct among pond-permanence classes, with the extremes of temporarily- and permanently- ponded wetlands differing most. Notably, macroinvertebrates in temporarily- ponded wetlands were not unique taxa specially adapted to low-permanence wetlands, but rather a subset of the community found in more permanent wetlands. In other words, macroinvertebrates at the family level exhibit a nested pattern of diversity best predicted by the permanence of ponded water in wetlands.