The Northern Prairie Pothole Region (NPPR) in Alberta, Canada contains numerous depressional wetlands which fill with the spring snow melt and dry throughout the course of the summer. NPPR wetlands are assigned a permanence class based on hydroperiod length. These wetlands are home to diverse communities of macroinvertebrates, which are an important trophic link between primary producers and higher order consumers. In many potholes, fish predation is the primary driver of macroinvertebrate community composition; however, the potholes in Alberta are largely fishless so the primary determinants of community composition are unclear. We have previously determined that macroinvertebrate communities in the NPPR are insensitive to surrounding land use. We suspected that this is because of the overwhelming influence of hydroperiod on macroinvertebrates and thus sought to test for differences in community composition among wetlands of differing permanence classes. In addition, we characterized macroinvertebrates by functional groups to test for associations between hydroperiod and desiccation strategies, feeding groups or behavioural guilds. We sampled aquatic macroinvertebrates from 87 wetlands of varying permanence classes in the NPPR. We performed multivariate analyses including non-metric multidimensional scaling (NMDS) ordination and multi-response permutation procedure (MRPP) to observe and test for differences in community composition among permanence classes.
Results/Conclusions
We found that macroinvertebrate community composition differed significantly among wetland permanence classes (MRPP: A=0.019, p < 0.0001). Distinct assemblages occupied temporary and permanent wetlands, but few taxa explicitly thrived in temporary wetlands. Rather, macroinvertebrates in temporary wetlands were subsets of the macroinvertebrates found in more permanent wetlands. To be successful in non-permanent marshes, macroinvertebrates must possess a suitable life history that allows them to tolerate or avoid periodic drying. This was clear in that taxa lacking dispersal or desiccation tolerance traits were absent in temporary marshes. All functional feeding groups and behavioural guilds were more abundant in permanent wetlands. The environmental covariates we measured (including dominant cations, turbidity and conductivity) did not strongly predict macroinvertebrate community composition. We suspect that a more important driver may be differences in emergent and submerged vegetation, which provide critical habitat for many macroinvertebrate taxa. Our research provides insight into the often complicated community ecology of wetland macroinvertebrates and the influence of hydroperiod on aquatic organisms in the NPPR.