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

Abstract

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.

Stochastic and deterministic processes drive wetland community assembly across a gradient of environmental filtering

“…Our measured total beta diversity and its turnover component was significantly lower than that of our null model for all three taxa, further suggesting that deterministic processes are influencing the assembly of wetland communities. In contrast, the nested component of beta diversity was higher than our null model in all cases, suggesting that there is a nested subset of ‘tolerant’ taxa (Gleason and Rooney ) that persist across the permanence gradient. This elevated nestedness only partially offsets the influence of deterministic processes on reducing beta diversity, because its contribution to total beta diversity is small relative to the contribution of turnover.…”

“…However, temporary pothole wetlands are likely to be more structurally similar to each other as they typically contain two vegetation zones (wet meadow and low prairie), whereas wetlands with longer hydroperiods can also support shallow and deep marsh zones as well as open water, each dominated by differing vegetation growth forms and canopy structures (Stewart and Kantrud 1971), though not necessarily by more species. More, macroinvertebrate diversity is influenced by vegetation microhabitat availability (Gleason et al ) and bird communities are in turn influenced by both vegetation (Robichaud and Rooney ) and macroinvertebrate communities (Wrubleski and Ross ). To confirm that water and sediment quality were not more heterogeneous among temporary wetlands, we examined these environmental variables grouped by permanence class (Supplementary material Appendix 6).…”

“…This ability to move easily among wetlands should enable birds to sort themselves along the wetland hydroperiod gradient and should reduce the influence of stochastic dispersal constraints such that beta diversity within permanence classes should be low. In contrast, wetland plants and aquatic macroinvertebrates are less mobile, and although wetland hydroperiod should influence what species are capable of persisting in a given wetland (Bolding , Gleason and Rooney ), we anticipate greater within‐permanence class beta diversity, especially due to species turnover. Thus, by considering multiple wetland‐dependent taxa that differ in their dispersal capacity, we should be able to resolve the importance of dispersal capacity in limiting the influence of stochastic processes on community assembly in prairie pothole wetlands.…”

“…These data were then averaged to estimate the relative cover of each species on a wetland basis. Details on floristic surveys are published in Bolding ().…”

“…We expect that deterministic processes will dominate when an environmental filter is particularly strong, such as in temporary wetlands, and that stochastic factors may be more evident when the filter is relaxed (Chase ). Further, this tradeoff between deterministic and stochastic processes along an environmental filter gradient should be most evident with relatively mobile species as they will be better able to sort along the environmental filter gradient by overcoming dispersal limitation (Aduse‐Poku et al ). In contrast, we predict that less mobile species should be more susceptible to stochastic processes and less well sorted, especially in dynamic environments.…”