Ecological Compromise: Can Alternative Beaver Management Maintain Aquatic Macroinvertebrate Biodiversity?

Pond leveling devices are a cost-effective means to reduce flooding by beavers, while still maintaining water levels in the associated wetland. However, their impacts on biodiversity and ecological function remain unknown, including their effects on aquatic macroinvertebrate assemblages. Macroinvertebrates in these wetland systems are important ecological indicators and play integral roles in ecosystem function through processing of organic matter and supplying energy to higher trophic levels. Immediately before and exactly one year after installing ten pond levelers in east-central Alberta, we sampled their aquatic macroinvertebrate communities among four different habitat types (beaver channel, beaver lodge, open water, vegetated edge). We then compared various measures of their biodiversity (e.g., Shannon index, evenness, species richness, and density) and community composition (e.g., ordination), including among functional feeding groups. Contrary to our hypotheses, we found no differences in all biodiversity measures for aquatic macroinvertebrates pre- and post-installation. Comparing functional feeding groups, omnivores decreased one year post-installation, while shredders increased. Similarly, there was no difference in macroinvertebrate use of within-pond habitats, and water chemistry measures were the same regardless of year. Management actions related to flooding by beavers often result in the regular dewatering of wetlands, with unknown consequences for aquatic biodiversity. Our findings suggest that with the more stable hydrologic environment they create, pond-leveling devices are able to maintain the macroinvertebrate biodiversity that was present prior to installation, thus providing both economic and ecological benefits when managing human-beaver interactions.