Asymmetrical Behavioral Interactions between the New Zealand Mud Snail, Potamopyrgus antipodarum, and Scraping, Collector-Gathering and Collector-Filtering Macroinvertebrates

ABSTRACT

Potamopyrgus antipodarum is an invasive species in North America, Europe, and Australia that has the potential, because of the high density that it can achieve in some habitats, to interfere with the foraging and attachment of native macroinvertebrates. Using in situ experiments on slate tiles, we examined foraging and attachment preferences and behavioral interactions between P. antipodarum and a grazing-scraping caddisfly (Helicopysche borealis), a collector-filtering caddisfly (Brachycentrus occidentalis), and collector-gathering mayflies in the family Baetidae. P. antipodarwn, H. boralis, and the baetid mayflies preferred to forage in high quality microhabitats when given the choice between high quality (with periphyton) and low quality (periphyton scrubbed off) patches. The presence of baetid mayflies interfered with P. antipodarum causing it to shift foraging into low quality microhabitats (about a 30% reduction), whereas P. antipodarum interfered with the foraging of baetid mayflies causing them to abandon the tops of tiles (about 25% reduction). When B. occidentalis was wandering on tile surfaces, it caused P. antipodarum to abandon the tops of tiles (about 15% reduction); however, the presence of P. antipodarum did not change the microhabitat use of B. occidentalis. Interactions between baetid mayflies and P. antipodarum were symmetrical, although the specific behavioral responses differed. Interactions between B. occidentalis and P. antipodarum were asymmetrical; B. occcidentalis affected P. antipodarum, but the opposite effect did not occur.