Foraging differences between the native snail, Fossaria sp. and the invasive New Zealand mudsnail (Potamopyrgus antipodarum) in response to phosphorus limitation

Hansen, Brenda; Krist, Amy; Tibbets, Teresa

Animals require food adequate in quantity and quality to grow and reproduce. Therefore, environments limited in key nutrients may promote competitive interactions, with the organisms best equipped to exploit these resources gaining a competitive advantage. We compared the foraging behavior of the New Zealand mudsnail (Potamopyrgus antipodarum), a worldwide invader that can dominate secondary productivity to Fossaria (Bakerlymnaea) bulimoides which is native to western North America to determine whether either of these animals modify their behavior to compensate for nutrient limitation. We used the amount of dietary phosphorus (P) as a measure of food quality, because P is often a limiting resource in freshwater ecosystems. We compared the feeding rate and food preference of each snail species to food containing two levels of P. Because potential competitors can also affect foraging decisions, we conducted additional experiments comparing the effects of conspecifics and heterospecifics under low and high biomass. Consistent with predictions, both species increased feeding rate of low P food, and P. antipodarum consumed more food per unit mass than Fossaria. However, only Fossaria displayed a preference for high P food. The two snails also differed in their response to interacting snails. Fossaria significantly reduced foraging activity in the presence of both conspecifics and heterospecifics, while P. antipodarum spent more time feeding under high conspecific density. Although the presence of high densities of P. antipodarum may negatively impact Fossaria in its native habitat, Fossaria’s ability to locate and preferentially feed on higher quality resources may mitigate some of the impact, potentially facilitating coexistence between these two species.