Altered Foraging Behavior Under Varying Food Quality: Does Increased Feeding Efficiency Mediate the Invasion Success of the Snail, Potamopyrgus Antipodarum?

Abstract

Resource competition can shape the species composition of an ecosystem. In environments where nutrients are limited in either quantity or quality, the organisms best equipped to exploit these resources may gain a competitive advantage. The New Zealand mudsnail (Potamopyrgus antipodarum), a successful invader of the Greater Yellowstone Ecosystem, may benefit from such an advantage. Potamopyrgus antipodarum is a parthenogenetic snail, with high growth rates, and a high percent of somatic phosphorus (P). Consequently, these snails should have a high demand for P. Because freshwater ecosystems are often limited in P, successful animals like P. antipodarum must be exceptionally efficient at acquiring P from their food, either through effective foraging or digestive efficiency. We conducted experiments comparing the feeding rate and foraging preference of P. antipodarum and the coexisting native snail, Fossaria sp., under two levels of P (low and high). We conducted additional experiments to examine how foraging preference is altered by the presence of conspecific and heterospecific interactors. Both species consumed low P food at a higher rate than high P food. However, only Fossaria preferred high P food when given a choice between patch quality, and only exhibited this preference when they alone. Additional experiments are needed to further explore the foraging behavior of these two species, and to determine if these differences mediate the invasion success of P. antipodarum.