A Case for Increased Foraging Success Under High Conspecific Densities in the New Zealand Mudsnail, Potamopyrgus Antipodarum

Abstract

An animalsâ fitness can be positively or negatively affected by the density of conspecifics. While density dependent increases in fitness, or Allee effects, have been a key focus of the management of declining populations of native organisms, they may also be exploited for the purpose of invasive species management. Although most Allee studies focus primarily on mate location, a threshold density of conspecifics may also be required for effective foraging. Potamopyrgus antipodarum is a successful invader that can reach very high densities. Previous studies have demonstrated that P. antipodarum benefits from certain high densities through increased reproduction and activity. To determine whether conspecific density positively affects the foraging ability of P. antipodarum, I conducted laboratory experiments with three increasing levels of density (one, five and 15 individuals, control targets were alone). Because the presence of interactors may also affect the type of food individuals choose, I also included two food options differing in the amount of phosphorus, which is an important nutrient known to be limited in one invaded stream. Although food choice was unaffected by conspecific density, P. antipodarum were more likely to feed and fed longer in the higher density treatments; target snails in the treatment containing 15 conspecifics fed three times as long as targets in the treatment with five conspecifics. These results provide further insight into the ecology of P. antipodarum, and their success as invaders. Further work is needed to determine how this species uses high density to locate food resources.