Density-dependent predation and predator preference for native prey may facilitate an invasive crab’s escape from natural enemies.

Abstract

Native predators can confer biotic resistance through consumption of invasive prey. However, early in the invasion process, native predators may initially ignore an invader when it is rare and only increase consumption once it becomes abundant. Furthermore, the willingness of native predators to consume novel invasive prey may be influenced by the similarity of the invader to other native prey species that are favored or familiar. Here we examined whether a native predator (the common mudcrab, Panopeus herbstii) consumes the invasive filter-feeding crab, Petrolisthes armatus as a function of Pe. armatus abundance relative to native prey and the similarity of Pe. armatus to native prey. Using choice experiments, we quantified consumption of invasive Pe. armatus when its abundance was either rare, equal, or more abundant than native prey that were either taxonomically similar (crab, Eurypanoepus depressus) or dissimilar (mussel, Geukensia demissa) to the invader. We found that the absolute consumption of invasive Pe. armatus increased as its relative availability increased, but only in treatments where the alternative prey was a native crab. This suggests that prior experience of the native predator with a similar prey may prime the predator to consume more invasive Pe. armatus. A hierarchical Bayesian analysis determined that both native prey species were preferentially consumed by the native predator Pa. herbstii even when native prey were rare or equal in abundance to invasive Pe. armatus. These results suggest that density-dependent predation plus a persistent preference for native prey by native Pa. herbstii predators may help explain how Pe. armatus escapes its natural enemies.