Integrity of predator assemblages controls the abundanceof the alien crab Percnon gibbesi

Abstract

Ecosystem resistance to species invasion is considered to be related to the abundance and diversity of native species (i.e. diversity-resistance hypothesis). In particular, the integrity of predator assemblages may enhance the control of prey populations through direct and indirect interactions (e.g.: different predation strategies by different predators, facilitative interactions among predators). Depletion of predators due to overfishing is therefore expected to enhance the abundance and ultimately the spread of alien prey species. Manipulative field experiments were performed to evaluate the effects of different abundance and diversity of predator assemblages on the invasion success of the alien crab Percnon gibbesi. The experiments were conducted in northwestern Sicily (Italy, Mediterranean Sea), in summer 2015, on bare rocky boulders, the habitat preferred by P. gibbesi. The study sites were characterized by significantly different species richness and abundance of the potential predators of P. gibbesi. Predation rate of different predator assemblages was assessed by means of tethering experiments on the alien crab. As predicted, predation rate on P. gibbesi resulted significantly higher in sites characterized by higher predator abundance and species richness than in sites with lower values. Our findings, although restricted to small spatial scales, support the diversity resistance hypothesis, revealing a negative relationship between the diversity of predator assemblages and the invasiveness (average abundance) of the alien species P. gibbesi.