Predatory functional response and prey choice identify predation differences between native/invasive and parasitised/unparasitised crayfish

BACKGROUND: Invasive predators may change the structure of invaded communities through predation and competition with native species. In Europe, the invasive signal crayfish Pacifastacus leniusculus is excluding the native white clawed crayfish Austropotamobius pallipes. METHODOLOGY AND PRINCIPAL FINDINGS: This study compared the predatory functional responses and prey choice of native and invasive crayfish and measured impacts of parasitism on the predatory strength of the native species. Invasive crayfish showed a higher (>10%) prey (Gammarus pulex) intake rate than (size matched) natives, reflecting a shorter (16%) prey handling time. The native crayfish also showed greater selection for crustacean prey over molluscs and bloodworm, whereas the invasive species was a more generalist predator. A. pallipes parasitised by the microsporidian parasite Thelohania contejeani showed a 30% reduction in prey intake. We suggest that this results from parasite-induced muscle damage, and this is supported by a reduced (38%) attack rate and increased (30%) prey handling time. CONCLUSIONS AND SIGNIFICANCE: Our results indicate that the per capita (i.e., functional response) difference between the species may contribute to success of the invader and extinction of the native species, as well as decreased biodiversity and biomass in invaded rivers. In addition, the reduced predatory strength of parasitized natives may impair their competitive abilities, facilitating exclusion by the invader

Invasive alien Crustacea: dispersal, establishment, impact and control

The subphylum Crustacea includes the most successful species among aquatic alien invaders. The impacts of invasive alien crustaceans (IAC) are often substantial, due to the complex trophic role of most of these species leading to cascading effects throughout the invaded ecosystems. IAC also have the potential to cause a shift in the ‘keystone’ ecosystem functions, changing energy flux and nutrient cycles which together affect critical ecosystem services such as biodiversity, fisheries yield and water quality. Although no individual trait appears to be a good predictor of invasion success, a combination of some characteristics such as eurytolerance, omnivory and certain r -selected life-history traits results in a high probability of alien crustacean species becoming invasive. Both environmental factors, such as habitat heterogeneity in the invaded ecosystems, and evolutionary factors, such as adaptations to new environmental conditions, also play important roles during establishment. Therefore, individual environmental niche models, including genetic algorithm, have the highest likelihood of providing useful predictive information about invasion success and spread of alien Crustacea. Attempts to control IAC through biocides or mechanical removal have had mixed success in the past but a strategic combination of different methods may lead to some success in the future