Abstract
AbstractIntroductions of predators can have strong effects on native ecosystems and knowledge of the prey size selection of invasive predators is pivotal to understand their impact on native prey and intraguild competitors. Here, we investigated the prey size selection of two invasive crabs (Hemigrapsus sanguineus and Hemigrapsus takanoi) recently invading European coasts and compared them with native shore crabs (Carcinus maenas) which are known to feed on similar prey species. In laboratory experiments, we offered different size classes of native blue mussels (Mytilus edulis) to different size classes of the crab species in an effort to identify the respective prey size preferences and potential overlap in prey size range of native and invasive crabs. In all three species, the preferred prey size increased with crab size reflecting general predator–prey size relationships. Prey size preference did not differ among the crab species, i.e. crabs showed similar mussel size preference in relation to carapace width. Given that additional morphological measurements showed that both of the invasive crab species have much larger claws relative to their body size compared with the native species, this finding was surprising and may relate to differential claw morphologies or structural strength. These results suggest that the invasive crabs exert predation pressure on the same size classes of native mussels as the native crabs, with potential effects on mussel population dynamics due to the high densities of the invaders. In addition, the overlap in prey size range is likely to result in resource competition between invasive and native crabs.
Highlights
Biological invasions are well recognised as one of the major drivers behind rapid ecological change worldwide (Pyšek & Richardson, 2010; Lowry et al, 2013) and have in many cases led to vast impacts in recipient ecosystems (Asner & Vitousek, 2005; Ehrenfeld, 2010; Simberloff, 2011)
Given that our morphological measurements showed that both invasive crabs have much larger claws relative to their body size compared with the native C. maenas, this finding is surprising
Studies on crab predation have generally shown a strong link between claw size or claw morphology and preferred prey size (Elner, 1980; Sanchez-Salazar et al, 1987; Mascaró & Seed, 2000) making it likely that the invasive crabs are more capable of opening larger mussels at a given crab size than the native crabs
Summary
Biological invasions are well recognised as one of the major drivers behind rapid ecological change worldwide (Pyšek & Richardson, 2010; Lowry et al, 2013) and have in many cases led to vast impacts in recipient ecosystems (Asner & Vitousek, 2005; Ehrenfeld, 2010; Simberloff, 2011). The impact of an invasive predator on native prey will depend on its prey species range (i.e. the number of different species preyed upon), with generalist predators likely affecting a wider range of prey species than specialist predators. Predation impacts can further be expected to differ among life-history stages and size classes within specific prey species as predators typically show prey size preference depending on their own body size (Brose et al, 2006; Brose, 2010). Knowledge of the prey species range and prey size preferences of invasive predators and the identification of potential overlap of both with native competitors is pivotal in understanding the impacts of invasive predators on native communities
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