Variable effects of an invasive species on the reproduction and distribution of native species in pond networks.
The arrival of non-native species in a community can be deleterious for native species. The joint investigation of several descriptors of native populations susceptible to invaders, under different invasion contexts, may help in predicting the outcome of their co-occurrence with invasive species. Moreover, empirical studies seldom document the relative importance of the effects of invasive species on native species compared with other factors. Using survey data, we evaluated whether reproduction (larval density) and distribution of breeding sites of three amphibian species (Rana dalmatina, Lissotriton helveticus, and Triturus marmoratus) were related to the presence of invasive red swamp crayfish Procambarus clarkii, compared to other native predators, habitat, and landscape features, in two pond networks that differed in invasion intensity. The red swamp crayfish was only negatively associated with the larval density of one amphibian species studied. Its effect size was similar to that of some native predators, and much smaller than that of the canopy cover of ponds. Amphibians were widespread in the two pond networks. The occupancy of only one species in each network was negatively related to crayfish presence, while the occupancy of all species was negatively related to fish presence. The distribution of amphibian breeding sites was positively associated with aquatic vegetation cover. Negative associations between amphibians and red swamp crayfish were detected only in a few cases, even in the most invaded area, and thus results were less alarming than in previous studies. Differences in ecological traits of native amphibians and interactions with other environmental factors may explain the variable effects of red swamp crayfish on native amphibian populations.