Wetland features, amphibian communities and distribution of the alien crayfish, Procambarus clarkii

Alien invasive species are a major threat to amphibians. The red swamp crayfish, Procambarus clarkii, is native of eastern North America but has been introduced worldwide, and can cause dramatic declines of amphibians. We analyzed the distribution of amphibians and of P. clarkii in an area of northern Italy where the crayfish has been recently introduced.We assessed the relationship between wetland features, the distribution of P. clarkii and the richness and structure of amphibian communities. We surveyed 114 wetlands, using a combination of standard methods; we recorded environmental features (size, depth, hydroperiod), and analyzed relationships using generalized additive models, including components taking into account spatial autocorrelation. We found the richest communities in wetlands with intermediate size and hydroperiod. Conversely, P. clarkii was associated to the largest, permanent wetlands. Amphibian communities were significantly nested; wetlands with intermediate size and hydroperiod hosted communities with less gaps than expected by chance. However, two species (Bufo bufo and Salamandra salamandra) were less nested than the other amphibians. Management focusing on relatively small, semipermanent wetlands, that are isolated from the main hydrographic network, may be an effective strategy for amphibian conservation, because these wetlands can have suboptimal features for P. clarkii. Nevertheless, these wetlands are not enough for the conservation of the whole amphibian community, because some species have peculiar requirements.