Latent extinction and invasion risk of crayfishes in the southeastern United States.

Crayfishes are both a highly imperiled invertebrate group as well as one that has produced many invasive species, which have negatively affected freshwater ecosystems throughout the world. We performed a trait analysis for 77 crayfishes from the southeastern United States in an attempt to understand which biological and ecological traits make these species prone to imperilment or invasion, and to predict which species may face extinction or become invasive in the future. We evaluated biological and ecological traits with principal coordinate analysis and classification trees. Invasive and imperiled crayfishes occupied different positions in multivariate trait space, although crayfishes invasive at different scales (extraregional vs. extralimital) were also distinct. Extraregional crayfishes (large, high fecundity, habitat generalists) were most distinct from imperiled crayfishes (small, low fecundity, habitat specialists), thus supporting the "two sides of the same coin" hypothesis. Correct classification rates for assignment of crayfishes as invasive or imperiled were high (70-80%), even when excluding the highly predictive but potentially confounding trait of range size (75-90%). We identified a number of species that, although not currently listed as imperiled or found outside their native range, possess many of the life-history and ecological traits characteristic of currently invasive or imperiled taxa. Such species exhibit a high latent risk of extinction or invasion and consequently should be the focus of proactive conservation or management strategies. Our results illustrate the utility of trait-based approaches for taxonomic groups such as invertebrates, for which detailed species-specific data are rare and conservation resources are chronically limited.