An assessment of life-history studies for USA and Canadian crayfishes: identifying biases and knowledge gaps to improve conservation and management

Life-history knowledge is central to basic and applied ecology, but recent reviews show that knowledge of life histories of many freshwater invertebrates is incomplete because of difficulty in conducting such studies or a general decline of interest in natural-history research. We review and summarize published life histories for crayfishes native to the USA and Canada. We document the rate of accumulation of crayfish life-history knowledge and biases and gaps in life-history knowledge by taxonomic group, geography, habitat preference, and conservation status. A total of 78 published studies (59 papers; several included life-history information for multiple species) covering 42 (12%) of the 347 USA and Canadian crayfishes recognized as of 2007 met our criteria for crayfish life-history studies. Life-history studies were lacking for crayfishes of conservation concern and stygobitic or primary burrowing-habitat specialists. Life-history knowledge is relatively complete for low-diversity freshwater ecoregions of northern and western North America, but lacking for high-diversity freshwater ecoregions of the southeastern USA. From 1972 to 2007, an average of 3.40 new crayfish species/y were described, whereas 0.63 species/y were added to the list of crayfishes with published life-history studies. Thus, taxonomic knowledge is expanding faster than ecological or life-history knowledge of these same species, inevitably limiting our ability to manage and conserve them. We conclude with suggestions for increasing publication of crayfish life-history studies, and priorities for regions, taxonomic groups, and life-history traits that require urgent attention. We also present a database of existing crayfish life-history studies for researchers interested in life-history questions and to provide a foundation for traits-based inquiries into crayfish macroecology and applied questions in conservation like the prediction of extinction and invasion risk.