Edinburgh Napier University

  Comparing life history variations between species helps understanding how different life history patterns may have evolved (Begon M, Harper JL, Townsend CR (1996) Ecology. Blackwell Science, Oxford). Here, we compare central aspects of the dynamics and life histories of the most abundant mangrove crabs in the north Brazilian Caeté estuary, the litter feeder Ucides cordatus versus four deposit-feeding fiddler crabs Uca cumulanta, Uca maracoani, Uca rapax and Uca vocator. Population structures are described, growth parameters and total mortality estimated, and breeding seasons and female maturity assessed. With the exception of reproduction, life history traits differ distinctly between the two groups and are discussed in view of the crabs’ different diets. Body size in Ucides is large (>90 mm carapace width) while maximum size of the four fiddler crabs is much smaller (13–35 mm). Ucides grows very slowly and has a life span of >10 years, while Uca spp. are fast growing, completing their life cycle within only 0.7–1.5 years. Despite these differences, females of all five species mature at a roughly comparable size/age relative to maximum size/total life span and all produce large numbers of small planktotrophic larvae developing in coastal waters. Similar reproductive but otherwise diverging life history traits in Ucides and Uca spp. suggest that the crabs’ diets, which vary in quality and digestibility, may have contributed to the evolution of the observed differences.