Abstract
The land crab Johngarthia planata (Stimpson, 1860) has been reported from the Baja California Peninsula and several oceanic islands in the Eastern Pacific as well as inshore islands of the Mexican, Costa Rican and Colombian coast. However, the species has not been observed on the continental mainland, as it is likely that the high diversity of terrestrial predators/competitors make the establishment of mainland populations nearly impossible. In this contribution, several new records of this species that have been observed in urban areas along the continental Pacific coast of Mexico are reported. These records demonstrate that the presence of humans does not necessarily have a negative impact on land crab species. Indeed, the presence of humans may actually discourage the presence of native crab predators/competitors and hence increase the likelihood of a successful mainland settlement of land crab species that are otherwise island and peninsula restricted. The presence of Johngarthia planata is ecologically relevant for coastal forests because gecarcinid crabs significantly influence plant recruitment and Johngarthia planata is considerably larger than the mainland species Gecarcinus quadratus.
Highlights
Macroevolutionary transitions between marine and non-marine habitats are uncommon and rarely lead to long-term success in the invaded habitat (Vermeij and Dudley 2000)
Paulay and Starmer (2011) attribute the absence of land crab species on the continental mainland to the presence of predators. This pattern is less pronounced in the Neotropics where Cardisoma crassum, C. guanhumi, Gecarcinus lateralis and G. quadratus share evolutionary traits which allow it to adapt to the conditions in a coastal band of the continental mainland (e.g. Bright 1966, Sherman 2002, Lindquist et al 2009)
Several studies strongly indicate that J. planata has not established populations along the Central American mainland coast, which agrees with the pattern of mainland absence observed in the four congeners
Summary
Macroevolutionary transitions between marine and non-marine habitats are uncommon and rarely lead to long-term success in the invaded habitat (Vermeij and Dudley 2000). Species of the Gecarcinus-group (including Johngarthia, Gecarcinus and Gecarcoidea (Türkay 1987) are dominant through sheer numbers, on some islands their mass exceeds the total mass of animals reported in tropical rain forests in Costa Rica and the central Amazon (Lindquist et al 2009) and they may occupy the top of the energy pyramid (Burggren and McMahon 1988) Despite their success on islands and possible dispersal in their larval stage via sea currents, most species of the Gecarcinus-group are absent from continental mainland habitats (Türkay 1987; see Paulay and Starmer 2011). In this study I report the first continental mainland records for J. planata and discuss the possibility that human presence might facilitate the mainland settlement of such a species
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