Ecological and Population Studies of Fiddler Crabs (Ocypodidae, Genus Uca) On a Mangrove Shore At Phuket Island, Western Peninsular Thailand

Abstract

Substrate characteristics, particularly grain size, and to a lesser extent presence or absence of mangrove vegetation, temperature, and tidal wetting, affect distribution, density, and sympatric associations of fiddler crabs, Uca forcipata, U. urvillei, U. vocans, U. triangularis, and U. lactea, on a mangrove shore on Phuket Island, western peninsular Thailand. Density of the small U. lactea was greater than that of the larger U. forcipata, U. urvillei, and U. vocans, and densities of sympatric species greater when the species involved differed markedly in size. Findings provide evidence suggesting interspecific competitive pressures exist between U. urvillei and U. lactea in substrates suited to both, the former restricting the density of the latter. Distances are greater between males' burrows intraspecifically (U. lactea) and interspecifically than between males' and females' burrows. Larger individual male U. vocans and U. lactea predominantly occur in the upper limits of their intertidal range, juveniles being more numerous at lower shore levels. Males were two to three times more abundant than females.