RELATIONSHIPS BETWEEN HEIGHT ON THE SHORE AND SIZE DISTRIBUTIONS OF THAIS SPP (GASTROPODA, MURICIDAE)

Average body sizes in a variety of marine animals have been reported to be correlated with height in the intertidal zone. This paper reports field observations on four species of Thais showing that the relationship between size distribution and intertidal height or subtidal depth is highly variable. Intertidal size gradients in Thais have been explained by a size dependent set of responses to light and gravity, but experiments reported here do not indicate that snails of different sizes behave differently with respect to the intertidal gradient per se and it is argued that, when there is a size gradient, it is produced by the direct responses of snails to factors such as shelter, temperature, desiccation, and food. It is suggested that a response to token stimuli is unlikely to evolve when the token stimuli are poorly correlated with the relevant environmental factors, especially if the latter can be monitored directly by the animal. © 1979.