Life history tactics in two species of desert snails

Abstract

Life history tactics of two sympatric species of desert snails are compared. It is concluded that the two species have adopted different strategies to cope with their harsh environment: Sphincterochila boissieri is closer to the K ‘syndrome’ of the K–r continuum, while Trochoidea seetzeni is closer to the r ‘syndrome’ endpoint. These different life histories are related to differences in the snails’ morphology —S. boissieri has a heavier shell. This is contrary to considerations from MacArthur and Wilson's (1967) theory, according to which each of the above strategies is expected to occur in a different environment — r selection in an unpredictable environment and K selection in a predictable one. It demonstrates that the K–r syndrome and the environmental factors which are said to be correlated with it are too simplistic to account for the complexity of life histories observed in nature.