The influence of temperature on the depth distribution of sympatric Erpobdellidae (Hirudinoidea)

Abstract

Inter- and intra-specific differences in the behavioral responses of two sympatric Erpobdellidae, Nephelopsis obscura and Erpobdella punctata, to overall water temperature change and thermal gradients were investigated in the laboratory. The results are compared with the seasonal migratory patterns recorded in lentic field habitats. While temperature preference does act as a directional factor in the spring movements to shallow water, only starved small N. obscura and starved large nonreproductive E. punctata showed a preference for colder temperatures after acclimation to a summer temperature of 20 °C. Thus, other components of the population do not use temperature as a cue for their movements to deeper waters in the autumn. It is suggested that the seasonal differential depth distributions shown by components of both species result in a spatial separation of potential competing size groups complementing the inter- and intra-specific size class differences in food resource utilization and temporal differences in resource allocation already demonstrated.