Distribution and activity patterns in an intertidal grazer assemblage: influence of temporal and spatial organization on interspecific associations

In consumer assemblages, the organization of individual foraging behavior, as well as spatial distribution, can largely determine environmental risks, and the intensity of intra-and interspecific interactions. We characterized distributional and behavioral patterns of the most common benthic grazers coexisting in the rocky shores of central Chile: the chiton Chiton granosus, the pulmonate limpet Siphonaria lessoni, the scurrinid limpet Scurria araucana and the keyhole limpet Fissurella crassa. C. granosus and F. crassa were strictly nocturnal foragers whereas S. lessoni foraged during daytime. Most S. araucana individuals foraged at night, but daytime foraging was also common. The spatial distribution at resting varied from aggregated for C. granosus and S. lessoni to a more dispersive pattern for F. crassa and S. araucana. C. granosus dispersed slightly from aggregation when foraging whereas S. lessoni foraged in tight conspecific aggregations. Foraging excursions varied from over 60 cm in F. crassa to less than 7 cm in S. araucana. Homing behavior ranged from extreme fidelity in F. crassa to low fidelity in S. lessoni. Positive associations were observed between C. granosus and F. crassa during resting and foraging whereas negative associations were observed between these species and S. lessoni. These general patterns varied little between 2 sites separated by a few kilometers. Interspecific competition might be important in structuring this guild, but it may affect only some species pairs. Direct interference in the use of shelter or while foraging, rather than food exploitation, seems the most likely mechanism. The marked differences in individual behavior among species, despite ample diet overlap, might translate into different functional effects, which should be explored in future experiments.