Interspecific aggression and behavioural dominance among four sympatric species of shrews

Abstract

Level of interspecific aggression should reflect intensity of interference competition, and large dominant and small subordinate species should develop aggressive and passive agonistic behaviours, respectively, to achieve stable coexistence. We tested these ideas, investigating interspecific behavioural dominance in a four-species community of shrews varying in body size (Sorex minutus L., 1766; Sorex araneus L., 1758; Neomys anomalus Cabrera, 1907; Neomys fodiens (Pennant, 1771)) by placing interspecific pairs in a neutral field. The order of dominance (determined on the basis of duration of offensive and defensive behaviours, total time spent in the shelter, and a "final shelter resident" index) corresponded to the order of body size: N. fodiens > N. anomalus > S. araneus > S. minutus. The highest number of conflicts and the least pronounced dominance of N. anomalus over S. araneus suggest that the interference competition was strongest between these species. The different social organization of N. anomalus (tolerant and gregarious versus intolerant and solitary in the other three species) did not decrease its aggressiveness and dominance rank. The larger Neomys species were more aggressive and initiated relatively more offensive behaviours, whereas the smaller Sorex species initiated more defensive behaviours. The presence of food and shelter did not intensify conflicts. Nevertheless, dominant species restricted the access of subordinate species to the shelter.