INTRASPECIFIC AND INTERSPECIFIC ANTAGONISTIC BEHAVIOR IN 2 SYMPATRIC SPECIES OF WATER SHREWS - NEOMYS-FODIENS AND N-ANOMALUS

Ethological mechanisms which diminish the aggression and competition a mong sympatric Neomys fodiens (Pennant, 1771) [FF] and N, anomalus Cab rera, 1907 [AA] were studied in enclosure conditions. The animals were kept and subsequently tested (11 FF and 10 AA) in 1- or 2-species gro ups, in enclosures measuring 275 X 135 cm or 135 X 135 cm. During 240 h of direct observation, social behaviours and patterns of hiding-plac e usage by water shrews were recorded. Mutual avoidance (individual oc cupation of the nest boxes, territoriality, and spatial dispersion in the enclosure), active antagonism (threats, combats, chases) and absen ce of typical social hierarchy were the most characteristic intraspeci fic relations of FF. A high level of tolerance and group-occupation of the nest boxes were the most characteristic intraspecific relations o f AA in socially stabilized communities. It seems that a group model o f life without hierarchic relations is appropriate for this species. I n mixed groups, FF dominated over AA. Over the course of time, the sta bilization of interspecific relations and decrease of interspecific co nflicts were observed. This may be the result of the habituation of on e species to the presence of another, and of active avoidance of predo minant species by submissive species (assemblage in 1 nest box, mainte nance of distance), in which the same, or very similar, communication systems could be involved.