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Competitive Relations between Sympatric Populations of Voles (Microtus montanus and M. pennsylvanicus)

Robert E. Stoecker
Journal of Animal Ecology
Vol. 41, No. 2 (Jun., 1972), pp. 311-329
DOI: 10.2307/3471
Stable URL: http://www.jstor.org/stable/3471
Page Count: 19
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Competitive Relations between Sympatric Populations of Voles (Microtus montanus and M. pennsylvanicus)
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Abstract

(1) Competitive interactions between sympatric populations of Microtus montanus and M. pennsylvanicus were studied in the field and in the laboratory by use of simulated natural conditions. Data were gathered over four years (1966-1969). (2) In the field, competition for space among reproductive females was indicated by the non-overlapping nature of home ranges. These data also support the possibility of intra- as well as inter-specific territoriality. In 1966 and 1968 the relative abundance of M. montanus to M. pennsylvanicus was approximately 50: 50; in 1969 it changed to 10: 90. This asynchronous trend in cycling was accompanied by a shift in habitat occurrence: M. montanus no longer utilized the wetter sites, and M. pennsylvanicus expanded their range to include the drier sites; M. pennsylvanicus probably obtained a competitive advantage arising through their numerical superiority. Removal of one species and the subsequent influx of the other suggests that inter-specific behavioural interactions are important in maintaining local habitat segregation. (3) In the laboratory, M. montanus was dominant to M. pennsylvanicus. Inter-specific aggression was more intense than intra-specific aggression. The least aggression occurred intra-specifically among M. pennsylvanicus. Males and females did not differ in their aggressiveness. Simulated habitat segregation was elicited by agonistic interactions: M. pennsylvanicus was excluded from a chamber containing dry Poa sod and restricted to a chamber containing wet Carex sod.

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