Habitat Relationships and Competition in Two Mediterranean Apodemus spp.

The populations of the two closely related and sympatric Apodemus mystacinus and A. sylvaticus were sampled at 12 different sites in the Mediterranean region of northern Israel. Nine habitat variables were also estimated. The sites were selected to represent the range of habitat types that exist in the area. In sites where relatively abundant populations occurred negative and significant correlation was found between the abundances of the two species. This result suggested that interspecific competition between the two species determined their abundances. However, high and significant correlation was also found between the density of A. mystacinus and the amount of foliage between 30 and 200 cm. Abundances of A. sylvaticus were significantly correlated with the percent of total vegetation cover. The biological basis of these statistical correlations is discussed and it is suggested that the observed correlations agree with the known information about the biology of the species. Using the multiple regression method suggested by Crowell and Pimm it was found that habitat variables alone can account for the observed abundances while the role of interspecific competition is probably very small. It was suggested that the results of the study support the theory of Rosenzweig about the power of habitat selection to separate the niches of ecologically similar species.