Effects of habitat fragmentation on the distribution and genetic diversity of populations in small mammal species

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We examined effects of fragmentation and isolation of habitats on spatial distribution and genetic diversity of small rodent species in Hokkaido, Japan. First, we investigated determinant ecological factors on the distribution of small rodents in a southern part of Obihiro, where there are many isolated woods with various sizes. Myodes rufocanus and Apodemus speciosus were captured in almost all woods but A. argenteus was captured in a limited number of woods. Logistic regression analysis indicated that the distribution of A. argenteus was related to the distance from a large forest beside a river. We also examined the distribution of Sciurus vulgaris by using the camera-trapping technique. Logistic regression analysis indicated that its distribution was related to the size of woods, distances from a large forest beside a river and the presence of Japanese walnuts. Next, we determined a partial sequence of mitochondrial DNA (436 bp) in 673 M rufocanus collected from 34 isolated woods (0.3-7.6 ha), and detected 76 different haplotypes. The number of samples within isolated-woods populations and the observed number of haplotypes were positively correlated. However, there was no correlation between the size of woods and the number of haplotypes within populations. When examined the relationship between geographic distance between woods and genetic distance between populations, no significant relationship was observed. These results suggest that effects of genetic drift within populations on genetic differentiation among populations are much greater than those of gene flow. Taken together, these studies suggest that some rodent species, such as M rufocanus, are distributed in every isolated wood, as if habitat isolation did not affect their distribution, but genetic effects of isolation are not small even in those species. We need to examine both distribution and genetics to preserve local populations of wild animals, especially those with small mobility capability.