Monday, November 1, 2010

Fox Snakes, Garter Snakes and Habitat Fragmentation

Roads, housing, and agriculture tend to fragment habitats and how this impacts wildlife, particularly reptiles is not fully understood. DiLeo et al. (2010)  investigated the effects of the fragmented landscapes of Southwestern Ontario, Canada on the genetic population structure of the eastern garter snake (Thamnophis sirtalis sirtalis) and the Eastern Fox Snake (Mintonius [Elaphe] gloydi) which are sympatric, but have distinct habitat preferences. The garter snake is a habitat generalist, while the fox snake is marsh specialist, is rarer, and is geographically restricted.  They used DNA microsatellite markers to examine genetic population structure of both species. Genetic clusters were overlaid on a habitat map to deduce possible physiognomic barriers to gene flow.  The results showed three genetic clusters for garter snakes and five for Fox Snakes. Each garter snake had a near equal probability of membership to two or more clusters with no cluster suggesting garter snakes comprise a single genetic population. Fox Snake, however, clustered to geographical  locations on the landscape, that roughly correlated with isolated patches of suitable habitat. The results suggest  fox snakes and garter snakes are impacted in different ways by the same landscape fragmentation or they may have dramatically different effective population sizes. Agricultural areas and roads separate existing populations of fox snakes and appear to be barriers to gene flow, while garter snake are unrestricted by these features. The authors suggest that fox snakes are more susceptible to habitat fragmentation than garter snakes and that they could benefit from having their patches of habitat connected by riparian corridors

Michelle F. DiLeo, Jeffrey R. Row and Stephen C. Lougheed. 2010. Discordant patterns of population structure for two co-distributed snake species across a fragmented Ontario landscape. Diversity and Distributions 16:571–581.

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