Variation in distribution and abundance of four sympatric species of snakes at Amherstburg, Ontario

Abstract

Mapping of the local distribution and abundance of 4 sympatric species of snakes in a 40 ha study area near Amherstburg, Ontario, revealed 4 strikingly different patterns. No seasonal variations in these distribution patterns were observed. The most widespread and abundant species in the study area was Butler's garter snake (Thamnophis butleri), which had a large portion of its population in a seasonally dry upland area. The restricted distribution of the eastern garter snake (T. s. sirtalis) corresponded well with the distribution of standing water and amphibian prey. The brown snake (Storeria dekayi) occurred primarily in moist areas of dense vegetation where slugs were common but extended further into the dry upland than T. s. sirtalis. The fox snake (Elaphe vulpina gloydi) was widespread but uncommon in both dry and moist portions of the study area. The existing literature has associated T. butleri and E. v. gloydi more often with moist situations. Competition with both T. s. sirtalis and S. dekayi may explain the scarcity of T. butleri in a relatively moist area where all 3 occurred together. The absence or rarity of T. s. sirtalis and S. dekayi in the dry upland where T. butleri was abundant may result from an inability of the former 2 spp. to withstand drought and/or a competitive advantage of T. butleri in this seasonally dry habitat. The suite of characteristics which adapt T. butleri to earthworm prey are also functionally useful in drought avoidance.