Urbanization in Ontario, like the growth of the the city of Toronto, leads to habitat degradation and loss which impairs the survival of snake populations. (Photo source: http://www.news.utoronto.ca/cities-grow-ontario)
Habitat disruption is the largest
threat to biodiversity in general, and Ontario snake species are not immune to
this (Groom et al. 2006). The areas where snake species tend to occur in
Ontario coincide with areas of high human density and extensive human
development, which has resulted in the fragmentation, degradation and even loss
of snake habitat. Habitat degradation and habitat loss refer to the alteration
of natural habitat so that the survival ability of species that live in these
areas is greatly reduced, in the case of habitat loss, habitat is completely
altered often leading to extirpation of the species (Groom et al. 2006). The
result of any form of habitat disturbance severely threatens the survival of populations,
and this is occurring in many of the Ontario snake species, for example the
foxsnake and eastern hog-nosed snake.
A study by Row et al. (2011)
observed reductions in population sizes of foxsnakes in Ontario and attributed
these declines to habitat degradation and loss for the purpose of agriculture
as well as residential and urban development. Analysis of mitochondrial DNA
sequences from these Ontario foxsnake populations indicated that the
anthropogenic habitat disturbances have impacted the genetic structure of snake
populations in a way that has facilitated population declines (Row et al.,
2011). The genetic analysis also shows that foxsnake population splits coincide
with times of development in southwest Ontario (Row et al., 2011). These results
indicate that human-caused habitat disturbances negatively impact foxsnake
populations, specifically they cause declines in population sizes and
facilitate the separation of populations.
Similar can be said for eastern
hog-nosed snakes. A study by Xuereb et al. (2015) studied this species in
Ontario, focusing in on the declining Wasaga population. The paper noted that
the area around this genetically distinct population had undergone extreme and
rapid land use change, mostly for the purpose of developing urban areas and
cottages, as well as agriculture. The extensive urbanization in the surrounding
area has confined this hog-nosed snake population to a very small habitat
(Xuereb et al. 2015). Genetic analysis shows that this anthropogenic range
reduction coincides with a genetic bottleneck, an extreme reduction in
population size and genetic diversity (Xuereb et al. 2015). Unsurprisingly the
genetic analysis also shows evidence of inbreeding in the small, isolated
population (Xuereb et al. 2015). As is discussed in another blog post, losses
of genetic diversity and inbreeding pose a serious threat to the persistence of
populations. This means that anthropogenic habitat disturbance has confined
and isolated the Wasaga population of eastern hog-nosed snakes, leading to
population declines and subsequent threats to the population’s survival.
It is the same kind of story for
most of the at-risk snake species in Ontario. Large-scale human activities such
as agriculture and development (mostly urbanization) alter a lot of natural
habitats, impairing the ability of individuals to survive and the ability of species
to persist. Complete loss and extreme reduction of habitats is causing
population declines, and the resulting populations are put more at risk due to
the genetic structure of small, isolated populations.
References:
Groom, M., G. Meffe and R.
Carroll. (2006). Principles of Conservation Biology, third edition. Sinauer,
Sunderland, MA.
Row, J. R., Brooks, R. J.,
Mackinnon, C. A., Lawson, A., Crother, B. I., White, M. and Lougheed, S. C.
(2011). Approximate Bayesian computation reveals the factors that influence
genetic diversity and population structure of foxsnakes. Journal of evolutionary
biology 24:2365-2377
Xuereb, A. T. J., Rouse,
J. D., Cunnington, G. and Lougheed, S. C. (2015). Population genetic structure
at the northern range limit
of the threatened eastern hog-nosed snake (Heterodon
platirhinos). Conservation Genetics 16:1265–1276.
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