Sunday, October 7, 2012

Urban Snakes from Brazil's Atlantic Forest

Helicops angulatus. JCM

Snake species living in urbanized areas are perhaps the most likely species to be studied. if for no other reason than the convenient access to the animals and study sites. While urban snake studies are relatively common in the USA and Eurasia, relatively few have been done in the tropics. Franca et al. (2012) describe the snake assemblage from the urban area of Rio Tinto city in Paraíba State, Northeast Brazil. They present data on composition and distribution as well as some natural history. Also, they compare the snake diversity of the urban area with the diversity in two nearby natural patches. The study included data on 161 individuals of 25 species in 16 genera from the urban area of Rio Tinto. Te most common species were:  Helicops angulatus, Bothrops leucurus, Epicrates assisi, and Philodryas patagoniensis. While most species were non-venomous, some venomous snakes were abundant in the urban area. Rarefaction curves did not reach stability and new species should be expected to be added to the Rio Tinto snake list in future studies.

The authors suggest that almost all snakes living in urban areas are continually under predation pressure from humans for several reasons. First, snakes are often killed whenever encountered by humans, who seldom discriminating between venomous and non-venomous species. Even plain gray or brown snakes, such as Liophis poecilogyrus or Philodryas patagoniensis, are considered by local people to be extremely dangerous. Almost all species documented in this study included at least one individual that had been killed by local people in Rio Tinto. Secondly, snakes must frequently cross roads in urban areas and are easy targets for drivers. Third, snakes in urban areas are subject to higher levels of parasitic infection and predation by exotic cats, dogs and chickens. Finally, habitat modification, loss, and fragmentation in urban areas can reduce food resources, reproduction sites, and gene flow, leading to local extinctions.Knowledge of the composition and abundance of snake species found in urban areas is an essential first step to understanding these relationships.  Urban ecosystems are increasing throughout the world, and urban ecology is attracting growing research interest and exploring the risks and benefits of snakes living in urban areas.

The entire article can be found on-line.

FRANÇA, R.C., GERMANO, C.E.S. & FRANÇA, F.G.R. Composition of a snake assemblage inhabiting an urbanized area in the Atlantic Forest of Paraíba State, Northeast Brazil. Biota Neotrop. 12(3):

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