Friday, May 6, 2011

Smooth Green Snake Population and Distribution Species

Although widely distributed in North America, and in numerous disjunct populations in the Great Plains and Rocky Mountain states, the status of the smooth green snake (Opheodrys vernalis) is poorly known in the Rocky Mountain Region of the USDA Forest Service. This species is known from scattered locations near streams in Nebraska and eastern South Dakota, but otherwise it may be rare in South Dakota, Nebraska, and Wyoming outside of the Black Hills and Bear Lodge Mountains. There are some indications that it is declining in numbers and geographical extent. However, the only protection provided in Region 2 is by the states of Wyoming, Colorado, and Nebraska where it is protected by state law, prohibiting commercial collection and limiting collection to individual use.

Smooth Green Snake

The smooth green snake is threatened through the direct and indirect consequences of habitat destruction from cattle grazing, logging, dewatering of streams, road building, pesticide use, and development, particularly in meadows, riparian areas, and mountain foothills. Smooth green snakes are at risk of mass mortality at communal den sites due to destruction, freezing, or flooding of dens. As with all snake species, the smooth green snake is susceptible to direct anthropogenic mortality from roads and human encounters. Populations could also decline because of reductions in invertebrate prey due to drought and other climatic extremes, or management actions such as the application of pesticides.

The loss of habitat and dispersal corridors, and the resulting isolation of populations, put this species at risk of reduced genetic variability, loss of recolonization or rescue potential through connection with other populations, and eventually local extinction. This snake’s small body size, moderate reproductive output, high hatchling and juvenile mortality, and low probability of dispersal out of occupied habitats exacerbate its sensitivity to environmental variability.

Smooth Green Snake

The smooth green snake is generally found in grassy habitats and foothills habitats. In some locations in the Black Hills and Bear Lodge Mountain it can be abundant in moist grass and understory habitats and along forest/meadow ecotones. The protection and preservation of currently occupied riparian and wet meadow habitats and their associated habitat mosaics in the Great Plains of eastern South Dakota and Nebraska, the Black Hills, Bear Lodge Mountains, and southern and central Rocky Mountains are essential to provide for the long-term survival of smooth green snakes in the West. Xerification of meadow habitats in all parts of the range due to climate change and/or exhaustion of surface water and groundwater supplies for irrigation and urban use are threats that will only increase in the future.

Studies of the effects of anthropogenic threats (e.g., pesticide use, roads, impoundments, heavy equipment use, water pollution, cattle grazing) on smooth green snakes and approaches for ameliorating those effects are needed. The lack of data about most aspects of the biology of smooth green snakes (e.g., local taxonomic and population status, abundance, population trends, genetics of isolated populations, detailed life history data, response to threats) is a serious impediment when considering detailed management options for this species. This deficiency could be corrected by a region-wide survey and long-term monitoring of smooth green snakes in conjunction with other herpetological survey efforts.

Smooth Green Snake

This species conservation assessment presents a review of taxonomic, biological, and ecological information about the smooth green snake (Opheodrys vernalis) in North America, with an emphasis on the status, distribution, and management implications for this species in the Rocky Mountain Region (Region 2) of the USDA Forest Service (USFS). Our goal was to supplement existing literature with as much current data as were available. We have attempted to understand and model the population dynamics of smooth green snakes to determine the crucial stages in their life cycle and to provide a range of possible scenarios and their consequences for population viability.

A model of smooth green snake geographical distribution is presented to improve researchers’ chances of finding additional populations and to focus limited research time and effort to those places that most likely support smooth green snake populations. We hope that these models will be useful to managers and others who seek to understand and contribute to the conservation of reptile.


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