Using satellite imagery to examine and predict habitat niche differences between two sympatric species of rattlesnake in Southern California.

详细信息   

• 作者：Erbas-White ; Kevin.
• 学历：Master
• 年：2014
• 毕业院校：California State University
• ISBN：9781321248333
• CBH：1525880
• Country：USA
• 语种：English
• FileSize：3117514
• Pages：72

文摘

The family Viperidae consists of a wide ranging and highly diverse group of snakes found on every continent except Antarctica. The genus Crotalus,commonly known as rattlesnakes,is a genus of pit-vipers endemic to the American continents. Within the study area of Southern California,five separate species of the genus Crotalus are found. This study focused on two of the five rattlesnake species the Southern Pacific Rattlesnake Crotalus oreganus helleri) and the Red Diamond Rattlesnake Crotalus ruber). While C. o. helleri is thought to be a widespread generalist species,C. ruber is considered a specialist species and is classified as a species of special concern by the California Department of Fish and Wildlife. Unlike most snakes which partition ecological resources through diet,the family Viperidae is believed to partition ecological resources through the division of habitat. Despite this,a previous study Dugan & Hayes 2011) using null model testing,established that habitat niche partitioning was not found to play a major role in the development of C. ruber and C. o. helleri. However,field sightings of the species indicated that habitat differences exist between these two species and could possibly play a factor in predicting species occurrence. Locational data was provided by the North American Field Herping Association and the Herpetological Education Research Project. 798 C. o. helleri and 444 C. ruber locations were used as a proxy to examine underlying vegetation,temperature,and precipitation. A normalized difference vegetation index created from a mosaic of three satellite images was used to examine terrestrial vegetation. Whereas a parameter-elevation regression on independent slopes model was used to examine temperature and precipitation differences between the study species. The results demonstrated that significant habitat differences exist between the study taxa. Individuals of C. o. helleri were found to reside in areas with higher amounts of vegetation and higher amounts of vegetative variation within their range. C. o. helleri was also found to reside in areas of higher precipitation and lower temperatures. Inversely,C. ruber sites were found to exist in areas of lower amounts of vegetation,lower vegetative variation,lower precipitation,and higher temperatures. A logistic regression was used to establish the role of the aforementioned variables in predicting the occurrence of study taxa. Vegetation density in an area was the greatest factor for predicting species,followed by vegetative variation,temperature and lastly precipitation. These findings reinforce field observations conducted over the years. It is possible that massive habitat change in an area may cause a demographic shift between species. More than likely this would affect populations of C. ruber negatively and promote a transformation of suitable C. ruber habitat to one which favors C. o. helleri in the future.