Potential Mortality Effects of Off-Highway Vehicles on the Flat-Tailed Horned Lizard (<Emphasis Type="Italic">Phrynosoma mcallii</Emphasis>): A Manipulative Experiment |
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Authors: | Tyler J Grant Jr" target="_blank">Paul F DohertyJr |
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Institution: | (1) Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, CO 50823-1474, USA;(2) Carlsbad Fish and Wildlife Office, 6010 Hidden Valley Road, Carlsbad, CA 92011, USA |
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Abstract: | Southern California desert public lands receive especially high levels of off-highway recreation due to large population centers
nearby and popular riding environments such as sand dunes. Controversy has developed over the flat-tailed horned lizard (Phrynosoma mcallii), previously a candidate for listing under the Endangered Species Act. Some evidence suggests lower lizard abundance in areas
of higher recreational use than in areas with low or no use. We designed a manipulative experiment to ensure maximum inference
in evaluating the direct impact of recreational riding of off-highway vehicles on lizards. Thirty-six lizards, in situ, were
treated with an off-highway vehicle treatment during hibernation season in three treatment groups: high impact, low impact,
and control. Treatments consisted of timed riding by off-highway vehicles. In all treatment groups survival was 100%, despite
hibernation of lizards at very shallow depths. Consequently, indirect effects of off-highway vehicles deserve increased attention.
The relative importance of direct versus indirect (i.e., degradation of lizard habitat) impacts caused by off-highway vehicles
remains unknown. These indirect effects may include the altering of vegetation, substrate, and prey. We recommend that a manipulative
approach be adopted to investigate these possibilities. |
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Keywords: | Off-highway vehicle Off-road vehicle Flat-tailed horned lizard Phrynosoma mcallii Manipulative experiment Public land Sonoran desert |
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