Estimating the distribution and occupancy of vernal pool breeding habitat in the northeastern United States.
Grant, Evan*,1, Bailey, Larissa1, Mattfeldt, Sandra1, Nanjappa, Priya1, Jung, Robin1, 1 North East Amphibian Research and Monitoring Initiative, Laurel, MD, USA
ABSTRACT- The status and trends of populations of vernal pool-associated amphibians in the northeastern United States are poorly understood at the landscape scale. In particular, the distribution of vernal pool habitats is not well known, due in part to their small size and temporary nature. As a result, there is no coherent integration of methods that provide inference on the status of amphibian populations and the distribution of their habitats. Here, we present a novel method for mapping and estimating the number of vernal pool habitats (using adaptive cluster sampling; ACS) at 7 National Parks and 9 National Wildlife Refuges in the Northeastern United States, and present results from the application of a proportion of area occupied (PAO) approach to estimating the amphibian occupancy of these habitats. The ACS method appears to provide reasonable estimates of the numbers of vernal pool wetlands at parks and refuges across the Northeastern United States, though initial comparisons with aerial photograph-mapped pools suggest that the ACS method may have a positive bias. In 2005, across parks and refuges, the estimated occupancy of vernal pools (accounting for detection probability) for spotted salamanders ranged from 0.465 to 1.0, and wood frogs ranged from 0.222 to 0.873. Occupancy was related to several variables at the local (pond-level), park/refuge, and landscape- level scales, including percent forest and wetland within a park/refuge, distance to nearest road, pond permanency and size. At the landscape scale, parks and refuges with less urbanization at in a 5 km buffer from the refuge boundary had higher occupancy of wood frogs and spotted salamanders, highlighting the importance of landscape position of these natural areas.
Key words: amphibian habitat, habitat occupancy, vernal pool
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