PRELIMINARY ASSESSMENT OF BREEDING-SITE OCCUPANCY, MICROHABITAT, AND SAMPLING FOR WESTERN TOAD MONITORING IN LOWER GLACIER BAY
Large-scale monitoring efforts directed at western toads (Bufo boreas), an amphibian reported to have undergone declines in Southeast Alaska, are most effective where baseline estimates of occupancy are not excessively low (e.g. <15%). To help inform and calibrate future monitoring efforts, we co...
| Main Authors: | , , , |
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.486.5882 http://www.seawead.org/amphibs/pyare_christensen_carstensen_adams_science_summary.pdf |
| Summary: | Large-scale monitoring efforts directed at western toads (Bufo boreas), an amphibian reported to have undergone declines in Southeast Alaska, are most effective where baseline estimates of occupancy are not excessively low (e.g. <15%). To help inform and calibrate future monitoring efforts, we conducted a preliminary assessment of western toads in the lower Glacier Bay area to evaluate breeding-site occupancy and related microhabitat characteristics, as well as to investigate sampling designs appropriate for monitoring in low-oc-cupancy landscapes. Although we did not correct for detection error and non-random selection of ponds, we observed low breeding-site occupancy (0.05; n=94). Microhabitat comparisons between occupied and unoccupied sites did not yield any strong patterns, but this is not surprising given our low sample size. Nonetheless, solar exposure, which was quite high at some breeding sites, pH, and succes-sional state are 3 variables that we feel warrant further investigation for the Glacier Bay area. Initial GIS-based simulations suggest that sampling designs composed of grid cells that are 0.0625 km2 (250 m x 250 m) to 0.25 km2 (500 m x 500 m), and cover at least 60 % of an area of interest, may be effective approaches for estimating occupancy at scales larger than individual ponds. When planning for moni-toring in low occupancy landscapes we recommend conducting a preliminary assessment to 1) gather and integrate habitat information to define monitoring-area boundaries, and 2) derive coarse-scale sampling units appropriate for monitoring trends in occupancy. |
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