National Capital Region Network 2009 amphibian monitoring: Synthesis of 2005-2009 data

Campbell Grant, Evan; Zipkin, Elise; Brand, Adrienne

This report describes ongoing amphibian monitoring efforts in the National Capital Region Network. Amphibian monitoring was initiated in 2005 and is currently concentrated in Chesapeake and Ohio Canal National Historic Park and Rock Creek Park, with stream (lotic) sampling also occurring in Prince William Forest Park. The objectives of the monitoring program are to develop an efficient long-term sampling design to: (1) describe the current distribution of amphibians and explore factors that may influence occupancy probabilities or distributional patterns, (2) determine if amphibian distributions are changing annually, and if so, explore whether occupancy changes are related to habitat quality and (3) provide information to aid in the generating and testing hypotheses that differentiate among possible causes of long-term changes in the proportion of area occupied among species, habitats, and park areas. Here, we present analysis from 2005-2009 and describe our findings related to the first two objectives. We discuss our results in the context of the National Capital Region Network’s continuing amphibian monitoring program. For the lentic habitats, we detected 12 amphibian species or species complexes in each year of sampling 33 wetlands from the Potomac Gorge area within Chesapeake and Ohio Canal National Historic Park (CHOH). Results from our model indicated only a 23% probability that there were greater than 12 species in the region suggesting that most, if not all species were observed on at least one occasion during the five years of sampling. We found that detection probabilities (the probability of detecting a species, given it is present at a site) were less than one and were strongly influenced by when sampling occurred (i.e., day of the year) but were only mildly variable between years. We investigated the relationships between wetland species richness and two important limiting variables in amphibian communities--habitat area and hydroperiod. Lentic species richness was generally highest in permanent, followed by semi-permanent, and lowest in temporary wetlands. Total richness (i.e., the average number of species at a wetland that were present in at least one year of sampling) ranged from 2.7 to 11.0 across the set of permanent wetlands (mean: 7.4; median: 9.0), from 3.2 to 10.0 in semi-permanent wetlands (mean: 6.8; median: 7.4) and from 0.3 to 10.0 in temporary wetlands (mean: 2.5; median: 1.4). The mean estimated richness for each year of the survey was variable in each of the wetlands, with some wetlands having fairly constant richness and others experiencing large annual changes. Annual wetland variability in richness varied independently of hydroperiod category. Increasing wetland area generally had a positive effect on species occurrence probabilities but the result was fairly minimal.

National Capital Region Network 2009 amphibian monitoring: Synthesis of 2005-2009 data

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