Amphibian Research and Occupancy Modeling in the South-Central Region of the Amphibian Research and Monitoring Initiative (ARMI)

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In response to growing public concerns about this loss of biodiversity, the U.S. Congress funded the Amphibian Research and Monitoring Initiative (ARMI), a national program coordinated by the U.S. Geological Survey.

The Science Issue and Relevance: Declines in the abundance and increases in extinction and extirpation of amphibian species have been observed in habitats around the world since at least 1989. Several hypotheses have been proposed to explain this trend. Widespread disease, climate change, and the interaction of the two are perhaps the leading hypotheses for “mysterious” declines of amphibians in relatively undisturbed protected areas. In agricultural and suburban landscapes, environmental contaminants and habitat loss or degradation are the leading factors in amphibian decline. In response to growing public concerns about this loss of biodiversity, the U.S. Congress funded the Amphibian Research and Monitoring Initiative (ARMI), a national program coordinated by the U.S. Geological Survey. The overall goal of this program is to monitor trends in amphibian populations on Department of the Interior (DOI) lands, and to study the causes of any detected declines in amphibian populations.

 

Cajun chorus frog

Cajun chorus frog (Photo by Brad M. Glorioso)

Methodology for Addressing the Issue: Time-constrained visual encounter surveys are used to sample amphibian populations. Sites are chosen randomly within each study stratum (management unit) in a manner such that any point has an equal likelihood of being chosen. A team of two or more observers visits each randomly chosen point no earlier than 30 minutes after sunset. The observers search a 20-meter radius circle around the point using powerful headlamps. All individual anurans (frogs and toads) observed are captured if possible, identified to species, and measured to obtain snout-vent length. In addition, all anuran species detected vocalizing are noted. Environmental data including air temperature, relative humidity, wind speed, water temperature, water depth, and time and date are also collected at each site. Between 30-70 sites are sampled per stratum, and each site is sampled on at least four separate occasions. Anuran data are analyzed in the site occupancy framework, which produces an estimate of the proportion of area occupied for each species given imperfect detection of the species using sampling covariates. Models may be fit using maximum likelihood methods or under a Bayesian inferential method using Markov-chain Monte Carlo simulation.

Blanchard's cricket frog

Blanchard’s cricket frog (Photo by Brad M. Glorioso)

 

Future Steps: Monitoring for site-occupancy of amphibians was suspended after the 2016 season at our long-term sites in the Atchafalaya Basin. However, ongoing monitoring efforts and research will continue related to threats to regional amphibians. Particular attention will be paid to federally threatened and endangered species. We will also continue efforts to use amphibian populations as indicators of ecosystem condition and restoration success.