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Occupancy and Index of Abundance of Eleutherodactylus wightmanae and E. brittoni along Elevational Gradients in West-Central Puerto Rico

Kelen D. Monroe1, Jaime A. Collazo2,*, Krishna Pacifici3, Brian J. Reich4,Alberto R. Puente-Rolón5, and Adam J. Terando6

1North Carolina Cooperative Fish and Wildlife Research Unit, Department of Applied Ecology, North Carolina State University, Raleigh, NC 27695, USA. 2US Geological Survey, North Carolina Cooperative Fish and Wildlife Research Unit, North Carolina State University, Raleigh, NC 27695, USA. 3Department of Forestry and Environmental Resources, Program in Fisheries, Wildlife, and Conservation Biology, North Carolina State University, Raleigh, North Carolina 27695, USA. 4Department of Statistics, North Carolina State University, Raleigh, NC 27695, USA. 5University of Puerto Rico, Department of Biology, Mayaguez, PR 00681, USA. 6US Geological Survey, Southeast Climate Science Center, Raleigh, NC 27695, USA. *Corresponding author.

Caribbean Naturalist, No. 40 (2017)

Abstract
Populations of Eleutherodactylus species in Puerto Rico have declined in recent decades due to habitat loss and long-term climatic changes. The conservation of these habitat specialists requires an understanding of factors influencing their abundance and distribution, which at present is scant. We estimated occupancy probability and the probability of encountering ≥2 indivivuals of E. wightmanae (Melodious Coqui or Wightman’s Robber Frog) and E. brittoni (Grass Coqui), species with contrasting habitat affinities, using multi-season, multi-state occupancy models. These parameters also served as an index of abundance (non-presence, 1, and ≥2 individuals). We modedled parameters as a function of seasonal temperature and humidity, long-term average monthly precipitation, and habitat covariates measured at survey sites along 2 elevation gradients in the southern slopes of west-central Puerto Rico. We collected survey data using passive acoustic recorders during 3 seasonal periods between February and July 2015. Occupancy patterns of both species was unimodal, containing higher probabilities (e.g., ≥0.5) at elevations between 400 m and 700 m, where long-term monthly precipitation vaired between 120 mm and 160 mm. Chances of encountering ≥2 individuals increased with ground cover for E. brittoni, and decreased with increasing canopy cover for E. wightmanae. Seasonal temperature and relative humidity did not influence occupancy or the probability of encountering ≥2 individuals, likely because covariates varied within known tolerance levels for Eleutherodactylus. Our findings help reduce local extinction probability through management of habitat conditions that increase the likelihood of encountering ≥2 individuals. We also detailed an analytical framework suitable to test hypotheses aimed at predicting potential impacts from land use and climatic changes, and species responses to conservation actions.

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