Population Density Estimates and Growth Rates of Eleutherodactylus coqui in Hawaii

Abstract

The Puerto Rican terrestrial frog (Eleutherodactylus coqui) has received considerable attention in Hawaii because of its rapid spread, loud mating calls, and its potential threat to native species. Thus far, its invasion potential on the Island of Hawaii remains poorly understood. Critical components for determining this potential are robust estimates of abundance and vital rates across habitat types. To address this lack of information, we used mark-recapture methods to estimate E. coqui survival and abundance, determine growth rates of adult male and female frogs, and relate densities to elevation, snout-vent length (SVL), habitat structure, and invertebrate abundance. Mean adult E. coqui density across eight sites was 62 6 12 adults/100 m 2 and ranged from 6-138 adults/100 m 2 . Our three-year mean adult density estimates were three times greater at three of our study sites (100 adults/100 m 2 ) than the highest long-term estimates from Puerto Rico (33 adults/100 m 2 ). Mean individual growth rates were 0.0078 mm/day (6 0.007 SD, N = 87) for males and 0.0097 mm/day (6 0.009 SD, N = 11) for females. Frogs of similar size were found to be growing slower in Hawaii than Puerto Rico. We found no relationship between elevation and E. coqui density or elevation and SVL or between invertebrate abundance and E. coqui density. However, there was a positive relationship between understory structure and E. coqui density. This relationship suggests that removing understory structure could reduce E. coqui densities, although other potential implications of this management treatment should be considered.