An invasive frog, Eleutherodactylus coqui, increases new leaf production and leaf litter decomposition rates through nutrient cycling in Hawaii

A frog endemic to Puerto Rico, Eleutherodactylus coqui, invaded Hawaii in the late 1980s, where it can reach densities of 50,000 individuals ha⁻¹. Effects of this introduced insectivore on invertebrate communities and ecosystem processes, such as nutrient cycling, are largely unknown. In two study sites on the Island of Hawaii, we studied the top-down effects of E. coqui on aerial, herbivorous, and leaf litter invertebrates; herbivory, plant growth, and leaf litter decomposition rates; and leaf litter and throughfall chemistry over 6 months. We found that E. coqui reduced all invertebrate communities at one of the two study sites. Across sites, E. coqui lowered herbivory rates, increased NH₄⁺ and P concentrations in throughfall, increased Mg, N, P, and K in decomposing leaf litter, increased new leaf production of Psidium cattleianum, and increased leaf litter decomposition rates of Metrosideros polymorpha. In summary, E. coqui effects on invertebrates differed by site, but E. coqui effects on ecosystem processes were similar across sites. Path analyses suggest that E. coqui increased the number of new P. cattleianum leaves and leaf litter decomposition rates of M. polymorpha by making nutrients more available to plants and microbes rather than through changes in the invertebrate community. Results suggest that E. coqui in Hawaii has the potential to reduce endemic invertebrates and increase nutrient cycling rates, which may confer a competitive advantage to invasive plants in an ecosystem where native species have evolved in nutrient-poor conditions.