Community-level response to habitat structure manipulations: An experimental case study in a tropical ecosystem

Abstract

Across the globe, environmental change is resulting in novel ecosystems that have altered habitat structure and functioning. Research is needed to understand how changes in habitat structure in these new ecosystems impact community interactions, especially when these manipulations are being proposed to reduce invasive species. We conducted an experiment in Hawaii to determine how changes in habitat structure, represented by leaf litter and understory vegetation, affect the abundance of an invasive generalist predator, the coqui frog (Eleutherodactylus coqui) and its potential prey (invertebrates). This study consisted of four treatments: two vegetation treatments (50% and 100% removal of vegetation with diameter at breast height <5cm) and two leaf litter treatments (50% and 100% removal). Removal of 50% of habitat structure, either vegetation or leaf litter, was not sufficient to produce long-term changes in coqui or invertebrate densities. Only full removal of habitat structure resulted in reduced densities of coqui after four months. The abundance of leaf litter invertebrates and invertebrates flying close to the forest floor was higher in the 100% vegetation removal treatment compared to leaf litter removal treatments, and the abundance of foliage invertebrates was higher in the 100% leaf litter removal treatment compared to vegetation removal treatments. Invertebrate responses were complicated because they not only responded to the loss of habitat but also the reduction of coquis in treatments. Coquis in treatments moved to microhabitats that contained increased prey. Treatments appeared to impact coquis by removing structure needed for diurnal retreats, breeding and foraging. In summary, both the 100% removal of leaf litter or vegetation can reduce coqui densities in relatively small (20m×20m) areas, even when surrounded by intact, invaded forest. This study provides greater understanding of the impact of habitat structure manipulation, a typical management employed to control an invasive frog, in a novel ecosystem.