The Re-colonization Ability of a Native Earthworm, Estherella spp., in Forests and Pastures in Puerto Rico
Populations of some native earthworm species are decreasing or disappearing due to human activities like habitat disturbance and introduction of exotic earthworms. Habitat disturbance can cause changes in soil physical structure and nutrient cycling, which may reduce native earthworm populations prior to the invasion of exotic earthworms. Our purpose was 1) to investigate habitat disturbance as a key process in the decline or extirpation of native earthworms, and 2) to measure the ability of native earthworms to re-colonize disturbed areas. We hypothesized that habitat disturbance will reduce the population of native earthworms and impede their re-colonization in those perturbed areas. We set up 48 soil mesocosms in three field sites representing different degrees of disturbance (abandoned pasture, young and mature forests) in the Cayey Mountains of Puerto Rico. Three individuals of the native earthworm, Estherella spp., were inoculated into each soil core to evaluate their re-colonization ability by measuring survivorship, growth rates and reproduction. We found that, in the absence of exotic earthworm species, the survivorship and growth rates of Estherella spp. in the pasture was not significantly different than that from young and mature forests during the first six months of re-colonization process. Our results suggest that habitat disturbance (changes in vegetation and soil properties) may not have significant influences on native earthworm (Estherella spp.) populations. We propose that biotic factors, such as competitive exclusion of native earthworms by exotic earthworms, may have considerable effects on retarding their re-colonization and/or causing the disappearance of native earthworm population in disturbed areas.