The effects of four types of anthropogenic disturbances on composition and abundance of terrestrial isopods (Isopoda: Oniscidea)

The Brazilian Atlantic Forest is currently reduced to about 12% of its original range. Among the components that make up its great diversity, there are species with the potential to be bioindicators, which can be very important for conservation-oriented studies. This study compares the species composition, abundance and sex ratio of terrestrial isopods in sites that show different anthropogenic disturbance histories and are located within four reserves in the Atlantic Forest of southwestern Brazil. Our study explores these crustaceans as indicators of anthropogenic disturbance. The influence of one of the following factors was explored in each protected area: 1) history of vegetation harvesting, 2) trail management, 3) Eucalyptus planting, and 4) edge effect. A total of 2,217 individuals of six species (Atlantoscia sp., Benthana werneri Lemos de Castro, 1958, Pseudodiploexochus tabularis (Barnard, 1932), Pudeoniscus obscures Lemos de Castro, 1973, Styloniscus spinosus (Patience, 1907), and Trichorhina sp.) were captured in pitfall traps. The composition of isopod species was different between most of the contrasting sites within reserves, and was similar among the less disturbed sites of different reserves. The total number of isopod individuals and the sex ratio were not different between the contrasting sites within most of the reserves and only the sex ratio of Atlantoscia sp. differed between contrasting sites of one protected area. Upon an individual analysis of each species, S. spinosus (an exotic species) was most abundant in more disturbed sites. The distributions of B. werneri and Atlantoscia sp. over time were relatively synchronous, except where S. spinosus was abundant. Our results also indicate that the exotic species S. spinosus may benefit from the vegetation mosaic produced by disturbance, so differences in abundance of this species may be useful for bioindication. A change in the spatial and temporal structure of Oniscidea communities caused by anthropogenic disturbance may have a cascade effect on ecological cycles because terrestrial isopods play a fundamental role in nutrient cycling.