Harvestmen in an Atlantic forest fragmented landscape: Evaluating assemblage response to habitat quality and quantity

Abstract

Despite the importance of considering arthropods in monitoring programs and conservation planning given their diversity in terrestrial ecosystems and potential in revealing environmental disturbances, most studies on the effects of habitat disturbances in tropical forests focused on vertebrates, plants and a few arthropod groups. By sampling 16 sites evenly distributed in four habitat categories (continuous mature and secondary forest and large and small secondary forest fragments), we investigated how harvestmen (Opiliones), which represent the third largest order of arachnids and have been poorly studied in tropical forests, are affected by habitat quality and quantity. Richness and abundance of rare species were strongly affected by habitat quality (first axis of principal component analysis on forest structure), increasing in less disturbed/mature forests. Richness, total abundance, abundance of rare species and of one of the three common species were higher in continuous forest, while only total abundance differed between large and small fragments. Detrended correspondence analysis revealed that just one species increased in abundance in fragments, while several others were associated with continuous and/or mature forest and that harvestman composition did not vary between large and small fragments. Our results suggest that harvestmen (1) are strongly affected by habitat quality and quantity, probably because, compared to other arthropod groups, they are relatively uniform in some relevant biological aspects (nocturnal predators dependent on microclimatic conditions that present low vagility); (2) are probably more indicative of intermediate-level disturbances, given the absence of species associated with highly-disturbed areas.