Arthropod diversity and assemblage structure response to deforestation and desertification in the Sahel of western Senegal

Abstract

Drylands are highly vulnerable to desertification and among the most endangered ecosystems. To understand how biodiversity responds to environmental degradation in these fragile ecosystems, we examined whether arthropod, beetle, spider and ant diversity and assemblage structure differed (1) between seasons, (2) among locations (3) between protected areas of tropical dry forest and adjacent communal lands suffering from desertification, as well as (4) how vegetation impacts assemblage structures. We established 12 plots spaced homogenously throughout each protected area and the adjacent communal land at three locations: Beersheba, Bandia and Ngazobil. Within each plot, we measured canopy closure, vegetation height, percent cover of bare ground, leaf litter, grasses and forbs and collected arthropods using pitfall traps during the 2014 dry (May) and rainy (September) seasons. We collected 123,705 arthropods representing 733 morphospecies, 10,849 beetles representing 216 morphospecies, 4969 spiders representing 91 morphospecies and 59,183 ants representing 45 morphospecies. Results showed greater arthropod and beetle diversities (P = 0.002–0.040) in the rainy season, no difference in diversity among locations for any taxonomic group and a difference (P ≤ 0.001) in diversity for all taxa between protected areas and communal lands. Assemblage structures of all taxa responded (P = 0.001) to vegetation characteristics, differed (P = 0.015–0.045) between seasons and, with a few exceptions, locations and fragments. Our results illustrate the importance of a multi-taxa approach in understanding biodiversity response to anthropogenic disturbances as well as the value of protected areas in preserving biodiversity of the Sahel.