Impact of different grazing systems on diversity, abundance and biomass of beetles (Coleoptera), a study from southern Namibia

Abstract

Two plots were compared in the Nama Karoo, southern Namibia, in order (a) to test the impact of different grazing systems on arthropod diversity and abundance and, (b) to select suitable indicators of degradation for restoration efforts. On these plots, bushes and the grass Stipagrostis obtusa dominated on Gellap-Ost whereas Nabaos was strongly degraded with denuded soil. Compared to Gellap-Ost, this reduction in resource and shelter availability was reflected by reduced abundance and diversity but increased biomass of beetles (Coleoptera) at Nabaos. Especially in predatory carabid beetles, reduction in numbers seems to be compensated by the occurrence of larger species. A negative feedback for ecosystem functions was postulated from the lower arthropod diversity. Active management tools are recommended to restore Nabaos. Carabid beetles are best suited as indicators of grazing impact in the Nama Karoo ecosytem as they differ in species composition, diversity, and abundance between the plots, and belong to one of the taxonomically better known groups. Despite their great ecological impact, tenebrionid beetles are less well suited as indicators in this system as they differ in relative abundance but less in species composition. Furthermore, many of the tenebrionid species are undescribed and many tenebrionid groups are unrevised.

Shrub encroachment is not always land degradation: Insights from ground‐dwelling beetle species niches along a shrub cover gradient in a semi‐arid Namibian savanna

“…To capture the highest diversity and abundance of beetles, we surveyed beetles during the peak of the rainy season (November to January) where the majority of species are active (Louw, ; Vohland et al, ).…”

“…The vegetation composition is a key determinant of the occurrence of beetle species (Liu et al, ), and, vice versa, beetles provide important ecosystem functions such as decomposition, nutrient cycling, and an increase in the availability of essential nutrients (Sitters et al, ) for plant growth. However, little is known on the ecology and niche differentiation of ground‐dwelling beetles in semi‐arid savannas (e.g., Shelef & Groner, ; Vohland, Uhlig, Marais, Hoffmann, & Zeller, ). This is particularly problematic because species‐specific knowledge of animal niches is fundamental to evaluate ecosystem functionality and to identify at which level shrub encroachment can be regarded as land degradation.…”

“…In our study, we analysed the species‐specific niche optima and niche breadths of the three major ground‐dwelling beetle families Carabidae, Tenebrionidae, and Scarabaeidae (Vohland et al, ) in semi‐arid African savanna rangelands. We were particularly interested in understanding to what degree single species benefit or suffer from shrub encroachment and whether beetle communities respond to shrub encroachment gradually or abruptly.…”

“…However, little is known on the ecology and niche differentiation of ground-dwelling beetles in semi-arid savannas (e.g., Shelef & Groner, 2011;Vohland, Uhlig, Marais, Hoffmann, & Zeller, 2005). This is particularly problematic because species-specific knowledge of animal niches is fundamental to evaluate ecosystem functionality and to identify at which level shrub encroachment can be regarded as land degradation.…”

Ground-dwelling arthropod communities present in three types of Cantabrian (NW Spain) heathland grazed by sheep or goats

“…Amongst terrestrial arthropods, harvestmen (Opiliones), wolf spiders (Araneae: Lycosidae) and ground beetles (Coleoptera: Carabidae) show distinct associations with specific habitats and are sensitive to habitat modification (e.g., Sankey & Savory, 1974;Rainio & Niemelä, 2003;Vohland et al, 2005). While certain Coleoptera might be more affected by changes in the floristic composition than in the structural features, other groups such as Araneae, Opiliones, Hemiptera or Orthoptera respond mainly to the structural characteristics of the plant canopy (Gardner, 1991;Gibson et al, 1992a;Dennis et al, 1998;Wettstein & Schmid, 1999;Rosa Garcia et al, 2009).…”