Is cattle grazing more important than landscape heterogeneity for grasshoppers in Afromontane grassland?

Abstract

Overgrazing is a major driver of habitat degradation, especially in southern Africa. Although grasshoppers are adapted to and benefit from natural disturbances, such as grazing by indigenous game and burning, we do not know how they respond to heavy cattle grazing, and how this response interacts with different fire regimes. We also do not know whether grasshoppers respond principally to these disturbances, to changes in the vegetation layer, or to larger landscape attributes (e.g. elevation). We addressed these questions in the topographically heterogeneous Central Midlands of KwaZulu-Natal Province, South Africa. We compared grasshopper assemblages among sites differing in grazing intensity (light, moderate and heavy), fire regime, rocky outcrops and vegetation structure, and attributes of landscape heterogeneity. The local environment (rocky outcrops, bare ground cover, grass height and total vegetation cover) was more important than landscape attributes for all measures of diversity. Grasshopper species richness was best explained by grazing intensity, with the specific response determined by fire regime. Greatest species richness was consistently recorded in heavily-grazed grassland. Thus, we found no evidence in support of the Intermediate Disturbance Hypothesis. Grasshopper assemblage composition of areas with light grazing was different from those with heavy grazing, but areas with light grazing were similar to those with moderate grazing under all fire regimes. Different suites of grasshopper species were adapted to changes in the local environment, with greatest diversity (Shannon H') associated with elevated levels of bare ground and sparse vegetation cover. The greatest proportion of rare, endemic and sensitive grasshoppers (incl. Lentula minuta, Machaeridia conspersa and Qachasia fastigiata) was associated with a greater proportion of vegetation cover. The sensitivity of grasshopper assemblages to fire-grazing interactions, and the habitat requirements of different suites of species necessitates consideration of different types (fire and grazing) as well as levels of disturbances when adjusting management practices. We recommend that conservation of rare, endemic and sensitive grasshoppers should be prioritized, as these are most vulnerable to local extirpation.

Identifying managerial legacies within conservation corridors using remote sensing and grasshoppers as bioindicators

“…Grasshoppers within conservation corridors respond strongly to the local vegetation structure and available bare ground (Bazelet and Samways 2011, Joubert‐van der Merwe and Pryke 2018). Our results also support this by showing that local plant species richness, vegetation structure, and bare ground have a significant influence on grasshopper assemblage composition.…”

“…However, invasion of the alien invasive plant Rubus cuneifolius (American bramble) into grasslands, has severe negative impacts on grassland bird diversity (Reynolds and Symes 2013), flower visiting insects (Hansen et al 2018), as well as on the restoration success of grasslands (Eckert et al 2019). Furthermore, domestic cattle roam throughout these corridors, causing some excessive grazing of the landscape, as manifested by changes in grasshopper assemblage composition (Joubert-van der Merwe and Pryke 2018).…”

Conservation Prioritization of Orthoptera Assemblages on a Mediterranean Island

“…Open forested sites, however, with high rock cover had a positive effect on the c i and StCI. It is well known that rocky substrates provide shelter and facilitate orthopterans' thermoregulation, especially in mountain regions [58][59][60]. These substrates foster endemic species such as Exodrymadusa inonrata and Modicogryllus cyprius, with high c i values, providing microclimate niches in open rocky areas [60].…”