The effect of stressors, disturbance regimes and environmental gradients on riparian arthropods: implications for management and conservation.

Abstract

Riparian zones remain highly threatened by anthropogenic activities and climate change despite being ecologically valuable ecosystems. Understanding their complex and dynamic nature is crucial to effectively restore, manage, and conserve them and their biodiversity. Therefore, this study aimed to examine the influence of riparian environmental gradients, stressors, and disturbance regimes on the biodiversity of terrestrial arthropods and their implications for management and conservation policies. The first objective was to systematically review, using PRISMA guidelines, the response of riparian arthropods to flooding, alien plant invasion, and river engineering at a global scale and identify potential management strategies. The second objective was to determine, at a local scale, whether seasonal changes, location and increasing distance along the uMngeni riparian habitats, and from these habitats to the adjacent uplands, affect ant and spider diversity, community composition, and their foraging strategies, using pitfall traps. Findings from the systematic review highlighted that terrestrial arthropods’ biodiversity was predominantly adversely affected by flooding, alien plant invasion, and river engineering due to changes in environmental conditions, although responses to alien plant invasion differed among taxa. At the local scale, ant and spider richness in the studied gradients were not affected by seasonality or distance from the river and along the river. However, during the wet season, ant abundance decreased with increasing distance from the riparian to the upland areas, while spider abundance increased. The representation of spider foraging strategies was affected by season and location (study sites: Umgenipoort vs Hilton), contrary to that of ants which was only influenced by distance. Distance from the riparian habitats to the uplands significantly influenced ant community composition, whereas seasonal variation was the primary driver of spider community composition. Species turnover mainly accounted for overall beta diversity, with some ant and spider species unique to specific distances within the studied gradients. To conserve riparian biodiversity and function from further threats, eligible studies from the systematic review suggested creating and protecting heterogeneous habitats within riparian zones, restoring native vegetation and natural water flow, while considering species-specific ecological needs. This study has highlighted the factors that compromise riparian biodiversity and ecological processes that explain the observed patterns, providing valuable insights for conservationists to predict ecological changes. It also highlights the need for collaboration and long-term monitoring to sustain biodiversity and ecosystem functions along riparian zones.