Strands of Connection: Livestock Grazing, Vegetation Density, and Orb-Weaver Spider Persistence

Abstract

Studies on the effects of grazing disturbances in grasslands have shown mixed results for spider diversity, mainly regarding their guilds. While ungrazing, low, and moderate grazing potentially enhance diversity of orb-weavers, heavy grazing seems to reduce specieś richness. On the population level, studies of orb-weavers are scarce, and the effects of grazing are unknow. In this way, we investigated the effects of different levels of grazing on population persistence of orb-weaver spiders, hypothesizing that low to intermediate disturbances benefit populations. We predict that high grazing, due to the removal of vegetation structure, will negatively affect occupancy and abundance of orb-weavers. For that, we experimentally controlled grazing pressure and obtained population occurrence and counts of two orb-weaver spider species,Argiope argentataandAlpaida quadrilorata. We found thatA. argentatawas directly affected by grazing, as it relies on higher vegetation for web-building. In contrast,A. quadrilorata, which occurs in cattle-resistant rosette plants, showed no effects of grazing.Implications for insect conservation:Our study emphasizes the need for balanced grazing practices and habitat conservation to protect orb-weaver spiders and other arthropods, as well as, species-specific effects for species from the same guild, underscoring their ecological significance in maintaining ecosystem stability.