Increased grazing intensity in pastures reduces the abundance and richness of ground spiders in an integrated crop-livestock system

Abstract

Ground spiders can reflect the impacts of land-use intensification. In an integrated annual crop-livestock system, the grazing intensification can negatively influence the abundance and richness of ground spiders. We evaluated the difference in abundance, family and species richness, and species composition of ground spiders in the soybean and pasture environments, and the effect of grazing intensity on the spider community under a soybean-pasture rotation. We hypothesized that pastures would have higher spider species richness and a distinct species composition and that the increase in grazing intensity would reduce spider abundance and species richness. We conducted an experiment in an integrated annual croplivestock system under a soybean-pasture rotation in southern Brazil that was managed for 14 years by alternating Glycine max for summer grain production and Avena strigosa + Lolium multiflorum for beef cattle grazing during the winter. We sampled four times over 2 years: twice after the grazing cycles and twice after the soybean harvests. Grazing intensification was measured as grazing heights of 10, 20, 30, and 40 cm. Pitfall traps were installed to capture ground spiders. A total of 2589 spiders were collected and classified into 23 families and 43 species. The abundance of spiders was seven times higher, and species richness was 35% higher in the postgrazing compared with the postsoybean environment. Linear mixed effects models showed that spider abundance and richness were strongly influenced by grazing height, particularly postgrazing, but the influence of grazing height on male spider abundance could still be detected in the postsoybean environment. We have shown for the first time that the management of grazing height affects the abundance and richness of spiders in an integrated annual crop-livestock system. To introduce a grazing cycle to a completely crop-centric production system and regulating grazing intensity can help maintain a more diverse spider community.

The role of a rosette‐shaped plant (Eryngium horridum, Apiaceae) on grassland spiders along a grazing intensity gradient

“…These relationships were mediated by the drastic reduction of the grassland complexity and biomass promoted by higher grazing pressures (e.g., Malumbres-Olarte et al, 2013;Ferreira et al, 2020), which resulted in scarce sheltering and foraging options for spiders, as well as increased exposure to stressful conditions such as desiccation. These negative effects of grazing intensity on spider diversity have been already recorded for other grassland communities (Bell et al, 2001;Freiberg et al, 2020). Under high grazing pressure, ungrazed tall-layer plants probably played the role of secure 'islands', protected from cattle disturbance, with space availability (Schmitz & Suttle, 2001), support for webs (Wright & Coyle, 2000), access to water and food resources, and amelioration of abiotic conditions (de Keer et al, 1989), allowing for the coexistence of more spider species.…”

“…The increase in grazing intensity usually favours the dominance of a short layer of prostrated grasses and forbs (Overbeck et al, 2007), while grazing alleviation or suppression favours tussock grasses and shrubs, developing a tall and homogeneous vertical structure (Quadros & Pillar, 1997). Wildlife responses to grazing in these ecosystems are largely taxa‐dependent (Ferreira et al, 2020), varying according to the organism's requirements regarding habitat openness and complexity (Luza et al, 2018; Andersen, 2019; Freiberg et al, 2020). Large herbivores can be very selective when browsing, which promotes grassland heterogeneity by generating a mosaic of grazed and ungrazed patches.…”

Riparian Vegetation Structure Influences Terrestrial Invertebrate Communities in an Agricultural Landscape

“…Other studies have made similar observations. Freiberg et al [70] mentioned Tetragnathidae species "exclusively" in ungrazed areas, in contrast with Lycosidae species that were abundant in grazed areas.…”

Epigean fauna in no-till systems, pasture, eucalyptus and native savanna in Uruçuí, Piauí, Brazil

“…The predominance of the Araneae group in FA may be associated with the accumulation of leaves in the reference area, as this greater amount of leaves provides greater heterogeneity in the burlap microhabitat. Research by Freiberg et al (2020) showed that in an annual crop-livestock integration system, grazing intensification can negatively influence the abundance and richness of terrestrial spiders.…”