Influence of Grazing by Large Mammals on the Spider Community of a Kenyan Savanna Biome

Abstract

Pitfall trap and sweep net samples were taken over a period of fifteen months (2002)(2003) in the Kenya Long-term Exclosure Experiment (KLEE), in which the presence of domestic and wild herbivores have been independently manipulated since 1995. ANOVA and ANCOVA showed that the exclosure treatments significantly affected plant cover, with the presence of cattle significantly reducing the relative vegetation cover and spider diversity. Herbivory by indigenous mega-and meso-herbivores did not have a significant influence on the diversity of the spider fauna, but abundance of three dominant species (Cyclosa insulana Costa (Araneidae), Argiope trifasciata ForskM (Araneidae) and Runcinia flavida Simon (Thomisidae)) decreased in cattle-grazed plots. In contrast, Aelurillus sp. became more prevalent where cattle have been grazing. Multivariate analyses revealed that the spider community responded to grazing pressure by aggregating into three groups that reflected control, cattle grazing and non-cattle grazing clusters. It was probable that the direct effects on vegetation mediated an indirect influence of herbivores on spider diversity. The relative vegetation cover was a positive predictor of spider diversity. Spider communities were found to be an indicator of the activity of mammals and could be used as indicators of land use changes and for bio-monitoring.

Evaluation of the design effects of different agropastoral systems on the diversity and density of spiders

“…Our results did not coincide with those of Dennis et al (2015), Warui et al (2005) and Bromham et al (1999) who mentioned that the presence of large herbivores (especially livestock during grazing) affects spiders indirectly through the reduction of vegetation cover, generating changes in the structure of the vegetation/architecture of particular plant species and increasing the abundance of pest species. We found that bigger grazing areas within the design translated into a greater mean alpha diversity and density of spiders in the community.…”

“…These families coincided partially with those recorded in crops of soybeans, alfalfa, wheat and cotton (Liljesthröm et al, 2002;Beltramo et al, 2006;Armendano & González, 2009Almada et al, 2012, respectively), where Anyphaenidae, Salticidae and Linyphiidae were the main families in terms of their abundance. These families are also represented with greater abundance in livestock systems (Toti et al, 2000;Warui et al, 2005), as well as in reserves and national parks (Corronca & Abdala, 1994;Rubio et al, 2004;Grismado, 2007;Avalos et al, 2009;Rubio, 2015).…”

Effects of grassland management practices on ant functional groups in central North America

“…Grazing, like fire, is a disturbance that can affect the abundance and diversity of fauna (Andresen et al 1990, Sutter and Ritchison 2005, Warui et al 2005) and flora (Towne et al 2005). Fire and grazing have also interacted for millennia Engle 2001, Archibald et al 2005), a process labeled as pyric herbivory (Fuhlendorf et al 2009) because fire alters distribution and foraging behavior of large ungulates in space and time.…”

Trap and soil monolith sampled edaphic spiders (arachnida: araneae) in Araucaria angustifolia forest

“…Others studies showed that enclosure treatments affected plant cover, with the presence of cattle significantly reducing the relative vegetation cover and spider diversity of a Kenyan savanna biome. In this study, the presence or absence of spider families were found to be an indicator of the anthropogenic disturbance and could be used for bio-monitoring, as indicators of land use changes (Warui et al, 2005). Therefore, the type of employed sampling method influences the results for spider family richness (Tables 2 and 3), as well as edaphic fauna abundance and diversity (Baretta et al, 2003;Barreiros et al, 2005).…”

“…Some authors suggest that the diversity in vegetation cover may also influence the composition and richness of spider communities (Rushton et al, 1987;Lawes et al, 2005;Warui et al, 2005). Variables potentially influencing family and species richness are litter, depth, bare ground, densities of dead and of living vegetation (Brennan et al, 2006).…”