Cattle grazing impacts on dung beetle communities and their ecological functions in the Brazilian Pantanal

Abstract

Grassy ecosystems dominate the tropics sustaining unique biodiversity and providing valuable ecological services to humankind. However, these ecosystems have been extensively cleared for agriculture and planted forests or used as pasture for livestock. Thus, the aim of this thesis was to assess the impact of cattle grazing on dung beetle community and its ecological functions in a tropical grassy ecosystem, inserted in Brazilian Pantanal. The insects were collected in 24 areas of native grasslands with different times of cattle grazing abandonment, in the Pantanal of Aquidauana, Mato Grosso do Sul, Brazil. In the first chapter, I evaluated the effects of cattle grazing on community metrics (abundance, biomass, richness, species composition and functional groups) and ecological functions (dung removal and soil bioturbation) performed by dung beetles, in 10 regularly grazed by cattle and six control ungrazed areas, used as pastures (> 20 years of abandonment). I found that the cattle grazing, despite causing changes in species composition, does not affect the abundance, richness, biomass and ecological functions performed by dung beetles. In the second chapter, I studied the successional trajectory of dung beetle communities after cattle grazing abandonment along a chronosequence of natural grasslands with different cattle grazing exclusion ages (0.4 – 22 years). I found a strong decrease of dung beetle abundance and species richness in the first ten years of cattle grazing abandonment. However, after ten years there is an increase in these parameters. After three years of abandonment the taxonomic composition was different from the control, with the formation of a species community distinct. Functional diversity was not affected by cattle grazing abandonment, demonstrating that it is less sensitive to cattle absence than taxonomic diversity. Thus, these results provide evidence that livestock farming in natural grasslands of Brazilian Pantanal do not cause significant impacts on the dung beetle community (mainly functional diversity) and their ecological functions. This demonstrates that livestock management (with reduced use of veterinary drugs) can integrate livestock production with biodiversity conservation, as well as provide opportunities to maintain native fields, without them being converted to other land uses. Finally, cattle grazing exclusion, in a relatively short time (20 years), may be an inefficient management tool for restoration and conservation of tropical grassy ecosystems.