Seasonal and daily variations in dung beetle assemblages (Coleoptera: Scarabaeidae) in two contrasting habitats in a livestock ranch in central Uruguay: implications for habitat management and species conservation

Abstract

Dung beetles play a vital role in the functioning and sustainability of agroecosystems. The temporal niche partitioning facilitates species coexistence by minimizing interspecific competition. Temporal activity patterns of dung beetles are influenced by various biotic and abiotic factors. Changes in land use by humans may alter activity patterns and spatial distribution. In this study we analyzed a) the seasonal variations in abundance and richness of dung beetle assemblages in two contrasting habitats within a ranch in Uruguay, and their relationship with environmental factors; b) the influence of the habitat on the daily patterns of flight activity of dung beetles, as well as seasonal and daily changes species composition; and c) the seasonal variations of daily activity patterns of the most abundant species. We sampled dung beetles every two weeks for a year with pitfall traps baited with carrion and cow and horse excrements in an open grazed pasture and a Eucalyptus plantation, used as a shelter for livestock. Each 24-hour sampling was divided into 5 intervals: morning, noon, afternoon, evening, and night. The seasonal variations of abundance and species richness of Scarabaeidae in both habitats were similar from midspring to mid-autumn, without activity in the winter season; temperature influenced these patterns. Diurnal dung beetles were more abundant than crepuscular and nocturnal in the open habitat but not clearly in the Eucalyptus plantation. However, the abundance and richness of nocturnal species were similar in both habitats. The daily activity period significantly influenced the segregation of dung beetles in both habitats. Species composition differed markedly between diurnal and crepuscular/nocturnal species without changes across seasons. Scarabaeinae species were mostly diurnal in grassland, while a nocturnal species was predominant in Eucalyptus plantation. Aphodiinae species were mainly active at dusk and night. We concluded that the daily activity of the species depends on the habitat, which should be considered when designing conservation measures for dung beetles in this region.