ABSTRACT
The aims of this study were to characterize the fauna of dung beetles and analyze their spatial and temporal diversity in a cattle ranch in the province of Chaco. Seven surveys were conducted in three environmental units: a forest fragment, a cattle pasture, and an open grassland. The efficiency of the sampling was assessed with non-parametric richness estimators, and attributes of the assemblage were evaluated. The species composition and the abundance distribution in each of the environmental units studied were compared using rank-abundance curves. The indicator value of each species was measured with the IndVal method. The relationship between richness, abundance, and environmental variables (temperature, precipitation, and relative humidity) was calculated by multivariate multiple regression analysis. A total of 3,356 adult individuals belonging to 29 species of the subfamily Scarabaeinae and to five species of Aphodiinae were captured. Dichotomius nisus (Olivier), Trichillum externepunctatum (Preudhomme), Canthon podagricus (Harold), Onthophagus hirculus (Mannerheim), Pseudocanthon aff. perplexus, Ontherus sulcator (Fabricius), and Ataenius platensis (Blanchard) were the most abundant. Diversity, species richness, and abundance were highest in the forest fragment and in spring and summer captures. Between 94% and 97% of the species present in the entire landscape were recorded. According to the analysis of similarity, the composition of the assemblage was different among habitats. Eurysternus caribaeus (Herbst), Eurysternus aeneus (Génier), and O. sulcator were indicators of the forest. In the three units, the coprophagous species represented more than 60% of the total species number. The rainfall regime, the temperature, and the heterogeneous use of the environmental units influenced the structure of dung beetle assemblages.
Subject(s)
Animal Distribution , Coleoptera , Spatio-Temporal Analysis , Animals , Argentina , Ecosystem , Forests , HumidityABSTRACT
Populations of T. infestans and T. sordida were studied between September 1988 and April 1989 with a view to discovering if any kind of interaction took place between them while they lives together in the same experimental unit and exploited the same food resource (chicken). The initial age structure for each species was: 27 N1, 7 N2, 11 N3, 3 N4, 8 N5, 4 males and 10 females. The population dynamics nutritional status, predation and gregarious behavior were estimated by means of a monthly census. The colonizing success of T. infestans was greater than that of T. sordida in view of the values obtained: fecundity (146 eggs/female), longevity (157.8 days) and mortality (39.4) compared with the values recorded for T. sordida: 118 eggs/female, 81.1 days and 54.0% respectively. The population growth of T. insfestans followed an exponential model, with a high nymphal recruitment rate, while the T. sordida population was early extinguished. In general, the average weight of T. infestans remained close to the initial values while that of T. sordida declined. Gregarious groups were formed principally in the inferior sector of wall 1 (near the host) with a higher aggregation in T. infestans. These results make it possible to propose the hypothesis of the competitive superiority of T. infestans.
