INTRA-AND INTERSPECIFIC AGGREGATION AMONG DUNG BEETLES (COLEOPTERA, SCARABAEOIDEA) IN AN ALPINE PASTURE

Spatial distribution of scarabeoid beetles on dung pats was studied in the Argentera Natural Park (southwestern Italian Alps) from June to S eptember in 1994 and 1995. Artificial dung pats were distributed evenl y within the study area (about 1400 m a.s.l.) and sampled at suitable dung ages (1-13 days). Two experimental tests were carried out. In the first test, experimental pats were covered with metallic nets which p revented the largest species from reaching the dung, whilst in the sec ond test a variable number of individuals of large or relatively large species was added to the experimental pats. The community was dominat ed by Aphodius species (19 out of 25 species), which usually were also the most abundant in the pats. The densities of most species were rel atively low most of the time with average abundances lower than two in dividuals per pat. Even though some interspecific differences were obs erved, ecological overlap between species was rather high with regard both to seasonality and succession in the dropping. Manipulative tests suggested that small beetles were not excluded by larger beetles. Pat terns of spatial distribution showed some degree of intra- and intersp ecific aggregation. Proximate mechanisms of aggregation are probably n on-specific. The ultimate cause of aggregation might be mate-finding. Alternatively, individuals might aggregate because the very same prese nce of beetles within a dung pat would modify its chemical status impr oving its quality. Intraspecific aggregation (measured by means of the J index) was much higher than interspecific aggregation (C index) whi ch suggests, according to the Aggregation Model, that interspecific co existence might be facilitated. However, the data gave no evidence for intra- and interspecific competition between adult beetles.