Abstract.  1. This study combines the results of laboratory experiments using representative assemblage components and pitfall trapping over a large geographical area to examine the hypothesis that ongoing interspecific competition structures Neotropical dung beetle assemblages.2. From Guatemala to Panama assemblages of large to medium‐sized, fast‐tunnelling dung beetles include a single large, nocturnal dichotomiine species, Dichotomius annae (Kohlmann & Solís, 1997). In competition experiments, this species out‐competed the medium‐sized coprine species, Copris lugubris Boheman and Phanaeus demon Laporte‐Castelnau, for dung and nesting space, in spite of earlier colonisation by the diurnal species, P. demon.3. Differences in the abundance of D. annae at Central American sites did not affect total fast‐tunnelling dung beetle assemblage richness over the rainy season. However, D. annae rank order was directly related to the probability of interspecific encounters (Hurlbert's Δ1) among species. These trends were also observed when species lists from published and unpublished studies of other large allopatric dichotomiine species, with a more northerly distribution, were included in the analyses.4. The results obtained suggest that where large dichotomiine species are abundant, their efficient pre‐emption of a considerable proportion of available resources drives all, or most, other fast‐tunnelling species to a lower population density, thereby decreasing assemblage diversity.

Se reporta por primera vez la presencia del escarabajo Digitonthophagus gazella (Fabricius, 1787). Además, se amplía el rango de distribución de Euoniticellus intermedius (Reiche, 1849) en El Salvador, a partir de información obtenida de colectas realizadas a lo largo de doce años y se presenta el mapa de distribución actual de E. intermedius en el territorio. Adicionalmente, se discute brevemente la situación actual de ambas especies en el país y Centroamérica.