Abstract:
The five species of adult nocturnal dung beetles (Scarabaeinae, Scarabaeidae) that
degrade most horse dung during the rainy season in Santa Rosa National Park, Costa
Rica, were censused with horse dung-baited traps from shortly before the rainy
season began until the end of the rainy season in a tropical deciduous forest and
nearby pasture. Dichotomius yucatan us and D. carolinus, small and large species
respectively, had their peak abundance during the first half of the rainy season, while
D. centrale, intermediate in size, had its peak adult abundance in the second half of
the rainy season. Adults of Copris lugubris, also intermediate in size, occurred at low
density throughout the rainy season. All but the rarest beetle species (Deltochilum
lobipes) were more abundant in the forest than in the pasture, with Dichotomius
centrale showing this habitat segregation most strongly. Homogenizing the dung
among the traps reduced the among-trap within-site variation in numbers of beetles
caught. The present dung beetle fauna is probably only a remnant of what was
supported by the Pleistocene megafauna. The patterns of horse and cow dung use by
the contemporary dung beetle fauna may well be nothing more than an ecological
response over the past 300 yr by species sufficiently flexible to have survived since
the Pleistocene on the dung rain generated by a native tropical fauna poor in large
mammals.
