Seasonal Change in Abundance of Large Nocturnal Dung Beetles (Scarabaeidae) in a Costa Rican Deciduous Forest and Adjacent Horse Pasture

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.