Assemblages of Dung Beetles Using Cattle Dung in Madagascar

Abstract

Malagasy dung beetles have evolved with a diverse group of primates (lemurs), the largest extant native herbivores on the island. The two main radiations include the endemic subtribe Helictopleurina (65 species) and the tribe Canthonini with several endemic genera (c. 170 species), both of which occur primarily in forests and feed on lemur faeces and carrion. Cattle were introduced to Madagascar about 1000 years ago, thereby establishing a completely new type of resource (cattle dung) for indigenous dung beetles. We report three striking patterns in the occurrence of dung beetles in cattle dung based on semi-quantitative sampling at nearly 80 localities across Madagascar. First, no dung beetles have shifted to use primarily cattle dung in wet forests, in contrast to other tropical regions, where ungulate dung is a key resource for dung beetles. Second, the community in open habitats includes 21 species (three Canthonini, six Helictopleurina, one Scarabaeini, four Onthophagini, six Aphodiini, and one Didactyliini), which is only a small fraction of the species number in comparable communities in mainland Africa. Third, nearly all species using cattle dung have maximally large geographic ranges across Madagascar, in marked contrast to relatively small ranges among forest-inhabiting species. This latter point applies also to four endemic Helictopleurina species, which have shifted to cattle dung in open areas and have subsequently expanded their ranges in comparison with their relatives inhabiting forests. The most numerous species in the community is the introduced Digitonthophagus gazella. We show that the abundance of D. gazella in local communities has no noticeable effect on the species composition in the remaining community.