NICHE DIFFERENTIATION IN TWO SYMPATRIC SIBLING BAT SPECIES, SCOTOPHILUS DINGANII AND SCOTOPHILUS MHLANGANII

Ecomorphological studies reveal the coexistence of many phenotypically similar bat species. If competition theory is correct, these species should occupy different niches. Here we investigate whether 2 sympatric sibling species of insectivorous bats, Scotophilus dinganii and Scotophilus mhlanganii, that ire similar it morphology also occupy similar niches as predicted by the ecomorphological paradigm. The only phenotypic differences we found between the 2 species were a 10-kHz difference in their echolocation frequencies (S. mhlanganii 42.6 +/- 1.6 kHz; S. dinganii 33.7 +/- 0 1.8 kHz) and a higher wing loading in S. mhlanganii (15.5 +/- 2.3 N/m(2)) compared to S. dinganii (13.6 +/- 1.5 N/m(2)) as a result of the former's similar mass but shorter wingspan. However, there was much overlap in the wing parameters, including wing loading, of the 2 species. In support of the ecomorphological paradigm, the similarity in their phenotypes was reflected in the absence of any detectable spatial or temporal differences in their habitat use (determined by radiotelemetry). Furthermore, subtle differences in skull morphology were correlated with subtle differences in the size of dietary items eaten. S. dinganii, with its larger skull, ate a wider range of insect prey sizes (11.2-18.9 mm) than S. mhlanganii (11.6-12. 2 mill). The most profound ecological difference between the 2 species was the use of different roosts. S. dinganii always was found in building roosts and S. mhlanganii always in trees. Thus, the ecological similarities with their phenotypic correlates support the ecomorphological paradigm. Assortative mating, resulting from the use of different roosts, combined with genetic drift, may explain the subtle differences reported here.