Seasonal and altitudinal structure of drosophilid communities on Mt Oku (Cameroon volcanic line)

Abstract

We assessed the potential of drosophilids as indicators of the response of tropical ecosystems to climatic factors over an annual cycle in the montane forest of Mt Oku, by collecting samples at seven sites evenly spaced from 2200m to 2800m asl. Only 0.1% of the 11,000 specimens collected belonged to invading species or those commensal with humans, showing the weakness of anthropogenic factors. Species abundance was highly skewed. One species, Zaprionus vittiger, made up 81% of the sample, whereas 42 of the 62 morphological species found were represented by fewer than 20 individuals. Many of the most abundant species occurred over a narrow period, in the dry or in the rainy season, others also occurred at intervening periods. These different patterns of population dynamics, determined a succession of species over the annual cycle. Abundant species departed significantly from each other in their distribution over collection sites. The drosophilid populations from the central African montane forests are highly dependent on climatic factors, either directly, or indirectly through climatic effects on the biotic environment of the insects.