Habitat type modifies geometry of elevational diversity gradients in geometrid moths (Lepidoptera Geometridae) on Mt Kilimanjaro, Tanzania

摘要

Changes in geometrid moth diversity are investigated at 61 plots representing various habitat types along an elevational gradient ranging from 1200 to 3700 m a.s.l. on the south-western slopes of Mt Kilimanjaro. Congruent with patterns commonly observed along elevational gradients, overall moth diversity decreases significantly with increasing altitude. A comparison between habitat types nevertheless reveals that this pattern is caused by significant decreases only in open and secondary forest habitats. Apparently in relation to less intensive agricultural management at higher elevations, diversity shows a slight increase with increasing elevation at agro-forestry plots. In mature forests, diversity increases significantly with increasing elevation. This unusual pattern may be explained by extremely wet microclimatic conditions at lower elevations and by boundary effects at higher elevations. Overall, the results demonstrate that generalizations of diversity gradients across heterogeneous habitat types are problematic and must be interpreted with great care.