Department of Physics, Chemistry and Biology (IFM)

A clear result from this study is the high level of heterogeneity encountered in the study area. Even between the traps placed in the understory, with lower variation in light and vegetation structure, large differences in butterfly assemblages were found. Similar large variation between traps only 50-100 m apart has been found in central Brazil (Pinheiro & Ortiz, 1992) and on Borneo (Hill et al., 2001). The variation in butterfly assemblages among the gap traps was even larger than in the understory, and shows the complexity of the rainforest, and gives an insight in the mechanisms behind the high diversity encountered in the Neotropics, and the higher species richness found in the gaps.

The vegetation in the rainforest is subject to regular natural disturbances, like tree falls opening up the canopy. If disturbances occur at an intermediate level, allowing climax and pioneer species to coexist in the same area, they might favor a higher biodiversity. The Intermediate Disturbances Hypothesis (Connell, 1978) is one of the theories explaining the maintenance of the high biodiversity in the neotropics, as already shown for the trees (Molino & Sabatier, 2001; Terborgh, 1992). The differences in intensity, duration, frequency, and extend of disturbances provide specific habitats (Shea et al., 2004), like gaps of different size, vegetation structure and composition, age, light level, resulting on a mosaic of different habitats among the rainforest. This patchy micro-successional habitat resulting from such disturbances affects the species in different ways and their responses are also specific and ensure a greater species richness.

We conclude that the heterogeneity within the rainforest is of major importance to maintain a high level of biodiversity among the butterfly assemblages. The presence of different habitats, following a gradient from an undisturbed understory to large newly formed open gaps, via other small dense or open gaps, is a necessary requirement for the coexistence of the species. The biodiversity of the tropical rainforest is maintained by the occurrence disturbances, and one example is the tree fall like the formation of gaps of different sizes resulting in different structure types of the vegetation. This creates a mosaic of specific habitats that favors different species. Taken as indicators, the nymphalids show a very species rich community, even in a small scale study and without any vertical stratification analysis, and we can then expect other species to follow the same pattern.