Applied and theoretical perspectives on the community dynamics of fruit-feeding butterflies

In this thesis, fruit-feeding butterflies (nymphalids) are used as a ‘study system’ for two broad aims: First, to develop an efficient and reliable rapid biodiversity assessment (RBA) protocol for monitoring Ghanaian forests (applied perspective) and second, to empirically evaluate neutral theory in mobile organisms (theoretical perspective). To achieve these two broad study aims, four individual studies, each with specific research questions and objectives were proposed for detailed investigation. The studies were conducted mainly in two protected forests in Ghana; Bia Biosphere Reserve (BIA) and Bobiri Forest Reserve (BOB) between August 2006 and November 2007 using transects and fruit-baited butterfly traps. The first study examined two potential biases (due to temporal variation and vertical stratification) associated with RBA in Ghanaian forests. Both individual numbers and species richness were on average three to four times higher in the understorey than in canopy traps with strikingly different species composition (only 10% overlap in species between the two communities). Considerable temporal variation was observed in species richness and individual abundance at both the canopy and understorey levels. The study justified the importance of taking into account the effects of temporal and vertical stratification when using fruit-feeding butterflies as the model system for RBAs in Ghanaian forests. The second study evaluated the efficiencies of two different bait- and trap- types. It also assessed how the age of bait influences RBA results. The new trap type (with reduced entry/exit) performed at least three times better than the conventional vanSomeren-Rydon trap, in terms of the number of individuals and species trapped per trap-day. Using the same scale of measure, the novel bait type (banana bait mixed with palmwine) was found to be more productive and hence, more efficient compared to the old bait which consisted of only mashed banana fruit. The study revealed that age of bait does affect both the number and kind of butterflies trapped. the results of the study iv suggest that, to make RBA more efficient, butterfly sampling need not exceed two days (if palmwine is mixed with mashed banana and allowed to ferment for 24 hours) or three days (when only mashed banana fermented for 24 hours is used as bait) on the same location. The third study sought to identify which fruit-feeding butterfly species-groups could be effectively used to monitor habitat changes in Ghanaian forests. The study indentified the genera Euriphene, Bebearia, Aterica, Gnophodes, Melanitis andEuphaedra as potential indicator taxa of good conditioned forest habitats. The small bodied-sized Bicyclus (mostly of the dorothea species-groups) were identified as effective indicator taxa of disturbed habitats. Both relative abundances and diversities of these potential identified indicator taxa could be used as metric for evaluating habitat quality or human-induced disturbance. Overall, the first three studies of the thesis indicated high prospects in the use of fruit-feeding butterflies as a model system for monitoring forests in Ghana. Based exclusively on the findings of the first three studies of this thesis, two kinds of RBA frameworks were proposed for monitoring forests in Ghana: i) ‘species and taxonomic surrogacy’ and ii) ‘All species’ approach. The choice of either approach largely depends on the availability of butterfly taxonomists and the intent of the mission. The fourth study (the theoretical perspective of the thesis) evaluated the relative contribution of neutral processes in shaping the butterfly assemblages, using both direct (confronting the neutral model to species abundance data) and indirect approaches (testing the predictions of neutral theory against independent data). The results indicated that nymphalid assemblages are structured largely by species’ (habitat) preference. However, neutral theory’s contribution to explaining the observed fruit-feeding butterfly assemblages in three forests in Africa lies largely in identifying dispersal limitation, as a key process regulating fruit-feeding butterfly community structure patterns.

Source: KNUST