The potential of land-use systems for maintaining tropical forest butterfly diversity

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Globally, tropical rainforest species are under increasing threat due to ongoing deforestation. We summarize published studies on effects of forest disturbance and conversion on tropical butterfly assemblages with a focus on forest species. Additionally, we use existing faunal monographs to extract information on the habitat affiliations of tropical forest butterflies. Based on these data, we quantify the importance of human-modified habitats for the conservation of tropical butterflies inhabiting forests across all major tropical regions. Although studies on effects of land use and forest conversion are biased by several methodological problems, the emerging pattern clearly indicates that (old-grown) secondary forests represent an important habitat type for maintaining a large proportion of forest butterflies in all major tropical regions. In contrast, agroforestry systems are only capable of protecting a small proportion of mostly widespread forest species tolerant against strong disturbance. Extinction risk of forest butterflies depends on the utilization of certain plant growth types, while host plant specialization alone does not have significant effects. Specifically, butterflies using trees as larval host plants are more likely to be absent in logged forest, whereas species that tend to be more abundant in logged forest are those with larvae feeding on lianas and grasses. Greater resource requirements may be one reason for a higher extinction risk of larger butterflies after forest fragmentation although not all studies found a relationship between extinction risk and body size. Butterfly species with narrow geographic ranges are particularly prone to local and global extinction. While widespread species dominate species assemblages of highly modified land-use systems and agroforests, endemic butterflies are more commonly found in old-growth forests. Our analyses covering all four major tropical regions underline the severe effects of forest modification. Land-use systems are only of minor importance for protecting forest butterfly species. Furthermore, they may only represent ecological sinks for a substantial proportion of the few forest species that are reported to occur in this habitat type. The future of tropical forest butterflies in all four major tropical regions hence depends on the strict protection of remaining large blocks of natural forests.