Importance of reserves, fragments, and parks for butterfly conservation in a tropical urban landscape

We assessed the effectiveness of forest reserves (i.e., protected old secondary and primary forests), fragments (i.e., scattered ruderal vegetation), and urban parks (i.e., artificially revegetated habitats) in conserving butterfly diversity in a highly urbanized tropical landscape (i.e., Singapore), by testing the hypothesis that forest reserves have the highest butterfly species richness among these habitats. We investigated which environmental factors (e.g., canopy cover) affect the distribution of butterflies across the habitats; and also tested the hypothesis that butterfly communities of different habitats have distinct ecological traits. Further, we examined the important determinants (e.g., area) of butterfly richness in urban parks, by testing the hypothesis that the number of potential larval host plant species occurring in the park is the best predictor of butterfly species richness. Rarefaction analyses showed that forest reserves had the highest number of species, number of unique species, density of species, and community evenness among the habitats, implying that, in urban landscapes, the least human-disturbed habitats should be given the highest conservation priority. Forest reserves and urban parks adjoining forests collectively accounted for 91% of all butterfly species recorded in this study, suggesting that their preservation will likely achieve maximum complementarity for effective butterfly conservation. Ordination analyses revealed that different butterfly species responded differently to environmental factors (e.g., canopy cover), highlighting the importance of maintaining environmental heterogeneity for the conservation of different butterfly species. Classification tree analysis indicated that butterfly communities of different habitats (e.g., forests, urban parks) have distinct ecological traits (e.g., host plant specificity), whereby urban avoiders were 89% likely to be forest dependent and 63% likely to be monophagous, while urban adapters were 87% likely to be cosmopolitan and 67% likely to be oligo- or polyphagous. Regression analyses showed that the number of potential larval host plant species and isolation from forests were important determinants of butterfly species richness in urban parks, indicating that urban parks should be revegetated with a diversity of potential larval host plants and should be situated as near as possible to a forest, in order to maximize their conservation value.