Limited erosion of genetic and species diversity from small forest patches: Sacred forest groves in an Afrotropical biodiversity hotspot have high conservation value for butterflies

Abstract

Sacred forest groves are often located in some of the world's hottest hotspots of biodiversity, and consequently have high potential conservation value. Recent efforts to quantify their value have focused nearly exclusively on a single component of diversity, species diversity within communities, which may or may not be an effective proxy for a second fundamental component of diversity, genetic diversity within populations. We studied fruit-feeding butterfly communities to simultaneously assess to what extent five small sacred groves have retained the level of species and genetic diversity found in two much larger forest reserves. We additionally evaluate whether measures correlate across habitat fragments to investigate how closely these two components of diversity mirror each other. We quantified the diversity and composition of the fruit-feeding butterfly communities at each site and also the haplotype diversity within three specific species that differ with respect to their sensitivity to habitat fragmentation. Of the multiple measures of species and genetic diversity computed, only rarefied species richness was correlated with forest fragment size and even in this case the relationship was weak. Importantly, the limited decline in species richness documented in the sacred groves was not due to species replacements, whereby common, broadly distributed, generalists supplanted more vulnerable species in these communities. Although similar processes are known to drive declines in both species and gene diversity, we found only limited evidence of positive species-genetic diversity correlations (SGDCs), and only in the species most sensitive to fragmentation. Thus, a conservation strategy that emphasizes species complementarity or richness may be ineffective at capturing other critical levels of biodiversity. Overall, our findings demonstrate that even very small forest patches can have a conservation value that rivals that of much larger forest reserves. The implementation of official national and international initiatives that preserve and strengthen existing community-based conservation practices is critically needed to ensure that indigenous conservation areas persist into the future.