Mangroves are an overlooked hotspot of insect diversity despite low plant diversity

Abstract

We here compare the tropical arthropod fauna across a freshwater swamp and six different forest types (rain-, swamp, dry-coastal, urban, freshwater swamp, mangroves) based on 140,000 barcoded specimens belonging to ca. 8,500 species. Surprisingly, we find that mangroves, a globally imperiled habitat that had been expected to be species-poor for insects, are an overlooked hotspot for insect diversity despite having low plant diversity. Our study reveals a species-rich mangrove insect fauna (>3,000 species) that is distinct (>50% of species are mangrove-specific), and has high species turnover across Southeast and East Asia. For most habitats, plant diversity is a good predictor for insect diversity, but mangroves are an exception and compensate for a comparatively low number of phytophagous and fungivorous insect species by supporting an unusually rich community of predators whose larvae feed in the productive mudflats. For the remaining tropical habitats, the insect communities have diversity patterns that are largely congruent across guilds. The discovery of such a sizeable and distinct insect fauna in a globally threatened habitat underlines how little is known about global insect biodiversity.