Changing pollinator communities along a disturbance gradient in the Sundarbans mangrove forest: a case study onAcanthus ilicifoliusandAvicennia officinalis

Abstract

The Sundarbans, the largest mangrove forest in the world and a UNESCO world heritage site has been facing an increasing pressure of habitat destruction. Yet, no study has been conducted to test how human disturbances are affecting plant-pollinator interactions in this unique ecosystem. Hence, our aim was to provide the first study of the impact of habitat loss and human disturbances on plantpollinator interactions in the Sundarbans. We selected 12 sites in the North-Western region of the Sundarbans, along a gradient of decreasing habitat loss and human activities from forest fragments near human settlements to continuous pristine forest, where we studied insect pollinators of two mangrove plant species, Acanthus ilicifolius and Avicennia officinalis. Our results show that different pollinator groups responded to the disturbance gradient differently. The abundance of Apis dorsata increased gradually from the village area towards the deep pristine forest. On the other hand, A. cerana and A. florea were found in the village sites and completely absent in the deep forest. Although pollinator community composition changed along the disturbance gradient, their efficacy in pollination did not seem to be significantly affected. However, lower plant diversity and low understory plant cover in the forest patches nearby the village indicated that the high anthropogenic activities not only affected pollinator community composition but also played a major negative role in the regeneration of the forest. Our study provides first insights into plantpollinator interactions in the Sundarbans and demonstrates that more research is needed to inform conservation of this unique habitat.