Protecting aquatic diversity in deforested tropical landscapes

Abstract

Global biodiversity is being lost due to extensive, anthropogenic land-use change. In Southeast Asia, biodiversity-rich forests are being logged and converted to oil-palm monocultures. The impacts of land-use change on freshwater ecosystems and biodiversity, remains largely understudied and poorly understood. I investigated the impacts of logging and conversion of tropical forest in 35 streams across a land-use gradient on freshwater fishes, a useful biotic indicator group, and a vital provisioning ecosystem service. This research was extended to quantify the benefits of riparian reserves in disturbed landscapes, and examine the interaction of land-use change with extreme climatic events. There are four key findings from this research. (1) Any modification of primary rainforest is associated with a loss of fish species and functional richness. (2) Streams in oil-palm plantations with riparian reserves of high forest quality, and a width of > 64m on either side, retain higher species richness and higher abundances of individual fish species. (3) Although relatively low in species richness, streams in oil-palm plantations retain high biomass of freshwater fish that is readily captured using cast nets (the primary method used by local people), providing an important protein source and supplementary income to local communities. (4) An extreme El Niño drought interacted antagonistically with land-use change, reducing the capture rate of N. everetti, one of the most common species in my study area. These results illustrate the critical impacts of land-use change on tropical freshwater ecosystems, and highlight the need to ensure riparian reserves are retained and primary forested areas are protected. Such actions will be needed to maintain freshwater diversity in modified tropical landscapes. Despite the impacts on fish communities due to land-use change, abundant, tolerant species appear to be resilient to climate-based stressors, while fish in headwater streams represent a sustainable food-resource for communities in human-modified landscapes.