Impacts of land-use change on freshwater biodiversity in Southeast Asia

Abstract

ln Southeast Asia, biodiversity-rich forests are lost to logging, tree monocultures, and mining at an unprecedented rate. Impacts of these land-use changes are largely unknown for freshwater biodiversity. Here, I addressed questions pertinent to understanding impacts of land-use change on the region's unique and highly diverse freshwater ichthyofauna.

In the first chapter, I examined possible ecological and life-history trait correlates of freshwater fish extinctions in Singapore, an example of a worst-case development scenario characterized by extensive deforestation and stream canalization. Unlike previous studies, extinctions were predicted by only local geographic range. This suggests that when streams are severely altered, local extinctions are driven by loss of entire communities, regardless of species traits.

As wholesale forest loss threatens range-restricted species, the second chapter informs conservation planning for the highly endemic peat swamp forest fishes. I used the matrix-calibrated species-area model -- which accounts for the ability of different landcovers to support biodiversity -- to forecast extinction hotspots under different development scenarios.

The establishment of oil palm monocultures is a major driver of lowland deforestation. However, no study has assessed the impact of oil palm on fishes, let alone potential mitigation strategies. In the third chapter, I sampled fish communities in streams within an oil palm plantation in Central Kalimantan, Indonesia. Compared to historical forest fish communities, streams surrounded by oil palm had lower species richness and functional diversity. However, retention of riparian reserves adjacent to streams mitigated these impacts.

In my fourth chapter, I performed a meta-analysis to assess the effectiveness of riparian reserves in conserving biodiversity within production landscapes globally. My results supported retention of riparian reserves as a global conservation strategy as they retained a high proportion of species present in continuous riparian forests at both transect and landscape scales.

Synthesizing these results, land-use change, particularly from forest to oil palm, negatively impacts fish communities in Southeast Asia. While peat forest conversion should be avoided as fishes inhabit the entire flooded landscape, land-sharing (between oil palm and forest riparian reserves) is effective in conserving lowland forest fishes in Southeast Asia, as well as many other taxa across different production landscapes globally.