Deforestation, habitat loss, and fragmentation are all linked and contribute to the current biodiversity catastrophe, with hydropower responsible for most of this degradation. River damming often floods extensive low-elevation areas in lowland tropical forests, while prior ridgetops frequently form insular forest patches.
In new research, researchers from the University of East Anglia, Portugal, and Brazil employed network theory to understand how insular habitat fragmentation influences tropical forest biodiversity. This method sees habitat patches and species as interconnected entities at the landscape scale, comprising a species-habitat system.
The study is published today in the journal Science Advances.
The authors investigated 22 habitat patches, including forest islands and three consecutive forest areas, created by the Balbina Hydroelectric Reservoir, one of the largest in South America. The 608 species surveyed belonged to eight different biological groups: mid-sized to large mammals, tiny non-flying mammals, understorey birds, reptiles, frogs, dung beetles, orchid bees, and plants.
The study found significant species extinction, particularly among large-bodied species, but this differed across the plant, vertebrate, and invertebrate groups. The survival of species diversity was influenced by island size, with only a few islands containing the greatest diversity.
As large swaths of tropical forest are fragmented and isolated into small habitat patches, they become increasingly rare. The destruction of bigger forest sites will have the most significant impact, most likely resulting in secondary extinctions of species that only exist at a single location or have greater geographic needs.
Small forest patches, on the other hand, support more species than one or a few larger patches of similar total size—hence the disappearance of smaller sites is also predicted to result in secondary extinctions.
Tropical developing countries are still hell-bent on creating vast hydropower reservoirs under the banner of ‘green’ energy.
Carlos Peres, Study Co-Author and Professor, Environmental Studies, University of East Anglia
“This is a double jeopardy because we lose both the unique lowland biodiversity and the carbon stocks of the now inundated old-growth forests,” he says.
Peres added, “Such actions also generate a powerful methane pump, never mind the huge financial costs of mega-dams compared to diffuse in-situ electrification based on low-impact renewables.”
“We need a much better strategic dialogue between sustainable energy security and biodiversity conservation, particularly in the world’s most biodiverse emergent economies.”
Dr. Ana Filipa Palmeirim of CIBIO-University of Porto, who analyzed a diverse landscape as a single unit, directed the study. “This approach allowed us to unveil previously unknown patterns, such as the simplification of the network structure and changes in important network parameters due to the loss of species affected by the dam,” says Dr. Palmeirim.
Dr. Carine Emer of the Rio de Janeiro Botanical Garden, and a study co-author, stated, “The beauty of this study lays in the combination of sophisticated network and statistical analyses, with the natural history of high-quality species inventories from an astonishing tropical living lab.”
“More than 3,000 islands were created 35 years ago due to the Uatumã River damming, and by studying these we were able to understand the functioning of such a complex and rich human-modified landscape.”
Palmeirim, A. F., et al. (2022) Emergent properties of species-habitat networks in an insular forest landscape. Science Advances. doi.org/10.1126/sciadv.abm0397.