Today’s post discusses the wider impacts of forest loss and comes from the team behind the recent article, Relationships between forest cover and fish diversity in the Amazon River floodplain.

In the Amazon and most other major tropical regions, large forested areas are being cleared for development of agriculture, hydropower and human settlements. Floodplain forests provide key habitats and food resources for fish, including several species that are important sources of protein and income for millions of people. In these forests, fish find abundant food, habitat, and nursery resources that are necessary for their survival and growth. Deforestation is a major impact to floodplain landscapes and, consequently, to fish biodiversity.

The recent paper, Relationships between forest cover and fish diversity in the Amazon River floodplain, sought to understand how deforestation affects fish diversity. Through a series of field expeditions, the research team collected data on fish community structure across a gradient of landscape, from nearly pristine to highly deforested areas, in the Lower Amazon River. This research demonstrated that spatial patterns of fish taxonomic and functional diversity are influenced by the extent of forest cover as well the spatial configuration of land-cover types and associated environmental variables. Several species and functional groups defined by life history, feeding, swimming/microhabitat-use strategies were positively associated with forest cover. Other species, including some that would be considered habitat generalists, were most common in areas dominated by herbaceous vegetation or open-water habitats associated with the opposite extreme of the forest cover gradient. An analysis of the differentiation in diversity among habitats, demonstrated that areas with more forest cover tended to have greater spatial variation in species composition than those dominated by herbaceous vegetation or open water. In addition, an analysis of the degree of uniqueness in species composition showed that habitats with greater forest cover tended to have unique combinations of species.

These results strongly imply that forest loss reduces spatial patterns of species turnover and likely increases the relative abundance and richness of species with good dispersal abilities and species classified as ecological generalists.  Author, Caroline Arantes notes:

“in our study, several species were strongly associated with forest cover, because they directly exploit resources that originate from forest vegetation. For example, herbivores consume fruits and seeds that fall into the water, and detritivorous fishes feed on abundant fine particulate organic matter and on biofilms containing fungi and other microorganisms within flooded forest. Our research indicates that forest supports unique taxonomic and functional fish diversity, therefore, deforestation of the Amazon floodplain leads to spatial homogenization of fish assemblages and reduced functional diversity”.

Unfortunately, mitigations and conservation strategies in these floodplains often suffer from deficiencies of design and implementation, or fail to protect landscapes at the scale of river catchments.  As Arantes points out:

“in the Brazilian Amazon, the existing protected area network was established based largely on the distributions of terrestrial taxa, with few protected areas specifically designated to protect aquatic ecosystems. As a result, there are no protected areas encompassing floodplains within our study area”.

The authors note that results demonstrating relationships among spatial patterns of fish diversity and gradients of land cover and local environmental variables strongly implies that conservation of Amazonian fish diversity requires maintenance of substantial forest cover within the floodplain landscape mosaic.

The full article, Relationships between forest cover and fish diversity in the Amazon River floodplain is available in Journal of Applied Ecology.