This blog post is provided by Dieison André Moi and tells the #StoryBehindthePaper for the paper ‘Human land-uses homogenize stream assemblages and reduce animal biomass production’, which was recently published in Journal of Animal Ecology. In their study, Dieison and colleagues evaluated the effects of four land-uses on taxonomic richness, functional and trait diversityof fishes, arthropods, and macrophytesbased on data from 61 stream sites in Amazonian rainforest and Uruguayan grassland biomes.

The human population is growing rapidly, – right now, 8 billion people inhabit Earth. Consequently, the exploitation of natural environments to fuel human needs is increasing. Among the main human activities modifying natural environments globally, are the conversion of natural landscapes for agriculture, livestock grazing, and urbanization. These land uses are associated with high species extinction rates and losses of species with unique functional traits, causing biotic homogenization globally.

Considering that animal and plant assemblages are interconnected through mutualistic interactions, when human land-uses reduce plant diversity, this might directly or indirectly affect animal diversity. Furthermore, increased animal and plant diversity tends to enhance the performance of ecosystem functions, for instance, increasing biomass production. Therefore, when human land-uses reduce animal and plant diversity, this might also reduce the functioning of natural environments.

In this context, we gathered data on fish, arthropod, and macrophyte assemblages from 61 stream sites in rainforest (Amazonian; Figure 1) and grassland (Uruguay; Figure 2) biomes. For each site, we measured the catchment cover of four human land-uses: (i) agriculture (soybean and corn crops), (ii) pasture (cattle and sheep grazing); (iii) urbanization (urban infrastructure); and (iv) afforestation (silviculture of Eucalyptus sp). For diversity metrics, we measured the taxonomic richness and functional diversity of fish, arthropod, and macrophyte assemblages (Figure 3). As an ecosystem functioning metric, we measured the biomasses of fish and arthropods. Specifically, we evaluated the effects of the four land-uses on taxonomic richness, multivariate functional diversity, and trait category diversity (recruitment and life-history, resource and habitat-use, and body size traits) of fishes, arthropods, and macrophytes. We also investigated whether such effects indirectly affect animal biomasses.

We found negative associations of agriculture, pasture, and urbanization with the taxonomic and functional diversity of fish, arthropods, and macrophytes. These human land-uses were also negatively associated with the diversity of recruitment and life-history, resource and habitat-use, and body size traits. There were no differences in animal and plant response directions to increased cover of agriculture, pasture, and urbanization. Similarly, the negative effects of human land-uses on animal and plant biodiversity consistently occurred in both rainforest and grassland streams. This revealed two key impacts. (i) The biodiversity of animal and plant assemblages decreased with increased cover of human land-uses. (ii) Different human land-uses combine to decrease stream biodiversity in a general way, regardless of the biome.

We also found positive relationships between animal diversity and animal biomass in both rainforest and grassland biomes. However, the relationship between animal diversity and biomass became non-significant or even negative in streams with high coverage of agriculture, pasture, and urbanization. Furthermore, agriculture, pasture, and urbanization jointly, decreased the animal biomass of stream environments, both directly and indirectly, probably through a reduction in fish, arthropod, and macrophyte biodiversity. These findings suggest that the ability of animal diversity to increase its biomass stock can be completely reduced in streams under high human land-use cover. In particular, our results provide novel evidence that multiple human land-uses, here agriculture, pasture, and urbanization, jointly, reduce animal and plant assemblage diversity in streams. The combined action of these land-uses can also trigger a multi-taxa homogenization and decrease the animal biomass stock of natural streams, both directly and indirectly via a reduction in animal and plant diversity.

Read the full paper

Moi, D. A., Barrios, M., Tesitore, G., Burwood, M., Romero, G. Q., Mormul, R. P., Kratina, P., Juen, L., Michelan, T. S., Montag, L. F. A., Cruz, G. M., García-Girón, J., Heino, J., Hughes, R. M., Figueiredo, B. R. S., & Teixeira de Mello, F. (2023). Human land-uses homogenize stream assemblages and reduce animal biomass production. Journal of Animal Ecology, 00, 1–14. https://doi.org/10.1111/1365-2656.13924

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