Human land‐uses homogenize stream assemblages and reduce animal biomass production

Abstract

Human land‐use change is a major threat to natural ecosystems worldwide. Nonetheless, the effects of human land‐uses on the structure of plant and animal assemblages and their functional characteristics need to be better understood. Furthermore, the pathways by which human land uses affect ecosystem functions, such as biomass production, still need to be clarified. We compiled a unique dataset of fish, arthropod and macrophyte assemblages from 61 stream ecosystems in two Neotropical biomes: Amazonian rainforest and Uruguayan grasslands. We then tested how the cover of agriculture, pasture, urbanization and afforestation affected the taxonomic richness and functional diversity of those three species assemblages, and the consequences of these effects for animal biomass production. Single trait categories and functional diversity were evaluated, combining recruitment and life‐history, resource and habitat‐use, and body size. The effects of intensive human land‐uses on taxonomic and functional diversities were as strong as other drivers known to affect biodiversity, such as local climate and environmental factors. In both biomes, the taxonomic richness and functional diversity of animal and macrophyte assemblages decreased with increasing cover of agriculture, pasture, and urbanization. Human land‐uses were associated with functional homogenization of both animal and macrophyte assemblages. Human land‐uses reduced animal biomass through direct and indirect pathways mediated by declines in taxonomic and functional diversities. Our findings indicate that converting natural ecosystems to supply human demands results in species loss and trait homogenization across multiple biotic assemblages, ultimately reducing animal biomass production in streams.

Habitat complexity mediates the impacts of human land-use on stream biodiversity

“…Although recent research has begun quantifying how human land-use intensi cation alters biodiversity [21][22][23] , analyses of how habitat complexity can mitigate such impacts are still lacking. Here we showed that sites with high-habitat complexity supported, on average, 10% more insect genera than sites with low-habitat complexity.…”

“…Importantly, water temperature was not available in our dataset and we only have information on air temperature. We recognize that air temperature cannot fully represent the thermal regime of the stream/river, but air-and water temperature are correlated 52 and many studies reported strong impacts of air temperature on aquatic biodiversity 3,22,23,26 . We modeled log-richness and log-density using a normal distribution, and LCBD ecoregional and LCBD national using beta distribution in the R package 'glmmTMB' 53 .…”

“…Assessing urban and cropland intensi cation. For each site, we quanti ed the catchment intensities of the two most common human land uses worldwide 1,23,38 : (1) urbanization and (2) cropland. We quanti ed urbanization by examining four geospatial indicators taken from the EPA's StreamCat dataset 39,40,46 that represent direct proxies of increasing urban areas: (i) human population in the catchment (PopDen_Cat) based on TIGER line les from the US Census (TIGER Lines) 47 , (ii) percentage of the catchment that has impervious surface (PctImp_Cat) based on the National Land Cover Database (NLCD) 47 , (iii) road density in the catchment (RdDens_Cat) from the US Census data (TIGER Lines 48 and (iv) percentage of the catchment composed of high-intensity human land use (PctUrbHi_Cat) (NLCD) 47 .…”

Trophic plasticity of omnivorous fishes in natural and human‐dominated landscapes

“…Pervasive land use change is among the primary causes of biodiversity loss and food web simplification, altering ecosystem functioning worldwide (Etard et al 2022;Kemp et al 2023;Moi et al 2023). The maintenance of healthy functioning ecosystems and high species diversity under increasing human pressure relies on food web rewiring and the ability of animals to shift their diet in disturbed ecosystems with scarce resources (Lu et al 2016;Kemp et al 2023).…”