Abstract
Abstract We investigated the mechanisms involved in the relationship between land-use changes and aquatic biodiversity, using stream fish assemblages of the Brazilian Savanna (i.e., Cerrado) as a study model. We tested the prediction that landscape degradation would decrease environmental heterogeneity and change predominant physical-habitat types, which in turn would decrease the functional diversity and alter the functional identity of fish assemblages. We sampled fish from 40 streams in the Upper Paraná River basin, and assessed catchment and instream conditions. We then conducted an ecomorphological analysis to functionally characterize all species (36) and quantify different facets of the functional structure of assemblages. We detected multiple pathways of the impacts from landscape changes on the fish assemblages. Catchment degradation reduced the stream-bed complexity and the heterogeneity of canopy shading, decreasing assemblage functional specialization and divergence. Landscape changes also reduced the water volume and the amount of large rocks in streams, resulting in decreased abundances of species with large bodies and with morphological traits that favor swimming in the water column. We conclude that land-use intensification caused significant changes in aquatic biodiversity in the Cerrado, reinforcing the need to pay special attention to this global hotspot.
Highlights
A primary goal of contemporary ecology is to understand how biotic communities respond to increasing human-induced pressures across ecosystems
Given that RP100 was positively associated with Functional Divergence (FDiv) (+0.40), Functional Evenness (FEve) (+0.32) and Functional Specialization (FSpe) (+0.27), Catchment Disturbance Index (CDI) had a negative indirect effect on these three functional diversity metrics through this pathway (Fig. 4A; see the product of the two significant direct effects linking them, from CDI to RP100 and from RP100 to functional indexes, in Tab. 3)
VCDENMID was positively associated with FSpe (+0.38), Functional Richness (FRic) (+0.36) and Functional Originality (FOri) (+0.51), meaning a negative indirect effect of CDI on these functional metrics (Fig. 4A; Tab. 3)
Summary
A primary goal of contemporary ecology is to understand how biotic communities respond to increasing human-induced pressures across ecosystems. More than 80% of the original vegetation has been modified for anthropogenic uses (Silva et al, 2013), but only 7% of the area is legally protected (Soares-Filho et al, 2014). This increasing rate of landscape degradation has led to extensive and intensive impacts on several ecosystems (Santos et al, 2017), including headwater streams and their biota (Carvalho, Tejerina-Garro, 2015; Agra et al, 2021)
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