River dams and the stability of bird communities: A hierarchical Bayesian analysis in a tropical hydroelectric power plant

The effects of anthropogenic disturbance upon the stability of wildlife
communities depend on the heterogeneity and connectivity of habitat
remnants on multiple scales. The number of hydroelectric dams in
biodiversity hotspots (Africa, South America and Asia) is growing rapidly.
To establish their environmental impact, it is essential to understand the
dynamics of wildlife communities before and following the establishment of
dams. We evaluated the impacts of the filling of the Serra do Facão
hydroelectric reservoir in the São Marcos river, central Brazil, upon the
bird community. Using data from 1,145 surveys across 20 sampling sites
over eight years, two years before and six years after the filling of the
reservoir, we assessed the resistance, i.e., maintenance close to an
equilibrium state during the disturbance, and resilience, i.e., ability to
return to the original state following the disturbance, of the bird
community. We used spatiotemporal hierarchical Bayesian models to assess
the effects of reservoir filling on five community parameters: abundance,
richness, phylogenetic diversity, functional diversity and species
composition. In the period subsequent to reservoir filling, there was (i)
a marked reduction in bird abundance, richness, phylogenetic diversity and
functional diversity, and (ii) a reduction in the proportion of forest
species, coupled with an increase in the proportion of savanna species.
Except for bird abundance, none of the other community attributes returned
to their original levels, even after six years. Our findings indicate that
Cerrado bird communities have both low resistance and low resilience to
habitat loss associated with the establishment of hydroelectric
reservoirs. Synthesis and applications. The environmental costs of
hydroelectric dams are still underestimated or neglected in Brazil. A new
paradigm in the assessment of their environmental impacts is warranted,
incorporating (i) models of spatiotemporal variations based on long-term
monitoring with surveys initiated before disturbances and (ii) measures of
functional and phylogenetic diversity, such that society can understand
the costs and benefits of the establishment of new hydroelectric dams and
make informed decisions. Biodiversity loss could be minimized by ensuring
the preservation and connectivity of alluvial habitats, capable of
maintaining the supply of resources and the functional and phylogenetic
attributes of bird communities associated with such habitats.