Floodplain land cover affects biomass distribution of fish functional diversity in the Amazon River

Caroline C Arantes,Kirk O Winemiller,Miguel Petrere,Leandro Castello,Carlos E C Freitas,Alex Asher,Laura L Hess

doi:10.1038/s41598-019-52243-0

Abstract

Land-cover change often shifts the distribution of biomass in animal communities. However, the effects of land-cover changes on functional diversity remain poorly understood for many organisms and ecosystems, particularly, for floodplains. We hypothesize that the biomass distribution of fish functional diversity in floodplains is associated with land cover, which would imply that fish traits affect behavioral and/or demographic responses to gradients of land cover. Using data from surveys of 462 habitats covering a range of land-cover conditions in the Amazon River floodplain, we fitted statistical models to explain landscape-scale variation in functional diversity and biomass of all fish species as well as subsets of species possessing different functional traits. Forest cover was positively associated with fish biomass and the strength of this relationship varied according to functional groups defined by life history, trophic, migration, and swimming-performance/microhabitat-use traits. Forty-two percent of the functional groups, including those inferred to have enhanced feeding opportunities, growth, and/or reproductive success within forested habitats, had greater biomass where forest cover was greater. Conversely, the biomass of other functional groups, including habitat generalists and those that directly exploit autochthonous food resources, did not vary significantly in relation to forest cover. The niche space occupied by local assemblages (functional richness) and dispersion in trait abundances (functional dispersion) tended to increase with forest cover. Our study supports the expectation that deforestation in the Amazon River floodplain affects not only fish biomass but also functional diversity, with some functional groups being particularly vulnerable.

Highlights

Land-cover change is a major cause of degradation of floodplain ecosystems worldwide[1,2], with expansion of cattle ranching and other kinds of agriculture leading to losses of biodiversity and biological productivity in tropical and subtropical regions[3]
We address two questions: Is the spatial distribution of fish biomass in the Amazon floodplain associated with land cover, and if so, can patterns be predicted from distributions of functional traits in local species assemblages? Answering these questions is critical for understanding species responses to land-cover change and for managing fisheries influenced by multiple anthropogenic stressors
Total fish biomass and biomass of several functional groups (42%) were positively associated with forest cover, and the strength of these relationships depended on the traits possessed by each group

Summary

Introduction

Land-cover change is a major cause of degradation of floodplain ecosystems worldwide[1,2], with expansion of cattle ranching and other kinds of agriculture leading to losses of biodiversity and biological productivity in tropical and subtropical regions[3]. We expected the size of the niche space occupied by local assemblages (i.e., functional richness) and dispersion of traits within that space (i.e., functional dispersion) to increase with forest cover as a reflection of greater habitat complexity, resource diversity, and niche diversity in forested landscapes. To test these hypotheses, we surveyed fishes from diverse habitats and used satellite-mapped landscape data for floodplains of the lower Amazon River. We modeled relationships between forest cover and total biomass of local fish assemblages as well as groups of species possessing different functional traits and degrees of importance for fisheries (Fig. 2, Tables 1 and 2). Our findings reveal the potential vulnerability of fish stocks, fishery production, and functional diversity to forest loss

Methods

Results

Conclusion