Disrupting the Biodiversity–Ecosystem Function Relationship: Response of Shredders and Leaf Breakdown to Urbanization in Andean Streams

Wilson Zúñiga-Sarango,Fernando P. Gaona,Valeria Reyes-Castillo,Carlos Iñiguez-Armijos

doi:10.3389/fevo.2020.592404

Wilson Zúñiga-Sarango, Fernando P. Gaona + Show 2 more

Open Access

https://doi.org/10.3389/fevo.2020.592404

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Abstract

Urbanization is a major driver of stream ecosystems impairment and often associated with multiple stressors and species loss. A challenge is to understand how those stressors alter the relationship between biodiversity and ecosystem functioning (B-EF). In Andean streams of southern Ecuador, we assessed the response of shredder diversity and organic matter breakdown (OMB) to urbanization and identified the urban-associated stressors disrupting the B-EF relationship. A leaf-litter bag experiment during stable flow conditions in 2016 was carried out to quantify total OMB and shredder-mediated OMB, which was estimated to represent the B-EF relationship. We calculated the taxonomic and functional diversity of shredder invertebrates associated with leaf packs. Also, a suite of physicochemical and habitat stressors was weekly measured during the field experiment. Along with the urbanization gradient, both taxonomic and functional diversity of shredders declined while OMB rates decayed. Shredders were absent and their contribution to OMB was null at the most urbanized sites. The B-EF relationship was interrupted through nutrient enrichment and physical habitat homogenization as a consequence of urbanization. These results demonstrate how species loss propagates to ecosystem functions in urbanized streams and how environmental stressors alter the B-EF relationship. Better land-use practices are crucial in Andean catchments to guarantee ecosystem services which are the result of successful B-EF relationships.

Highlights

Aquatic ecosystems contain high biodiversity, but at the same time, they exhibit faster species loss than marine or terrestrial ecosystems (Collen et al, 2014; Sánchez-Bayo and Wyckhuys, 2019)
Urbanization negatively affected the functional richness and Rao’s quadratic entropy (RaoQ) of shredder invertebrates, but the response of functional diversity was a gradual decrease along the urbanization gradient (Figures 2C,D)
The relationship of biodiversity and ecosystem functioning (B-EF) has been extensively studied in temperate ecosystems (Tilman et al, 2014), it is still necessary to understand how environmental disturbance gradients can alter this relationship in neotropical streams

Summary

Introduction

Aquatic ecosystems contain high biodiversity, but at the same time, they exhibit faster species loss than marine or terrestrial ecosystems (Collen et al, 2014; Sánchez-Bayo and Wyckhuys, 2019). The riparian margins of urbanized streams typically suffer native vegetation loss with invasions of exotic plants (Guida-Johnson et al, 2017). When these stream characteristics are altered by urbanization there will be adverse consequences for the macroinvertebrate communities (Roy et al, 2003; de Jesús-Crespo and Ramírez, 2011; Hassett et al, 2018), resulting in species loss (Chadwick et al, 2006; Urban et al, 2006) that can lead to a disruption of the biodiversity–ecosystem function relationship (Meyer et al, 2005; Tilman et al, 2014). The interruption of this interaction can turn into a serious issue at the ecosystem level when keystone species are removed or replaced from streams (Iñiguez-Armijos et al, 2016)

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