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

Abstract

Urbanization is a major driver of stream ecosystem impairment and is typically 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). Amongst the 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 measured weekly during the field experiment. Along with the urbanization gradient, both taxonomic and functional diversity of shredders declined while OMB rates decreased. Shredders were absent and their contribution to OMB was null at the most urbanized sites. The B-EF relationship was interrupted through nutrient enrichment, physical habitat homogenization, riparian vegetation disturbance, and leaflitter availability as a consequence of urbanization. Our results demonstrate how species loss spreads to and affects 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.

An Assessment of the Rational Range of Eco-Compensation Standards: A Case Study in the Nujiang Prefecture, Southwestern China

“…However, dramatic changes in land-use patterns, such as rapid urbanization and transformation for agriculture and forestry, have had a considerable impact on the ecosystems [2,3]. It has brought about a series of challenges, including environmental pollution, climate change, loss of species, and the degradation of ecosystem functions [4][5][6][7], which ultimately undermines the wellbeing of humans themselves. Much effort has been expended in responding to these environmental crises.…”

The Good, the Bad, and the Ugly of Urbanization: Response of a Bird Community in the Neotropical Andes

“…Loja is a small-medium sized city relative to other Ecuadorian cities, with a contribution of around 6% of the national population (Information taken from the INEC 2022 web portal). It is located in the valley and has spread out toward the outskirts, replacing native vegetation first into pasture and then to urban areas (Figure 1), displaying a gradient of transformation to urban areas (Zúñiga-Sarango et al, 2020). The actual landscape in the area exhibits a city surrounded by pastureland dedicated to cattle ranching with the native vegetation restricted to the headwaters (Iñiguez-Armijos et al, 2016;Ordóñez-Delgado et al, 2016).…”

“…These watersheds are part of the city, despite that they are not entirely covered by urban areas. Our experimental set up is similar to others that studies have previously used to assess the effects of this urbanization gradient on terrestrial (Gaona et al, 2021) and aquatic (Zúñiga-Sarango et al, 2020) insects, as well as on riparian vegetation (Chuquimarca et al, 2019) and stream ecosystems (Iñiguez-Armijos et al, 2022).…”

“…The effects of urbanization have been evaluated using different taxonomic groups, such as plants (Kowarik, 2008), insects (McIntyre, 2000Blair, 2001;Gaona et al, 2021), aquatic macroinvertebrates (Zúñiga-Sarango et al, 2020), mammals (McIntyre, 2000, amphibians and reptiles (Hutto and Barrett, 2021), and birds (Pennington and Blair, 2011;McClure et al, 2015;Maure et al, 2018;Souza et al, 2019;Morelli et al, 2021;Valente-Neto et al, 2021). Birds tend to be especially affected by urbanization due to their high degree of specialization (Beaumont et al, 2011;Hermes et al, 2018).…”

“…The Tropical Andes host more than 25% of the world's bird species in a territory that corresponds to approximately 3% of the planet's surface (BirdLife International and Conservation International, 2005). Despite its importance for birds, this region is one of the most threatened, mainly due to a rapid land transformation (Jetz et al, 2007), urbanization being one of the most critical pressures on biodiversity (Ramirez-Villegas et al, 2014;Zúñiga-Sarango et al, 2020). Consequently, more than 10% of the bird species in the region are seriously threatened (IUCN, 2021).…”