Responses of aquatic food webs to the addition of structural complexity and basal resource diversity in degraded Neotropical streams

Abstract

The loss of riparian forests can disrupt the structure and function of lotic ecosystems through increased habitat homogenization and decreased resource diversity. We conducted a field experiment and manipulated structural complexity and basal resource diversity to determine their effect on multiple aspects of community and food-web structure of degraded tropical streams. In-stream manipulations included the addition of woody debris (WD) and the addition of wood and leaf packs (WLP). The addition of structural complexity to degraded streams promoted detritus retention and had a positive effect on stream taxonomic richness, abundance and biomass. At the conclusion of the experiment, abundance and richness in the WD-treated reaches increased by over 110% and 80%, respectively, while abundance and richness in the WLP-treated reaches increased by over 280% and 170% respectively. Wood debris and leaves were consumed only by few taxa. Detritivorous taxa were the most abundant trophic guild at the beginning and at the end of the experiment. Food webs in treated reaches were relatively more complex in terms of links and species at the conclusion of the experiment, with highest maximum food chain length in the WD treatments and highest number of trophic species, links, link density, predators and prey at the WLP treatment. Despite differences observed in diet-based food webs, there was little variation in isotopic niche space, likely due to the high degree of omnivory and trophic redundancy, which was attributed to the importance of fine detritus that supported a broad range of consumers. Even in these degraded streams, aquatic taxa responded to the addition of increased complexity suggesting that these efforts may be an effective first step to restoring the structure and function of these food webs.

Intercontinental trends in functional and phylogenetic structure of stream fish assemblages

“…Structural complexity in streams often is associated with higher species richness and functional diversity (Ceneviva-Bastos, Montaña, Schalk, Camargo, & Casatti, 2017;Emslie, Cheal, & Johns, 2014;Kovalenko et al, 2012;Mouillot, Graham, Villéger, Mason, & Bellwood, 2013). Our results overall indicated the dominant influence of environmental filtering and were consistent with the stress-dominance hypothesis.…”

“…Structural complexity has been shown to reduce both abiotic and biotic stresses by providing a refuge from harsh environmental conditions and predators (Kovalenko et al, ). Structural complexity in streams often is associated with higher species richness and functional diversity (Ceneviva‐Bastos, Montaña, Schalk, Camargo, & Casatti, ; Emslie, Cheal, & Johns, ; Kovalenko et al, ; Mouillot, Graham, Villéger, Mason, & Bellwood, ). Our results overall indicated the dominant influence of environmental filtering and were consistent with the stress‐dominance hypothesis.…”

Ichthyofauna diet changes in response to urbanization: the case of upper Paranapanema River basin (Brazil)

“…Despite the importance of riparian forest as the main source of allochthonous resources (Pusey and Arthington 2003), land use in many hydrographic basins will continue to be used in human activities, such as agriculture and livestock. Therefore, conservation measures should be encouraged (see examples in Casatti et al 2015) to stimulate the increase of in-stream variability if it is intended to promote fish diversity avoiding functional redundancy (Bordignon et al 2015;Casatti et al 2015;Ceneviva-Bastos et al 2017).…”

Fish assemblage convergence along stream environmental gradients: an intercontinental analysis

“…Structurally complex microhabitats may contain more abundant or higher quality food resources and also provide shelter for avoidance of predators and harsh environmental conditions, such as high water velocity (Kovalenko et al 2012). Thus, the loss of instream structures, such as large woody debris, generally reduces fish functional diversity (Kovalenko et al 2012, Mouillot et al 2013, Emslie et al 2014, Ceneviva-Bastos et al 2017. Many human impacts tend to reduce the structural complexity of stream habitats, resulting in the decline or elimination of ecological specialists (Brejão et al 2018) and lower functional trait diversity (Leitão et al 2017).…”