More of the Same: High Functional Redundancy in Stream Fish Assemblages from Tropical Agroecosystems

Abstract

In this study, we investigated the influence of environmental variables (predictor variables) on the species richness, species diversity, functional diversity, and functional redundancy (response variables) of stream fish assemblages in an agroecosystem that harbor a gradient of degradation. We hypothesized that, despite presenting high richness or diversity in some occasions, fish communities will be more functionally redundant with stream degradation. Species richness, species diversity, and functional redundancy were predicted by the percentage of grass on the banks, which is a characteristic that indicates degraded conditions, whereas the percentage of coarse substrate in the stream bottom was an important predictor of all response variables and indicates more preserved conditions. Despite being more numerous and diverse, the groups of species living in streams with an abundance of grass on the banks perform similar functions in the ecosystem. We found that riparian and watershed land use had low predictive power in comparison to the instream habitat. If there is any interest in promoting ecosystem functions and fish diversity, conservation strategies should seek to restore forests in watersheds and riparian buffers, protect instream habitats from siltation, provide wood debris, and mitigate the proliferation of grass on stream banks. Such actions will work better if they are planned together with good farming practices because these basins will continue to be used for agriculture and livestock in the future.

Influence of environmental features at multiple scales and spatial structure on stream fish communities in a tropical agricultural region

“…In tropical streams, although studies about scale-related effects are still scarce, the findings are similar to those of temperate environments. For example, in tropical agricultural landscapes both catchment-and local-scale features affected both functional and taxonomic diversity of stream fish communities (Cruz et al 2013;Bordignon et al 2015;Santos et al 2015; but see Casatti et al 2015). However, it should be mentioned that although catchment variables are important (Roth et al 1996), in most cases local-scale variables accounted for the most variation in fish community structure (Lammert & Allan 1999;Wang et al 2003;Diana et al 2006;Johnson et al 2007).…”

“…homogeneous landscape) is not able to overcome the impact of local-scale variables (Heino et al 2007;Casatti et al 2015).…”

“…Although there is a substantial number of studies that address this issue (Lammert & Allan 1999;Diana et al 2006;Johnson et al 2007;Cianfrani et al 2012), including in tropical streams (Cruz et al 2013;Casatti et al 2015;Santos et al 2015), the relative importance of catchment-versus local-scale factors for stream biota has remained elusive (Roth et al 1996;Cianfrani et al 2012). Studies addressing the issue are necessary because the assessment of catchment-stream relationships using a hierarchical classification can aid in conservation, restoration, and management of freshwater systems (Frissell et al 1986;Cianfrani et al 2012;Feld 2013;Dembkowski & Miranda 2014) and provides a more efficient and holistic view of these (Dembkowski & Miranda 2014).…”

Effect of the riparian vegetation removal on the trophic network of Neotropical stream fish assemblage

“…However, higher values of food niche overlap (H') and of community specialization (H 2 ) (Table 2) were observed in the forested stretch. Although some authors (Agostinho et al, 2008;Zeni and Casatti, 2014) relate impacted environments with habitat simplification and homogenization, which would reduce the food resources supply to the fish fauna, Casatti et al (2015) discuss that the presence of grass on the banks in pasture streams provides food resources such as leaves and roots and also retains organic matter. Moreover, they may also provide additional microhabitats used by macroinvertebrates that may serve as food for the fish fauna.…”

“…Moreover, Casatti et al (2015) have found that although environments without riparian vegetation may have higher richness and diversity of fish, they also have a high functional redundancy, mostly related to feeding. Those impacted environments are generally simpler, with high habitat homogenization and low allochthonous resources supply (Zeni and Casatti, 2014).…”