Thresholds of freshwater biodiversity in response to riparian vegetation loss in the Neotropical region

Abstract

Protecting riparian vegetation around streams is vital in reducing the detrimental effects of environmental change on freshwater ecosystems and in maintaining aquatic biodiversity. Thus, identifying ecological thresholds is useful for defining regulatory limits and for guiding the management of riparian zones towards the conservation of freshwater biota. Using nationwide data on fish and invertebrates occurring in small Brazilian streams, we estimated thresholds of native vegetation loss in which there are abrupt changes in the occurrence and abundance of freshwater bioindicators and tested whether there are congruent responses among different biomes, biological groups and riparian buffer sizes. Mean thresholds of native vegetation cover loss varied widely among biomes, buffer sizes and biological groups: ranging from 0.5% to 77.4% for fish, from 2.9% to 37.0% for aquatic invertebrates and from 3.8% to 43.2% for a subset of aquatic invertebrates. Confidence intervals for thresholds were wide, but the minimum values of these intervals were lower for the smaller riparian buffers (50 and 100 m) than larger ones (200 and 500 m), indicating that land use should be kept away from the streams. Also, thresholds occurred at a lower percentage of riparian vegetation loss in the smaller buffers, and were critically lower for invertebrates: reducing only 6.5% of native vegetation cover within a 50‐m riparian buffer is enough to cross thresholds for invertebrates. Synthesis and applications. The high variability in biodiversity responses to loss of native riparian vegetation suggests caution in the use of a single riparian width for conservation actions or policy definitions nationwide. The most sensitive bioindicators can be used as early warning signals of abrupt changes in freshwater biodiversity. In practice, maintaining at least 50‐m wide riparian reserves on each side of streams would be more effective to protect freshwater biodiversity in Brazil. However, incentives and conservation strategies to protect even wider riparian reserves (~100 m) and also taking into consideration the regional context will promote a greater benefit. This information should be used to set conservation goals and to create complementary mechanisms and policies to protect wider riparian reserves than those currently required by the federal law.

Pollution tolerance, flight capacity and natural history explain metacommunity structure in high-altitude stream insects

“…It is important to highlight that the watersheds analyzed showed very different land uses and the interaction among these landscape components at different scales seemed to have a direct influence on the limnological (local) attributes selected in the adjusted model, for both characterizations, taxonomic and functional. As shown by Allan (2004), Sensolo et al (2012), Alemu et al (2017) and Dala-Corte et al(2020), the components of the landscape matrix can act alone or jointly on aquatic biota, which apparently also can be evidenced in our data. We realized that there was an interaction among the variables at the different scales analyzed, and these can have been the necessary local triggers for the dispersive processes in these metacommunities.…”

“…Finally, besides the multiple responses recorded in this study, we highlight the importance of a compartmentalized approach to environmental variables when studying metacommunity patterns, especially in altitude streams. Understanding how local and regional components act on biodiversity is extremely important for conservation programs, especially considering that often the Brazilian law aspects do not comply with their function of preserving continental aquatic ecosystems (Dala-Corte et al, 2020).…”

Land use and local environment affect macroinvertebrate metacommunity organization in Neotropical stream networks

“…So far, scientific attention has focused on the local scale effects of land use on freshwater ecosystems, that is, the relationship between land use and habitat modification (Martinuzzi et al., 2014). At this scale, land use can degrade riparian zones and instream habitats in different ways (Dala‐Corte et al., 2020; Simião‐Ferreira et al., 2018; Siqueira et al., 2015). For example, the loss of riparian vegetation causes biological changes such as the replacement of habitat specialist species by opportunistic and generalist ones (Castro et al., 2018; Heino, 2013; Siqueira et al., 2015), the reduction of organic matter inputs (Tiegs et al., 2019) and an increase in fine sediment inputs linked to streambed siltation (Feld et al., 2018).…”

A novel approach to quantifying trophic interaction strengths and impact of invasive species in food webs

“…While the abundance of invertebrates generally increases with vegetation coverage in freshwaters (Godinho et al 1994(Godinho et al , 1997Olson et al 1995;Batzer and Wissinger 1996;Dala-Corte et al 2020), the higher consumption of invertebrates by M. salmoides in the more complex habitat should not be solely related to their higher abundance. Indeed, the abundance of fish (an energetically richer prey type) increased in a similar manner in this location.…”