Threshold responses of Amazonian stream fishes to timing and extent of deforestation

Abstract

Deforestation is a primary driver of biodiversity change through habitat loss and fragmentation. Stream biodiversity may not respond to deforestation in a simple linear relationship. Rather, threshold responses to extent and timing of deforestation may occur. Identification of critical deforestation thresholds is needed for effective conservation and management. We tested for threshold responses of fish species and functional groups to degree of watershed and riparian zone deforestation and time since impact in 75 streams in the western Brazilian Amazon. We used remote sensing to assess deforestation from 1984 to 2011. Fish assemblages were sampled with seines and dip nets in a standardized manner. Fish species (n = 84) were classified into 20 functional groups based on ecomorphological traits associated with habitat use, feeding, and locomotion. Threshold responses were quantified using threshold indicator taxa analysis. Negative threshold responses to deforestation were common and consistently occurred at very low levels of deforestation (<20%) and soon after impact (<10 years). Sensitive species were functionally unique and associated with complex habitats and structures of allochthonous origin found in forested watersheds. Positive threshold responses of species were less common and generally occurred at >70% deforestation and >10 years after impact. Findings were similar at the community level for both taxonomic and functional analyses. Because most negative threshold responses occurred at low levels of deforestation and soon after impact, even minimal change is expected to negatively affect biodiversity. Delayed positive threshold responses to extreme deforestation by a few species do not offset the loss of sensitive taxa and likely contribute to biotic homogenization.

Fish assemblage convergence along stream environmental gradients: an intercontinental analysis

“…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). No apparent patterns were evident between traits and water depth, suggesting that depth was not a strong filter for traits examined in this study.…”

Trait–environment relationships in Amazon stream fish assemblages

“…This software was also used to mea- Table S2). These traits were first described by Gatz Jr (1979) and continue to be relevant for the understanding of features of the feeding behaviour, locomotion and habitat preferences of fish (Brejão, Hoeinghaus, Perez-Mayorga, Ferraz, & Casatti, 2017;Leitão et al, 2016). These traits were first described by Gatz Jr (1979) and continue to be relevant for the understanding of features of the feeding behaviour, locomotion and habitat preferences of fish (Brejão, Hoeinghaus, Perez-Mayorga, Ferraz, & Casatti, 2017;Leitão et al, 2016).…”

Land cover, riparian zones and instream habitat influence stream fish assemblages in the eastern Amazon

“…In addition, past land-use change could have a legacy effect on contemporary biodiversity; thus, there may be time lags for observable responses to impacts (Iwata, Nakano, & Inoue, 2003;Zeni et al, 2017). Such time lags could mask impacts of land-use change on stream fish assemblages such that interpretations of analyses using contemporary landscape features (e.g., deforested catchments) suggest resilience of fish assemblages to landscape change when in fact the timescale was too short to detect a response (Brejão et al, 2018;Iwata et al, 2003;Zeni et al, 2017). For example, the lack of strong relationships between catchment land use and fish assemblage composition and structure in this study could be partly due to a time lag in response of instream habitat to changes in land use and/or a lag in assemblage response to instream habitat change.…”

“…Baseline data that represent relatively "pristine" conditions are lacking in most instances, which can undermine the ability of studies to interpret ecological dynamics in response to land cover change . Lastly, long-term monitoring studies should also incorporate data on spatial relationships (e.g., this study) as well as the history (e.g., Zeni et al, 2017) and rate (e.g., Brejão et al, 2018) of land cover change. Other physical habitat variables (channel morphology, substrate, water velocity, submerged wood structure, riparian vegetation cover and human influence) should also be monitored because they have been shown to influence aquatic biota in various ways depending on the region and associated environmental conditions (Kaufmann et al, 1999;Peck et al, 2006).…”

“…Land-use change is an important driver of biodiversity change in freshwater ecosystems (Allan, 2004). Small streams are particularly sensitive to landscape alteration due to the importance of catchment inputs for maintenance of instream habitat and food web dynamics (e.g., Brejão, Hoeinghaus, Pérez-Mayorga, Ferraz, & Casatti, 2018;Leal et al, 2017;Sweeney et al, 2004). For example, deforestation can increase sedimentation and reduce woody debris inputs, resulting in simplified and homogenised habitats and altered hydrology and water chemistry (Cardinale, Palmer, Swan, Brooks, & Poff, 2002).…”