Links between riparian landcover, instream environment and fish assemblages in headwater streams of south‐eastern Brazil

Abstract

We hypothesised and tested a hierarchical organisation model where riparian landcover would influence bank composition and light availability, which in turn would influence instream environments and control fish assemblages. The study was conducted during the dry season in 11 headwater tributaries of the Sorocaba River in the upper Paraná River Basin, south‐eastern Brazil. We focused on seven environmental factors each represented by one or multiple environmental variables and seven fish functional traits each represented by two or more classes. Multivariate direct gradient analyses suggested that riparian zone landcover can be considered a higher level causal factor in a network of relations that control instream characteristics and fish assemblages. Our results provide a framework for a hierarchical conceptual model that identifies singular and collective influences of variables from different scales on each other and ultimately on different aspects related to stream fish functional composition. This conceptual model is focused on the relationships between riparian landcover and instream variables as causal factors on the organisation of stream fish assemblages. Our results can also be viewed as a model for headwater stream management in that landcover can be manipulated to influence factors such as bank composition, substrates and water quality, whereas fish assemblage composition can be used as indicators to monitor the success of such efforts.

Ichthyofauna of the Mamanguape river basin, Northeastern, Brazil

“…This habitat modification, besides of other harms imposed to the ecossistem, opens the area for human activities, which further compromises the stability of the system as previously mentioned by Andrade (1997). The damage to the river's health and to the organisms inhabiting it caused by the removal of riparian vegetation is already well explored in the literature (Sweeney et al 2004;Casatti et al 2009;Teresa & Casatti 2010;Cruz et al 2013). …”

Functional differentiation between fish assemblages from forested and deforested streams

“…The traithabitat relationship shown in these studies highlights the influences of environmental constraints on community composition (Poff, 1997). Trait-based frameworks are a promising way to explore changes in the structure of fish communities following environmental change (Cruz et al, 2013).…”

“…Deforestation may also reduce the input or retention of sediment and other material from the surrounding terrestrial environment (Pusey & Arthington, 2003), in turn influencing water quality and substrate composition (Cruz et al, 2013). Finally, riparian deforestation may favour marginal grass and weed proliferation (Pusey & Arthington, 2003;Rocha et al, 2009), which benefits some fish species (Rocha et al, 2009).…”

Fish complementarity is associated to forests in Amazonian streams

“…Deforestation at the watershed or at the riparian buffer scale, affect stream characteristics at the local scale (Cruz et al, 2013), such as flow, depth, substrate composition, litter amount, stability of stream banks, and structural complexity (Gorman & Karr, 1978;Lorion & Kennedy, 2009;Casatti et al, 2009). Considering that the influence of these variables on species occurrence depends on their functional traits (Goldstein & Meador, 2005;Teresa & Casatti, 2012), it is presumable that the effects of deforestation on the functional structure of communities are mediated by changes at finer spatial scales.…”