Changes in distance decay relationships after river regulation: similarity among fish assemblages in a large Amazonian river

Abstract

The construction of large dams has changed natural hydrology of many rivers in South America. Considering that little is known about the reorganisation of nonmigratory fish assemblages following an impoundment, we investigated changes caused by the construction of Lajeado Dam on the spatial distribution of nonmigratory fish along the Tocantins River, a large Amazonian river. In particular, we investigated changes in distance decay of community similarity (initial similarity and halving distance) in periods that preceded and followed the construction of the dam. For this study, we analysed data collected over a four‐year period, including seven sites distributed along the Tocantins River (~270 km). Initial similarity showed high values and little variation over the years. Halving distance, on the other hand, changed considerably after impoundment, showing progressive smaller values. In the first 2 years after impoundment, halving distance decreased by more than half of the initial value, indicating changes in distance decay relationships. An ordination analysis nonmetric multidimensional scaling (NMDS) indicated substantial changes in assemblage structure between pre‐ and postimpoundment periods, especially in sites close to the dam. In addition, after river regulation, we recorded shifts in species abundance across sites, while numerical dominance increased and local richness decreased in sites near the dam. Our results indicate that the dam changed diversity gradients along the river corridor, increasing the distance decay of assemblage similarity. All these findings evidence that nonmigratory fish assemblages are particularly vulnerable to river regulation.

Short-term changes in energy allocation by Hemiodontidae fish after the construction of a large reservoir (Lajeado Dam, Tocantins River)

“…Reservoir environments, therefore, lack the factors that trigger the reproductive cycle, preventing fish to allocate energy to such process. We highlight that species that showed clear alteration in energy allocation patterns (H. unimaculatus and A. robertsi) were captured mainly in lentic sites after the impoundment -a region more affected by the impoundment (Araújo et al, 2013).…”

“…Hemiodontidae fish are medium-sized, iteroparous and rheophylic, they can perform reproductive sustain populations in areas affected by impoundments (Gomes & Miranda, 2001;Oliveira et al, 2005;Terra & Araújo, 2010;Petesse & Petrere Jr., 2012;Araújo et al, 2013). Hypotheses have been proposed to explain these changes, including changes/losses of feeding resources, habitats and particular environmental settings that are important to specific life history stages .…”

“…A possibility of population persistence is the use of areas located upstream, where recruitment may ensue. There is a relevant fluvial segment between Lajeado and Peixe Angical Dam, with the presence of tributaries and small floodplains (Agostinho et al, 2011;Araújo et al, 2013). In this case, the impoundment may work as feeding and/or residence site, while remnant lotic stretches and associated environments work as spawning grounds and nursery.…”

“…Although they provide undeniable social and economic benefits, they also cause significant negative effects on the fish fauna . Many studies have documented changes in species abundance and composition in areas affected by large dams, resulting in significant alterations in the structure of populations and assemblages (e.g., Santos, 1995;Mérona et al, 2001;Agostinho et al, 2008;Petesse & Petrere Jr., 2012;Araújo et al, 2013). Most Neotropical fish species do not colonize the reservoir environment because of ecological restrictions imposed by the loss of resources, habitats and conditions, which are important to specific life history stages such as growth, maintenance and reproduction .…”

Feeding and reproductive ecology of Cichla piquiti Kullander & Ferreira, 2006 within its native range, Lajeado reservoir, rio Tocantins basin

“…Species that have pre-adaptations to complete their life cycle (e.g., feeding, reproduction and growth) in the reservoir acquire biological relevance and can dominate fish assemblages Araújo et al, 2013). Some non-migratory species, in particular, play a central role in structuring new assemblages, playing important ecological functions in the reservoir (Hoeinghaus et al, 2009).…”