The application of general successional theory to stream ecosystems has not been widely addressed due to a lack of long‐term studies on stream channels at sufficiently large spatial scales. Wolf Point Creek in Glacier Bay, Alaska, a lake‐fed stream that began to emerge from under glacial ice in the mid‐1940s, offers an opportunity to address this imbalance. We examine the stream's development from 1977 to 2005, with reference to concepts of succession and community assembly. Dispersal constraints have influenced the succession, as non‐insect taxa required at least 20 years to colonize. We suggest that tolerance is a major mechanism of macroinvertebrate community assembly. Most taxa, with the exception of the cold‐tolerant first colonizers, have persisted within the community following colonization, although relative abundance has changed markedly with time. However, biotic processes do influence colonization and succession. Redd (nest) digging by spawning salmon creates disturbed patches that facilitate the persistence of some early colonizers, and riparian vegetation facilitates colonization by caddisflies and chironomids. We further suggest that both deterministic and stochastic elements influence succession and community assembly in streams. Our study highlights the importance of reestablishing riparian vegetation during stream restoration programs and of increased in‐stream habitat complexity from inputs of coarse woody debris to improve nutrient retention, particularly of salmon carcasses.

Abstract-Studies investigating the use of biomarkers in pesticide risk assessment have greatly increased in recent years; however, issues concerning the ecological meaning of enzymatic responses have proved controversial. Ideally a good biomarker response should be modulated by the environmental contaminants alone and demonstrate a predictable behavior towards certain types of toxins. As these premises are rarely observed, the present study aims to outline research that has contributed to an understanding of the behavior of two widely used biomarkers, cholinesterase and glutathione-S-transferase, describing environmental and biotic factors that affect their response in freshwater invertebrates. Studies were performed in the main classes of aquatic invertebrates with these biomarkers and conclusions were reached concerning their behavior towards the main classes of pesticides. Links between biomarker responses and conventional endpoints were evaluated so that ecological relevance could be attributed to enzymatic responses. Toxicity of mixtures was investigated, and cases of synergism and antagonism were pointed out as factors changing the expected toxicity of aquatic systems and leading to misinterpretations of biomarker responses. Finally, the use of biomarkers as a tool for biomonitoring and in situ assays was investigated, with discussion of advantages and disadvantages of their use.

In contrast to the fast-paced dam construction and river ecosystem alteration which is taking place in the neotropics, ecological knowledge about the effects on fish fauna are still scarce. To contribute with knowledge on the effects of damming on fish fauna, we assessed the response of fish assemblages to the construction of a run-of-the-river dam in an Amazonian river by selecting eight sampling sites along a longitudinal gradient in the vicinity of a new hydroelectric dam. Sites were sampled monthly through a 1-year period before dam closure (2004)(2005), 1 year after closure (2006)(2007), and 5 years after closure (2011)(2012). Following dam closure, there was an initial overall increase in fish abundance and richness across sites. However, despite the initial upsurge, after 5 years, populations were reduced and communities contracted to a level of diversity below that observed prior to dam closure. Respective sites demonstrated distinct ecological responses that were related to the environmental characteristics of their transformed habitats. Important changes in fish assemblages were visible in a shortterm period of 5 years after dam closure. Therefore, monitoring fish species assemblages in a longer term is important to assess the consequences of a decrease in diversity.

Summary Heino et al. () identified the weak explanatory power of abundance data as an important limitation of macroinvertebrate trait analysis. This limitation may be an artefact of analytical design. The widespread practice of combining logarithmically transformed abundance data with trait frequencies, log(x + 1)*(trait frequency), represents a nonlinear abundance weighting of trait frequencies, as opposed to an expression of trait abundances per se. Because the addition of logarithmic data is equivalent to multiplication on an arithmetic scale, summing these abundance‐weighted frequencies provides an inconsistent scaling of trait abundance that may confound quantitative comparison. We provide examples of the options for estimating trait abundance from data on macroinvertebrate abundance and trait frequencies and discuss the meaning of numerical data in the context of analytical objectives. In the light of the contrasting methods that have been employed to analyse trait data for benthic macroinvertebrates, the conclusion that the explanatory power of trait abundance is inferior to that of taxonomic abundance may be premature.

Damming is one of the main causes of the global decline in freshwater biodiversity.Yet, many hydroelectric dams are being built (or planned) in the Neotropics, where the high species diversity and lack of basic ecological knowledge provide a major obstacle to understanding the effects of this environmental change, which has been mostly described from the perspective of taxonomic change. However, this approach does not account for biological function. Trait-based analysis provides an alternative approach to bioassessment. We assessed the impact of dam closure on the functional structure of fish communities of a Neotropical river by applying trait-based analyses to the response of individual traits aggregated at the assemblage level. Fish data were collected during three distinct time periods (1 year before, 1 year after and 5 years after dam closure), at eight sites located downstream of the dam, in the reservoir, transition zone and upstream. The results indicated that reproduction strategies (migration and parental care) and diet (detritivores) were the trait categories mostly affected by the dam, with the response of downstream assemblages differing from upstream of the dam. A trait-based analysis to the impact of damming on fish communities appears to be a promising approach using an initial descriptive analysis of individual traits and regression models of multiple traits that reflect species' adaptation to the new environment. This study provides both an alternative and complementary approach to taxonomic assessment of impacts from damming, contributing towards a more robust evaluation of the response of fish communities to dams. K E Y W O R D Sbiomonitoring, damming, fishes, functional diversity, traits, tropical river

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Neotropical freshwaters host some of the most biodiverse ecosystems in the world and are among the most threatened by habitat alterations. The high number of species and lack of basic ecological knowledge provide a major obstacle to understanding the effects of environmental change. We assessed the impact of dam closure on the fish communities of a neotropical river by applying simple descriptions of community organizations: species abundance distribution and abundance biomass comparison curves. Fish data were collected using gillnets during three distinct time periods (1 year before, 1 year after and 5 years after dam closure), at eight sites located downstream of the dam, in the reservoir, transition zone and upstream. A total of 69 343 individuals representing 260 species were recorded. Dam closure was associated with changes in the organization of fish communities at all sites. Species richness tended to increase immediately after dam closure while evenness decreased. Changes in taxonomic structure (richness and evenness) were accompanied by a change in the distribution of biomass with the proportionate contribution by smaller individuals significantly increased relative to larger individuals. Five years on, richness had fallen to below pre‐closure levels at all sites, while the comparative stability of assemblages in the transformed habitats was reflected by biomass‐abundance distribution patterns that approximated pre‐disturbance ratios. This simplistic analysis provided a sensitive and informative assessment of ecological conditions, which highlights the impact to ecosystem process and ecological networks and has particular value in regions where a lack of detailed ecological knowledge precludes the application of traditional bioassessment methods. Copyright © 2015 John Wiley & Sons, Ltd.