ABSTRACT

Dams are expected to decrease fish diversity because they deeply alter downstream environment. However, such decline has not been consistently observed although profound modifications in the structure and/or composition of fish communities were generally recorded, and were linked to modifications of the downstream environment. In this work we analyze data from observations made before and almost 10 years after the completion of a hydroelectric dam in the neotropics. We monitored fish diversity below that dam and compared the taxonomic and functional structures of the samples between the pre-and post-dam periods. A significant decrease in species richness was evidenced. Taxonomic and trophic structures were significantly different between the two periods. Conversely, the functional structure of samples based on reproductive traits did not change significantly after the damming. Concerning feeding habits, a large increase in relative abundance of detritivores and a parallel decrease of fish species feeding on terrestrial food sources were observed in samples taken 6-9 years after closure of the dam as compared with samples taken before the dam.

In this study, we investigated functional structure patterns of tropical headwater and river fish assemblages. We hypothesised that environmental conditions are primarily structuring headwater streams leading to functionally clustered assemblages, whereas processes that favour functional overdispersion would guide river assemblages. For 27 headwater streams and 22 rivers, we used eight functional traits for calculating two functional indexes: mean pairwise distance (MPD) and net relatedness index (NRI). We performed linear regressions between indexes and species richness, a multiple regression between NRI and eight environmental variables and a variation partitioning to disentangle the role of environment and space on NRI. Our findings indicate that fish assemblages of headwaters are structured by environmental conditions as most assemblages in this habitat displayed a tendency to clustering and MPD/NRI were not correlated with species diversity, whereas the opposite pattern was observed for river habitat. Four environmental variables (channel depth, water velocity, dissolved oxygen and turbidity) explain 56% of functional structure variation. These variables seem to function as selective filters in headwaters, whereas channel depth may be determinant for functional overdispersion of river fish assemblages. Components associated with space are also influencing the functional structure. Limitations of species dispersal through space (between both habitat types) appear as a possible cause to this. In this sense, both environmental conditions and processes linked with space are capable of influencing the functional structure of tropical headwater streams and river fish assemblages.

a global database for metacommunity ecology, integrating species, traits, environment and space alienor Jeliazkov et al. #the use of functional information in the form of species traits plays an important role in explaining biodiversity patterns and responses to environmental changes. although relationships between species composition, their traits, and the environment have been extensively studied on a case-by-case basis, results are variable, and it remains unclear how generalizable these relationships are across ecosystems, taxa and spatial scales. to address this gap, we collated 80 datasets from trait-based studies into a global database for metaCommunity Ecology: Species, Traits, Environment and Space; "CEStES". Each dataset includes four matrices: species community abundances or presences/absences across multiple sites, species trait information, environmental variables and spatial coordinates of the sampling sites. the CEStES database is a live database: it will be maintained and expanded in the future as new datasets become available. By its harmonized structure, and the diversity of ecosystem types, taxonomic groups, and spatial scales it covers, the CEStES database provides an important opportunity for synthetic trait-based research in community ecology. Background & SummaryA major challenge in ecology is to understand the processes underlying community assembly and biodiversity patterns across space 1,2 . Over the three last decades, trait-based research, by taking up this challenge, has drawn increasing interest 3 , in particular with the aim of predicting biodiversity response to environment. In community ecology, it has been equated to the 'Holy Grail' that would allow ecologists to approach the potential processes underlying metacommunity patterns 4-7 . In macroecology, it is common to study biodiversity variation through its taxonomic and functional facets along gradients of environmental drivers 8-10 . In biodiversity-ecosystem functioning research, trait-based diversity measures complement taxonomic ones to predict ecosystem functions 11 offering early-warning signs of ecosystem perturbation 12 .The topic of Trait-Environment Relationships (TER) has been extensively studied across the globe and across the tree of life. However, each study deals with a specific system, taxonomic group, and geographic region and uses different methods to assess the relationship between species traits and the environment. As a consequence, we do not know how generalizable apparent relationships are, nor how they vary across ecosystems, realms, and taxonomic groups. In addition, while there is an emerging synthesis about the role of traits for terrestrial plant communities 13,14 , we know much less about other groups and ecosystem types.To address these gaps, we introduce the CESTES database -a global database for metaCommunity Ecology: Species, Traits, Environment and Space. This database assembles 80 datasets from studies that analysed empirical multivariate trait-environment relationships between 1996 (the first...

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This study analyzes the interaction of fish assemblages with 14 physicochemical and hydrogeomorphological variables at 31 sampling stations along the watershed of the Meia Ponte River, Upper Paraná Basin, Central Brazil, during low and high water seasons in 2001. This river and its tributaries drain both urban and agricultural areas. Fish were caught with sieves along a 100 m stretch demarcated in every sampling site, where environmental variables were also measured. A total of 3508 individuals belonging to 31 species were collected. Fish abundance and environmental data matrices were submitted to a multivariate analysis of co-inertia. Two axes were retained for interpretation (total variance explained = 63.65%) indicating that pH, water temperature, conductivity, chemical dissolved oxygen, and turbidity, all have an influence on fish assemblage structure. The co-structure found (fish assemblages and physicochemical variables) is correlated in both of the axes considered (r = 0.73 and r = 0.68, respectively), and is statistically significant (Monte Carlo test, P \ 0.001). This co-structure is regulated by seasonality, but is influenced by fish habitat preferences, spawning and available food, the extent and effects of anthropogenic activities (domestic sewage, agriculture, ranching, urban areas) and the position of sampling stations along the watershed.

We investigated functional patterns of fish assemblages of two adjacent basins (Araguaia and Tocantins) to test whether their headwater stream fish assemblages are more functionally (dis)similar than expected by chance and whether these (dis)similarities are related to differences of environmental conditions between basins. We used an analysis of similarities (ANOSIM) on a functional dissimilarity matrix to test for (dis)similarities between fish assemblages of both basins. We performed RLQ and fourth-corner analyses to determine fish species trait-environment relationship. Our results revealed functional dissimilarities between fish assemblages of both basins and significant species trait-environment relationships, suggesting that environmental conditions are driving such dissimilarities. Inter-basin dissimilarities are mainly driven by altitudinal and water temperature gradients, whereas dissimilarities among streams within the basins are influenced by channel depth, turbidity and conductivity. These five environmental variables mostly affected six fish species traits (body mass, water column position, substrate preference, parental care, foraging locality and migration) in different manners. This study is an attempt to understand functional trends of fish assemblages in a tropical region that remains poorly known but severely threatened.Nós investigamos os padrões funcionais das assembleias de peixes de duas bacias adjacentes (Araguaia and Tocantins) para testar se as assembleias de peixes de seus riachos de cabeceira são funcionalmente mais (dis)similares do que o esperado ao acaso e se estas (dis)similaridades estão relacionadas a diferenças nas condições ambientais entre as bacias. Nós utilizamos uma análise de similaridades (ANOSIM) sobre uma matriz de dissimilaridade funcional para testar por (dis)similaridades entre as assembleias de peixes das duas bacias. Nós realizamos análises de RLQ e fourth-corner para determinar a relação entre o ambiente e a estrutura funcional das assembleias de peixes. Nossos resultados revelaram dissimilaridades funcionais entre as assembleias de peixes de ambas as bacias e relações significativas entre atributos das espécies e o ambiente, sugerindo que as condições ambientais estão direcionando tais dissimilaridades. As dissimilaridades entre bacias são influenciadas principalmente pelos gradientes de altitude e temperatura da água, enquanto as dissimilaridades entre os riachos na bacia pela profundidade do canal, turbidez e condutividade. Estas cinco variáveis ambientais afetaram principalmente seis atributos das espécies de peixes (massa corporal, posição na coluna de água, preferência por substrato, cuidado parental, local de forrageio e migração) de diferentes maneiras. Este estudo é uma tentativa para entender os padrões funcionais das assembleias de peixes de uma região ainda pouco conhecida, mas, seriamente ameaçada.

The João Leite River is located in the upper Paraná basin, Central Brazil. It drains areas covered by Cerrado vegetation interspersed with urban and agricultural areas. This study aims to asses changes of the fish assembleges structure along a undisturbed-impacted gradient in ten stream stretches using ecological descriptors, a similarity index and the abundancebiomass relationship (ABC curves). The fish were collected during the dry period using electrofishing gear in stretches of 50 m. Results show that the environmental variation observed along the undisturbed-impacted gradient considered influences on fish assemblage structure. Both richness and diversity differences between fish assemblages are partially influenced by stream stretch orthonian order and anthropogenic impacts. ABC curves classified six stream stretches located in preserved or impacted areas as undisturbed while four stretches were classified as disturbed. This is attributed to the influence of the undisturbed habitat within the conservation unit and the presence of K-or r-strategist species. This type of study contributes to an understanding of the effects of aquatic environment conservation on the Brazilian Cerrado core area, where the choice of conservation areas prioritizes terrestrial over aquatic aspects.O ribeirão João Leite está localizado no alto da bacia do rio Paraná, Brasil Central, onde drena áreas cobertas por vegetação tipo Cerrado intercaladas com áreas urbanas e agrícolas. Este estudo objetiva avaliar as mudanças na estrutura das assembleias de peixes ao longo de um gradiente ambiental (não perturbado-impactado) em trechos de dez riachos utilizando descritores ecológicos, um índice de similaridade e a relação abundância-biomassa (curvas ABC). Os peixes foram coletados durante o período da estiagem em trechos de 50 m utilizando a pesca elétrica. Os resultados indicam que a variabilidade ambiental observada ao longo do gradiente considerado influencia na estrutura das assembleias de peixes. As diferenças observadas entre a riqueza e diversidade das assembleias de peixes são parcialmente influenciadas pela ordem do riacho e os impactos antropogênicos. As curvas ABC classificam seis trechos localizados em áreas preservadas ou impactadas como não perturbados e quatro como perturbados. Isto é atribuído à influência do habitat preservado presente na unidade de conservação e à presença de espécies com estratégias K-ou r-. Este tipo de estudo contribui ao entendimento dos efeitos da conservação do ambiente aquático na área central do Cerrado brasileiro, onde as escolhas de áreas de conservação dão prioridade aos aspectos terrestres em detrimento dos aquáticos.