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Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%-18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost.

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Instream wood plays important chemical, physical and ecological functions in aquatic systems, benefiting biota directly and indirectly. However, human activities along river corridors have disrupted wood recruitment and retention, usually leading to reductions in the amount of instream wood. In the tropics, where wood is believed to be more transient, the expansion of agriculture and infrastructure might be reducing instream wood stock even more than in the better studied temperate streams. However, research is needed to augment the small amount of information about wood in different biomes and ecosystems of neotropical streams. Here we present the first extensive assessment of instream wood loads and size distributions in streams of the wet-tropical Amazon and semi-humid-tropical Cerrado (the Brazilian savanna). We also compare neotropical wood stocks with those in temperate streams, first comparing against data from the literature, and then from a comparable dataset from temperate biomes in the USA. Contrary to our expectations, Amazon and Cerrado streams carried similar wood loads, which were lower than the world literature average, but similar to those found in comparable temperate forest and savanna streams in the USA. Our results indicate that the field survey methods and the wood metric adopted are highly important when comparing different datasets. But when properly compared, we found that most of the wood in temperate streams is made-up of a small number of large pieces, whereas wood in neotropical streams is made up of a larger number of small pieces that produce similar total volumes. The character of wood volumes among biomes is linked more to the delivery, transport and decomposition mechanisms than to the total number of pieces. Future studies should further investigate the potential instream wood drivers in neotropical catchments in order to better understand the differences and similarities here detected between biomes and climatic regions.

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We investigated the mechanisms involved in the relationship between land-use changes and aquatic biodiversity, using stream fish assemblages of the Brazilian Savanna (i.e., Cerrado) as a study model. We tested the prediction that landscape degradation would decrease environmental heterogeneity and change predominant physical-habitat types, which in turn would decrease the functional diversity and alter the functional identity of fish assemblages. We sampled fish from 40 streams in the Upper Paraná River basin, and assessed catchment and instream conditions. We then conducted an ecomorphological analysis to functionally characterize all species (36) and quantify different facets of the functional structure of assemblages. We detected multiple pathways of the impacts from landscape changes on the fish assemblages. Catchment degradation reduced the stream-bed complexity and the heterogeneity of canopy shading, decreasing assemblage functional specialization and divergence. Landscape changes also reduced the water volume and the amount of large rocks in streams, resulting in decreased abundances of species with large bodies and with morphological traits that favor swimming in the water column. We conclude that land-use intensification caused significant changes in aquatic biodiversity in the Cerrado, reinforcing the need to pay special attention to this global hotspot.(AU)

Investigamos os mecanismos envolvidos na relação entre mudanças de uso da terra e biodiversidade aquática, utilizando a ictiofauna de riachos do Cerrado como modelo de estudo. Testamos a predição de que a degradação da paisagem reduz a heterogeneidade ambiental e muda os tipos predominantes de habitat, por sua vez, diminuindo a diversidade e alterando a identidade funcional de comunidades de peixes. Amostramos 40 riachos da bacia do Alto Rio Paraná, e avaliamos as condições da drenagem e do habitat físico local. Em seguida, conduzimos uma análise ecomorfológica para caracterizar funcionalmente todas as espécies (36) e quantificar diferentes facetas da estrutura funcional das comunidades. Detectamos múltiplos caminhos de impacto das alterações da paisagem sobre a ictiofauna. A degradação das bacias de drenagem reduziu complexidade do leito e heterogeneidade no sombreamento pelo dossel, diminuindo especialização e divergência funcional das comunidades. Alterações na paisagem também reduziram volume de água e quantidade de pedras grandes nos riachos, resultando em diminuição na abundância de espécies de maior porte e com atributos morfológicos que favorecem a natação na coluna d'água. Concluímos que a intensificação dos usos da terra causa alterações significativas para a biodiversidade aquática no Cerrado, reforçando a necessidade de especial atenção a este hotspot global.(AU)

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We investigated the mechanisms involved in the relationship between land-use changes and aquatic biodiversity, using stream fish assemblages of the Brazilian Savanna (i.e., Cerrado) as a study model. We tested the prediction that landscape degradation would decrease environmental heterogeneity and change predominant physical-habitat types, which in turn would decrease the functional diversity and alter the functional identity of fish assemblages. We sampled fish from 40 streams in the Upper Paraná River basin, and assessed catchment and instream conditions. We then conducted an ecomorphological analysis to functionally characterize all species (36) and quantify different facets of the functional structure of assemblages. We detected multiple pathways of the impacts from landscape changes on the fish assemblages. Catchment degradation reduced the stream-bed complexity and the heterogeneity of canopy shading, decreasing assemblage functional specialization and divergence. Landscape changes also reduced the water volume and the amount of large rocks in streams, resulting in decreased abundances of species with large bodies and with morphological traits that favor swimming in the water column. We conclude that land-use intensification caused significant changes in aquatic biodiversity in the Cerrado, reinforcing the need to pay special attention to this global hotspot.(AU)

Investigamos os mecanismos envolvidos na relação entre mudanças de uso da terra e biodiversidade aquática, utilizando a ictiofauna de riachos do Cerrado como modelo de estudo. Testamos a predição de que a degradação da paisagem reduz a heterogeneidade ambiental e muda os tipos predominantes de habitat, por sua vez, diminuindo a diversidade e alterando a identidade funcional de comunidades de peixes. Amostramos 40 riachos da bacia do Alto Rio Paraná, e avaliamos as condições da drenagem e do habitat físico local. Em seguida, conduzimos uma análise ecomorfológica para caracterizar funcionalmente todas as espécies (36) e quantificar diferentes facetas da estrutura funcional das comunidades. Detectamos múltiplos caminhos de impacto das alterações da paisagem sobre a ictiofauna. A degradação das bacias de drenagem reduziu complexidade do leito e heterogeneidade no sombreamento pelo dossel, diminuindo especialização e divergência funcional das comunidades. Alterações na paisagem também reduziram volume de água e quantidade de pedras grandes nos riachos, resultando em diminuição na abundância de espécies de maior porte e com atributos morfológicos que favorecem a natação na coluna d'água. Concluímos que a intensificação dos usos da terra causa alterações significativas para a biodiversidade aquática no Cerrado, reforçando a necessidade de especial atenção a este hotspot global.(AU)

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Conservation initiatives overwhelmingly focus on terrestrial biodiversity, and little is known about the freshwater cobenefits of terrestrial conservation actions. We sampled more than 1500 terrestrial and freshwater species in the Amazon and simulated conservation for species from both realms. Prioritizations based on terrestrial species yielded on average just 22% of the freshwater benefits achieved through freshwater-focused conservation. However, by using integrated cross-realm planning, freshwater benefits could be increased by up to 600% for a 1% reduction in terrestrial benefits. Where freshwater biodiversity data are unavailable but aquatic connectivity is accounted for, freshwater benefits could still be doubled for negligible losses of terrestrial coverage. Conservation actions are urgently needed to improve the status of freshwater species globally. Our results suggest that such gains can be achieved without compromising terrestrial conservation goals.

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Agricultural expansion and intensification are major threats to tropical biodiversity. In addition to the direct removal of native vegetation, agricultural expansion often elicits other human-induced disturbances, many of which are poorly addressed by existing environmental legislation and conservation programmes. This is particularly true for tropical freshwater systems, where there is considerable uncertainty about whether a legislative focus on protecting riparian vegetation is sufficient to conserve stream fauna.To assess the extent to which stream fish are being effectively conserved in agricultural landscapes, we examined the spatial distribution of assemblages in river basins to identify the relative importance of human impacts at instream, riparian and catchment scales, in shaping observed patterns. We used an extensive dataset on the ecological condition of 83 low-order streams distributed in three river basins in the eastern Brazilian Amazon.We collected and identified 24,420 individual fish from 134 species. Multiplicative diversity partitioning revealed high levels of compositional dissimilarity (DS) among stream sites (DS = 0.74 to 0.83) and river basins (DS = 0.82), due mainly to turnover (77.8% to 81.8%) rather than nestedness. The highly heterogeneous fish faunas in small Amazonian streams underscore the vital importance of enacting measures to protect forests on private lands outside of public protected areas.Instream habitat features explained more variability in fish assemblages (15%-19%) than riparian (2%-12%), catchment (4%-13%) or natural covariates (4%-11%). Although grouping species into functional guilds allowed us to explain up to 31% of their abundance (i.e. for nektonic herbivores), individual riparian - and catchment - scale predictor variables that are commonly a focus of environmental legislation explained very little of the observed variation (partial R2 values mostly <5%).Policy implications. Current rates of agricultural intensification and mechanization in tropical landscapes are unprecedented, yet the existing legislative frameworks focusing on protecting riparian vegetation seem insufficient to conserve stream environments and their fish assemblages. To safeguard the species-rich freshwater biota of small Amazonian streams, conservation actions must shift towards managing whole basins and drainage networks, as well as agricultural practices in already-cleared land.

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In the present study, we assessed the ecomorphology of two species of Astyanax in streams with different substrates found in the Rio São Francisco Basin. The dominant substrate of each stream was defined as either "fine" (0 to 2 mm), "gravel" (2 to 250 mm), "rock" (> 250 mm), or "leaf bank". We analyzed a total of 22 ecomorphological attributes of Astyanax intermedius Eigenmann, 1908 (127 individuals) and Astyanax rivularis (Lütken, 1875) (238 individuals) adults. We detected significant ecomorphological differences between the populations of A. rivularis and A. intermedius from habitats with different types of substrates. However, the two species did not show the same morphological differences depending on the type of substrate. These results confirmed the hypothesis that individuals from environments with different characteristics may have different ecomorphological patterns. Knowing that morphology is associated with habitat use and available resources, the loss of a resource or a modification in the environment may directly affect the permanence of a species, leading to a loss of morphologic diversity.(AU)

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RESUMO

In the present study, we assessed the ecomorphology of two species of Astyanax in streams with different substrates found in the Rio São Francisco Basin. The dominant substrate of each stream was defined as either "fine" (0 to 2 mm), "gravel" (2 to 250 mm), "rock" (> 250 mm), or "leaf bank". We analyzed a total of 22 ecomorphological attributes of Astyanax intermedius Eigenmann, 1908 (127 individuals) and Astyanax rivularis (Lütken, 1875) (238 individuals) adults. We detected significant ecomorphological differences between the populations of A. rivularis and A. intermedius from habitats with different types of substrates. However, the two species did not show the same morphological differences depending on the type of substrate. These results confirmed the hypothesis that individuals from environments with different characteristics may have different ecomorphological patterns. Knowing that morphology is associated with habitat use and available resources, the loss of a resource or a modification in the environment may directly affect the permanence of a species, leading to a loss of morphologic diversity.

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This study aimed to investigate the local and regional patterns of habitat use by Piabina argentea Reinhardt, 1867 in four different rivers from the Velhas River basin. Water velocity, depth and substrate were measured at each sampling site. Ecomorphological analysis was performed using 17 ecomorphological attributes and 40 specimens from each river. Although the populations overlapped in morphological space, Canonical Discriminant Analysis showed that they were statistically different, mainly the population from the Velhas River. The most important attributes in the analysis were compression index, relative body depth, and index of ventral flattening. The local patterns of habitat use were not similar between all rivers, but in general, the regionalpattern was slow flowing habitat with 20 to 40 cm and 60 to 80 cm of depth and sand, silte+clay and leave banks as substrate. Considering the physical characteristics of each river and the pattern of regional habitat use, a great amount of the species requirements was observed in the four rivers. Nevertheless, a silted river like the Velhas seems to have higher water velocity, shallower habitat and fine particle substrate, which fulfill most of the species habitat requirements.

O presente estudo teve como objetivo investigar os padrões local e regional de uso de habitat de Piabina argentea Reinhardt, 1867 em quatro diferentes rios da bacia do rio das Velhas. Os habitat amostrados foram caracterizados quanto à velocidade da água, profundidade e tipo de substrato. Para a análise ecomorfológica, foram calculados 17 atributos ecomorfológicos de 40 exemplares de cada rio. Embora estas populações tenham se sobreposto no espaço ecomorfológico, a Análise Discriminante Canônica mostrou haver diferença significativa entre elas, principalmente da população do rio das Velhas em relação às demais. A separação se deu em termos do índice de compressão, altura relativa do corpo e índice de achatamento ventral. Os padrões locais de seleção de habitat não foram congruentes em todos os rios, mas em geral, houve predomínio do padrão regional: habitat lênticos, profundidade entre 20 e 40 cm e 60 e 80 cm e substrato areia, silte+argila e banco de folhas. Considerando as características físicas de cada rio e o padrão regional da espécie, a maior parte dos seus requerimentos de habitat é contemplada nos quatro rios. Entretanto, um corpo d'água assoreado como o trecho do rio das Velhas, tende a ter maiores velocidades da água, menores profundidades e substrato finos, o que atende em parte à seleção de habitat da espécie estudada.

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