The Neotropical realm still represents a great challenge to our understanding of species distribution patterns and the role played by different drivers of biodiversity. The paper by Coutant et al. ...(2022) is a great advance towards a holistic approach to quantifying the contribution of environmental and anthropogenic factors that drive community assembly in the Amazon, and how we can apply such knowledge to guide future monitoring programmes. Disentangling the relative roles played by multiple drivers of biodiversity allowed them to also highlight hotspot areas hosting unique freshwater fish diversity and to pinpoint conservation priorities.
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.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•Sensitive taxa respond to deforestation in a non-linear manner.•Sensitive taxa more sensitive to catchment forest loss than to riparian forest loss.•Sensitive taxa offer early-warning signals of ...ecological damage from forest loss.•Brazil needs expanded forested riparian & catchment protections.
Deforestation is a major threat globally, but especially in tropical regions because they are biodiversity strongholds and carbon storehouses. Some studies have reported changes in species richness and composition in lotic ecosystems with increased forest-loss in their catchment, presumably resulting from the replacement of sensitive taxa by more resistant or tolerant taxa. Also, sensitive taxa respond to deforestation in a non-linear manner and fish and macroinvertebrates have different sensitivities to landscape pressures. Therefore, it is useful to determine the effects of forest-loss on widespread sensitive or threshold taxa in aquatic ecosystems. We used Threshold Indicator Taxa Analysis (TITAN) to assess forest-loss and land use history impacts in 92 eastern Amazonian stream sites. We determined TITAN peak-change thresholds for fish at 1% and 6% of forest-loss at total-catchment and local-riparian spatial extents, respectively, and at 2% and 40% of land-use intensity change at total-catchment and local-riparian spatial extents, respectively. For macroinvertebrates, TITAN peak-change thresholds were 1% and 11% of forest loss at total-catchment and local-riparian spatial extents, respectively, and at 3% of land-use intensity change for both total-catchment and local-riparian spatial extents. Because of these thresholds, inherent ecoregional variability and key literature, we have three major recommendations. 1) Logging should be prohibited in riparian reserves that are at least 100-m wide on each side of headwater streams and in a network of catchments across all biomes and as many landscape types as possible. 2) An ecologically and statistically rigorous monitoring program with standard methods should be implemented to assess and regulate land uses better. 3) Conservation planning areas should consider aquatic biota as well as terrestrial biota.
Agricultural land use is a primary driver of environmental impacts on streams. However, the causal processes that shape these impacts operate through multiple pathways and at several spatial scales. ...This complexity undermines the development of more effective management approaches, and illustrates the need for more in‐depth studies to assess the mechanisms that determine changes in stream biodiversity. Here we present results of the most comprehensive multi‐scale assessment of the biological condition of streams in the Amazon to date, examining functional responses of fish assemblages to land use. We sampled fish assemblages from two large human‐modified regions, and characterized stream conditions by physical habitat attributes and key landscape‐change variables, including density of road crossings (i.e. riverscape fragmentation), deforestation, and agricultural intensification. Fish species were functionally characterized using ecomorphological traits describing feeding, locomotion, and habitat preferences, and these traits were used to derive indices that quantitatively describe the functional structure of the assemblages. Using structural equation modeling, we disentangled multiple drivers operating at different spatial scales, identifying causal pathways that significantly affect stream condition and the structure of the fish assemblages. Deforestation at catchment and riparian network scales altered the channel morphology and the stream bottom structure, changing the functional identity of assemblages. Local deforestation reduced the functional evenness of assemblages (i.e. increased dominance of specific trait combinations) mediated by expansion of aquatic vegetation cover. Riverscape fragmentation reduced functional richness, evenness and divergence, suggesting a trend toward functional homogenization and a reduced range of ecological niches within assemblages following the loss of regional connectivity. These results underscore the often‐unrecognized importance of different land use changes, each of which can have marked effects on stream biodiversity. We draw on the relationships observed herein to suggest priorities for the improved management of stream systems in the multiple‐use landscapes that predominate in human‐modified tropical forests.
Context
Land use change and forest degradation have myriad effects on tropical ecosystems. Yet their consequences for low-order streams remain very poorly understood, including in the world´s largest ...freshwater basin, the Amazon.
Objectives
Determine the degree to which physical and chemical characteristics of the instream habitat of low-order Amazonian streams change in response to past local- and catchment-level anthropogenic disturbances.
Methods
To do so, we collected field instream habitat (i.e., physical habitat and water quality) and landscape data from 99 stream sites in two eastern Brazilian Amazon regions. We used random forest regression trees to assess the relative importance of different predictor variables in determining changes in instream habitat response variables.
Results
Multiple drivers, operating at multiple spatial scales, were important in determining changes in the physical habitat and water quality of the sites. Although we found few similarities in modelled relationships between the two regions, we observed non-linear responses of specific instream characteristics to landscape change; for example 20 % of catchment deforestation resulted in consistently warmer streams.
Conclusions
Our results highlight the importance of local riparian and catchment-scale forest cover in shaping instream physical environments, but also underscore the importance of other land use changes and activities, such as road crossings and upstream agriculture intensification. In contrast to the property-scale focus of the Brazilian Forest code, which governs environmental regulations on private land, our results reinforce the importance of catchment-wide management strategies to protect stream ecosystem integrity.
Abstract 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.
Resumo 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.
1. 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. 2. 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. 3. 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. 4. 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%). 5. Policy implications. Current rates of agricultural intensification and mechanization 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.
Protecting riparian vegetation around streams is vital in reducing the detrimental effects of environmental change on freshwater ecosystems and in maintaining aquatic biodiversity. Thus, identifying ...ecological thresholds is useful for defining regulatory limits and for guiding the management of riparian zones towards the conservation of freshwater biota.
Using nationwide data on fish and invertebrates occurring in small Brazilian streams, we estimated thresholds of native vegetation loss in which there are abrupt changes in the occurrence and abundance of freshwater bioindicators and tested whether there are congruent responses among different biomes, biological groups and riparian buffer sizes.
Mean thresholds of native vegetation cover loss varied widely among biomes, buffer sizes and biological groups: ranging from 0.5% to 77.4% for fish, from 2.9% to 37.0% for aquatic invertebrates and from 3.8% to 43.2% for a subset of aquatic invertebrates. Confidence intervals for thresholds were wide, but the minimum values of these intervals were lower for the smaller riparian buffers (50 and 100 m) than larger ones (200 and 500 m), indicating that land use should be kept away from the streams. Also, thresholds occurred at a lower percentage of riparian vegetation loss in the smaller buffers, and were critically lower for invertebrates: reducing only 6.5% of native vegetation cover within a 50‐m riparian buffer is enough to cross thresholds for invertebrates.
Synthesis and applications. The high variability in biodiversity responses to loss of native riparian vegetation suggests caution in the use of a single riparian width for conservation actions or policy definitions nationwide. The most sensitive bioindicators can be used as early warning signals of abrupt changes in freshwater biodiversity. In practice, maintaining at least 50‐m wide riparian reserves on each side of streams would be more effective to protect freshwater biodiversity in Brazil. However, incentives and conservation strategies to protect even wider riparian reserves (~100 m) and also taking into consideration the regional context will promote a greater benefit. This information should be used to set conservation goals and to create complementary mechanisms and policies to protect wider riparian reserves than those currently required by the federal law.
Resumo
Proteger a vegetação no entorno de riachos é vital para reduzir os efeitos das mudanças ambientais sobre os ecossistemas aquáticos e para a manutenção de sua biodiversidade. Assim, a identificação de limiares ecológicos é útil para regular os limites de uso e para orientar o manejo de zonas ripárias, visando a conservação da biota aquática.
Usando dados de peixes e invertebrados aquáticos de pequenos riachos do Brasil, nós estimamos os limiares de perda de vegetação nativa nos quais ocorrem mudanças abruptas na ocorrência e abundância de bioindicadores aquáticos. Também testamos se existem respostas congruentes entre os diferentes biomas, grupos biológicos e áreas de vegetação ripária (buffers).
Os valores médios dos limiares de perda de vegetação nativa variaram marcadamente entre biomas, tamanhos de buffer e grupos biológicos: entre 0,5% e 77,4% para peixes, entre 2,9% e 37,0% para invertebrados aquáticos e entre 3,8% e 43,2% para um subconjunto de invertebrados aquáticos. Os intervalos de confiança dos limiares foram amplos, mas os valores mínimos dos intervalos foram reduzidos para os menores buffers ripários (50 e 100 m) em comparação com os maiores (200 e 500 m), indicando que o uso do solo deve ser mantido longe dos riachos. Além disso, os limiares ocorreram em menores porcentagens de perda de vegetação ripária nos buffers menores, e foram criticamente baixos para invertebrados aquáticos: uma redução de apenas 6,5% da cobertura de vegetação nativa no buffer ripário de 50 m é suficiente para ultrapassar os limiares de perda de invertebrados.
Síntese e aplicações. A elevada variabilidade dos limiares de declínio abrupto da biodiversidade aquática em resposta a perda de vegetação ripária nativa sugere cautela no uso de uma largura única de proteção ripária para ações de conservação e definição de políticas nacionais. Os bioindicadores mais sensíveis podem ser usados como sinais precoces que alertam a aproximação de mudanças abruptas na biodiversidade aquática. Na prática, manter reservas ripárias (áreas de preservação permanente—APP) de pelo menos 50 m de largura, em ambos os lados dos riachos, parece ser mais efetivo em proteger a biodiversidade de água doce do Brasil. Contudo, incentivos e estratégias de conservação que protejam reservas ripárias ainda maiores (~100 m de largura) e que levem em consideração o contexto regional podem promover um maior benefício. Essas informações podem ser usadas para definir metas de conservação e para criar mecanismos e políticas complementares para proteger reservas ripárias (APP) ainda maiores do que aquelas atualmente requeridas pela lei federal.
The high variability in biodiversity responses to loss of native riparian vegetation suggests caution in the use of a single riparian width for conservation actions or policy definitions nationwide. The most sensitive bioindicators can be used as early warning signals of abrupt changes in freshwater biodiversity. In practice, maintaining at least 50‐m wide riparian reserves on each side of streams would be more effective to protect freshwater biodiversity in Brazil. However, incentives and conservation strategies to protect even wider riparian reserves (~100 m) and also taking into consideration the regional context will promote a greater benefit. This information should be used to set conservation goals and to create complementary mechanisms and policies to protect wider riparian reserves than those currently required by the federal law.
Consider both water and land
When designing terrestrial reserves, it is common to consider the needs of species and systems from a terrestrial perspective, with an assumption that any freshwater ...systems will benefit as well. Leal
et al.
tested this assumption by analyzing data from two locations in the Brazilian Amazon and found that it is far from accurate: Terrestrial systems confer little benefit to freshwater systems (see the Perspective by Abell and Harrison). However, the authors also found that integrating the needs of freshwater species into overall reserve planning increased freshwater benefits by 600% while only decreasing terrestrial outcomes by 1%. They argue that reserve planning must take freshwater systems into account if they are to protect across both realms.
Science
, this issue p.
117
; see also p.
38
A study of terrestrial and freshwater species in the Amazon suggests that the conservation needs of freshwater species need to be actively considered.
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.
Stream degradation in Amazonia is outpacing our ability to effectively monitor it for three key reasons: (1) Many changes are cumulative and occur gradually; (2) Scientists have failed to clearly ...link anthropogenic disturbances with ecological and economic indicators of concern to decision makers and the public; (3) There are too many potential indicators to assess in a cost-effective manner. Therefore, we sought to assess congruency at three taxonomic resolutions (species, genus and family) and between assemblages (fish species and macroinvertebrate genera) and groups of taxa (fish: Characiformes and Siluriformes; macroinvertebrates: Anisoptera, Heteroptera, Odonata, Trichoptera, Zygoptera, EPT Ephemeroptera, Plecoptera and Trichoptera and THZ Trichoptera, Heteroptera and Zygoptera). To do so, we assessed taxonomic, land-use and habitat data from 92 stream sites in the eastern Amazonian state of Pará. We found that anthropogenic disturbances of our sites influenced abundance and incidence of macroinvertebrate and fish taxa, but the two assemblages responded to slightly different stressors. Family and genera levels were suitable substitutes for similarity patterns measured at the macroinvertebrate genera and fish species levels, respectively. Odonata, Trichoptera, EPT and THZ were highly congruent with whole macroinvertebrate assemblage (genus level) variation. Characiformes was also congruent with whole fish assemblage (species level) variation. Congruence among macroinvertebrates and fish was intermediate (55% to 79%) and related to differing responses to environmental variables. Our results suggest that some groups (e.g., Odonata, Trichoptera and Characiformes) are useful surrogates of macroinvertebrate or fish assemblages to evaluate anthropogenic disturbance in Amazonian streams.
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