Trait–environment relationships in Amazon stream fish assemblages

Studies of trait–environment relationships provide important tools for the prediction of the response of biological communities to environmental alterations. The Amazon basin presents enormous potential for the development of research on this type of relationship, given the diversity of both its fish fauna and the aquatic ecosystems this fauna inhabits. The present study investigated the association between local environmental variables and the functional traits of fish in 54 streams of six major Amazonian basins. We identified the relationship between the characteristics of the streams (channel morphology, channel habitat units, riparian vegetation cover, large woody fragments and instream cover for aquatic organisms) and fish traits related to locomotion, habitat use and feeding behaviour. The fish fauna of the broader, deeper and more slowly flowing streams was dominated by nektobenthic species that exploit autochthonous resources such as fish and invertebrates. In narrow, fast‐flowing streams, by contrast, there was a predominance of benthic fishes with varying feeding habits, including periphytivorous and invertivorous species. Narrow, shady streams were inhabited by nektonic species adapted for the exploitation of resources from the marginal vegetation. The results of this study contribute to the understanding of the association between the functional structure of fish assemblages and local environmental variables in Amazonian streams. We hope that these findings will stimulate further research into the natural variation in stream fish assemblages that will ensure the development of more effective management strategies that better protect these important aquatic ecosystems.     

Trait‐based ecology of fishes: A quantitative assessment of literature trends and knowledge gaps using topic modelling

Species traits are a new data currency to enhance our understanding of ecological patterns and processes. Trait‐based studies of fishes are numerous in comparison with other animal groups, reflecting the diversity of fish forms and functions they provide to aquatic ecosystems. We conduct a retrospective examination of literature to identify knowledge gaps and provide guidance for future research in trait‐based fish ecology. We apply an automated text mining and topic modelling to track the evolution of research topics within peer‐reviewed articles of functional traits in marine and freshwater fishes published over the past half century, explore the inter‐connections among those topics and identify emerging avenues for investigation. By mapping the topic landscape of the literature, 16 latent topics emerged that vary in their prevalence. Our results show a decline in the frequency of studies using reproductive traits to model and explore the way fish allocate energy for reproduction, and increase in studies reporting functional diversity metrics and utilizing the concept of multivariate functional space. Research focused on contributions of fish traits to ecosystem functioning also has increased in frequency. We revealed large gaps in information between growing and decreasing topics and that these gaps were derived from different types of traits being considered. We suggest that scientists break‐free from the traditions of their research field by targeting investigations that: (a) apply functional diversity metrics to a broader assortment of traits, (b) focus on traits influencing energy allocation to growth/reproduction and (c) integrate trophic‐web and behavioural studies with other topics.     

Biogeographical region and environmental conditions drive functional traits of estuarine fish assemblages worldwide

Assessing trait–environment relationships is crucial for predicting effects of natural and human‐induced environmental change on biota. We compiled a global database of fish assemblages in estuaries, functional traits of fishes and ecosystem features of estuaries. And we quantified the relative importance of ecosystem features as drivers of patterns of fish functional traits among estuaries worldwide (i.e. drivers of the proportions of fish traits). In addition to biogeographical context, two main environmental gradients regulate traits patterns: firstly temperature, and secondly estuary size and hydrological connectivity of the estuary with the marine ecosystem. Overall, estuaries in colder regions, with larger areas and with higher hydrological connectivity with the marine ecosystem, have higher proportions of marine fish (versus freshwater), macrocarnivores and planktivores (versus omnivores, herbivores and detritivores) and larger fish, with greater maximum depth of distribution and longer lifespan. The observed trait patterns and trait–environment relationships are likely generated by multiple causal processes linked to physiological constraints due to temperature and salinity, size‐dependent biotic interactions, as well as habitat availability and connectivity. Biogeographical context and environmental conditions drive species richness and composition, and present results show that they also drive assemblage traits. The observed trait patterns and trait–environment relationships suggest that assemblage composition is determined by the functional role of species within ecosystems. Conservation strategies should be coordinated globally and ensure protection of an array of estuaries that differ in ecosystem features, even if some of those estuaries do not support high species richness.     

Realizing the potential of trait‐based approaches to advance fisheries science

Analysing how fish populations and their ecological communities respond to perturbations such as fishing and environmental variation is crucial to fisheries science. Researchers often predict fish population dynamics using species‐level life‐history parameters that are treated as fixed over time, while ignoring the impact of intraspecific variation on ecosystem dynamics. However, there is increasing recognition of the need to include processes operating at ecosystem levels (changes in drivers of productivity) while also accounting for variation over space, time and among individuals. To address similar challenges, community ecologists studying plants, insects and other taxa increasingly measure phenotypic characteristics of individual animals that affect fitness or ecological function (termed “functional traits”). Here, we review the history of trait‐based methods in fish and other taxa, and argue that fisheries science could see benefits by integrating trait‐based approaches within existing fisheries analyses. We argue that measuring and modelling functional traits can improve estimates of population and community dynamics, and rapidly detect responses to fishing and environmental drivers. We support this claim using three concrete examples: how trait‐based approaches could account for time‐varying parameters in population models; improve fisheries management and harvest control rules; and inform size‐based models of marine communities. We then present a step‐by‐step primer for how trait‐based methods could be adapted to complement existing models and analyses in fisheries science. Finally, we call for the creation and expansion of publicly available trait databases to facilitate adapting trait‐based methods in fisheries science, to complement existing public databases of life‐history parameters for marine organisms.     

Influence of forest cover and mesohabitat types on functional and taxonomic diversity of fish communities in Neotropical lowland streams

Abstract – In this study, we investigated how taxonomic and functional diversity of fish communities is influenced by forest cover and mesohabitat types in Neotropical lowland streams. We sampled fish fauna of 126 five‐metre‐long mesohabitats using an electrofishing unit in forested (n = 3) and deforested (n = 3) streams in the upper Paraná River basin, south‐eastern Brazil. According to velocity and depth, three mesohabitat types have been considered: riffles (shallow and fast‐flowing habitat), pools (deep and slow‐flowing habitat) and runs (intermediate depth and velocity). Seven functional traits and 27 trait categories related to ecological, behavioural and life‐history aspects of fish were considered. Our results indicate that forest cover and mesohabitat type influence fish communities in different ways. Whereas deforestation affects communities primarily through changes in diversity (functional and taxonomic), mesohabitat types determine changes in the functional composition. The increased diversity in deforested mesohabitats is driven by a decrease in species turnover among habitat patches within streams. This can be attributed to new feeding opportunities and microhabitat availabilities in deforested streams so favours the occurrence of species having a particular set of traits, indicating a strong habitat–trait relationship.     

Unintended consequences and trade‐offs of fish passage

We synthesized evidence for unintended consequences and trade‐offs associated with the passage of fishes. Provisioning of fish passageways at dams and dam removals are being carried out increasingly as resource managers seek ways to reduce fragmentation of migratory fish populations and restore biodiversity and nature‐like ecosystem services in tributaries altered by dams. The benefits of provisioning upstream passage are highlighted widely. Possible unwanted consequences and trade‐offs of upstream passage are coming to light, but remain poorly examined and underappreciated. Unintended consequences arise when passage of native and desirable introduced fishes is delayed, undone (fallback), results in patterns of movement and habitat use that reduce Darwinian fitness (e.g. ecological traps), or is highly selective taxonomically and numerically. Trade‐offs arise when passage decisions intended to benefit native species interfere with management decisions intended to control the unwanted spread of non‐native fishes and aquatic invertebrates, or genes, diseases and contaminants carried by hatchery and wild fishes. These consequences and trade‐offs will vary in importance from system to system and can result in large economic and environmental costs. For some river systems, decisions about how to manage fish passage involve substantial risks and could benefit from use of a formal, structured process that allows transparent, objective and, where possible, quantitative evaluation of these risks. Such a process can also facilitate the design of an adaptive framework that provides valuable insights into future decisions.     

海洋牧场生态系统稳定性及其对干扰的响应—研究现状、问题及建议

海洋牧场建设是实现我国近海渔业资源恢复、生态系统和谐发展与蓝碳增汇的重要途径。近年来,在快速发展的同时也面临着诸多问题与挑战,极大制约了产业的健康发展。在海洋牧场建设过程中,关于生境营造和资源增殖的基础理论薄弱,对其生态系统稳定性与抗干扰能力认识不清,尤其对小尺度海洋牧场生态系统的结构及其功能实现过程,以及生态承载力知之甚少。亟需针对其人工鱼礁等生境营造的环境效应和增殖放流的资源补充效应开展理论印证和定量研究,以充分认识这些人为扰动的双重性。本文查阅了相关文献90余篇,简要回顾了国内外关于人工鱼礁生境营造的水动力环境特征、生源要素迁移过程、生物群落构建机制和局地生态系统稳定性评价等方面的研究进展。强调了小尺度海洋牧场生态系统结构的复杂性与动态性,重点关注了鱼礁群布局对牧场海域水动力环境、沉积物和生源要素演变的影响,以及在增殖放流等人为扰动下生物群落的物种共存机制。围绕海洋牧场生态系统稳定性与抗干扰能力等关键问题,从水动力驱动、生源要素表征、生物群落重建及生态系统健康等4个方面探讨了目前研究的不足与发展方向,以为海洋牧场人工鱼礁、海藻床等生境营造以及资源修复模式优化提供参考。     

Fish trait diversity in littorals of two floodplain lakes of the highly biodiverse Caura River,Venezuela

We studied the trait diversity and structure in the fish communities of two floodplain lakes of the Caura River: Aricagua and Paramuto, during one hydrological cycle. We calculated taxonomic and a functional alpha and beta diversities and made comparisons among hydrological seasons and among habitats within each lake based on rarefactions. The trait structure was explored with an RLQ (analysis of a table R of environmental conditions, a table L of abundances of species and a table Q of species traits) analysis, and pairwise relationships between environmental variables and traits were explored with fourth‐corner analyses. Despite its smaller extension, Paramuto showed higher alpha taxonomic and trait diversities. The substrates of open sand and those covered by leaf litter were the most diverse habitats in terms of both species and traits. The trait structure of the fish communities was influenced by the hydrological seasons, the lakes as well as water pH and temperature, and in a lesser degree dissolved oxygen, habitat type and total dissolved solids in the water. These factors constitute the habitat templet for the fish community's composition and trait structure.     

Restricted movement of prairie fishes in fragmented riverscapes risks ecosystem structure being ratcheted downstream

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Fishes and the environmental status of South African estuaries

Abstract More than 100 fish species are associated with southern African estuaries, many of which are caught by recreational anglers and/or commercial fishermen. Mismanagement of either a catchment or an estuary invariably leads to an impoverished system which is of little value to fishes or people. By taking this cause-and-effect scenario to its logical conclusion, it should be possible to assess the ‘state’ of an estuary by monitoring the biological ‘health’ of the aquatic community. Fishes are a dominant and highly visible component of the estuarine fauna and, by virtue of their key positions in the aquatic food web, can reflect either natural or anthropogenic alterations to the environment. In addition, their mobility enables them to respond rapidly to both deteriorating and improving estuarine conditions. Such attributes may assist scientists and managers in being better able both to assess the magnitude of detrimental impacts, and to monitor the ecosystem response to ameliorative actions. This paper attempts to show that an understanding of the biology and ecology of fishes associated with estuaries can lead to the identification of threats to the environment and result in improved management of these systems. The use of fish communities as an indicator of estuarine health is also examined, and ways of incorporating biological and ecological data into decision-support systems are discussed. The adoption of a set of environmental quality objectives for South African estuaries, together with a system of appropriate environmental quality standards, is recommended.     

河流生态系统结构功能模型研究

回顾了河流生态系统结构功能模型的研究进展，介绍了多种重要的概念和模型。在此基础上，提出了河流生态系统结构功能整体模型，它是由河流流态－生态结构功能４维连续体模型、水文情势－河流生态过程耦合模型、地貌景观空间异质性－生物群落多样性耦合模型３个子模型组成。整体模型建立了河流流态、水文情势和地貌景观这３大类生境因子与河流生态系统结构功能和生态过程的相关关系，基本上抽象概括了河流生态系统的主要特征。在模型中除了考虑自然力因素以外，还考虑了水利水电工程设施的干扰作用。     

Functional aquatic ecosystems,inland fisheries and the Millennium Development Goals

Freshwater allocation in an environment of increasing demand and declining quality and availability is a major societal challenge. While biodiversity and the needs of local communities are often in congruence, the over‐riding necessity of meeting national demands for power, food and, increasingly, mitigation of the hydrological effects of climate change, often supersedes these. Sophisticated models of ecosystem function to establish environmental flows are difficult to implement and consequently have generally failed to reduce rates of biodiversity and habitat loss, resulting in disenfranchisement of local communities resulting from dam construction and water abstraction for industry and agriculture. There are no agreed standards upon which a fairer allocation of resources can be made and thus a pragmatic approach to the resolution of these conflicts is clearly needed. While having generally negative impacts on biodiversity and traditional lifestyles, creation of new infrastructure and active management generates national economic growth and much‐needed employment. Intensification of usage in watersheds already expropriated for human enterprise can spare land needed for the biodiversity that will fuel adaptation for the future. Taking advantage of a range of mitigation technologies and building their cost into the investment plans for water management infrastructure can improve the cost/benefit ratio of water control infrastructure and may be a more practical and efficacious approach to the valuation of fisheries and the maintenance of other essential services from functional aquatic ecosystems.     

Selection on the timing of migration and breeding: A neglected aspect of fishing‐induced evolution and trait change

Fishing can drive changes in important phenotypic traits through plastic and evolutionary pathways. Size‐selective harvest is a primary driver of such trait change, has received much attention in the literature and is now commonly considered in fisheries management. The potential for selection on behavioural traits has received less study, but mounting evidence suggests that aggression, foraging behaviour and linked traits can also be affected by fishing. An important phenomenon that has received much less attention is selection on reproductive phenology (i.e., the timing of breeding). The potential for this type of “temporal selection” is widespread because there is often substantial variability in reproductive phenology within fish populations, and fisheries management strategies or fishermen's behaviours can cause fishing effort to vary greatly over time. For example, seasonal closures may expose only early or late breeding individuals to harvest as observed in a range of marine and freshwater fisheries. Such selection may induce evolutionary responses in phenological traits, but can also have demographic impacts such as shortened breeding seasons and reduced phenotypic diversity. These changes can in turn influence productivity, reduce the efficacy of management, exacerbate ongoing climate‐driven changes in phenology and reduce resilience to environmental change. In this essay, we describe how fisheries management can cause temporal variability in harvest, and describe the types of selection on temporal traits that can result. We then summarize the likely biological consequences of temporally selective fishing on populations and population complexes and conclude by identifying areas for future research.     

Dam cascade in run-of-river systems promotes homogenisation of fish functional traits in a plateau river

Impoundments caused by dams are often responsible for intense changes in physical, chemical, geomorphological and hydrological characteristics of rivers, and are one of the main causes in global freshwater biodiversity declines. When these changes derive from multiple cascading dams, the cumulative effect can amplify, causing more pronounced consequences than each individual reservoir, which may affect, among other factors, the biotic and functional conditions of fish fauna. We aim to evaluate the impact of dam cascades on fish functional diversity by applying trait-based analysis. We evaluate the functional attributes (functional indices and community-weighted means of trait values) and environmental variables at 11 sites, which encompassed different segments affected by the hydroelectric plants (transition, reservoir, reduced discharge section and tributary) in the Antas River Basin dam cascade system located in southern Brazil. The spatial differences of the functional indices (richness, evenness, divergence, dispersion and diversity) as well as the weighted averages of each functional trait were tested through analysis of variance. The most affected functional characteristics were those related to habitat exploration by detritivorous species, especially the use of food resources and body shape, as well as the type of swimming movement. These traits were more representative at the most downstream site of the complex. Thus, our results suggest that the cascade of dams acts in the functional homogenisation of the ichthyofauna in the intermediate stretches, mainly reflecting physical changes in habitat.     

The role of floods and droughts on riverine ecosystems under a changing climate

Floods and droughts are key driving forces shaping aquatic ecosystems. Climate change may alter key attributes of these events and consequently health and distribution of aquatic species. Improved knowledge of biological responses to different types of floods and droughts in rivers should allow the better prediction of the ecological consequences of climate change‐induced flow alterations. This review highlights that in unmodified ecosystems, the intensity and direction of biological impacts of floods and droughts vary, but the overall consequence is an increase in biological diversity and ecosystem health. To predict the impact of climate change, metrics that allow the quantitative linking of physical disturbance attributes to the directions and intensities of biological impacts are needed. The link between habitat change and the character of biological response is provided by the frequency of occurrence of the river wave characteristic—that is the event's predictability. The severity of impacts of floods is largely related to the river wave amplitude (flood magnitude), while the impact of droughts is related to river wavelength (drought duration).     

Macroalgal meadow habitats support fish and fisheries in diverse tropical seascapes

Canopy‐forming macroalgae can construct extensive meadow habitats in tropical seascapes occupied by fishes that span a diversity of taxa, life‐history stages and ecological roles. Our synthesis assessed whether these tropical macroalgal habitats have unique fish assemblages, provide fish nurseries and support local fisheries. We also applied a meta‐analysis of independent surveys across 23 tropical reef locations in 11 countries to examine how macroalgal canopy condition is related to the abundance of macroalgal‐associated fishes. Over 627 fish species were documented in tropical macroalgal meadows, with 218 of these taxa exhibiting higher local abundance within this habitat (cf. nearby coral reef) during at least one life‐history stage. Major overlap (40%–43%) in local fish species richness among macroalgal and seagrass or coral reef habitats suggest macroalgal meadows may provide an important habitat refuge. Moreover, the prominence of juvenile fishes suggests macroalgal meadows facilitate the triphasic life cycle of many fishes occupying diverse tropical seascapes. Correlations between macroalgal canopy structure and juvenile abundance suggests macroalgal habitat condition can influence levels of replenishment in tropical fish populations, including the majority of macroalgal‐associated fishes that are targeted by commercial, subsistence or recreational fisheries. While many macroalgal‐associated fishery species are of minor commercial value, their local importance for food and livelihood security can be substantial (e.g. up to 60% of landings in Kenyan reef fisheries). Given that macroalgal canopy condition can vary substantially with sea temperature, there is a high likelihood that climate change will impact macroalgal‐associated fish and fisheries.     

Size‐based sexual dimorphism of nitrogen excretion in livebearing fishes

Nitrogen (N) and phosphorus (P) are important limiting or co‐limiting nutrients in many aquatic ecosystems. Consumers such as fishes can significantly impact the balance and redistribution of these nutrients through consumer‐driven nutrient recycling. Intraspecific variation in nutrient excretion rates can therefore have significant ecosystem impacts. Among individuals of sexually dimorphic consumers, variation in population size structure and sex ratio could potentially have impacts of similar magnitude. We tested for the effects of body size and sex on consumer‐driven nutrient recycling by measuring N and P excretion rates from eight species of poeciliid fishes. We found a strong positive effect of size on N excretion rates, as has been previously described among species. However, we found no effect of size on P excretion rates, nor did we find any difference in N or P excretion rates between sexes. Our work provides a preliminary analysis of how sexual dimorphism can lead to disparate nutrient excretion rates within consumer populations. These results indicate that variation in population sex ratios of sexually dimorphic consumers could have impacts at the ecosystem scale.     

Beyond Individual Transferrable Quotas: methodologies for integrating ecosystem impacts of fishing into fisheries catch rights

While there has been a growing concern for the adverse ecological impacts of fishing, progress on incorporating these into operational fisheries management has been slow. Many fisheries management organizations have addressed the problem of overharvesting and over‐capitalization first. In this domain, the question of access regulation has gained growing recognition as a key dimension of fisheries sustainability, leading to recommendation and progressive implementation of rights‐based systems, in particular Individual Transferrable Quotas (ITQs). While adjustments in fishing capacity resulting from the implementation of these systems may entail a reduction in some unwanted ecosystem impacts of fishing, it is also recognized that they will not be sufficient to achieve the ecological outcomes increasingly demanded by the global community. There is thus a need to examine the possibilities for a common management framework for dealing with both over‐capitalization of fisheries and adverse ecological effects of fishing. In this paper, we examine the feasibility of incorporating greater ecosystem goods and services into ITQ policy instruments initially designed with a narrow focus on commercial target species. We consider the advantages and limitations of alternative approaches in this respect and identify some of the practical issues associated with the different alternatives, in particular the underpinning knowledge requirements. We argue that given the need for increasingly streamlined management processes, further investigation into practical ways forward in this domain is crucial if management of fisheries is to achieve economic efficiency while fully encompassing the ecologically sustainable development objectives of ecosystem‐based fisheries management.     

Heads you win,tails you lose: Life‐history traits predict invasion and extinction risk of the world's freshwater fishes

1. Freshwater fishes have the distinction of being both a highly imperilled taxonomic group as well as one that has produced many invasive species with widespread ecological impacts. Faced with the difficult task of identifying those species with the greatest need for management action, ecologists have turned to using predictive suites of ecological and life‐history traits to provide reasonable estimates of fish invasion and extinction risk. Whether traits associated with invasiveness are the inverse of those associated with imperillment, known as the ‘two‐sides‐of‐the‐same‐coin’ hypothesis, remains unclear.
2. A global trait analysis (including maximum total body size, longevity, size at maturation, age at maturation, fecundity and egg size) for 6293 freshwater fishes was conducted to examine the trait correlates of species proneness to invasion or extinction. A meta‐analytical procedure was deployed using univariate and multivariate trait analyses that accounted for the effects of shared phylogeny.
3. Mean trait differences (measured as Hedges' d effect size) were found between invasive and threatened species when compared with native species, thus supporting the two‐sides‐of‐the‐same‐coin hypothesis for freshwater fish. Invasive species were characterized by larger body size, greater longevity, delayed maturation and higher fecundity than threatened species. Furthermore, invasive species were found to display greater trait variability compared with threatened species, suggesting that different traits may be selected at different stages of the invasion process (from pathway entrainment to establishment) whereas more specific trait combinations may predispose species to higher extinction risk.
4. The present study demonstrated a strong trait basis to global‐scale invasion risk and extinction vulnerability for freshwater fishes. Given that both time and resources are too limited for detailed species‐by‐species assessments, the results suggest that trait correlates provide a reasonable estimate of invasion and extinction risk that can inform more targeted and proactive conservation strategies.