Testing local and global stressor impacts on a coastal foundation species using an ecologically realistic framework

Despite the abundance of literature on organismal responses to multiple environmental stressors, most studies have not matched the timing of experimental manipulations with the temporal pattern of stressors in nature. We test the interactive effects of diel‐cycling hypoxia with both warming and decreased salinities using ecologically realistic exposures. Surprisingly, we found no evidence of negative synergistic effects on Olympia oyster growth; rather, we found only additive and opposing effects of hypoxia (detrimental) and warming (beneficial). We suspect that diel‐cycling provided a temporal refuge that allowed physiological compensation. We also tested for latent effects of warming and hypoxia to low‐salinity tolerance using a seasonal delay between stressor events. However, we did not find a latent effect, rather a threshold survival response to low salinity that was independent of early life‐history exposure to warming or hypoxia. The absence of synergism is likely the result of stressor treatments that mirror the natural timing of environmental stressors. We provide environmental context for laboratory experimental data by examining field time series environmental data from four North American west coast estuaries and find heterogeneous environmental signals that characterize each estuary, suggesting that the potential stressor exposure to oysters will drastically differ over moderate spatial scales. This heterogeneity implies that efforts to conserve and restore oysters will require an adaptive approach that incorporates knowledge of local conditions. We conclude that studies of multiple environmental stressors can be greatly improved by integrating ecologically realistic exposure and timing of stressors found in nature with organismal life‐history traits.     

Quantifying the evidence for ecological synergies

There is increasing concern that multiple drivers of ecological change will interact synergistically to accelerate biodiversity loss. However, the prevalence and magnitude of these interactions remain one of the largest uncertainties in projections of future ecological change. We address this uncertainty by performing a meta-analysis of 112 published factorial experiments that evaluated the impacts of multiple stressors on animal mortality in freshwater, marine and terrestrial communities. We found that, on average, mortalities from the combined action of two stressors were not synergistic and this result was consistent across studies investigating different stressors, study organisms and life-history stages. Furthermore, only one-third of relevant experiments displayed truly synergistic effects, which does not support the prevailing ecological paradigm that synergies are rampant. However, in more than three-quarters of relevant experiments, the outcome of multiple stressor interactions was non-additive (i.e. synergies or antagonisms), suggesting that ecological surprises may be more common than simple additive effects.     

Coastal and estuarine ecological risk assessment: the need for a more formal approach to stressor identification

Application of ecological risk assessment to coastal and estuarine systems is accelerating although it initially lagged behind applications to land and freshwaters. Broader spatial and temporal scales, and multiple stressor integration are appropriately being considered more frequently in all risk assessment activities. This expansion and integration is essential for coastal risk assessment. Because coastal assessments must deal with co-occurrence of several candidate stressors manifesting within broad spatial and temporal scales, wider use of formal methods for assessing causal linkages is needed. Simple Bayesian inference techniques are discussed here to demonstrate their utility in quantifying the belief warranted by available information. The applicability of Bayesian techniques is illustrated with two examples, possible causes of fish kills on the Mid-Atlantic US coast and possible causes of hepatic lesions in fish of Puget Sound (Washington, US).     

Conceptualizing ecosystem tipping points within a physiological framework

Connecting the nonlinear and often counterintuitive physiological effects of multiple environmental drivers to the emergent impacts on ecosystems is a fundamental challenge. Unfortunately, the disconnect between the way “stressors” (e.g., warming) is considered in organismal (physiological) and ecological (community) contexts continues to hamper progress. Environmental drivers typically elicit biphasic physiological responses, where performance declines at levels above and below some optimum. It is also well understood that species exhibit highly variable response surfaces to these changes so that the optimum level of any environmental driver can vary among interacting species. Thus, species interactions are unlikely to go unaltered under environmental change. However, while these nonlinear, species‐specific physiological relationships between environment and performance appear to be general, rarely are they incorporated into predictions of ecological tipping points. Instead, most ecosystem‐level studies focus on varying levels of “stress” and frequently assume that any deviation from “normal” environmental conditions has similar effects, albeit with different magnitudes, on all of the species within a community. We consider a framework that realigns the positive and negative physiological effects of changes in climatic and nonclimatic drivers with indirect ecological responses. Using a series of simple models based on direct physiological responses to temperature and ocean pCO₂, we explore how variation in environment‐performance relationships among primary producers and consumers translates into community‐level effects via trophic interactions. These models show that even in the absence of direct mortality, mismatched responses resulting from often subtle changes in the physical environment can lead to substantial ecosystem‐level change.     

Motifs in bipartite ecological networks: uncovering indirect interactions

Indirect interactions play an essential role in governing population, community and coevolutionary dynamics across a diverse range of ecological communities. Such communities are widely represented as bipartite networks: graphs depicting interactions between two groups of species, such as plants and pollinators or hosts and parasites. For over thirty years, studies have used indices, such as connectance and species degree, to characterise the structure of these networks and the roles of their constituent species. However, compressing a complex network into a single metric necessarily discards large amounts of information about indirect interactions. Given the large literature demonstrating the importance and ubiquity of indirect effects, many studies of network structure are likely missing a substantial piece of the ecological puzzle. Here we use the emerging concept of bipartite motifs to outline a new framework for bipartite networks that incorporates indirect interactions. While this framework is a significant departure from the current way of thinking about bipartite ecological networks, we show that this shift is supported by analyses of simulated and empirical data. We use simulations to show how consideration of indirect interactions can highlight differences missed by the current index paradigm that may be ecologically important. We extend this finding to empirical plant–pollinator communities, showing how two bee species, with similar direct interactions, differ in how specialised their competitors are. These examples underscore the need to not rely solely on network‐ and species‐level indices for characterising the structure of bipartite ecological networks.     

Using a network framework to quantitatively select ecological indicators

Ecological indicators are often constructed as an integrated set to represent key information and characteristics of the ecosystem which are tightly linked to management objectives. As an effective tool, ecological indicators play an increasingly important role in ecosystem monitoring, assessment and management. Reasonable selection of an indicator is a prerequisite for effectively using it. A defined protocol with scientific rigor to select ecological indicators is imperative to solve the challenges in ecological indicator selection. This paper compares the Causal Network (CN) with the Ecological Hierarchy Network (EHN) as a framework to select ecological indicators. These frameworks are not exclusive but interdependent in constructing a network framework. Based on the network framework, a quantitative ecological indicator selection method is demonstrated through a theoretical example. In the selection process, the criteria and requirements considering the balance of science and utility are proposed and translated into quantitative constraints of a selection model. By resolving the model under a mathematical operation, the human arbitrary disturbance will be reduced and random selection minimized.     

Contribution of Chemoautotrophic Production to Freshwater Macroinvertebrates in a Headwater Stream Using Multiple Stable Isotopes

We estimated the food sources of macroinvertebrates using carbon, nitrogen, and sulfur stable isotopes in a headwater stream. Stream food webs, including macroinvertebrates, rely on production from autochthonous and allochthonous photosynthesis. We found that a freshwater grazer, the snail Semisulcospira libertina, may assimilate different food sources, based on stable carbon and nitrogen isotope evidence from snail muscle and the much lighter sulfur isotope signature than those of other associated macroinvertebrates. Previous studies have shown the importance of methanotrophic and sulfur bacteria in reductive environments (clay and organic‐rich sediments) as food sources for macroinvertebrates. Our results show that the production by chemoautotrophic bacteria contributes to the food sources of a snail in a stream. Thus, the chemoautotrophic bacteria are important in the freshwater food webs, even in mostly aerobic habitats. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

食物网稳定性机制研究进展:一个基于等级系统的框架

食物网理论沟通了群落生态学和生态系统生态学,将生物多样性和生态系统功能的研究统一起来,是理解生态系统运作机制的关键。自从1973年Robert May的经典研究引发著名的"复杂性-稳定性"论辩之后,人们认识到食物网的稳定性是其结构维持、功能发挥和动态演化的一个重要前提,并开始了对食物网稳定性机制的探索。早期研究主要关注只包含拓扑关系的定性食物网,但后来人们逐渐认识到相互作用强度的重要性,并提出了诸如自限性、弱相互作用、适应性捕食等一系列机制。本文系统梳理了过往研究中模块层面的各类稳定性机制和全网层面对各模块的整合机制,从而清晰地展示了"模块-全网"双层框架的全貌。通过在其基础上的扩展,进而提出了一个基于等级系统的食物网稳定性框架,并从动力学和能量学角度,对各层级内部的稳定性机制以及层级之间的关系进行了探讨,以期为建立普适的食物网稳定性理论提供一些思路。未来的研究方向包括：①将稳定性机制的研究从食物网扩展到更一般的生态网络;②综合考虑生物物理要素、动力学稳定性、系统对能流功率的追求、环境的平稳程度、演化历史等影响因素,从而得到关于食物网结构和动态的更为深刻的认识。     

Parasite prevalence in an intermediate snail host is subject to multiple anthropogenic stressors in a New Zealand river system

Most ecosystems are exposed to multiple stressors acting in concert and their combined effects on parasite prevalence in freshwater, marine and terrestrial habitats are largely unknown. We investigated the relationships between farming intensity, water abstraction intensity and parasite prevalence in the mud snail Potamopyrgus antipodarum from 20 stream sites within the Manuherikia River catchment (New Zealand) by using generalized linear models and an information-theoretic model-selection approach. Three trematode taxa that use water birds as definitive hosts were found in the snail host. The average prevalence of all parasites infecting Potamopyrgus in the catchment was 5%. Microphallus sp. “lively”, the most common parasite, was most prevalent at high farming intensity and low water abstraction, besides showing an antagonistic interaction between the two agricultural stressors. These findings highlight the importance of considering multiple stressors and their potential interactions when studying host–parasite systems. Because snails often play key roles in aquatic communities, providing an important link between primary producers and higher trophic levels, and are a common intermediate host to a high diversity of trematode parasites, this host–parasite model system may represent a promising bioassessment tool for detecting anthropogenic disturbances in freshwater systems.     

Stressor interactions in freshwater habitats: Effects of cold water exposure and food limitation on early‐life growth and upper thermal tolerance in white sturgeon,Acipenser transmontanus

相似文献   

Using the AMOVA framework to estimate a standardized genetic differentiation measure

Comparison of population structure between studies can be difficult, because the value of the often-used FST-statistic depends on the amount of genetic variation within populations. Recently, a standardized measure of genetic differentiation was developed based on GST, which addressed this problem, though no method was provided to estimate this standardized measure without bias. Here I present a method to estimate a standardized measure of population differentiation based on the analysis of molecular variance framework. One advantage of the method is that it can be readily expanded to include different hierarchical levels in the tested population structure.     

Approaches to integrating genetic data into ecological networks

As molecular tools for assessing trophic interactions become common, research is increasingly focused on the construction of interaction networks. Here, we demonstrate three key methods for incorporating DNA data into network ecology and discuss analytical considerations using a model consisting of plants, insects, bats and their parasites from the Costa Rica dry forest. The simplest method involves the use of Sanger sequencing to acquire long sequences to validate or refine field identifications, for example of bats and their parasites, where one specimen yields one sequence and one identification. This method can be fully quantified and resolved and these data resemble traditional ecological networks. For more complex taxonomic identifications, we target multiple DNA loci, for example from a seed or fruit pulp sample in faeces. These networks are also well resolved but gene targets vary in resolution and quantification is difficult. Finally, for mixed templates such as faecal contents of insectivorous bats, we use DNA metabarcoding targeting two sequence lengths (157 and 407 bp) of one gene region and a MOTU, BLAST and BIN association approach to resolve nodes. This network type is complex to generate and analyse, and we discuss the implications of this type of resolution on network analysis. Using these data, we construct the first molecular‐based network of networks containing 3,304 interactions between 762 nodes of eight trophic functions and involving parasitic, mutualistic and predatory interactions. We provide a comparison of the relative strengths and weaknesses of these data types in network ecology.     

Bioenergetic food webs as a means of linking toxicological effects across scales of ecological organization

Although significant progress has been made in ourability to predict population-level consequences oftoxic effects on individuals, extending thispredictive ability to communities, functional guilds,and ecosystems will require more integration ofecological theory into environmental science. Bioenergetics and food webs have long been centralthemes in ecology and greatly expanded ourunderstanding of nature. Although numerousenergetic-based toxicological endpoints have beendeveloped, few have extended this framework beyond theindividual level. Most energetic endpoints includeindividual growth, and only occasionally is thisintegrated with population dynamics. However,population-level energetic analyses (e.g., secondaryproduction) integrate individual and populationprocesses, and provide two key parameters: consumptionand energy flow. Within a food web framework,estimates of consumption and energy flow throughpopulations facilitate linking population-levelcontaminant effects to ecosystem-level effects. Several examples are given to illustrate the utilityof this approach.     

Endocrine disruption in aquatic systems: up‐scaling research to address ecological consequences

Endocrine‐disrupting chemicals (EDCs) can alter biological function in organisms at environmentally relevant concentrations and are a significant threat to aquatic biodiversity, but there is little understanding of exposure consequences for populations, communities and ecosystems. The pervasive nature of EDCs within aquatic environments and their multiple sub‐lethal effects make assessments of their impact especially important but also highly challenging. Herein, we review the data on EDC effects in aquatic systems focusing on studies assessing populations and ecosystems, and including how biotic and abiotic processes may affect, and be affected by, responses to EDCs. Recent research indicates a significant influence of behavioural responses (e.g. enhancing feeding rates), transgenerational effects and trophic cascades in the ecological consequences of EDC exposure. In addition, interactions between EDCs and other chemical, physical and biological factors generate uncertainty in our understanding of the ecological effects of EDCs within aquatic ecosystems. We illustrate how effect thresholds for EDCs generated from individual‐based experimental bioassays of the types commonly applied using chemical test guidelines [e.g. Organisation for Economic Co‐operation and Development (OECD)] may not necessarily reflect the hazards associated with endocrine disruption. We argue that improved risk assessment for EDCs in aquatic ecosystems urgently requires more ecologically oriented research as well as field‐based assessments at population‐, community‐ and food‐web levels.     

Trophic interactions between native and introduced fish species in a littoral fish community

The trophic interactions between 15 native and two introduced fish species, silverside Odontesthes bonariensis and rainbow trout Oncorhynchus mykiss, collected in a major fishery area at Lake Titicaca were explored by integrating traditional ecological knowledge and stable‐isotope analyses (SIA). SIA suggested the existence of six trophic groups in this fish community based on δ¹³C and δ¹⁵N signatures. This was supported by ecological evidence illustrating marked spatial segregation between groups, but a similar trophic level for most of the native groups. Based on Bayesian ellipse analyses, niche overlap appeared to occur between small O. bonariensis (<90 mm) and benthopelagic native species (31·6%), and between the native pelagic killifish Orestias ispi and large O. bonariensis (39%) or O. mykiss (19·7%). In addition, Bayesian mixing models suggested that O. ispi and epipelagic species are likely to be the main prey items for the two introduced fish species. This study reveals a trophic link between native and introduced fish species, and demonstrates the utility of combining both SIA and traditional ecological knowledge to understand trophic relationships between fish species with similar feeding habits.     

Combined impacts of warming and salinisation on trophic interactions and mortality of a specialist ephemeral wetland predator

相似文献   

Seasonal contrasts in carbon resources and ecological processes on a tropical floodplain

1. Globally, tropical floodplains are highly productive ecosystems. This is largely because of predictable seasonal rains providing replenishing floodwaters that stimulate nutrient turnover which, in turn, substantially boosts both primary and secondary productivity. This is associated with concomitant shifts in the types of primary producers and associated food webs. 2. The Magela Creek floodplain on Kakadu National Park in northern Australia is one of the most studied tropical freshwater ecosystems in Australia and provides an opportunity to collate and examine information on organic carbon sources and pathways through food webs to gain a fundamental understanding of how these systems may function. 3. We reviewed biophysical information published since the early 1980s to construct an assessment of the carbon resources for the channel and floodplain. 4. We conclude that macrophytes, largely in the form of grasses and aquatic plants, produce the greatest above‐ground biomass on the Magela Creek floodplain. Although macrophytes provide suitable substrata for the attachment of epiphytes, they do not appear to be an important carbon source for aquatic consumers themselves. Nevertheless, macrophytes do provide critical seasonal food and habitat structure for other producers and consumers on the floodplain, such as the abundant magpie geese. 5. We developed a generalised conceptual food web and carbon budget contrasting the ‘wet’ and ‘dry’ seasons for the Magela Creek system, as a representative of tropical seasonal floodplain systems. 6. Our conceptual model of tropical floodplains indicates that knowledge of the seasonal and spatial links and exchanges between the floodplain and the river is critical in understanding ecosystem function.     

Credit of ecological interactions: A new conceptual framework to support conservation in a defaunated world

As defaunation spreads through the world, there is an urgent need for restoring ecological interactions, thus assuring ecosystem processes. Here, we define the new concept of credit of ecological interactions, as the number of interactions that can be restored in a focal area by species colonization or reintroduction. We also define rewiring time, as the time span until all the links that build the credit of ecological interactions of a focal area have become functional again. We expect that the credit will be gradually cashed following refaunation in rates that are proportional to (1) the abundance of the reintroduced species (that is expected to increase in time since release), (2) the abundance of the local species that interact with them, and (3) the traits of reintroduced species. We illustrated this approach using a theoretical model and an empirical case study where the credit of ecological interactions was estimated. This new conceptual framework is useful for setting reintroduction priorities and for evaluating the success of conservation initiatives that aim to restore ecosystem services.     

Trophic interactions between bacterial-feeding nematodes in plant rhizospheres and the nematophagous fungus Hirsutella rhossiliensis to suppress Heterodera schachtii

Trophic exchanges in soil food webs may suppress populations of pest organisms. We hypothesize that the suppressive condition of soils might be enhanced by manipulating components of the food web. Specifically, by enhancing populations of bacterial-feeding nematodes, propagule density of the nematophagous fungus Hirsutella rhossiliensis should increase and constrain populations of Heterodera schachtii, a plant-parasitic nematode. The rhizospheres of Crotalaria juncea and Vicia villosa stimulated population growth of the bacterial-feeding nematode, Acrobeloides bodenheimeri, but not of the nematodes Caenorhabditis elegans or Rhabditis cucumeris. The rhizospheres of Tagetes patula, Eragrostis curvula, and Sesamum indicum had no effect on any of the bacterial-feeding nematodes investigated. Acrobeloides bodenheimeri was most susceptible to parasitism by the nematophagous fungus H. rhossiliensis with 35% of individuals being parasitized in a laboratory assay. In three separate trials, parasitism of H. schachtii by H. rhossiliensis was not enhanced when populations of A. bodenheimeri were amplified in a suitable rhizosphere.