Standardized ecological indicators to assess aquatic food webs: The ECOIND software plug-in for Ecopath with Ecosim models

Ecological indicators are useful tools to analyse and communicate historical changes in ecosystems and plausible future scenarios while evaluating environmental status. Here we introduce a new plug-in to the Ecopath with Ecosim (EwE) food web modelling approach, which is widely used to quantitatively describe aquatic ecosystems. The plug-in (ECOIND) calculates standardized ecological indicators. We describe the primary functionality of ECOIND and provide an example of its application in both static and temporal-spatial dynamic modelling, while we highlight several related features including a new taxonomy input database (species traits) and the ability to analyse input uncertainty on output results. ECOIND adds new capabilities to the widely used EwE food web modelling approach and enables broadening its applications into biodiversity and conservation-based frameworks to contribute to integrated ecosystem analyses.     

基于关键功能组的河道内生态需水计算

河道内生态需水是目前生态学、水文学和水资源学研究的热点领域,现有计算方法中从生态系统功能完整性的角度出发计算生态需水的较少。首先利用Ecopath模型对小清河流域2014年5月、8月、11月生态系统内群落间营养关系进行了模拟,分析得到了小清河流域生态系统关键功能组;然后,利用栖息地适应性指数(HSI)确定了各关键鱼类生存和繁殖的适宜流速及水位;最后,耦合多物种的适宜流速及水位,利用改进后的AEHRA法计算生态需水量。结果显示,小清河流域鱼类非产卵期(1月-3月、8月-12月)上、中、下游生态需水量分别为4.28m3/s、0.74m3/s、3.47m3/s;产卵期上、中、下游生态需水量分别为23.52m3/s、5.96m3/s(8.65m3/s)、37.38m3/s。与Tennant法比较,本方法计算结果可以将生态系统健康状况维持在"一般"水平以上,即可以满足流域内大多数水生物需水量,同时,该方法计算结果显示出鱼类产卵期与非产卵期的生态需水量差异,为流域内跨季节调水提供依据。     

Major biomass fluctuations in lake food webs – An example in the peri-alpine Lake Annecy

In aquatic ecosystems, young of the year (YOY) fish often exhibit strong interannual fluctuations. Because these fish prey on zooplankton and are preyed upon by piscivorous fish, strong fluctuations in their abundance may have important impacts on food web functioning. The static Ecopath model was used to assess potential impacts of strong fluctuations in YOY perch in the deep peri-alpine Lake Annecy. We modeled two contrasting years in terms of YOY perch biomass: a situation with a high biomass of YOY perch and a situation with a low biomass of YOY perch. Additionally, five models were derived from the two initial models to better explore the effects of YOY perch biomass fluctuations on food web functioning. Disparities were revealed in terms of the activity of the system (volume of flows) and the trophic transfer efficiency. When the YOY perch biomass was high, the volume of flows within the system was less important, but the trophic transfers were more efficient than when the biomass was low. The high biomass of YOY perch appeared to facilitate transfers from low to high trophic levels. The results indicated that strong variabilities in the abundance of YOY fish had little impact on the main food web flows and pathways because of the capacity of predators to feed on various prey (omnivory) but could induce significant differences in food web properties (e.g. ascendancy, robustness) and organization (e.g. cycling, mean trophic level).     

Ecosystem modelling of data-limited fisheries: How reliable are Ecopath with Ecosim models without historical time series fitting?

Long-term time series data are not available for many of the African Great Lakes. This precludes fitting ecosystem model parameters to time series data, and we do not know how reliable non-fitted models are compared to fitted ones in terms of predicting consequences of alternative management strategies. To investigate this, we generate a historical Ecopath with Ecosim (EwE) model for Lake Victoria (East Africa), fitted to time series data (1980–2015), and a present-day EwE model (representing average conditions for the period 2010–2015). We do scenario simulations using the present-day model and the comparable 2015 end-state of the historical model, and test if incorporating information on short-term biomass trends by adjusting biomass accumulation (BA) parameter in the present-day model increases its reliability. We find that there are differences in model predictions, but those differences can be lessened by adjusting BA terms in the present-day model to reflect biomass trends from short-term empirical data. We also compare the models with and without fitted vulnerability parameters. The models generally give comparable results for the dominant commercial fisheries at low fishing pressure; when fishing mortality is increased, the models give variable predictions. This study adds to the current understanding of the limitations of EwE models that are not challenged to reproduce long-term historical fishery responses to perturbations. We conclude that for the less productive groups, as well as groups that suffer heavy mortality (either due to predation or fisheries), it may be appropriate to use negative BA as first draft assumption in present-day models.     

Towards the development of an ecosystem model for the Hamilton Harbour,Ontario, Canada

Our main objective is to undertake a synthesis of the Hamilton Harbour ecosystem and to elucidate the relative importance of the underlying trophic relationships using the mass-balance modeling software Ecopath with Ecosim (EwE). We present a conceptual model comprising all the essential food web components of the system, which was parameterized using both local and literature-based information. Among the trophic relationships considered by the Hamilton Harbour ecosystem model, our analysis highlights the central role of round goby demonstrating a wide range of effects on a number of functional groups at both higher and lower trophic levels. Several ecosystem attributes (e.g., primary production/biomass, biomass/total throughput, system omnivory index, amount of recycled throughput, and Finn's cycling index) provide evidence that the Hamilton Harbour is an immature and fairly simple system with linear food chain structure, although the internal redundancy and the system overhead estimates indicate that the Harbour possesses substantial reserves to overcome external perturbations. The aggregation of the ecosystem into discrete trophic levels suggests that most of the trophic flows are concentrated within the first two trophic levels, while flows were practically insignificant at the higher trophic levels of the food web. The fairly low ecotrophic efficiency values for both carnivorous and herbivorous cladocerans are indicative of low zooplanktivory levels in the system. Finally, our study identifies knowledge gaps and critical next steps to rigorously assess the credibility of the model and to consolidate its use for predictive purposes.     

基于Ecopath的小清河河流生态系统关键功能组分析

关键功能组对于维持生态系统结构完整、功能完善具有重要意义。为此,本研究引入国际惯用的营养通道模型—Ecopath,定量分析计算了水生态系统结构组成及营养关系,并通过生态系统内物质、能量流动的方向与数量确定了水生生态系统关键种,提出了一套关键功能组构建的方法。将该方法应用于小清河流域,结果显示小清河流域关键功能组成员随季节有很大变动:春季包括青鳉、鲫、水丝蚓、原生动物、隐藻;夏季变为青鳉、泥鳅(包括大鳞副泥鳅)、水丝蚓、原生动物、黄藻;秋季则为泥鳅(包括大鳞副泥鳅)、餐、秀丽白虾、轮虫、裸藻)。本方法可为水生态文明建设提供明确的水生态系统保护重点物种,为流域生态需水计算、水生态健康修复及水生态文明建设提供管理和决策依据。     

Reviewing uncertainty in bioenergetics and food web models to project invasion impacts: Four major Chinese carps in the Great Lakes

Bioenergetics and food web models are tools available for understanding and projecting the impacts of aquatic species invasions on food web structure and energy allocation of an ecosystem. However, uncertainty is inherent in modeling the impact of invasive species in novel ecosystems as assumptions must be made about physiological responses to novel environments and interactions with existing (native and non-native) species. Here we use the four major Chinese carps (FMCC) in the Laurentian Great Lakes as a case study to categorize and describe the suite of uncertainties inherent in projecting the impact of invasive species with bioenergetics and food web models. We approach this case study in a decision analytic framework, describing structural uncertainties, environmental variation, partial observability, partial controllability, and linguistic uncertainty. Finally, we review and give suggestions for how the use of methods including adaptive management, scenario planning, sensitivity analyses, and value of information as well as efforts to ensure clarity in language and model structure can enable modelers and managers to reduce and account for key uncertainties and make better decisions for the control of invasive species.     

Water level fluctuations and the ecosystem functioning of lakes

Hydrological regimes are key drivers of productivity and structure in freshwater ecosystems but are increasingly impacted by human activity. Using 17 published food web models of 13 African lakes as a case study, we explored relationships between seasonal and interannual water level fluctuations and 15 attributes related to ecosystem function. We interpreted our results in the context of Odum's ecosystem maturity hypothesis, as systems with higher magnitude fluctuations may be kept at an earlier maturity stage than those that are relatively stable. The data we compiled indicate that long-term changes in the hydrological regimes of African lakes have already taken place. We used Least Absolute Shrinkage and Selection Operator (LASSO) regression to examine relationships between ecosystem attributes and seven physical characteristics. Of these characteristics, interannual water level fluctuation magnitude was the most frequently retained predictor in the regression models. Our results indicate that interannual water level fluctuations are positively correlated with primary and overall production, but negatively correlated with fish diversity, transfer efficiency, and food chain length. These trends are opposite those expected with increasing ecosystem maturity. Interestingly, we found seasonal water level fluctuations to be positively correlated with biomass. An increase in standing biomass is generally associated with more mature ecosystems. However, we found that less production and biomass occurred at high trophic levels in highly fluctuating compared to relatively stable systems. This synthesis provides evidence that water level fluctuations are a key process influencing ecosystem structure and function in lakes.     

How long-term water level changes influence the spatial distribution of fish and other functional groups in a large shallow lake

We numerically explored the effects of long-term water level changes on biotic biomass and spatial distribution of fish in a large shallow lake. We calibrated Ecospace model (Ecopath with Ecosim modelling suite) with data from various functional groups (ranging from phytoplankton to piscivorous fish), and considered 14 different habitats. Two scenarios representing, respectively, a long-term water-level increase and decrease by 1 m were constructed and run for a period of thirty eight years (1979–2016). The results showed a very uneven spatial distribution of fish biomass in the lake, with the highest concentration in the southern basin. The 1 m decrease scenario caused a diminution in the biomass of all groups but piscivorous fish. The 1 m increase scenario saw a weak decrease in most species biomass. Consequently, in both scenarios, long-term water level changes would be generally detrimental to the lake biota. In the context of more frequent climate-induced hydrological fluctuations, we encourage the use of these simulations as effective tools for future prediction and assessment of ecosystem-based fisheries management and ecological status maintenance of shallow lakes.