Size-based Models Research Articles

Improving the biological realism of predator-prey size relationships in food web models alters ecosystem dynamics.

Body-size relationships between predators and prey exhibit remarkable diversity. However, the assumption that predators typically consume proportionally smaller prey often underlies size-dependent predation in ecosystem models. In reality, some animals can consume larger prey or exhibit limited changes in prey size as they grow larger themselves. These distinct predator-prey size relationships challenge the conventional assumptions of traditional size-based models. Cephalopods, with their diverse feeding behaviours and life histories, offer an excellent case study to investigate the impact of greater biological realism in predator-prey size relationships on energy flow within a size-structured ecosystem model. By categorizing cephalopods into high and low-activity groups, in line with empirically derived, distinct predator-prey size relationships, we found that incorporating greater biological realism in size-based feeding reduced ecosystem biomass and production, while simultaneously increasing biomass stability and turnover. Our results have broad implications for ecosystem modelling, since distinct predator-prey size relationships extend beyond cephalopods, encompassing a wide array of major taxonomic groups from filter-feeding fishes to baleen whales. Incorporating a diversity of size-based feeding in food web models can enhance their ecological and predictive accuracy when studying ecosystem dynamics.

Managing fisheries for maximum nutrient yield.

Wild‐caught fish are a bioavailable source of nutritious food that, if managed strategically, could enhance diet quality for billions of people. However, optimising nutrient production from the sea has not been a priority, hindering development of nutrition‐sensitive policies. With fisheries management increasingly effective at rebuilding stocks and regulating sustainable fishing, we can now begin to integrate nutritional outcomes within existing management frameworks. Here, we develop a conceptual foundation for managing fisheries for multispecies Maximum Nutrient Yield (mMNY). We empirically test our approach using size‐based models of North Sea and Baltic Sea fisheries and show that mMNY is predicted by the relative contribution of nutritious species to total catch and their vulnerability to fishing, leading to trade‐offs between catch and specific nutrients. Simulated nutrient yield curves suggest that vitamin D, which is deficient in Northern European diets, was underfished at fishing levels that returned maximum catch weights. Analysis of global catch data shows there is scope for nutrient yields from most of the world's marine fisheries to be enhanced through nutrient‐sensitive fisheries management. With nutrient composition data now widely available, we expect our mMNY framework to motivate development of nutrient‐based reference points in specific contexts, such as data‐limited fisheries. Managing for mMNY alongside policies that promote access to fish could help close nutrient gaps for coastal populations, maximising the contribution of wild‐caught fish to global food and nutrition security.

Size-selective predation by three estuarine zooplanktivorous fish species

Context Zooplanktivorous fish are a key link between abundant zooplankton and higher trophic levels but the foraging behaviour of zooplanktivorous fish is not fully understood. Selective feeding behaviours have been observed, with many species of planktivorous fish targeting certain species and sizes of zooplankton for prey. However, why certain size classes of zooplankton are preferred remains unclear. Aim This study investigated prey selection by three zooplanktivorous fish species through the lens of optimal foraging theory. Methods We assessed the size structure of zooplankton in the environment and compared this with the size distribution of zooplankton in gut contents from three zooplanktivorous fish. Key results The targeted prey size of Atypichthys strigatus and Scorpis lineolata aligns with the prey size classes in the environment that contain the highest overall biomass. Trachurus novaezelandiae showed little evidence of targeting these size classes. Conclusions These prey sizes therefore represent the most efficient prey to target because the return on foraging effort is greatest. By contrast, T. novaezelandiae showed only an underselection of large and small prey. Implications By incorporating this information on this key trophic link between zooplankton and fish, ecosystem models could better resolve the size dependant predation, particularly in size-based models.

A size-structured matrix model to simulate dynamics of marine community size spectrum.

Several types of size-based models have been developed to model the size spectra of marine communities, in which abundance scales strongly with body size, using continuous differential equations. In this study, we develop a size-structured matrix model, which can be seen as a discretization of the Mckendrick-von Foerster equation, to simulate the dynamics of marine communities. The developed model uses a series of simple body size power functions to describe the basic processes of predator–prey interactions, reproduction, metabolism, and non-predation mortality based on the principle of mass balance. Linear size spectra with slopes of approximately –1 are successfully reproduced by this model. Several examples of numerical simulations are provided to demonstrate the model’s behavior. Size spectra with cut-offs and/or waves are also found for certain parameter values. The matrix model is flexible and can be freely manipulated by users to answer different questions and is executed over a shorter numerical calculation running time than continuous models.

On the context-dependent scaling of consumer feeding rates.

The stability of consumer-resource systems can depend on the form of feeding interactions (i.e. functional responses). Size-based models predict interactions - and thus stability - based on consumer-resource size ratios. However, little is known about how interaction contexts (e.g. simple or complex habitats) might alter scaling relationships. Addressing this, we experimentally measured interactions between a large size range of aquatic predators (4-6400mg over 1347 feeding trials) and an invasive prey that transitions among habitats: from the water column (3D interactions) to simple and complex benthic substrates (2D interactions). Simple and complex substrates mediated successive reductions in capture rates - particularly around the unimodal optimum - and promoted prey population stability in model simulations. Many real consumer-resource systems transition between 2D and 3D interactions, and along complexity gradients. Thus, Context-Dependent Scaling (CDS) of feeding interactions could represent an unrecognised aspect of food webs, and quantifying the extent of CDS might enhance predictive ecology.

Size-based approaches to aquatic ecosystems and fisheries science: a symposium in honour of Rob Peters

This special issue honours Rob Peters’ outstanding contributions to the field of aquatic ecology. It focuses on the size spectrum approach — in which individual organisms, rather than species, are the most basic biological unit — and highlights applications of this approach to fisheries management. The 21 papers in this issue cover three subject areas: (i) the use of size spectra to characterize variation in community structure, (ii) the development of size-based models of ecosystem dynamics to address fisheries questions, and (iii) applications of size-based theory to examine the consequences of variation in predator–prey size relationships, body size – trophic level relationships, and body size – life history relationships. The empirical studies herein demonstrate the utility of size spectra as indicators of population or community structure and for detecting impacts associated with environmental change. Future research focused on refining size-based sampling methods, standardizing metrics and analytical methods, understanding model sensitivity to the underlying assumptions, and comparative studies across ecosystems will enhance our ability to reliably interpret changes in size spectrum characteristics, thus facilitating their use as indicators of ecological change.

The theoretical foundations for size spectrum models of fish communities

Size spectrum models have emerged from 40 years of basic research on how body size determines individual physiology and structures marine communities. They are based on commonly accepted assumptions and have a low parameter set, making them easy to deploy for strategic ecosystem-oriented impact assessment of fisheries. We describe the fundamental concepts in size-based models about food encounter and the bioenergetics budget of individuals. Within the general framework, three model types have emerged that differ in their degree of complexity: the food-web, the trait-based, and the community models. We demonstrate the differences between the models through examples of their response to fishing and their dynamic behavior. We review implementations of size spectrum models and describe important variations concerning the functional response, whether growth is food-dependent or fixed, and the density dependence imposed on the system. Finally, we discuss challenges and promising directions.

Review of integrated size-structured models for stock assessment of hard-to-age crustacean and mollusc species

Abstract Punt, A. E., Huang, T., and Maunder, M. N. 2013. Review of integrated size-structured models for stock assessment of hard-to-age crustacean and mollusc species. – ICES Journal of Marine Science, 70:16–33. Crustaceans and molluscs such as crabs, rock lobsters, prawns, abalone, and oysters constitute large and valuable fisheries. However, assessments of these species are hampered because they cannot be production aged, in contrast to many teleosts. The major data sources for these species, in addition to catch and abundance index data, are the size compositions of the catches and of any fishery-independent indices. Assessments of such species have been conducted using age-based methods of stock assessment, as well as surplus production models. However, size-structured methods are now preferred because they can make full use of size-composition data, are able to integrate multiple sources of data, and produce the types of outputs which are needed for management purposes. An advantage of size-based models over age-based models is that all processes can be size-based, and these processes can modify the (unmodelled) size-at-age distribution. We review these methods, highlighting the choices that need to be made when developing integrated size-structured stock assessments, the data sources which are typically available and how they are used for parameter estimation, and contrast a number of such assessments worldwide.

Season and prey type influence size dependency of predator−prey body mass ratios in a marine fish assemblage

Marine and freshwater food webs are strongly structured by size-dependent preda- torprey interactions. Predatorprey body mass ratios (PPMR) are important parameters in size- based food-web models, but studies evaluating the temporal stability of PPMR or its relationship to predator feeding modes are scant. Using a large data set of predatorprey pairs from a diverse fish community sampled in summer, fall, and winter, we showed that community-level PPMR var- ied with predator mass in a nonlinear (dome-shaped) manner. PPMR was higher in the summer relative to the fall and winter for all predator body size classes regardless of whether prey were fish or invertebrate. Further, the size dependency of PPMR was dome-shaped for invertebrate prey but positive and linear for fish prey. We empirically show that community-level PPMR is dynamic rather than fixed, which is in agreement with general expectations set by simulation studies of biomass spectra. However, we are presently unable to identify the specific processes underlying these patterns. Size-based models of marine ecosystems offer considerable promise over traditional taxa-based approaches, and our analyses provide insight into major patterns of variation in PPMR in a temperate marine system.

Who is eating whom? Morphology and feeding type determine the size relation between planktonic predators and their ideal prey

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 445:1-12 (2012) - DOI: https://doi.org/10.3354/meps09502 FEATURE ARTICLE Who is eating whom? Morphology and feeding type determine the size relation between planktonic predators and their ideal prey Kai W. Wirtz* Institute of Coastal Research, Helmholtz-Zentrum Geesthacht, Germany *Email: kai.wirtz@hzg.de ABSTRACT: Body size determines the position of organisms in plankton food webs. The mass or diameter ratio between predators and their optimal prey is therefore a central element of size-based models, which attempt to link consumer groups across trophic levels. Despite a renaissance of size-based approaches in plankton ecology, however, this relation still lacks a generic and also mechanistically sound formulation. An empirically derived constant value of this ratio cannot describe the wide scatter in optimal prey diameter for specific predator size classes, especially in the mesozooplankton range. In this study, I propose that a given morphometric ratio between feeding-related apparatus and total body volume decreases when predator size increases. This ratio decrease is due to the additional need for structural components in larger organisms for maintaining intra-body transport. Non-isometric scaling results in a non-linear dependency of optimal prey size on predator diameter. This dependency defines an average relation which enables the quantitative definition of feeding mode. This new trait variable explains a component of the variability in optimal prey diameter that is independent of predator diameter. Feeding mode as a trait can be interpreted as activity during grazing, mostly in terms of speed regulation in swimming or in feeding-current generation. Feeding mode, in concert with the classical trait predator size, accurately determines optimal prey size. This was extensively tested using literature data for the entire plankton domain. The theory predicts increasing feeding activity in larger consumer species. It elucidates how successional shifts in the composition of zooplankton communities are linked to weakly coupled changes in mean body size and feeding mode. KEY WORDS: Zooplankton grazing · Optimal prey size · Biomechanics · Size-based model Full text in pdf format Information about this Feature Article Supplementary material NextCite this article as: Wirtz KW (2012) Who is eating whom? Morphology and feeding type determine the size relation between planktonic predators and their ideal prey. Mar Ecol Prog Ser 445:1-12. https://doi.org/10.3354/meps09502 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 445. Online publication date: January 20, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Application of nitrogen stable isotope analysis in size‐based marine food web and macroecological research

Interacting human and environmental pressures influence the structure and dynamics of marine food webs. To describe and predict the effects of these pressures, theoretical advances need to be supported by a capacity to validate the underlying models and assumptions. Here, we review recent applications of nitrogen stable isotope analysis in marine food web and macroecological research, with a focus on work that has paralleled a resurgence of interest in the development and application of size-based models. Nitrogen stable isotope data have been used to estimate intra- and inter-specific variation in trophic level, predator-prey size ratios, transfer efficiency, food chain length, relationships between predator and prey species diversity and the dynamics of energy use. Many of these estimates have contributed to the development, testing and parameterisation of food web and ecosystem models, some of which have been used to establish baselines for assessing the scale of human impacts. The interpretation of results depends on assumed fractionation but, when supported by sensitivity analyses and experimental validation, nitrogen stable isotope data provide valuable insights into the structuring of marine communities and ecosystems.

Seasonal variations in phytoplankton growth and microzooplankton grazing in a temperate coastal embayment, Korea

Microzooplankton grazing on coastal phytoplankton was determined by the dilution method from May 2002 to April 2003 at a fixed site located in the Jinhae Bay, Korea. During the dilution experiments, our study site exhibited a wide range of chlorophyll a concentrations (0.29–127.42 μg l −1), and the species composition of the phytoplankton community changed dramatically over a year, shifting from the predominance of chain-forming diatoms, particularly Chaetoceros spp., Leptocylindrus danicus, Pseudonitzschia pungens, and Skeletonema costatum, between May and September 2002, to a massive bloom of the dinoflagellates, Alexandrium spp. in October 2002, to a dominance of cryptophytes ( Chroomonas sp.) between November 2002 and March 2003, and then again to a prevalence of diatoms toward the end of the experiment. Both nutrients enriched ( μ n ) and in situ phytoplankton growth rates ( μ 0) showed pronounced seasonal variations, ranging from 0.11 to 2.87 d −1 and from −0.63 to 2.08 d −1, respectively. With regard to both variables, the lowest values were obtained during the fall and winter seasons. The average ratio of μ 0/ μ n was 0.96 (SE = 0.08), thereby indicating that phytoplankton growth in the study site was not nutrient-limited. Microzooplankton grazing rates showed the large fluctuations (0–3.86 d −1) over an annual cycle, with non-significant and/or negative grazing frequently (62% of 29 measurements) detected. Relatively high grazing rates did occur frequently at the times during which a large phytoplankton biomass and/or large-sized phytoplankton dominance were observed. Our results contribute to the growing body of evidence suggesting that microzooplankton are important phytoplankton consumers in communities dominated by large phytoplankton, and also bolster the notion that size-based models of food web relationships may be of limited predictive value. The observed large fluctuations in grazing rates over a year, coupled with frequent non-significant and/or negative grazing, indicate that intensive and long-term measurements of microzooplankton grazing are required for a better understanding of the interaction between phytoplankton and microzooplankton in a highly dynamic coastal ecosystem.

Modelling an exploited marine fish community with 15 parameters – results from a simple size-based model

AbstractTo measure and predict the response of fish communities to exploitation, it is necessary to understand how the direct and indirect effects of fishing interact. Because fishing and predation are size-selective processes, the potential response can be explored with size-based models. We use a simulation approach to describe the relationship between size spectrum slope and overall fishing mortality and to try to understand how a linear spectrum might be maintained. The model uses 15 parameters to describe a 13-“species” fish community, where species are defined by their maximum body size and the general relationship between size and life-history characteristics. The simulations allow us to assess the role of changes in the strength and type of density dependence in controlling the response to fishing, and to investigate the trade-off between catches and stock status of the different species. The outputs showed that the linear slope of the size spectrum was a function of community exploitation rate. Density-dependent controls, specifically predation mortality and the extent of compensation in the stock-recruit relationship, were key mechanisms in maintaining a linear spectrum. A linear spectrum emerged independent of the rate of compensation in the stock-recruit relationship. When this rate was low, the effects of changes in fishing mortality on predator abundance dominated those on spawning-stock biomass, whereas the dominance was reversed when the compensation rate in the stock-recruit relationship was high. The approach allows us to explore the effects of different fishing mortality schedules on properties of the fish community, to assess how fishing affects species with different life histories in mixed fisheries, and to assess the effects of selectively fishing different size classes. The simulations indicate that the size classes to be included when developing and interpreting size-based metrics must be carefully considered in relation to the trophic structure and likely strength of predatory interactions in the community. Runs with different fishing mortality by size suggest that the dynamics of predation cannot compensate fully for changing rates and patterns of exploitation, implying that the effects of selectively fishing different size classes should be assessed on a case-by-case basis.

Hatching asynchrony, survival, and the fitness of alternative adult morphs in Ambystoma talpoideum.

The mole salamander, Ambystoma talpoideum, exhibits both aquatic (gilled) and terrestrial (metamorphosed) adult morphologies. Previous studies have shown the existence of body-size advantages associated with the terrestrial morph in A. talpoideum and other polymorphic salamanders (e.g., A. tigrinum). However, aquatic adult A. talpoideum mature at a younger age and often breed earlier than terrestrial adults. We tested the hypothesis that early maturation and reproduction in aquatic adults increase fitness (irrespective of body size). We reared larval A. talpoideum in mesocosms and varied the timing of hatching, with early-hatching larvae representing the offspring from early-breeding aquatic adults, and late-hatching larvae representing the offspring of later-breeding terrestrial adults. Our results demonstrate significantly higher survival rates among early-hatchlings relative to late-hatching conspecifics, supporting the hypothesis that early reproduction may be an important mechanism mediating the polymorphism in A. talpoideum. We discuss our results within the context of size-based models of the fitness of alternative life-cycles.

Predicting abundance-body mass relationships in benthic infaunal communities

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 276:289-292 (2004) - doi:10.3354/meps276289 Predicting abundance-body mass relationships in benthic infaunal communities T. A. Dinmore*, S. Jennings Centre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Lowestoft, NR33 OHT, UK *Email: t.a.dinmore@cefas.co.uk ABSTRACT: The body size composition of benthic communities is commonly described using abundance-body mass relationships (size spectra). We tested whether the slopes of these relationships in a central North Sea infaunal community could be predicted from the energy available to different size-classes of animals. The results showed that the observed slopes were consistent with predictions of slope based on available energy at mass, where available energy was calculated from empirical measurements of trophic level (using nitrogen stable isotope analysis) and estimated trophic transfer efficiency. If our preliminary findings prove to apply more widely, then our macroecological approach may be refined to validate size-based models of community structure to explain regional differences in size structure and to underpin the development of new disturbance indicators. KEY WORDS: Abundance-body mass relationships · Macroecology · Energetic equivalence · Size spectra · Benthic invertebrates · Stable isotope analysis · Trophic structure Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 276. Online publication date: August 02, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Linking size-based and trophic analyses of benthic community structure

Models of biomass size spectra assume that organisms with higher body mass feed at higher trophic levels, but explicit empirical tests of this pattern are rare. We used nitrogen stable iso- topes (δ 15 N) as an index of the trophic level in a benthic fish and invertebrate size-spectrum, and demonstrated that body mass was positively and significantly related to trophic level. This pattern was consistent with the expectation that predator-prey relationships led to powerful size-based trophic structuring in marine communities and ecosystems. Further analysis of intra- and interspecific relationships between body mass and trophic level in the community showed that increases in trophic level across the size spectrum were predominantly a consequence of intra-specific increases in trophic level with body mass and not a consequence of larger species (species with greater maximum body mass) feeding at higher trophic levels. We confirmed the absence of strong inter-specific rela- tionships between maximum body mass and trophic level with cross-species and phylogenetic com- parative approaches. Size-based models are easier and cheaper to parameterise than most food-web models. Subject to the persistence of relationships between body mass and trophic level in space and time, our results suggest that size spectra could be parameterised with body mass-trophic level rela- tionships and used to describe the trophic structure of some marine communities and ecosystems.

A size-based ecosystem model for pelagic waters

Size-based models offer a holistic approach to understanding the structure and function of pelagic ecosystems, compared to simple models in which the entire system is represented by a single phytoplankton and zooplankton species. In this study, a one-dimensional size spectral model is constructed to simulate the temporal and vertical variability in the microbial community, nutrients and primary productivity. The approach taken is based on published allometric relationships governing physiological and ecological processes for phytoplankton and zooplankton. Since these allometric relationships are objective estimators of ecological parameters and are not dependent on knowledge of particular species, these models can be used to describe general features of the ecosystem. The model is driven by light, temperature and nutrient availability and is applied to an oligotrophic system in the Sargasso Sea-the Bermuda Atlantic Time Series (BATS) station, where field data on size spectra has recently been acquired. The model is able to reproduce the general overall features of this oceanic ecosystem fairly well: It depicts a late winter/early spring bloom and low production during the summer and fall months. In addition, a deep subsurface phytoplankton biomass maximum is produced in the summer, consistent with field measurements. The model prediction for size spectra is reasonably successful, although further refinement is necessary. As a whole, the model is fairly robust and can also be applied to ecosystems of different trophic state.

The size-based dynamics of plankton food webs. II. Simulations of three contrasting southern Benguela food webs

Size-based models are used to simulate planktonic food webs for the euphoric zones of three contrasting southern Benguela ecosystems, coastal stratified waters of the Agulhas Bank, a coastal upwelling area, and an oligotrophic area representative of SE Atlantic oceanic waters. In the models, phytoplankton are divided into four size categories and zooplankton into five All parameters describing flows are derived using body-size relationships Nitrogen is assumed to be limiting in ail three ecosystems, and other physical factors, such as light, are kept constant for simplicity. Initial pulses of new nitrogen in the Agulhas Bank (10 mg-at N m −3 ) and coastal upwelling models (25 mg-at N m −3 ) respectively simulate mixing and upwelling. Continuous inputs of new nitrogen into the Agulhas Bank (0.6 mg-at N m −3 day −1 ) and oceanic models (0 1 mg-at N m −3 day ) simulate turbulent diffusion into the euphotic zone across the nutricline The Agulhas Bank simulations depict a fluctuating standing stock of phytoplankton, dominated by different size classes at different times Large (net-) phytoplankton are important in this model only during periods of enhanced nitrogen supply. The phytoplankton bloom in the upwelling simulation is dominated by nano- and net-phytoplankton. The oceanic simulation depicts a phytoplankton community dominated by small cells (<5 μm), the populations of which remain at a relatively constant biomass of ∼40 mg C m −3 . In all three simulations the smallest autotrophs generally are responsible for the greatest proportion of primary production. The simulated heterotroph communities consist of varying biomasses of different-sized organisms. The Agulhas Bank and coastal upwelling simulations become dominated by micro- and meso-zooplankton, whereas small beterotrophs dominate the oceanic simulation. Different size classes of heterotrophs are important at different times in nitrogen regeneration, although zooflagellates (1–5 μm) were shown to be the most important regenerators on average. In the stratified Agulhas Bank and SE Atlantic oceanic simulations, regenerated production is generally greater than new production. In the Benguela upwelling simulation, new production is replaced by regenerated production as the phytoplankton bloom matures after upwelling and new nitrogen is exhausted. Average f -ratios were greatest (∼0 75) in newly upwelled water, decreasing for coastal stratified (0.25) and oligotrophic oceanic regions (0.14). Simulated model communities compare well with field observations in terms of standing stocks and size composition, suggesting that the model results accurately reflect nature. Up to seven-step ‘food chains’ occur in all three simulated ecosystems, but in practice most of the carbon is transferred via three effective trophic categories Long transfer pathways are important for planktivorous pelagic fish production in the oceanic simulation, short pathways in the coastal upwelling simulation, and intermediate-length pathways in the simulation of stratified coastal waters. Very little (<13%) of total photosynthetically fixed carbon potentially is available to pelagic fish in the simulations, and most carbon is lost through respiration and sinking. Nevertheless, the carbon potentially available to pelagic fish in the upwelling simulation is sufficient to sustain the pelagic fish production measured in the southern Benguela region. A revised food web model of plankton communities depicts the relative importance of different carbon and nitrogen flow pathways in different marine systems.