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Julia L. Blanchard - One of the best experts on this subject based on the ideXlab platform.

  • ensemble projections of future climate change impacts on the eastern bering sea food web using a multispecies Size Spectrum model
    Frontiers in Marine Science, 2020
    Co-Authors: Julia L. Blanchard, Jonathan C P Reum, Kirstin K Holsman, Kerim Aydin, Anne B Hollowed, Albert J Hermann, Wei Cheng
    Abstract:

    Characterization of uncertainty (variance) in ecosystem projections under climate change is still rare despite its importance for informing decision-making and prioritizing research. We developed an ensemble modeling framework to evaluate the relative importance of different uncertainty sources for food web projections of the Eastern Bering Sea (EBS). Specifically, dynamically downscaled projections from Earth System Models (ESM) under different greenhouse gas emission scenarios (GHG) were used to force a multispecies Size Spectrum model (MSSM) of the EBS food web. In addition to ESM and GHG uncertainty, we incorporated uncertainty from different plausible fisheries management scenarios reflecting shifts in the total allowable catch of flatfish and gadids and different assumptions regarding temperature-dependencies on biological rates in the MSSM. Relative to historical averages (1994-2014), end-of-century (2080-2100 average) ensemble projections of community spawner stock biomass, catches, and mean body Size (± standard deviation) decreased by 36% (± 21%), 61% (± 27%), and 38% (± 25%), respectively. Long-term trends were, on average, also negative for the majority of species, but the level of trend consistency between ensemble projections was low for most species. Projection uncertainty for model outputs from ~2020 to 2040 was driven by inter-annual climate variability for 85% of species and the community as a whole. Thereafter, structural uncertainty (different ESMs, temperature-dependency assumptions) dominated projection uncertainty. Fishery management and GHG emissions scenarios contributed little (<10%) to projection uncertainty, with the exception of catches for a subset of flatfishes which were dominated by fishery management scenarios. Long-term outcomes were improved in most cases under a moderate “mitigation” relative to a high “business-as-usual” GHG emissions scenario and we show how inclusion of temperature-dependencies on processes related to body growth and intrinsic (non-predation) natural mortality can strongly influence projections in potentially non-additive ways. Narrowing the spread of long-term projections in future ensemble simulations will depend primarily on whether the set of ESMs and food web models considered behave more or less similarly to one another relative to the present models sets. Further model skill assessment and data integration are needed to aid in the reduction and quantification of uncertainties if we are to advance predictive ecology.

  • energetically relevant predator prey body mass ratios and their relationship with predator body Size
    Ecology and Evolution, 2019
    Co-Authors: Jonathan C P Reum, Julia L. Blanchard, Kirstin K Holsman, Kerim Aydin, Simon Jennings
    Abstract:

    Food web structure and dynamics depend on relationships between body Sizes of predators and their prey. Species-based and community-wide estimates of preferred and realized predator-prey mass ratios (PPMR) are required inputs to Size-based Size Spectrum models of marine communities, food webs, and ecosystems. Here, we clarify differences between PPMR definitions in different Size Spectrum models, in particular differences between PPMR measurements weighting prey abundance in individual predators by biomass (r bio) and numbers (r num). We argue that the former weighting generates PPMR as usually conceptualized in equilibrium (static) Size Spectrum models while the latter usually applies to dynamic models. We use diet information from 170,689 individuals of 34 species of fish in Alaskan marine ecosystems to calculate both PPMR metrics. Using hierarchical models, we examine how explained variance in these metrics changed with predator body Size, predator taxonomic resolution, and spatial resolution. In the hierarchical analysis, variance in both metrics emerged primarily at the species level and substantially less variance was associated with other (higher) taxonomic levels or with spatial resolution. This suggests that changes in species composition are the main drivers of community-wide mean PPMR. At all levels of analysis, relationships between weighted mean r bio or weighted mean r num and predator mass tended to be dome-shaped. Weighted mean r num values, for species and community-wide, were approximately an order of magnitude higher than weighted mean r bio, reflecting the consistent numeric dominance of small prey in predator diets. As well as increasing understanding of the drivers of variation in PPMR and providing estimates of PPMR in the north Pacific Ocean, our results demonstrate that that r bio or r num, as well as their corresponding weighted means for any defined group of predators, are not directly substitutable. When developing equilibrium Size-based models based on bulk energy flux or comparing PPMR estimates derived from the relationship between body mass and trophic level with those based on diet analysis, weighted mean r bio is a more appropriate measure of PPMR. When calibrating preference PPMR in dynamic Size Spectrum models then weighted mean r num will be a more appropriate measure of PPMR.

  • from bacteria to whales using functional Size spectra to model marine ecosystems
    Trends in Ecology and Evolution, 2017
    Co-Authors: Julia L. Blanchard, Ryan F. Heneghan, Jason D. Everett, Anthony J. Richardson, Rowan Trebilco
    Abstract:

    Size-based ecosystem modeling is emerging as a powerful way to assess ecosystem-level impacts of human- and environment-driven changes from individual-level processes. These models have evolved as mechanistic explanations for observed regular patterns of abundance across the marine Size Spectrum hypotheSized to hold from bacteria to whales. Fifty years since the first Size Spectrum measurements, we ask how far have we come? Although recent modeling studies capture an impressive range of Sizes, complexity, and real-world applications, ecosystem coverage is still only partial. We describe how this can be overcome by unifying functional traits with Size spectra (which we call functional Size spectra) and highlight the key knowledge gaps that need to be filled to model ecosystems from bacteria to whales.

  • Zooplankton Are Not Fish: Improving Zooplankton Realism in Size-Spectrum Models Mediates Energy Transfer in Food Webs
    Frontiers in Marine Science, 2016
    Co-Authors: Ryan F. Heneghan, Jason D. Everett, Julia L. Blanchard, Anthony J. Richardson
    Abstract:

    The evidence for an equal distribution of biomass from bacteria to whales has led to development of Size-Spectrum models that represent the dynamics of the marine ecosystem using Size rather than species identity. Recent advances have improved the realism of the fish component of the Size-Spectrum, but these often assume that small fish feed on an aggregated plankton Size-Spectrum, without any explicit representation of zooplankton dynamics. In these models, small zooplankton are grouped with phytoplankton as a resource for larval fish, and large zooplankton are parameterized as small fish. Here we investigate the impact of resolving zooplankton and their feeding traits in a dynamic Size-Spectrum model. First, we compare a base model, where zooplankton are parameterized as smaller fish, to a model that includes zooplankton-specific feeding parameters. Second, we evaluate how the parameterization of zooplankton feeding characteristics, specifically the predator-prey mass ratio (PPMR), assimilation efficiency and feeding kernel width, affects the productivity and stability of the fish community. Finally, we compare how feeding characteristics of different zooplankton functional groups mediate increases in primary production and fishing pressure. Incorporating zooplankton-specific feeding parameters increased productivity of the fish community, but also changed the dynamics of the entire system from a stable to an oscillating steady-state. The inclusion of zooplankton feeding characteristics mediated a trade-off between the productivity and resilience of the fish community, and its stability. Fish communities with increased productivity and lower stability were supported by zooplankton with a larger PPMR and a narrower feeding kernel – specialized herbivores. In contrast, fish communities that were stable had lower productivity, and were supported by zooplankton with a lower PPMR and a wider feeding kernel – generalist carnivores. Herbivorous zooplankton communities were more efficient at mediating increases in primary production, and supported fish communities more resilient to fishing. Our results illustrate that zooplankton are not just a static food source for larger organisms, nor can they be resolved as very small fish. The unique feeding characteristics of zooplankton have enormous implications for the dynamics of marine ecosystems, and their representation is of critical importance in Size-Spectrum models, and end-to-end ecosystem models more broadly.

  • parameter uncertainty of a dynamic multispecies Size Spectrum model1
    Canadian Journal of Fisheries and Aquatic Sciences, 2016
    Co-Authors: Michael A Spence, Paul G Blackwell, Julia L. Blanchard
    Abstract:

    Dynamic Size Spectrum models have been recognized as an effective way of describing how Size-based interactions can give rise to the Size structure of aquatic communities. They are intermediate-com...

Brian J Shuter - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of the responsiveness of the crustacean zooplankton community Size Spectrum to environmental change and an exotic invader in a sample of canadian shield lakes
    Canadian Journal of Fisheries and Aquatic Sciences, 2020
    Co-Authors: Lauren Emily Barth, Brian J Shuter, Gary W Sprules, Charles K Minns, James A Rusak
    Abstract:

    We evaluated the crustacean zooplankton Size Spectrum as an indicator of lake characteristics and ecosystem change. First, we used time-series from seven Canadian Shield lakes to identify the facto...

  • calibration of the zooplankton community Size Spectrum as an indicator of change in canadian shield lakes
    Canadian Journal of Fisheries and Aquatic Sciences, 2019
    Co-Authors: Lauren Emily Barth, Brian J Shuter, Charles K Minns, William Gary Sprules, James A Rusak
    Abstract:

    Developing the crustacean zooplankton community Size Spectrum into an indicator of change in lakes requires quantification of the natural variability in the Size Spectrum related to broad-scale sea...

  • predator bioenergetics and the prey Size Spectrum do foraging costs determine fish production
    Journal of Theoretical Biology, 2013
    Co-Authors: Henrique C Giacomini, Brian J Shuter, Nigel P Lester
    Abstract:

    Most models of fish growth and predation dynamics assume that food ingestion rate is the major component of the energy budget affected by prey availability, while active metabolism is invariant (here called constant activity hypothesis). However, increasing empirical evidence supports an opposing view: fish tend to adjust their foraging activity to maintain reasonably constant ingestion levels in the face of varying prey density and/or quality (the constant satiation hypothesis). In this paper, we use a simple but flexible model of fish bioenergetics to show that constant satiation is likely to occur in fish that optimize both net production rate and life history. The model includes swimming speed as an explicit measure of foraging activity leading to both energy gains (through prey ingestion) and losses (through active metabolism). The fish is assumed to be a particulate feeder that has to swim between consecutive individual prey captures, and that shifts its diet ontogenetically from smaller to larger prey. The prey community is represented by a negative power-law Size Spectrum. From these rules, we derive the net production of fish as a function of the Size Spectrum, and this in turn establishes a formal link between the optimal life history (i.e. maximum body Size) and prey community structure. In most cases with realistic parameter values, optimization of life history ensures that: (i) a constantly satiated fish preying on a steep Size Spectrum will stop growing and invest all its surplus energy in reproduction before satiation becomes too costly; (ii) conversely, a fish preying on a shallow Size Spectrum will grow large enough for satiation to be present throughout most of its ontogeny. These results provide a mechanistic basis for previous empirical findings, and call for the inclusion of active metabolism as a major factor limiting growth potential and the numerical response of predators in theoretical studies of food webs. & 2013 Elsevier Ltd. All rights reserved.

Lauren Emily Barth - One of the best experts on this subject based on the ideXlab platform.

Simon Jennings - One of the best experts on this subject based on the ideXlab platform.

  • energetically relevant predator prey body mass ratios and their relationship with predator body Size
    Ecology and Evolution, 2019
    Co-Authors: Jonathan C P Reum, Julia L. Blanchard, Kirstin K Holsman, Kerim Aydin, Simon Jennings
    Abstract:

    Food web structure and dynamics depend on relationships between body Sizes of predators and their prey. Species-based and community-wide estimates of preferred and realized predator-prey mass ratios (PPMR) are required inputs to Size-based Size Spectrum models of marine communities, food webs, and ecosystems. Here, we clarify differences between PPMR definitions in different Size Spectrum models, in particular differences between PPMR measurements weighting prey abundance in individual predators by biomass (r bio) and numbers (r num). We argue that the former weighting generates PPMR as usually conceptualized in equilibrium (static) Size Spectrum models while the latter usually applies to dynamic models. We use diet information from 170,689 individuals of 34 species of fish in Alaskan marine ecosystems to calculate both PPMR metrics. Using hierarchical models, we examine how explained variance in these metrics changed with predator body Size, predator taxonomic resolution, and spatial resolution. In the hierarchical analysis, variance in both metrics emerged primarily at the species level and substantially less variance was associated with other (higher) taxonomic levels or with spatial resolution. This suggests that changes in species composition are the main drivers of community-wide mean PPMR. At all levels of analysis, relationships between weighted mean r bio or weighted mean r num and predator mass tended to be dome-shaped. Weighted mean r num values, for species and community-wide, were approximately an order of magnitude higher than weighted mean r bio, reflecting the consistent numeric dominance of small prey in predator diets. As well as increasing understanding of the drivers of variation in PPMR and providing estimates of PPMR in the north Pacific Ocean, our results demonstrate that that r bio or r num, as well as their corresponding weighted means for any defined group of predators, are not directly substitutable. When developing equilibrium Size-based models based on bulk energy flux or comparing PPMR estimates derived from the relationship between body mass and trophic level with those based on diet analysis, weighted mean r bio is a more appropriate measure of PPMR. When calibrating preference PPMR in dynamic Size Spectrum models then weighted mean r num will be a more appropriate measure of PPMR.

  • evaluating targets and trade offs among fisheries and conservation objectives using a multispecies Size Spectrum model
    Journal of Applied Ecology, 2014
    Co-Authors: Julia L. Blanchard, Ken Haste Andersen, Finlay Scott, Niels T Hintzen, G J Piet, Simon Jennings
    Abstract:

    Marine environmental management policies seek to ensure that fishing impacts on fished populations and other components of the ecosystem are sustainable, to simultaneously meet objectives for fisheries and conservation. For example, in Europe, targets for (i) biodiversity, (ii) food web structure as indicated by the proportion of large fish and (iii) fishing mortality rates for exploited species that lead to maximum sustainable yield, F-MSY,F- are being proposed to support implementation of the Marine Strategy Framework Directive. Efforts to reconcile any trade-offs among objectives need to be informed by knowledge on the consequences of alternate management actions. We develop, calibrate and apply a multispecies Size Spectrum model of the North Sea fish community to assess the response of populations and the community to fishing. The model predicts species' Size distributions, abundance, productivity and interactions and therefore provides a single framework for evaluating trade-offs between population status, community and food web structure, biodiversity and fisheries yield. We show that the model can replicate realistic fish population and community structure and past responses to fishing. We assess whether meeting management targets for exploited North Sea populations (fishing species at F-MSY) will be sufficient to meet proposed targets for biodiversity and food web indicators under two management scenarios (status quo and F-MSY). The recovery in biodiversity indicators is 60% greater when fishing populations at F-MSY than if status quo (2010) fishing rates are maintained. The probability of achieving a food web target was 60% under both scenarios in spite of major community restructuring revealed by other indicators of community Size structure. Synthesis and applications. Our model can be applied to evaluate indicator targets and trade-offs among fisheries and conservation objectives. There is a significant probability that reductions in fishing mortality below F-MSY would be needed in Europe if managers make a binding commitment to a proposed large fish indicator target, with concomitant reductions in fisheries yield.

  • linking Size based and trophic analyses of benthic community structure
    Marine Ecology Progress Series, 2002
    Co-Authors: Simon Jennings, John K. Pinnegar, Nicholas Polunin, Karema J Warr
    Abstract:

    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 isotopes (d15N) 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 relationships between maximum body mass and trophic level with cross-species and phylogenetic comparative 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 relationships and used to describe the trophic structure of some marine communities and ecosystems.

James A Rusak - One of the best experts on this subject based on the ideXlab platform.

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