Size-based Model Research Articles

The association between jaundice and poorly differentiated pancreatic neuroendocrine neoplasms (Ki67 index > 55.0%)

BackgroundJaundice occurs in some pancreatic disease. However, its occurrences and role in pancreatic neuroendocrine neoplasms (PNENs) has not been well studied. In this study we showed the association between jaundice and the risk of high grade and poorly differentiated PNENs.MethodsNinety-three patients with head-neck PNENs were included. Poorly differentiated pancreatic neuroendocrine neoplasms were defined by a ki67 index > 55.0%. Logistic regression was used to show the association between demographic information, clinical signs and symptoms and the risk of poorly differentiated tumors. A nomogram model was developed to predict poorly differentiated tumor.ResultsEight of 93 PNEN patients (8.6%) had jaundice. The age and ki67 index in patients with jaundice were significantly higher than those patients without jaundice. All jaundice occurred in patients with grade 3 PNENs. Mutivariable regression analysis showed that age (odds ratio(OR) = 1.10, 95% confidence interval (CI):1.02–1.19), tumor size (OR = 1.42, 95%CI:1.01-2.00) and jaundice (OR = 14.98, 95%CI: 1.22-184.09) were associated with the risk of poorly differentiated PNENs. The age and size combination showed a good performance in predicting poorly differentiated PNENs (area under the curve (AUC) = 0.81, 95% CI: 0.71–0.90). The addition of jaundice further improved the age- and size-based model (AUC = 0.86, 95% CI: 0.78–0.91). A nomogram was developed based on age, tumor size and jaundice.ConclusionOur data showed that jaundice was associated with the risk of high grade PNENs and poorly differentiated PNENs.

Changes in sea floor productivity are crucial to understanding the impact of climate change in temperate coastal ecosystems according to a new size-based model

The multifaceted effects of climate change on physical and biogeochemical processes are rapidly altering marine ecosystems but often are considered in isolation, leaving our understanding of interactions between these drivers of ecosystem change relatively poor. This is particularly true for shallow coastal ecosystems, which are fuelled by a combination of distinct pelagic and benthic energy pathways that may respond to climate change in fundamentally distinct ways. The fish production supported by these systems is likely to be impacted by climate change differently to those of offshore and shelf ecosystems, which have relatively simpler food webs and mostly lack benthic primary production sources. We developed a novel, multispecies size spectrum model for shallow coastal reefs, specifically designed to simulate potential interactive outcomes of changing benthic and pelagic energy inputs and temperatures and calculate the relative importance of these variables for the fish community. Our model, calibrated using field data from an extensive temperate reef monitoring program, predicts that changes in resource levels will have much stronger impacts on fish biomass and yields than changes driven by physiological responses to temperature. Under increased plankton abundance, species in all fish trophic groups were predicted to increase in biomass, average size, and yields. By contrast, changes in benthic resources produced variable responses across fish trophic groups. Increased benthic resources led to increasing benthivorous and piscivorous fish biomasses, yields, and mean body sizes, but biomass decreases among herbivore and planktivore species. When resource changes were combined with warming seas, physiological responses generally decreased species’ biomass and yields. Our results suggest that understanding changes in benthic production and its implications for coastal fisheries should be a priority research area. Our modified size spectrum model provides a framework for further study of benthic and pelagic energy pathways that can be easily adapted to other ecosystems.

Overexploitation of round sardinella may lead to the collapse of flat sardinella: What lessons can be drawn for shared stocks

This paper describes the fisheries and presents quantitative stock assessments for two stocks of Sardinella in the waters of NW Africa. More robust stock assessments are now possible because of improved sampling in Mauritania and Senegal. Round sardinella (S. aurita), which has a wider distribution than flat sardinella (S. maderensis), is the most important species targeted by the different artisanal and industrial fleets. The industrial fleet is located beyond 13 miles from the coast, taking mainly adults. The average size in the offshore fishery, although it has decreased, remains above 26 cm. The species is also exploited by an artisanal fleet using small purse seiners. Two types of assessment model were applied: a production model and size-based model. The abundance indices were consistent, and showed a continuous decline, increasing in rate in recent years. The Just Another Bayesian Biomass Assessment (JABBA) model (applied for the first time) appeared to be appropriate for the abundance indices (Root Mean Squared Error (RMSE) 18.3–19.2 % for the two models). The results of the two models are consistent in showing increasing fishing mortality and declining biomass for both stocks over the time series. According to the JABBA model, the situation for the round sardinella stock is now critical (biomass at approximately 5 % of unexploited biomass (B0) and 10 % of biomass capable of producing maximum sustainable yields (Bmsy), with fishing mortality 2.5 times above Fmsy), and the flat sardinella is also overfished and suffering massive overfishing (B estimated at 18 %B0 and 25 %Bmsy, with fishing mortality more than 11 times above Fmsy). The results of the Length-based Bayesian Biomass (LBB) model are much more optimistic. It still concludes that both stocks are suffering overfishing (round sardinella F at ∼1.4 times Fmsy proxy, flat sardinella ∼2.2 times Fmsy proxy), but estimates that only the flat sardinella is overfished (B 28%B0 and 80 %Bmsy), while the round sardinella stock is not overfished (B 40 %B0 and 120 %Bmsy). However, these results are not consistent with the abundance index from acoustic surveys (used in the JABBA model) and overall are thought to be less robust. Signs of heavy exploitation have been observed for round sardinella for several years. This situation has been exacerbated since the arrival in late 2016 in the Mauritanian zone of efficient semi-industrial purse seiners targeting small pelagics. The various indirect assessment models used show a difficult stock situation for the round sardinella, on which many fishing communities in the area depend. Abundance indices from acoustic survey confirm the state of overexploitation of this resource. This situation has directed effort towards the flat sardinella, which is characterized by a more coastal distribution and limited migration. This species has been showing signs of overexploitation since 2019. We highlight this result for flat sardinella, which was previously not thought to be overexploited, and propose that managers should also consider how the estimated maximum sustainable catch and fishing mortality can be appropriately distributed between the different fleets in different countries, to ensure that future industry planning in the countries of the region is compatible with the sustainability of these critical stocks. This is a very complex task, as it involves not only discussions between neighboring countries, but also difficult decisions within countries about the economic and socio-economic importance of different fisheries sectors. It is essential that these reflections start immediately.

Planktonic prey size selection reveals an emergent keystone predator effect and niche partitioning.

Marine herbivorous protists are often the dominant grazers of primary production. We developed a size-based model with flexible size-based grazing to encapsulate taxonomic and behavioral diversity. We examined individual and combined grazing impacts by three consumer sizes that span the size range of protistan grazers- 5, 50, and 200 μm-on a size-structured phytoplankton community. Prey size choice and dietary niche width varied with consumer size and with co-existence of other consumers. When all consumer sizes were present, distinct dietary niches emerged, with a range of consumer-prey size ratios spanning from 25:1 to 0.4:1, encompassing the canonical 10:1 often assumed. Grazing on all phytoplankton size classes maximized the phytoplankton size diversity through the keystone predator effect, resulting in a phytoplankton spectral slope of approximately -4, agreeing with field data. This mechanistic model suggests the observed size structure of phytoplankton communities is at least in part the result of selective consumer feeding.

Detecting mortality variation to enhance forage fish population assessments

Abstract Contemporary stock assessment models used by fisheries management often assume that natural mortality rates are constant over time for exploited fish stocks. This assumption results in biased estimates of fishing mortality and reference points when mortality changes over time. However, it is difficult to distinguish changes in natural mortality from changes in fishing mortality, selectivity, and recruitment. Because changes in size structure can be indicate changes in mortality, one potential solution is to use population size-structure and fisheries catch data to simultaneously estimate time-varying natural and fishing mortality. Here we test that hypothesis, using a simulation experiment to test performance for four alternative estimation models that estimate natural and fishing mortality from size structure and catch data. We show that it is possible to estimate time-varying natural mortality in a size-based model, even when fishing mortality, recruitment, and selectivity are changing over time. Finally, we apply the model to North Sea sprat, and show that estimates of recruitment and natural mortality are similar to estimates from an alternative multispecies population model fitted to additional data sources. We recommend exploring potential trends in natural mortality in forage fish assessments using tools such as the one presented here.

Effects of sex-specific fishing mortality on sex ratio and population dynamics of Gulf of Mexico greater amberjack

The US Gulf of Mexico stock assessment of greater amberjack Seriola dumerili assumes a 1:1 male:female sex ratio. However, the observed sex ratio in the landed catch is 1:1.8, and for fish >1 m fork length is 1:2.4. To theoretically explore whether this female-skewed sex ratio may arise due to differential fishing mortality between the sexes, we used a sex-specific age- and size-based model to investigate how different fishing mortality rates could create a female-skew in the landed catch as well as its subsequent effects on reproductive potential. When fishing mortality rates in the model were equal between the sexes, the sex ratio of the landed catch was approximately 1:1 for all legal-sized fish, and approximately 1:2.4 for fish >1 m FL. However, reproductive potential decreased in comparison to the corresponding scenario with equal fishing mortality rates when fishing mortality rates between the sexes were changed to create the 1:1.8 sex ratio observed in the landed catch. This modeling study demonstrates one possible route that could explain the female-skewed sex ratios observed in the landed catch, and indicates that sex ratio values other than 1:1 should be considered in future stock assessments for Gulf of Mexico greater amberjack.

Allocation, not male resistance, increases male frequency during epidemics: a case study in facultatively sexual hosts.

Why do natural populations vary in the frequency of sexual reproduction? Virulent parasites may help explain why sex is favored during disease epidemics. To illustrate, we show a higher frequency of males and sexually produced offspring in natural populations of a facultative parthenogenetic host during fungal epidemics. In a multi-year survey of 32 lakes, the frequency of males (an index of sex) was higher in populations of zooplankton hosts with larger epidemics. A lake mesocosm experiment established causality: experimental epidemics produced a higher frequency of males relative to disease-free controls. One common explanation for such a pattern involves Red Queen (RQ) dynamics. However, this particular system lacks key genetic specificity mechanisms required for the RQ, so we evaluated two other hypotheses. First, individual females, when stressed by infection, could increase production of male offspring vs. female offspring (a tenant of the "Abandon Ship" theory). Data from a life table experiment supports this mechanism. Second, higher male frequency during epidemics could reflect a purely demographic process (illustrated with a demographic model): males could resist infection more than females (via size-based differences in resistance and mortality). However, we found no support for this resistance mechanism. A size-based model of resistance, parameterized with data, revealed why: higher male susceptibility negated the lower exposure (a size-based advantage) of males. These results suggest that parasite-mediated increases in allocation to sex by individual females, rather than male resistance, increased the frequency of sex during larger disease epidemics.

Population Status Assessment and Restoration Modeling of White AbaloneHaliotis sorenseniin California

White abalone Haliotis sorenseni was listed as endangered in 2001 because of severe declines throughout southern California due to overfishing. Populations continue to decline despite the closure of the fishery in 1996. There has been little to no evidence of recruitment in southern California from population surveys and in artificial reefs targeting white abalone recruitment since the listing of the species. A 13-y time series of white abalone abundance in prime habitat, surveyed with a remote-operated vehicle, was used in a population viability analysis to quantify: (1) the population decline and (2) the time to reach a quasi-extinction threshold. The annual decline in the population is 12%, which is comparable to adult natural mortality rates for abalone species. The quasi-extinction threshold of 1,000 individuals is met within 15 y. These results confirm that the white abalone populations in southern California are at high risk of extinction, and highlight the importance of active stocking and restoration for the species. To inform restoration, a deterministic density-dependent size-based matrix model was developed to investigate different stocking scenarios, incorporating an innovative method for modeling low populations by setting the reproductive term as a function of adult density to mimic a reproductive Allee effect. A minimum density of 0.14 abalone/m2 of stocked juveniles led to a maximum population growth rate (λ) of more than or equal to 1 for the model population within 10 y but that recovery was poor (mean λ15–20 ≤ 1.0) over time if the level of juvenile stocking was less than 0.23 abalone/m2 in the model population. The innovative approach of incorporating adult density into the reproductive term in the model quantitatively shows how low population densities can impact threatened and endangered species, and may be widely used for other species. These results can not only help guide stocking strategies but also allow for the quantitative evaluation of white abalone under the guidance of the IUCN Red List of Threatened Species, suggesting that white abalone should be considered Critically Endangered.

Comparing model predictions for ecosystem-based management

Ecosystem modeling is becoming an integral part of fisheries management, but there is a need to identify differences between predictions derived from models employed for scientific and management purposes. Here, we compared two models: a biomass-based food-web model (Ecopath with Ecosim (EwE)) and a size-structured fish community model. The models were compared with respect to predicted ecological consequences of fishing to identify commonalities and differences in model predictions for the California Current fish community. We compared the models regarding direct and indirect responses to fishing on one or more species. The size-based model predicted a higher fishing mortality needed to reach maximum sustainable yield than EwE for most species. The size-based model also predicted stronger top-down effects of predator removals than EwE. In contrast, EwE predicted stronger bottom-up effects of forage fisheries removal. In both cases, the differences are due to the presumed degree of trophic overlap between juveniles of large-bodied fish and adult stages of forage fish. These differences highlight how each model’s emphasis on distinct details of ecological processes affects its predictions, underscoring the importance of incorporating knowledge of model assumptions and limitation, possibly through using model ensembles, when providing model-based scientific advice to policy makers.

Are small fishes more sensitive to habitat loss? A generic size-based model

Habitat loss represents the greatest threat to freshwater biodiversity. The potential for life history attributes to correlate with the risks associated with habitat loss represents a possible mechanism for more effective and rapid assessments, especially in data-limited situations. Body size correlates with many other life history attributes and is a good starting point for investigating correlates with habitat loss. Here, we use a generic stage-based matrix population model, parameterized using length-based allometries, to investigate if such a mechanism exists. Our analysis revealed that small species (shorter maximum body length) were initially more sensitive to the loss of habitat. Moreover, distinct stage-based patterns exist showing an increased sensitivity of population growth rate for small species to both habitat loss and vital rate perturbations of pre-adult stages. This indicates that the pre-adult period represents a critical stage for the continued production of small species and increased importance of the conservation of habitat used by young-of-the-year and juvenile fishes.

Projecting spatiotemporal changes in suitable climate conditions to regenerate trees using niche differences between adult and juvenile trees

Assessing suitable climate conditions to regenerate trees over a large area is of great importance to investigate potential impacts of climate change. In this study, we developed a size-based species distribution model (SBSDM) to assess spatiotemporal changes in the tree regeneration niche separately from the growth niche in adults. Siebold’s beech (Fagus crenata) was selected as the target species. We projected (1) areas where adult and juvenile potential habitats (PHs) overlapped, (2)only-adult PHs, (3) only-juvenile PHs, and (4) non-habitats for 2080–2099 using the SBSDM, a distribution dataset from the Phytosociological Releve Database of Japan, and a future climatic dataset from 24 general circulation models (GCMs). We also projected juvenile PHs for all decades between 2011 and 2099 using four representative GCMs to assess potential lost decades of the regeneration niche. The SBSDM provided sufficient projections of adult and juvenile tree distributions as well as their niche differences under the current climate. Overlapping areas and only-adult PHs were projected to decrease by the end of this century. An increase in only-juvenile PHs was projected to occur in snowy regions, with juvenile PHs starting to decrease in warm and less snowy regions. Furthermore, juvenile PHs are expected to decrease widely around 2060 as well as at the end of this century due to considerable rapid warming around those times. We conclude that regeneration of F. crenata will start to decline in 2060, but snowy conditions will postpone the timing of the regeneration loss, causing an increase in only-juvenile PHs.

Two takes on the ecosystem impacts of climate change and fishing: Comparing a size-based and a species-based ecosystem model in the central North Pacific

We compare two ecosystem model projections of 21st century climate change and fishing impacts in the central North Pacific. Both a species-based and a size-based ecosystem modeling approach are examined. While both models project a decline in biomass across all sizes in response to climate change and a decline in large fish biomass in response to increased fishing mortality, the models vary significantly in their handling of climate and fishing scenarios. For example, based on the same climate forcing the species-based model projects a 15% decline in catch by the end of the century while the size-based model projects a 30% decline. Disparities in the models’ output highlight the limitations of each approach by showing the influence model structure can have on model output. The aspects of bottom-up change to which each model is most sensitive appear linked to model structure, as does the propagation of interannual variability through the food web and the relative impact of combined top-down and bottom-up change. Incorporating integrated size- and species-based ecosystem modeling approaches into future ensemble studies may help separate the influence of model structure from robust projections of ecosystem change.

Viability of Sea Fan Populations Impacted by Disease: Recruitment versus Incidence

Diseases are a threat to the viability of an increasing number of coral populations. In this study we analyze the effect of infection and recruitment rate on the viability and structure of sea fan (Gorgonia ventalina) populations using a size-based matrix model parameterized with data from field studies. The model predicts that the viability of sea fan populations is strongly influenced by disease incidence and recruitment. Under high recruitment rate, the disease incidence threshold for population viability is 0.12/yr. However, populations with no or low incidence may also go locally extinct given persistent low recruitment. The model also predicts an effect of recruitment on disease prevalence. Everything else being equal, sites with low recruitment will exhibit higher disease prevalence than ones with high recruitment, particularly in medium and large colonies. Elasticity analysis reveals that changes in colony survivorship are likely to have the strongest effect on population growth rate, particularly given low recruitment. We conclude that under current levels of incidence sea fan populations in the Caribbean are not at risk. However, future epizootics are likely to produce local extinctions particularly if coinciding spatially or temporally with low recruitment.

Trait‐based representation of diatom functional diversity in a plankton functional type model of the eutrophied southern North Sea

We introduce a trait‐based description of diatom functional diversity to an existing plankton functional type (PFT) model, implemented for the eutrophied coastal ecosystem in the Southern Bight of the North Sea. The trait‐based description represents a continuum of diatom species, each characterized by a distinct cell volume, and includes size dependence of four diatom traits: the maximum growth rate, the half‐saturation constants for nutrient uptake, the photosynthetic efficiency, and the relative affinity of copepods for diatoms. Through competition under seasonally varying forcing, the fitness of each diatom varies throughout time, and the outcome of competition results in a changing community structure. The predicted seasonal change in mean cell volume of the community is supported by field observations: smaller diatoms, which are more competitive in terms of resource acquisition, prevail during the first spring bloom, whereas the summer bloom is dominated by larger species which better resist grazing. The size‐based model is used to determine the ecological niche of diatoms in the area and identifies a range of viable sizes that matches observations. The general trade‐off between small, competitive diatoms and large, grazing‐resistant species is a convenient framework to study patterns in diatom functional diversity. PFT models and trait‐based approaches constitute promising complementary tools to study community structure in marine ecosystems.

Demand forecasting model for slow moving items

Demand forecasting for a slow moving product is a critical area of concern and becomes crucial to find the optimistic forecast value for a slow moving product which results in huge inventory ultimately affecting the cost. The two new models namely probabilistic demand model (PDM) and demand size-based model (DSBM) have been developed in this work by modifying the Croston’s model. Probabilistic demand model (PDM) has been developed by considering actual probabilities in the demand size per period and demand size-based model (DSBM) by directly estimating the demand size without any average per period considerations. Comparative study with the commonly used demand forecasting methods shows that the models follow close approximations to them and are versatile with different values of smoothening constant.

Estimating Biomass, Recruitment, and Harvest Rate for the Pacific Yellowleg Shrimp Farfantepenaeus californiensis from a Size-Based Model

Catch-at-size data were analyzed for Farfantepenaeus californiensis from fishing seasons 1978/1979 to 1994/1995. The catch-at-size model could be fitted to the catch-at-size data for the different fishing seasons. It was observed that the recruitment to the fishery changed suddenly during the study period, and the recruitment to the fishery may occur over a range of length classes. The recruits were defined as size classes less than 93.5mmin abdominal length. Recruitment varied from 200–3,800 million recruits. In contrast, the size classes were larger than 93.5 mm in terms of abdominal length, and the number of adults varied from 3,500,000–50,000,000. In the study zone, it was not common to find remnant biomass of adults. Consequently, the most abundant size intervals of abdominal length were 62.4 mm, 67 mm, and 72.2 mm. The results of the harvest rate-at-size showed that the size interval from 65–80mmin abdominal length was less than 0.05. The highest levels of harvest rate-at-size were estimated to be 85–125mm in abdominal length, with an estimated variation of 0.6–0.9. It was observed that individuals less than 93.5 mm in abdominal length are in the range of length classes in which recruitment to the fishery occurs. These recruits support the fishing pressure and the yield of the fishery; in contrast, the presence of adults is scarce. Therefore, this fishery in the region is strongly recruitment dependent.

Size-based predictions of food web patterns

We employ size-based theoretical arguments to derive simple analytic predictions of ecological patterns and properties of natural communities: size-spectrum exponent, maximum trophic level, and susceptibility to invasive species. The predictions are brought about by assuming that an infinite number of species are continuously distributed on a size–trait axis. It is, however, an open question whether such predictions are valid for a food web with a finite number of species embedded in a network structure. We address this question by comparing the size-based predictions to results from dynamic food web simulations with varying species richness. To this end, we develop a new size- and trait-based food web model that can be simplified into an analytically solvable size-based model. We confirm existing solutions for the size distribution and derive novel predictions for maximum trophic level and invasion resistance. Our results show that the predicted size-spectrum exponent is borne out in the simulated food webs even with few species, albeit with a systematic bias. The predicted maximum trophic level turns out to be an upper limit since simulated food webs may have a lower number of trophic levels, especially for low species richness, due to structural constraints. The size-based model possesses an evolutionary stable state and is therefore un-invadable. In contrast, the food web simulations show that all communities, irrespective of number of species, are equally open to invasions. We use these results to discuss the validity of size-based predictions in the light of the structural constraints imposed by food webs.

Trait-mediated indirect effects, predators, and disease: test of a size-based model

Increasing prevalence of wildlife disease accentuates the need to uncover drivers of epidemics. Predators can directly influence disease prevalence via density-mediated effects (e.g., culling infected hosts leading to reduced disease prevalence). However, trait-mediated indirect effects (TMIEs) of predators can also strongly influence disease--but predicting a priori whether TMIEs should increase or decrease disease prevalence can be challenging, especially since a single predator may elicit responses that have opposing effects on disease prevalence. Here, we pair laboratory experiments with a mechanistic, size-based model of TMIEs in a zooplankton host, fungal parasite, multiple predator system. Kairomones can either increase or decrease body size of the host Daphnia, depending on the predator. These changes in size could influence key traits of fungal disease, since infection risk and spore yield increase with body size. For six host genotypes, we measured five traits that determine an index of disease spread (R 0). Although host size and disease traits did not respond to kairomones produced by the invertebrate predator Chaoborus, cues from fish reduced body size and birth rate of uninfected hosts and spore yield from infected hosts. These results support the size model for fish; the birth and spore yield responses should depress disease spread. However, infection risk did not decrease with fish kairomones, thus contradicting predictions of the size model. Exposure to kairomones increased per spore susceptibility of hosts, countering size-driven decreases in exposure to spores. Consequently, synthesizing among the relevant traits, there was no net effect of fish kairomones on the R 0 metric. This result accentuates the need to integrate the TMIE-based response to predators among all key traits involved in disease spread.

Mechanistic origins of variability in phytoplankton dynamics: Part I: niche formation revealed by a size-based model

This paper aims to unravel the complexity of how cell size determines major ecological and physiological functions in unicellular algae. It assembles recent mechanistic descriptions for size dependencies of respiration and maximal resource uptake rates. New dependencies are derived for mortality due to sinking and grazing. The model also describes how internal nutrient quota varies within an autotrophic community due to the allometry of nutrient uptake. Net production, grazing, and sedimentation can be shown to be uni- or multi-modal functions of cell size, in accordance with literature data. Grazing mortality attains maxima at distinct prey sizes, which result from overlaying major zooplankton feeding spectra. Sedimentation vanishes for small cells due to Stokes’ law, but also for huge diatoms as long as they are vital. Their greater degree of vacuolation possibly promotes the capacity of buoyancy regulation. After synthesizing the physiological, morphological, and ecological relationships, intricate and eventually multi-modal growth–size dependencies arise. This niche building may explain part of the great diversity in phytoplankton. Multi-modal allometries can also induce paradoxical community shifts or enlarge the variety of community responses to external changes.

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.