Predator Population Size Research Articles

Size-dependent functional response of the round goby Neogobius melanostomus; implications for more accurate impact potential calculation

Abundance and per-capita foraging efficiency are essential factors for predicting and quantifying an invasive predator impact on prey, i.e., the impact potential (IP). However, population structure is not included in the calculation, and IP accuracy might be improved by incorporating predator body size. The population structure of the round goby Neogobius melanostomus, a highly invasive predator, was surveyed in the Elbe River. We determined the functional response (FR, per capita foraging) of the three most abundant size classes of N. melanostomus on the water louse Asellus aquaticus. We then calculated the IP for each size class and for the entire population with (the actual impact potential – IPA) and without (the impact potential for limit size rage – IPLSR) population body size structure (based on FR of the medium size class). All three size classes of the predator showed type II FR with respect to A. aquaticus. The estimated FR parameters, attack rate and handling time, as well as the maximum feeding rate, were size dependent. Despite the lowest per capita foraging efficiency, small individuals displayed the highest IP among the tested size classes because of their high abundance. Conversely, medium and large individuals, although showing highest per capita foraging efficiency, displayed lower IP. Hence, IPA showed more precise IP calculations compared to IPLSR. Overestimation of the potential impact as a consequence of omitting predator population size structure was negligible at the investigated locality. The IP of the N. melanostomus population five years post-invasion can be accurately calculated based on the FR of medium-sized fish.

Impacts of Predation-Driven Allee Effect in a Predator–Prey Model

In the present work, we introduce one of the most significant biological factors — predator-driven Allee effect in a modified Leslie–Gower (LG) model. Our mathematical analyses include local stability analysis, Hopf bifurcation analysis, direction of Hopf bifurcation and Bogdanov–Tankens bifurcation around the coexisting equilibrium point. We also perform numerical simulations to validate our analytical results and to explore rich dynamics. Our results indicate that introducing predator-driven Allee effect not only destabilizes the system but also changes the characteristics of Hopf bifurcation from supercritical to subcritical. The system exhibits two types of bistability behavior between prey-free equilibrium and coexisting equilibrium, and prey-free equilibrium and limit cycle oscillation. Further, we explore an interesting result that the probability of extinction risk of prey population of modified LG system with predator-driven Allee effect is much higher in comparison to modified LG system when Allee term is absent. We have also demonstrated that predation-driven Allee effect increases extinction risk of prey population when the initial predator population size is large.

Numerical approach to an age-structured Lotka-Volterra model.

We study the impact of an age-dependent interaction in a structured predator-prey model. We present two approaches, the PDE (partial differential equation) and the renewal equation, highlighting the advantages of each one. We develop efficient numerical methods to compute the (un)stability of steady-states and the time-evolution of the interacting populations, in the form of oscillating orbits in the plane of prey birth-rate and predator population size. The asymptotic behavior when species interaction does not depend on age is completely determined through the age-profile and a predator-prey limit system of ODEs (ordinary differential equations). The appearance of a Hopf bifurcation is shown for a biologically meaningful age-dependent interaction, where the system transitions from a stable coexistence equilibrium to a collection of periodic orbits around it, and eventually to a stable limit cycle (isolated periodic orbit). Several explicit analytical solutions are used to test the accuracy of the proposed computational methods.

Field Evaluation of Organophosphorus Insecticides, Chlorpyrifos and Fungal Bio-Pesticides, Beauveria bassiana Towards the Sugar Beet Moth Scrobipalpa ocellatella (Lepidoptera: Gelechiidae) and Studying their Effect on the Population Size of the Associated Arthropod Predators in the Egyptian Sugar Beet Fields.

Field Evaluation of Organophosphorus Insecticides, Chlorpyrifos and Fungal Bio-Pesticides, Beauveria bassiana Towards the Sugar Beet Moth Scrobipalpa ocellatella (Lepidoptera: Gelechiidae) and Studying their Effect on the Population Size of the Associated Arthropod Predators in the Egyptian Sugar Beet Fields.

Conservation implications of forage base requirements of a marine predator population at carrying capacity

SummaryPrey depletion may contribute to marine predator declines, yet the forage base required to sustain an unfished population of predatory fish at carrying capacity is unknown. We integrated demographic and physiological data within a Bayesian bioenergetic model to estimate annual consumption of a gray reef shark (Carcharhinus amblyrhynchos) population at a remote Pacific atoll (Palmyra Atoll) that are at carrying capacity. Furthermore, we estimated the proportion of the atoll's reef fish biomass production consumed by the gray reef sharks, assuming sharks either partially foraged pelagically (mean 7%), or solely within the reef environment (mean 52%). We then predicted the gray reef shark population potential of other, less remote Pacific Ocean coral reef islands, illustrating that current populations are substantially smaller than could be supported by their forage base. Our research highlights the utility of modeling how far predator population sizes are from their expected carrying capacity in informing marine conservation.

Predator-Prey in Tumor-Immune Interactions: A Wrong Model or Just an Incomplete One?

Tumor-immune interactions are often framed as predator-prey. This imperfect analogy describes how immune cells (the predators) hunt and kill immunogenic tumor cells (the prey). It allows for evaluation of tumor cell populations that change over time during immunoediting and it also considers how the immune system changes in response to these alterations. However, two aspects of predator-prey type models are not typically observed in immuno-oncology. The first concerns the conversion of prey killed into predator biomass. In standard predator-prey models, the predator relies on the prey for nutrients, while in the tumor microenvironment the predator and prey compete for resources (e.g. glucose). The second concerns oscillatory dynamics. Standard predator-prey models can show a perpetual cycling in both prey and predator population sizes, while in oncology we see increases in tumor volume and decreases in infiltrating immune cell populations. Here we discuss the applicability of predator-prey models in the context of cancer immunology and evaluate possible causes for discrepancies. Key processes include “safety in numbers”, resource availability, time delays, interference competition, and immunoediting. Finally, we propose a way forward to reconcile differences between model predictions and empirical observations. The immune system is not just predator-prey. Like natural food webs, the immune-tumor community of cell types forms an immune-web of different and identifiable interactions.

Predator-Prey Model with Refuge, Fear and Z-Control

In this paper, we consider a predator-prey model incorporating fear and refuge. Our results show that the predator-free equilibrium is globally asymptotically stable if the ratio between the death rate of predators and the conversion rate of prey into predator is greater than the value of prey in refuge at equilibrium. We also show that the co-existence equilibrium points are locally asymptotically stable if the value of the prey outside refuge is greater than half of the carrying capacity. Numerical simulations show that when the intensity of fear increases, the fraction of the prey inside refuge increases; however, it has no effect on the fraction of the prey outside refuge, in the long run. It is shown that the intensity of fear harms predator population size. Numerical simulations show that the application of Z-control will force the system to reach any desired state within a limited time, whether the desired state is a constant state or a periodic state. Our results show that when the refuge size is taken to be a non-constant function of the prey outside refuge, the systems change their dynamics. Namely, when it is a linear function or an exponential function, the system always reaches the predator-free equilibrium. However, when it is taken as a logistic equation, the system reaches the co-existence equilibrium after long term oscillations.

Trophic cascade in a marine protected area with artificial reefs: spiny lobster predation mitigates urchin barrens.

An ultimate benefit of marine protected areas (MPAs) is to reverse trophic cascades caused by human-driven collapse of critical ecological interactions. Here we demonstrate that, despite a small scale (0.28km2 ) and not being fully protected, an MPA with strict fishing management and habitat enhancement by artificial reefs (ARs) in southwest Japan can lead to well-established macroalgal communities on widespread sea urchin barrens through cascading effects of predator recovery. Areas with low urchin densities occurred in and around daytime lobster (Panulirus japonicus) shelters primarily formed by quarry-rock ARs inside the MPA. We confirmed in the laboratory that lobsters preyed on two dominant sea urchins (Echinometra sp. A and Heliocidaris crassispina), with size- and species-dependent predation. The area with few urchins extended farther (˜65m) from an AR with numerous lobsters than from a natural shelter (patch reef) with far fewer lobsters. Causation of this pattern was confirmed by a tethering experiment showing that predation on urchins was similarly high at and near lobster shelters but decreased at ˜100m from the AR to a similar level as at an unprotected site. Time-lapse photography revealed that predation on tethered urchins was due mostly to the largest size class of lobsters (>100mm carapace length), which comprised only 7% of the population, highlighting the importance of large-sized lobsters in controlling urchin abundance in localized areas adjacent to urchin-dominated barrens. Despite an ongoing once-a-year fishing event permitted within the MPA, lobster populations were persistent, demonstrating that the cascading effect of the lobsters on urchins and ultimately macroalgae was robust to temporary reductions in predator population size. Erect macroalgal cover was not simply accounted for by snapshot urchin density or biomass, suggesting a hysteresis effect of the phase shifts between macroalgal dominance and urchin barren states.

Effects of the prey landscape on the fitness of the bacterial predators Bdellovibrio and like organisms.

Bdellovibrio and like organisms (BALOs) are obligate predatory bacteria commonly encountered in the environment. In dual predator-prey cultures, prey accessibility ensures optimal feeding and replication and rapid BALO population growth. However, the environmental prey landscape is complex, as it also incorporates non-prey cells and other particles. These may act as decoys, generating unproductive encounters which in turn may affect both predator and prey population dynamics. In this study, we hypothesized that increasing decoy:prey ratios would bring about increasing costs on the predator's reproductive fitness. We also tested the hypothesis that different BALOs and decoys would have different effects. To this end, we constructed prey landscapes including periplasmic or epibiotic predators including two types of decoy under a large range of initial decoy:prey ratio, and mixed cultures containing multiple predators and prey. We show that as decoy:prey ratios increase, the maximal predator population sizes is reduced and the time to reach it significantly increases. We found that BALOs spent less time handling non-prey (including superinfection-immune invaded prey) than prey cells, and did not differentiate between efficient and less efficient prey. This may explain why in multiple predator and prey cultures, less preferred prey appear to act as decoy.

Populations of high‐value predators reflect the traits of their prey

The extent to which prey traits combine to influence the abundance of predators is still poorly understood, particularly for mixed predators in sympatry and in aquatic ecosystems. In this study, we characterise prey use and distribution in iconic bird (grey wagtails and Eurasian dippers) and fish species (brown trout and Atlantic salmon) to assess whether prey traits could predict populations of these four riverine predators. Specifically, we hypothesised that: 1) prey key traits would predict predator populations more effectively than 2) diversity of prey traits, 3) the taxonomic abundance or richness of prey (known as traditional or mass‐effect types of biodiversity) or 4) the prevailing environmental conditions. Combined predator population sizes were predicted better by a few key traits – specifically those revealing prey habitat use, size and drifting behaviour – than by prey diversity or prey trait diversity or environmental conditions. Our findings demonstrate that the complex relationships between prey assemblages and multiple predator species can be represented mechanistically when the key prey traits that govern encounter and consumption rates are identified. Given their apparent potential to reveal trophic relationships, and to complement more traditional measures of prey abundance, we advocate further development of trait‐based approaches in predator–prey research.

Numerical modelling of the population of grey seal (Halichoerus grypus) from the Baltic Sea in the context of reduction of damage to fishing economy

The work is a source material for organizations dealing with the management of the aquatic environment, including regulating the population of species that pose a real threat to fishermen. Predators, which have no natural enemies in the Baltic Sea environment, including the grey seal, have been part of the conflict between fisheries users and ecologists for decades. As part of establishing a system for conducting grey seal population control programs that will not affect the number of colonies, but will only allow real control over the excessive exploitation of fishing nets by this species mathematical models have been created. Due to the difficulties in obtaining actual data as input data for modeling natural populations, the proposed model is based only on expert data, therefore it is dedicated only to the seal species. The development of the population size can be ensured depending on such factors as herd size, hunting and procedures for birth rate and mortality. On the basis of multivariate analysis and the application of the created algorithm, several sample schemes were formulated for the large and small grey seal swarm. The authors gave the government administration a tool to implement the anticipated programs limiting the size of the grey seal predator population.

Molecular Ecological Network Analyses: An Effective Conservation Tool for the Assessment of Biodiversity, Trophic Interactions, and Community Structure

Global biodiversity is threatened by the anthropogenic restructuring of animal communities, rewiring species interaction networks in real-time as individuals are extirpated or introduced. Conservation science and adaptive ecosystem management demand more rapid, quantitative, and non-invasive technologies for robustly capturing changing biodiversity and quantifying species interactions. Here we develop molecular ecological network analyses (MENA) as an ecosystem assessment tool to address these needs. To construct the ecological network, we used environmental DNA from feces to identify the plant and mammal diet of two carnivores: puma (Puma concolor) and bobcat (Lynx rufus); two omnivores: coyote (Canis latrans) and gray fox (Urocyon cinereoargenteus); and two herbivores: black-tailed deer (Odocoileus hemionus) and black-tailed jackrabbit (Lepus californicus) in a well-studied Californian reserve. To evaluate MENA as a comprehensive biodiversity tool, we applied our framework to identify the structure of the network, patterns of trophic interactions, key species, and to assess its utility in capturing the biodiversity of the area. The high dietary taxonomic resolution enabled the assessment of species diversity, niche breadth and overlap. The network analysis revealed a dense ecological network with a high diversity of weakly connected species and a community that is highly modular and non-nested. The significant prevalence of tri-trophic chain and exploitative competition patterns indicates (i) the removal or reintroduction of a top predator would trigger a trophic cascade within this community, directly affecting their prey and indirectly the plant communities, and (ii) the potential impact of indirect effects between two predators that consume the same prey. These results suggest that the recent resurgence of puma in the study area may impact the herbaceous and woody vegetation and the population size of other predators. This effect of fluctuating predator populations and plant communities could be predicted through MENA’s fine-scale assessment of the diet selection and the identified keystone species. Although just using a subset of species, MENA more rapidly, accurately, and effectively captured the broader biodiversity of the area in comparison to other methodologies. MENA reconstructed and unveiled the hidden complexity in trophic structure and interaction networks within the community, providing a promising toolkit for biodiversity and ecosystem management.

Non-consumptive effects stabilize herbivore control over multiple generations.

Understanding the factors that influence predator-prey dynamics requires an investigation of oscillations in predator and prey population sizes over time. However, empirical studies are often performed over one or fewer predator generations. This is particularly true for studies addressing the non-consumptive effects of predators on prey. In a previous study that lasted less than one predator generation, we demonstrated that two species of parasitoid wasps additively suppressed aphid populations through a combination of consumptive and non-consumptive effects. However, the non-consumptive effects of one wasp reduced the reproductive success of the other, suggesting that a longer-term experiment may have revealed antagonism between the wasps. The goal of our current study is to evaluate multi-generation consumptive and non-consumptive interactions between pea aphids (Acyrthosiphon pisum) and the wasps Aphidius ervi and Aphidius colemani. Aphidius ervi is a common natural enemy of pea aphids. Aphidius colemani is a non-consumptive enemy that does not consume pea aphids, but negatively affects pea aphid performance through behavioral disturbance. Large field cages were installed to monitor aphid abundance in response to the presence and absence of both species of wasp over four weeks (two parasitoid generations). We found that the non-consumptive enemy A. colemani initially controlled the pea aphid population, but control in the absence of parasitism was not sustainable over the long term. Aphidius ervi suppressed pea aphids through a combination of consumptive and non-consumptive effects. This suppression was more effective than that of A. colemani, but aphid abundance fluctuated over time. Suppression by A. ervi and A. colemani together was complementary, leading to the most effective and stable control of pea aphids. Therefore, promoting a diverse natural enemy community that contributes to pest control through consumptive and non-consumptive interactions may enhance the stability of herbivore population suppression over time.

The lethal 23%: predator demography influences predation risk for threatened prey

AbstractGlobally, wildlife managers often control predator populations to protect biodiversity, livestock or other valued resources. Most assume that the predation impact of each individual predator is the same and that removing any individual predator produces a benefit to the target species. However, research suggests predation efficacy can vary within a predator species according to phenotypic characteristics. Understanding these individual differences may be critical for managing predation impacts on particular categories of prey including small populations where predation effects are amplified. We used dietary data from 1748 feral cats euthanized over 30 years during a control programme in arid Australia to determine whether any predator attributes could predict their effect on different prey weight classes. Feral cats in our study ate a wide range of prey including reptiles, mammals, birds and invertebrates. Demography (body mass) was a highly significant predictor of diet. Cats weighing 3 kg fed predominantly on prey <50 g increasing to >500 g when cats attained a body mass of 6 kg. Of more significance was that diet varied between demographic groups but also within a single demographic group (adult males) based on body mass, with results having significant implications for threatened prey. Modelling indicated that for a fixed predator population size, the predation rate on prey in a >500 g weight class increased by 28% when the ratio of large (>4.2 kg) to small adult males varied according to its natural range (12%–80% over the 30‐year study). Results suggest that variations in predator demography can significantly impact predation rates on prey species and should be included in predator–prey models for small prey populations. On average, large male cats comprised 23% of the population and our findings suggest that targeting this ‘lethal demographic’ and manipulating predator demography should be prioritized along with lowering predator density to reduce predation impacts on prey weighing more than 500g.

Threats from the air: Damselfly predation on diverse prey taxa.

To understand the diversity and strength of predation in natural communities, researchers must quantify the total amount of prey species in the diet of predators. Metabarcoding approaches have allowed widespread characterization of predator diets with high taxonomic resolution. To determine the wider impacts of predators, researchers should combine DNA techniques with estimates of population size of predators using mark-release-recapture (MRR) methods, and with accurate metrics of food consumption by individuals. Herein, we estimate the scale of predation exerted by four damselfly species on diverse prey taxa within a well-defined 12-ha study area, resolving the prey species of individual damselflies, to what extent the diets of predatory species overlap, and which fraction of the main prey populations are consumed. We identify the taxonomic composition of diets using DNA metabarcoding and quantify damselfly population sizes by MRR. We also use predator-specific estimates of consumption rates, and independent data on prey emergence rates to estimate the collective predation pressure summed over all prey taxa and specific to their main prey (non-biting midges or chironomids) of the four damselfly species. The four damselfly species collectively consumed a prey mass equivalent to roughly 870 (95% CL 410-1,800) g, over 2months. Each individual consumed 29%-66% (95% CL 9.4-123) of its body weight during its relatively short life span (2.1-4.7days; 95% CL 0.74-7.9) in the focal population. This predation pressure was widely distributed across the local invertebrate prey community, including 4 classes, 19 orders and c. 140 genera. Different predator species showed extensive overlap in diets, with an average of 30% of prey shared by at least two predator species. Of the available prey individuals in the widely consumed family Chironomidae, only a relatively small proportion (0.76%; 95% CL 0.35%-1.61%) were consumed. Our synthesis of population sizes, per-capita consumption rates and taxonomic distribution of diets identifies damselflies as a comparatively minor predator group of aerial insects. As the next step, we should add estimates of predation by larger odonate species, and experimental removal of odonates, thereby establishing the full impact of odonate predation on prey communities.

Predator population size structure alters consumption of prey from epigeic and grazing food webs.

Numerous studies have found that predators can suppress prey densities and thereby impact important ecosystem processes such as plant productivity and decomposition. However, prey suppression by spiders can be highly variable. Unlike predators that feed on prey within a single energy channel, spiders often consume prey from asynchronous energy channels, such as grazing (live plant) and epigeic (soil surface) channels. Spiders undergo few life cycle changes and thus appear to be ideally suited to link energy channels, but ontogenetic diet shifts in spiders have received little attention. For example, spider use of different food channels may be highly specialized in different life stages and thus a species may be a multichannel omnivore only when we consider all life stages. Using stable isotopes, we investigated whether wolf spider (Pardosa littoralis, henceforth Pardosa) prey consumption is driven by changes in spider size. Small spiders obtained > 80% of their prey from the epigeic channel, whereas larger spiders used grazing and epigeic prey almost equally. Changes in prey consumption were not driven by changes in prey density, but by changes in prey use by different spider size classes. Thus, because the population size structure of Pardosa changes dramatically over the growing season, changes in spider size may have important implications for the strength of trophic cascades. Our research demonstrates that life history can be an important component of predator diet, which may in turn affect community- and ecosystem-level processes.

Dynamics of a discrete-time stage-structured predator–prey system with Holling type II response function

A discrete-time model of predator–prey dynamics with Holling type II response function is proposed. Each species considered has its age structure which is typical for natural communities. The bifurcations, dynamic modes and a possibility of its shifting are studied for the proposed model. The stability loss of a non-trivial fixed point is realised according to Neimark–Sacker and Feigenbaum scenarios. The phase space structure of multistability areas in which a variation of current numbers of prey or predator can shift the dynamic modes is analysed using basins of attraction. Particular attention is paid to the investigation of the feasible values of the parameters in which the model has a biological meaning. To understand the mechanisms of interspecific interaction influence on each species dynamics in a community, we compare cases with and without interspecific interaction. The presence of interspecific interaction in the community increases the variety of emerging dynamic modes of the predator population size.

A review of methods for quantifying spatial predator–prey overlap

AbstractBackgroundStudies that attempt to measure shifts in species distributions often consider a single species in isolation. However, understanding changes in spatial overlap between predators and their prey might provide deeper insight into how species redistribution affects food web dynamics.Predator–prey overlap metricsHere, we review a suite of 10 metrics [range overlap, area overlap, the local index of collocation (Pianka's O), Hurlbert's index, biomass‐weighted overlap, asymmetrical alpha, Schoener's D, Bhattacharyya's coefficient, the global index of collocation and the AB ratio] that describe how two species overlap in space, using concepts such as binary co‐occurrence, encounter rates, spatial niche similarity, spatial independence, geographical similarity and trophic transfer. We describe the specific ecological insights that can be gained using each overlap metric, in order to determine which is most appropriate for describing spatial predator–prey interactions for different applications.Simulation and case studyWe use simulated predator and prey distributions to demonstrate how the 10 metrics respond to variation in three types of predator–prey interactions: changing spatial overlap between predator and prey, changing predator population size and changing patterns of predator aggregation in response to prey density. We also apply these overlap metrics to a case study of a predatory fish (arrowtooth flounder, Atheresthes stomias) and its prey (juvenile walleye pollock, Gadus chalcogrammus) in the Eastern Bering Sea, AK, USA. We show how the metrics can be applied to understand spatial and temporal variation in the overlap of species distributions in this rapidly changing Arctic ecosystem.ConclusionsUsing both simulated and empirical data, we provide a roadmap for ecologists and other practitioners to select overlap metrics to describe particular aspects of spatial predator–prey interactions. We outline a range of research and management applications for which each metric may be suited.

A simple Gause‐type predator–prey model considering social predation

The consumer–resource relationships are among the most fundamental of all ecological relationships and have been the focus of ecology since its beginnings. Usually are described by nonlinear differential equation systems, putting the emphasis in the effect of antipredator behavior (APB) by the prey; nevertheless, a minor quantity of articles has considered the social behavior of predators.In this work, two predator–prey models derived from the Volterra model are analyzed, in which the equation of predators is modified considering cooperation or collaboration among predators.It is well known that competition among predators produces a stabilizing effect on system describing the model, since there exists a wide set in the parameter space where the system has a unique equilibrium point in the phase plane, which is globally asymptotically stable.Meanwhile, the cooperation can originate more complex and unusual dynamics. As we will show, it is possible to prove that for certain subset of parameter values the predator population sizes tend to infinite when the prey population goes to extinct.This apparently contradicts the idea of a realistic model, when it is implicitly assumed that the predators are specialist, ie, the prey is its unique source of food. However, this could be a desirable effect when the prey constitutes a plague.To reinforce the analytical result, numerical simulations are presented.

Prey switching and consumption by seabirds in the central California Current upwelling ecosystem: Implications for forage fish management

Abstract Effective ecosystem-based fishery management involves assessment of foraging interactions among consumers, including upper level predators such as marine birds and humans. Of particular value is information on predator energetic and consumption demands and how they vary in response to the often volatile dynamics of forage populations, as well as the factors that affect forage availability and potential prey switching. We examined the prey requirements of common murre (Uria aalge), Brandt's cormorant (Phalacrocorax penicillatus), and rhinoceros auklet (Cerorhinca monocerata) in the central California Current over a 30-year period, 1986–2015. We developed a bioenergetics model that incorporates species-specific values for daily basic energy needs, diet composition, energy content of prey items and assimilation efficiency, and then projected results relative to stock size and levels of commercial take of several species. The most common forage species consumed were juvenile rockfish (Sebastes spp.), northern anchovy (Engraulis mordax), smelt (Osmeridae), and market squid (Doryteuthis opalescens). Total biomass of forage species consumed during the breeding season varied annually from 8500 to >60,000 metric ton (t). Predator population size and diet composition had the greatest influence on overall prey consumption. The most numerous forage species consumed in a given year was related to abundance estimates of forage species derived from an independent ecosystem assessment survey within the central place foraging range of breeding avian predators. The energy density of dominant prey consumed annually affected predator energy expenditure during chick rearing and whether prey switching was required. Increased forage species take by predators, as revealed by seabirds, may be adding consumptive pressure to key forage fish populations, regardless of the potential additional impacts of commercial fisheries. Improving estimates of consumption by predators and fisheries will promote more effective management from an ecosystem perspective.