Prey Cycles Research Articles

Reversed predator-prey cycles are driven by the amplitude of prey oscillations.

Ecoevolutionary feedbacks in predator–prey systems have been shown to qualitatively alter predator–prey dynamics. As a striking example, defense–offense coevolution can reverse predator–prey cycles, so predator peaks precede prey peaks rather than vice versa. However, this has only rarely been shown in either model studies or empirical systems. Here, we investigate whether this rarity is a fundamental feature of reversed cycles by exploring under which conditions they should be found. For this, we first identify potential conditions and parameter ranges most likely to result in reversed cycles by developing a new measure, the effective prey biomass, which combines prey biomass with prey and predator traits, and represents the prey biomass as perceived by the predator. We show that predator dynamics always follow the dynamics of the effective prey biomass with a classic ¼‐phase lag. From this key insight, it follows that in reversed cycles (i.e., ¾‐lag), the dynamics of the actual and the effective prey biomass must be in antiphase with each other, that is, the effective prey biomass must be highest when actual prey biomass is lowest, and vice versa. Based on this, we predict that reversed cycles should be found mainly when oscillations in actual prey biomass are small and thus have limited impact on the dynamics of the effective prey biomass, which are mainly driven by trait changes. We then confirm this prediction using numerical simulations of a coevolutionary predator–prey system, varying the amplitude of the oscillations in prey biomass: Reversed cycles are consistently associated with regions of parameter space leading to small‐amplitude prey oscillations, offering a specific and highly testable prediction for conditions under which reversed cycles should occur in natural systems.

Genetic variation determines which feedbacks drive and alter predator–prey eco‐evolutionary cycles

AbstractEvolution can alter the ecological dynamics of communities, but the effects depend on the magnitudes of standing genetic variation in the evolving species. Using an eco‐coevolutionary predator–prey model, I identify how the magnitudes of prey and predator standing genetic variation determine when ecological, evolutionary, and eco‐evolutionary feedbacks influence system stability and the phase lags in predator–prey cycles. Here, feedbacks are defined by subsystems, i.e., the dynamics of a subset of the components of the whole system when the other components are held fixed; ecological (evolutionary) feedbacks involve the direct and indirect effects between population densities (species traits) and eco‐evolutionary feedbacks involve the direct and indirect effects between population densities and traits. When genetic variation is low in both species, ecological feedbacks and eco‐evolutionary feedbacks involving either the predator or the prey trait have the strongest effects on system stability, when genetic variation is high in one species, evolutionary and eco‐evolutionary feedbacks involving that species’ trait have the strongest effects, and, when genetic variation is high in both species, evolutionary feedbacks involving one or both traits and eco‐coevolutionary feedbacks involving both traits have the strongest effects. I present the biological conditions under which each feedback can destabilize the whole system and cause predator–prey cycles. Predator–prey cycles can also arise when all feedbacks are stabilizing. This counterintuitive outcome occurs when feedbacks involving many variables are more stabilizing than feedbacks involving fewer variables or vice versa. I also identify how the indirect effects of prey and predator density on the predator dynamics (mediated by evolutionary responses in one or both species) alter the phase lags in predator–prey cycles. I present conditions under which the trait‐mediated indirect effects introduce delays that cause the lag between prey and predator peaks to increase. This work explains and unifies empirical and theoretical studies on how predator–prey coevolution alters the dynamics of predator–prey systems and how those effects depend on the magnitudes of prey and predator standing genetic variation.

The impact of a predator on the outcome of competition in the three-trophic food web

We study the effects of predation on the competition of prey populations for two resources in a chemostat. We investigate a variety of small food web compositions: the bi-trophic food web (two resources—two competing prey) and the three-trophic food web (two resources—two prey—generalist predator) comparing different model formulations: substitutable resources and essential resources, namely Liebig's minimum law model (perfect essential resources) and complementary resources formulations. The prediction of the outcome of competition is solely based on bifurcation analysis in which the inflow of resources into the chemostat is used as the bifurcation parameter. We show that the results for different bi-trophic food webs are very similar, as only equilibria are involved in the long-term dynamics. In the three-trophic food web, the outcome of competition is manifested largely by non-equilibrium dynamics, i.e., in oscillatory behavior. The emergence of predator–prey cycles leads to strong deviations between the predictions of the outcome of competition based on Liebig's minimum law and the complementary resources. We show that the complementary resources formulation yields a stabilization of the three-trophic food web by decreasing the existence interval of oscillations. Furthermore, we find an exchange of a region of oscillatory co-existence of all three species in Liebig's formulation by a region of bistability of two limit cycles containing only one prey and the predator in the complementary formulation.

Biological control of the chestnut gall wasp with T. sinensis: A mathematical model

The Asian chestnut gall wasp Dryocosmus kuriphilus, native of China, has become a pest when it appeared in Japan, Korea, and the United States. In Europe it was first found in Italy, in 2002. In 1982 the host-specific parasitoid Torymus sinensis was introduced in Japan, in an attempt to achieve a biological control of the pest. After an apparent initial success, the two species seem to have locked in predator–prey cycles of decadal length. We have developed a spatially explicit mathematical model that describes the seasonal time evolution of the adult insect populations, and the competition for finding egg deposition sites. In a spatially homogeneous situation the model reduces to an iterated map for the egg density of the two species. While, for realistic parameters, the map would support the hypothesis of biological control, the full model, in the same parameter range, does not give such a clear-cut answer. In particular, according to the spatially explicit model, the introduction of T. sinensis would spark a traveling wave of the parasitoid population that destroys the pest on its passage. Then, depending on the value of the diffusion coefficients of the two species, the pest may later be able to re-colonize the empty area left behind the wave. When this occurs the two populations do not seem to attain a state of spatial homogeneity, but produce an ever-changing pattern of traveling waves.

Theoretical impacts of habitat loss and generalist predation on predator–prey cycles

Certain herbivores and their predators undergo high amplitude periodic fluctuations in abundance in northern latitudes but exhibit damped cyclic dynamics in their respective southern ranges. Generalist predators and habitat disturbance have been identified as two features of southern habitats that may contribute to the attenuation of cycles in southern latitudes. Using the snowshoe hare and Canada lynx as model species, we employed a reaction–diffusion–advection framework with reaction terms taken from the May and Rosenzweig–MacArthur models to study the relative and joint damping impacts of generalist predation and habitat loss on predator–prey cycles. We found that generalist predation has consistently strong stabilizing effects and may represent a threat to the persistence of specialized predators. Habitat loss also ultimately results in the loss of cycles, but cycle amplitude and animal densities may not always decrease monotonically with habitat loss. The joint damping impacts of generalists and habitat loss can be severe, consistent with observations of low cycle amplitude, high predation rates, and significant habitat loss in the southern ranges of cyclic species. Elevated generalist predation rates at patch edges and in the surrounding matrix hasten cycle attenuation in situations that lead to increased prey exposure to generalists, including small patch sizes, higher movement rates into the matrix, and increased prey density at patch edges. The dominant driver of cycle attenuation, as well as cycle response to habitat disturbance, may vary between regions and systems. Field data that help clarify the relationships between habitat loss and fragmentation, generalist density and behavior, and cyclic activity would be invaluable in informing future modeling and conservation efforts.

Variable prey development time suppresses predator–prey cycles and enhances stability

Although theoretical models have demonstrated that predator-prey population dynamics can depend critically on age (stage) structure and the duration and variability in development times of different life stages, experimental support for this theory is non-existent. We conducted an experiment with a host-parasitoid system to test the prediction that increased variability in the development time of the vulnerable host stage can promote interaction stability. Host-parasitoid microcosms were subjected to two treatments: Normal and High variance in the duration of the vulnerable host stage. In control and Normal-variance microcosms, hosts and parasitoids exhibited distinct population cycles. In contrast, insect abundances were 18-24% less variable in High- than Normal-variance microcosms. More significantly, periodicity in host-parasitoid population dynamics disappeared in the High-variance microcosms. Simulation models confirmed that stability in High-variance microcosms was sufficient to prevent extinction. We conclude that developmental variability is critical to predator-prey population dynamics and could be exploited in pest-management programs.

Hunting and Prey Switching by Chimpanzees (Pan troglodytes schweinfurthii) at Ngogo

Predation can have major effects on vertebrate population dynamics, including predator–prey cycles that occur on multiple time scales when predators switch between preferred and alternative prey and changes in the abundance of preferred prey when the availability of alternative prey changes. Predation has been an important selective force in primate social evolution and may regulate some primate populations, but assessing its impact is often difficult. Chimpanzees (Pan troglodytes) provide opportunities for direct collection of data on predation intensity by following habituated predators because they regularly prey on a variety of vertebrates, including other primates. Chimpanzees mostly hunt red colobus monkeys (Procolobus spp.) wherever they live in sympatry. Previous reports have documented heavy predation on red colobus by chimpanzees in the unusually large Ngogo community, in Kibale National Park, Uganda, and have shown an apparent decline in the local red colobus population. Here, we update information on predation at Ngogo, give further evidence of a red colobus population decline, and ask whether the chimpanzees have made more effort to hunt alternative prey in response. Data collected between 1995 and 2014 show that the rate of alternative prey hunts has increased significantly, while the rate of red colobus hunts has declined. Predation on red colobus peaked in 2002; other prey have since accounted for significantly higher proportions of hunts and prey captures. The overall hunting rate has not changed significantly, but per capita meat availability has decreased because hunts of alternative prey lead to fewer captures than hunts of red colobus. The likelihood that the chimpanzees hunt red colobus on encounter has not changed significantly. In contrast, the likelihood of hunting on encounter has increased (redtail monkeys, Cercopithecus ascanius; gray-cheeked mangabeys, Lophocebus albigena) or remained stable (guerezas, Colobus guereza) for other primates that are major alternative prey species. Encounter rates have not changed for redtails and mangabeys, but the guereza encounter rate has decreased. These results imply that the red colobus population is not recovering and raise the possibility that the chimpanzees are having a negative impact on the guereza population. Chimpanzees are not obligate carnivores, but this may make them prone to cause such impacts because their own populations are probably not limited by those of their prey.

Ontogenetic specialism in predators with multiple niche shifts prevents predator population recovery and establishment

The effects of ontogenetic niche shifts on community structure and dynamics are underexplored, despite the occurrence of such shifts in the majority of animal species. We studied the form of niche shifts in a predator that exhibits multiple ontogenetic niche shifts, and analyzed how this life history complexity affects the size‐structured predator–prey dynamics in the system. The predator represents either an ontogenetic generalist, exhibiting a partial shift to predation (in which case an alternative resource is also available) or an ontogenetic specialist, exhibiting a complete shift (in which case the predator depends entirely on predation). We showed two effects on community dynamics from accounting for a complete niche shift to predation: (1) occurrence of alternative stable community states (coexistence and a prey‐only community state) and (2) occurrence of deterministic extinction following initially successful invasion (predators can invade an equilibrium with only prey, but are bound to go extinct after a few generations). Both phenomena are due to the match or mismatch in the timing of predators and suitably sized prey and the growth trajectory of the predator, which is plastic, due to the population feedback on available resources. In the case of persistence without invasion (alternative stable community states), slow growth during the pre‐piscivorous life stage is necessary to stay in tune with the prey cycle; in the case of extinction following invasion, slow growth through the pre‐piscivorous life stage causes the predator to reach the completely piscivorous stage when there is no prey available to feed upon. Somatic growth rates are directly coupled to food availability, which, in turn, is the result of density‐dependent feedbacks in the system. Since they primarily determine these density‐dependent feedbacks, the ontogenetic niche shifts in predator life history structure the community to a major extent.

Coevolution can reverse predator–prey cycles

A hallmark of Lotka-Volterra models, and other ecological models of predator-prey interactions, is that in predator-prey cycles, peaks in prey abundance precede peaks in predator abundance. Such models typically assume that species life history traits are fixed over ecologically relevant time scales. However, the coevolution of predator and prey traits has been shown to alter the community dynamics of natural systems, leading to novel dynamics including antiphase and cryptic cycles. Here, using an eco-coevolutionary model, we show that predator-prey coevolution can also drive population cycles where the opposite of canonical Lotka-Volterra oscillations occurs: predator peaks precede prey peaks. These reversed cycles arise when selection favors extreme phenotypes, predator offense is costly, and prey defense is effective against low-offense predators. We present multiple datasets from phage-cholera, mink-muskrat, and gyrfalcon-rock ptarmigan systems that exhibit reversed-peak ordering. Our results suggest that such cycles are a potential signature of predator-prey coevolution and reveal unique ways in which predator-prey coevolution can shape, and possibly reverse, community dynamics.

Dampening prey cycle overrides the impact of climate change on predator population dynamics: a long‐term demographic study on tawny owls

Predicting the dynamics of animal populations with different life histories requires careful understanding of demographic responses to multifaceted aspects of global changes, such as climate and trophic interactions. Continent-scale dampening of vole population cycles, keystone herbivores in many ecosystems, has been recently documented across Europe. However, its impact on guilds of vole-eating predators remains unknown. To quantify this impact, we used a 27-year study of an avian predator (tawny owl) and its main prey (field vole) collected in Kielder Forest (UK) where vole dynamics shifted from a high- to a low-amplitude fluctuation regime in the mid-1990s. We measured the functional responses of four demographic rates to changes in prey dynamics and winter climate, characterized by wintertime North Atlantic Oscillation (wNAO). First-year and adult survival were positively affected by vole density in autumn but relatively insensitive to wNAO. The probability of breeding and number of fledglings were higher in years with high spring vole densities and negative wNAO (i.e. colder and drier winters). These functional responses were incorporated into a stochastic population model. The size of the predator population was projected under scenarios combining prey dynamics and winter climate to test whether climate buffers or alternatively magnifies the impact of changes in prey dynamics. We found the observed dampening vole cycles, characterized by low spring densities, drastically reduced the breeding probability of predators. Our results illustrate that (i) change in trophic interactions can override direct climate change effect; and (ii) the demographic resilience entailed by longevity and the occurrence of a floater stage may be insufficient to buffer hypothesized environmental changes. Ultimately, dampened prey cycles would drive our owl local population towards extinction, with winter climate regimes only altering persistence time. These results suggest that other vole-eating predators are likely to be threatened by dampening vole cycles throughout Europe.

Effects of prey metapopulation structure on the viability of black‐footed ferrets in plague‐impacted landscapes: a metamodelling approach

Summary Species interactions have been largely ignored in extinction risk assessment. However, the black‐footed ferret Mustela nigripes exemplifies a class of endangered species for which strong species interactions cannot be ignored. This species is an obligate predator of prairie dogs Cynomys spp., and sylvatic plague Yersinia pestis epizootics threaten to undermine recovery efforts by functionally eliminating the prey base. Multispecies ‘metamodelling’ techniques offer new opportunities for exploring population dynamics under strong species interdependencies and disease. To investigate ferret extinction risk in plague‐affected landscapes, we simultaneously modelled plague epidemiological processes, prairie dog metapopulation dynamics and ferret demographic responses. Ferret population dynamics were investigated at an important release site (Conata Basin in South Dakota) and for 500 artificial prey landscapes spanning a wide range of realistic colony configurations (e.g. total area, # colonies, spatial clustering) and demographic characteristics. Our simulation models indicate that ferrets are unlikely to persist through episodes of plague at Conata Basin unless they can access prey resources from a wider region or unless management actions can otherwise substantially reduce plague transmission. We show that large, diffuse prairie dog metapopulations (those with colonies spread over a region >2500 km2) are most likely to support ferret populations in plague‐affected landscapes. Our results also highlight the potential importance of metapopulation connectivity in fuelling plague epizootics and thereby imperilling black‐footed ferret conservation efforts. We describe a cycle (c. 5‐ to 25‐year period) of plague‐driven population crashes that is an emergent property of our models, and which can destabilize ferret populations. Synthesis and applications. On the basis of our models, we conclude that few North American prairie dog complexes cover sufficient land area to sustain black‐footed ferret populations through plague‐driven crashes in prey abundance. Consequently, our results underscore the importance of working with many constituents to conserve large prairie dog landscapes in addition to continued development of plague mitigation tools. In addition, the strong relationship between plague‐induced oscillatory prey cycles and predator population persistence highlights the potential conservation benefits of imposing strategic barriers to connectivity in areas over which plague outbreak cycles are strongly synchronous.

Nonlinear effect of dispersal rate on spatial synchrony of predator-prey cycles.

Spatially-separated populations often exhibit positively correlated fluctuations in abundance and other population variables, a phenomenon known as spatial synchrony. Generation and maintenance of synchrony requires forces that rapidly restore synchrony in the face of desynchronizing forces such as demographic and environmental stochasticity. One such force is dispersal, which couples local populations together, thereby synchronizing them. Theory predicts that average spatial synchrony can be a nonlinear function of dispersal rate, but the form of the dispersal rate-synchrony relationship has never been quantified for any system. Theory also predicts that in the presence of demographic and environmental stochasticity, realized levels of synchrony can exhibit high variability around the average, so that ecologically-identical metapopulations might exhibit very different levels of synchrony. We quantified the dispersal rate-synchrony relationship using a model system of protist predator-prey cycles in pairs of laboratory microcosms linked by different rates of dispersal. Paired predator-prey cycles initially were anti-synchronous, and were subject to demographic stochasticity and spatially-uncorrelated temperature fluctuations, challenging the ability of dispersal to rapidly synchronize them. Mean synchrony of prey cycles was a nonlinear, saturating function of dispersal rate. Even extremely low rates of dispersal (<0.4% per prey generation) were capable of rapidly bringing initially anti-synchronous cycles into synchrony. Consistent with theory, ecologically-identical replicates exhibited very different levels of prey synchrony, especially at low to intermediate dispersal rates. Our results suggest that even the very low rates of dispersal observed in many natural systems are sufficient to generate and maintain synchrony of cyclic population dynamics, at least when environments are not too spatially heterogeneous.

Variable cost of prey defense and coevolution in predator–prey systems

Predation acts as a selective pressure, driving prey adaptation. Predators can also evolve counter‐defenses to increase the likelihood of successful attack. Investment in either trait can be costly, leading to a trade‐off between the traits and other fitness components. Costs for defense have been shown experimentally to depend on environmental factors such as resource availability. This suggests that costs can increase with population size, rather than remaining constant as models often assume. Using a quantitative trait model with predator–prey coevolution, we investigate how both population and trait dynamics are affected by density‐dependent prey defense cost (“variable cost”) vs. density‐independent cost (“fixed cost”). We assume predator counter‐defense cost is always density independent. We also investigate the effect of relative speeds of prey and predator evolution on population and trait dynamics, by varying a parameter that determines each population's additive genetic variance. For both models, increasing the speed of predator evolution always has a stabilizing effect on the dynamics, while increasing the speed of prey evolution (within a biologically reasonable range) is largely destabilizing. Within the plausible range of prey evolution speed, variable cost of prey defense is more stabilizing than fixed cost. Our results suggest that density‐dependent costs of defense can have important effects on predator–prey dynamics, even when evolution is relatively slow. Our results might also help to explain why many real populations do not display predator–prey cycles.

Predator–prey oscillations can shift when diseases become endemic

In epidemiology, knowing when a disease is endemic is important. This is usually done by finding the basic reproductive number, R0, using equilibrium-based calculations. However, oscillatory dynamics are common in nature. Here, we model a disease with density dependent transmission in an oscillating predator–prey system. The condition for disease persistence in predator–prey cycles is based on the time-average density of the host and not the equilibrium density. Consequently, the time-averaged basic reproductive number R0¯ is what determines whether a disease is endemic, and not on the equilibrium-based basic reproductive number R0⁎. These findings undermine any R0 analysis based solely on steady states when predator–prey oscillations exist for density dependent diseases.

How does adaptive consumer movement affect population dynamics in consumer–resource metacommunities with homogeneous patches?

This article uses simple models to explore the impact of adaptive movement by consumers on the population dynamics of a consumer–resource metacommunity consisting of two identical patches. Consumer–resource interactions within a patch are described by the Rosenzweig–MacArthur predator–prey model, and these dynamics are assumed to be cyclic in the absence of movement. The per capita movement rate from one patch to the other is an increasing function of the difference between the per capita birth minus death rate in the destination patch and that in the currently occupied patch. Several variations on this model are considered. Results show that adaptive movement frequently creates anti-phase cycles in the two patches; these suppress the predator–prey cycle and lead to low temporal variation of the total population sizes of both species. Paradoxically, even when movement is very sensitive to the fitness difference between patches, perfect synchrony of patches is often much less likely than in comparable systems with random movement. Under these circumstances adaptive movement of consumers often generates differences in the average properties of the two patches. In addition, mean global densities and responses to global perturbations often differ greatly from similar systems with no movement or random movement.

Phase locking, the Moran effect and distance decay of synchrony: experimental tests in a model system

Spatially separated populations of many species fluctuate synchronously. Synchrony typically decays with increasing interpopulation distance. Spatial synchrony, and its distance decay, might reflect distance decay of environmental synchrony (the Moran effect), and/or short-distance dispersal. However, short-distance dispersal can synchronize entire metapopulations if within-patch dynamics are cyclic, a phenomenon known as phase locking. We manipulated the presence/absence of short-distance dispersal and spatially decaying environmental synchrony and examined their separate and interactive effects on the synchrony of the protist prey species Tetrahymena pyriformis growing in spatial arrays of patches (laboratory microcosms). The protist predator Euplotes patella consumed Tetrahymena and generated predator-prey cycles. Dispersal increased prey synchrony uniformly over both short and long distances, and did so by entraining the phases of the predator-prey cycles. The Moran effect also increased prey synchrony, but only over short distances where environmental synchrony was strongest, and did so by increasing the synchrony of stochastic fluctuations superimposed on the predator-prey cycle. Our results provide the first experimental demonstration of distance decay of synchrony due to distance decay of the Moran effect. Distance decay of the Moran effect likely explains distance decay of synchrony in many natural systems. Our results also provide an experimental demonstration of long-distance phase locking, and explain why cyclic populations provide many of the most dramatic examples of long-distance spatial synchrony in nature.

Predator manipulation experiments: impacts on populations of terrestrial vertebrate prey

Quantifying the relative impacts of top‐down vs. bottom‐up control of ecosystems remains a controversial issue, with debate often focusing on the perennial question of how predators affect prey densities. To assess predator impacts, we performed a worldwide meta‐analysis of field experiments in which the densities of terrestrial vertebrate predators were manipulated and the responses of their terrestrial vertebrate prey were measured. Our results show that predation indeed limits prey populations, as prey densities change substantially after predator manipulations. The main determinant of the result of an experiment was the efficiency of predator manipulation. Positive impacts of predator manipulation appeared to increase with duration of the experiment for non‐cyclic prey, while the opposite was true for cyclic prey. In addition, predator manipulation showed a large positive impact on cyclic prey at low prey densities, but had no obvious impact at peak prey densities. As prey population densities generally respond predictably to predator manipulations, we suggest that control of introduced vertebrate predators can be used to effectively conserve and manage native wildlife. However, care should be taken when controlling native predators, especially apex species, owing to their importance as strong interactors and the biodiversity value of their habitats. We discuss gaps in our knowledge of predator–prey relationships and methodological issues related to manipulation experiments. An important guideline for future studies is that adequate monitoring of predator numbers before and during the experiment is the only way to ensure that observed responses in prey populations are actually caused by changes in predation impacts.

Internally driven alternation of functional traits in a multispecies predator–prey system

The individual functional traits of different species play a key role for ecosystem function in aquatic and terrestrial systems. We modeled a multispecies predator-prey system with functionally different predator and prey species based on observations of the community dynamics of ciliates and their algal prey in Lake Constance. The model accounted for differences in predator feeding preferences and prey susceptibility to predation, and for the respective trade-offs. A low food demand of the predator was connected to a high food selectivity, and a high growth rate of the prey was connected to a high vulnerability to grazing. The data and the model did not show standard uniform predator-prey cycles, but revealed both complex dynamics and a coexistence of predator and prey at high biomass levels. These dynamics resulted from internally driven alternations in species densities and involved compensatory dynamics between functionally different species. Functional diversity allowed for ongoing adaptation of the predator and prey communities to changing environmental conditions such as food composition and grazing pressure. The trade-offs determined whether compensatory or synchronous dynamics occurred which influence the variability at the community level. Compensatory dynamics were promoted by a joint carrying capacity linking the different prey species which is particularly relevant at high prey biomasses, i.e., when grazers are less efficient. In contrast, synchronization was enhanced by the coupling of the different predator and prey species via common feeding links, e.g., by a high grazing pressure of a nonselective predator. The communities had to be functionally diverse in terms of their trade-offs and their traits to yield compensatory dynamics. Rather similar predator species tended to cycle synchronously, whereas profoundly different species did not coexist. Compensatory dynamics at the community level thus required intermediately strong tradeoffs for functional traits in both predators and their prey.

Biophysical ocean observation in the southeastern Bering Sea

Integrated ocean observation, from physical and atmospheric forcing mechanisms to the distribution and abundance of top‐level predators, is critical to the investigation of marine ecosystems and the impact of climate change on them. We integrated data from a biophysical mooring in the southeast Bering Sea to create a one‐year snapshot of ocean dynamics in this remote large marine ecosystem. Distinct patterns in production (chlorophyll), zooplankton biovolume (copepods and euphausiids) and the occurrence of zooplankton predators (fin and right whales) were defined and related to discrete features in the annual physical cycle. Peaks in prey and predator cycles were linked to spikes in fluorescence that occurred at the onset of water column stratification in late spring 2006 and the appearance of sea ice in late winter 2007. These data illustrate the capability and potential of integrated ocean observing systems (IOOS) to describe seasonal variability and linkages in a remote marine ecosystem.

Carotenoids in nestling Montagu’s harriers: variations according to age, sex, body condition and evidence for diet-related limitations

Carotenoids are colored pigments forming the basis of many avian social traits. Before their utilization carotenoids must be acquired through diet and mobilized for specific uses. The relationships between carotenoid-based coloration, circulating carotenoids and body condition have been well studied in adult birds, but little is known in nestlings. Here, we investigated variations in carotenoid-based coloration in a raptor nestling, the Montagu's harrier (Circus pygargus), both in captivity and in natural conditions, and within a vole (poor-carotenoid source and cyclic prey) specialist population. We studied these variations according to nestling age and sex, and possible limitations in carotenoid availability by comparing years of contrasted prey abundance and using carotenoid supplementation experiments. Captive nestlings, fed only with mice, were strongly carotenoid limited. Wild nestlings were also carotenoid limited, especially in a year of high vole abundance. Nestlings were in better condition but less colored during a peak vole abundance year than during a low vole abundance year, when harriers targeted more alternative preys (birds, insects). Thus, variation in vole abundance resulted in a de-coupling of body condition and carotenoid-based coloration in this population. This suggested that the positive relation between the body condition and carotenoid-based traits, typically found in adult birds, could be restricted to adults or nestlings of species that feed on carotenoid-rich food. Our results should stimulate more work on the functions and mechanisms of carotenoid-based traits in nestlings, which deserve more attention and most likely differ from those of adult birds.