Article

The adaptation of generalist predators’ diet in a multi-prey context: insights from new functional responses

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Abstract

The ability for a generalist consumer to adapt its foraging strategy (the multi-species functional response, MSFR) is a milestone in ecology as it contributes to the structure of food webs. The trophic interaction between a generalist predator, as the red fox or the barn owl, and its prey community, mainly composed of small mammals, has been empirically and theoretically widely studied. However, the extent to which these predators adapt their diet according to both multi-annual changes in multiple prey species availability (frequency dependence) and the variation of the total prey density (density dependence) is unexplored.We provide a new general model of MSFR disentangling changes in prey preference according to variation of prey frequency (switching) and of total prey density (we propose the new concept of “rank switching”). We apply these models to two large data sets of red fox and barn owl foraging. We show that both frequency-dependent and density-dependent switching are critical properties of these two systems, suggesting that barn owl and red fox have an accurate image of the prey community in terms of frequency and absolute density. Moreover, we show that negative switching, which can lead to prey instability, is a strong property of the two systems.

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... Active prey selection is based on active decisions of the forager to accept or to avoid a prey (Stephens et al. 2007, Toft 1999. What is often overlooked is that the selectivity for a certain prey type by a generalist predator (i.e. its proportional representation in a predator's diet relative to its proportional representation in the environment) can be highly dynamic depending on the prey community composition (Baudrot et al. 2016, Owen-Smith & Mills 2008, Schmidt et al. 2012a. The selectivity for a certain prey type i by generalist predators can be constant, i.e. it does not change with changing prey community composition. ...
... The selectivity for a certain prey type i by generalist predators can be constant, i.e. it does not change with changing prey community composition. The selectivity for prey i can change with total density of overall prey availability, change with absolute density of the prey type i in the environment, and/or relative density of the prey type i (Baudrot et al. 2016). ...
... The change in selectivity for prey can arise, for example, when predators use different optimization criteria at low and high prey densities. They can behave opportunistically when they are highly energy-limited but they can become more selective at high prey densities (Baudrot et al. 2016, Riechert 1991, Stephens et al. 2007). The change in selectivity for prey can also arise as generalist predators try to achieve the optimal composition of nutrients that enhances their fitness by consuming various prey types in a certain ratio (Mayntz et al. 2005, Schmidt et al. 2012a, b, Toft et al. 2019. ...
Article
Prey selection by generalist predators can be highly dynamic depending on the prey community structure. However, the dynamics of prey selection at the stage of prey entrapping are rarely investigated in trap-building predators, probably because their traps have been previously considered to intercept mobile prey proportionally to its availability in environment. Here we investigated the dynamics of prey selection by the orb-weaving spider Gasteracantha hasselti (Araneidae) depending on the composition of the available prey in tropical lowland forests located in northeastern Thailand. We found that Gasteracantha captured a wide variety of prey but selected, on average, mostly Coleoptera and Diptera. The selectivity of Gaster-acantha's webs for Coleoptera was constant across the changes in overall prey availability and prey composition. The web selectivity for Hemiptera decreased rapidly with increasing relative densities of Hemiptera in the environment. The selectivity for Diptera and Hymen-optera increased and decreased, respectively, with their absolute densities in the environment. The relative selectivity of Gasteracantha's traps for a particular prey type was driven by the presence and density of the highly selected prey rather than overall prey density. The results show that the selectivity of Gasteracantha's traps for prey had both fixed and dynamic components and the dynamic component was determined by the relative as well as absolute densities of the particular prey types in the environment.
... They are widely used to describe predator-prey interactions but describe also perfectly well the consumption of resources by a population. Baudrot et al. (2016) reference nine different MSFRs in the case of predator-prey system and suggest that Holling III function well captured the growing reduction of one consumer population according to the level on resource. Such functions have also been used by Tilman to describe the dynamics of multi plant species competing for one limited resource (Tilman, 1988;Gillet, 2008a). ...
... Following considerations on functional responses from Baudrot et al. (2016), we introduced a switch on resource-consumer interactions. In this N red i function it corresponds to an inflection point on a mineral N value that depends on the considered species. ...
... We model this grazing by referring to functional responses of predator-prey systems. We refer to a comparison of several functional responses from Baudrot et al. (2016) and, finally, we capture this switch by a Holling III function, defined in equation (II.19) by setting ng = 2 and denoting τ grazing the set of intervals of grazing days. ...
Thesis
La modélisation dynamique des systèmes écologiques constitue une méthode incontournable pour comprendre,prédire et contrôler la dynamique des écosystèmes semi-naturels, qui fait intervenir des processuscomplexes. Le principal objectif de cette thèse est de développer un modèle permettant de simuler la dynamiqueà moyen terme de la végétation herbacée dans les prairies permanentes, en tenant compte à lafois de la productivité et de la biodiversité. Les prairies sont des réservoirs présentant une forte biodiversitévégétale, qui soutiennent de nombreux services écosystémiques. Sur le plan agricole, cette importantediversité contribue à la qualité de la production fourragère, et de plus, elle permet une plus grande résistancede la végétation face à des changements climatiques (réchauffement moyen, vagues de chaleur etde sécheresse).Pourtant, cette notion clé de biodiversité n’est que faiblement prise en considération dans la modélisationde l’écosystème prairial : elle est souvent absente ou alors présente sous une forme très simplifiée. Enréponse à ces considérations, ces travaux de thèse présentent la construction d’un modèle de successionbasé sur des processus, décrit par un système d’équations différentielles ordinaires, qui représente ladynamique de la végétation aérienne des prairies tempérées. Ce modèle intègre les principaux facteursécologiques impactant la croissance et la compétition des espèces herbacées, et peut s’ajuster à n’importequel niveau de diversité, par le choix du nombre et de l’identité des espèces initialement présentes dansl’assemblage. Ce formalisme mécaniste de modélisation nous permet alors d’analyser les relations qui lientdiversité, productivité et stabilité, en réponse à différentes conditions climatiques et différents modes degestion agricole.[...]Ces résultats soulignent alors le besoin de prendre en compte le rôle clé joué par la biodiversité dansles modèles de l’écosystème prairial, de par son impact sur le comportement des dynamiques simulées.De plus, pour rendre correctement compte des interactions au sein de la végétation, le nombre d’espècesconsidéré dans le modèle doit être suffisamment important. Enfin, nous comparons les simulations devégétation de ce modèle à des mesures issues de deux sites expérimentaux, la prairie de fauche d’Oensingen,et le pâturage de Laqueuille. Les résultats de ces comparaisons sont encourageants et soulignentla pertinence du choix et de la représentation des processus écologiques clés qui composent ce modèlemécaniste.Ce travail de thèse propose donc un modèle, en total adéquation avec les besoins actuels en terme demodélisation de l’écosystème prairial, qui permet de mieux comprendre la dynamique de la végétationherbacée et les interactions entre productivité, diversité et stabilité.
... They are widely used to describe predator-prey interactions but describe also perfectly well the consumption of resources by a population. Baudrot et al. (2016) reference nine different MSFRs in the case of predator-prey system and suggest that Holling III function well captured the growing reduction of one consumer population according to the level on resource. Such functions have also been used by Tilman to describe the dynamics of multi plant species competing for one limited resource (Tilman, 1988;Gillet, 2008a). ...
... Following considerations on functional responses from Baudrot et al. (2016), we introduced a switch on resource-consumer interactions. In this N red i function it corresponds to an inflection point on a mineral N value that depends on the considered species. ...
... We model this grazing by referring to functional responses of predator-prey systems. We refer to a comparison of several functional responses from Baudrot et al. (2016) and, finally, we capture this switch by a Holling III function, defined in equation (II.19) by setting ng = 2 and denoting τ grazing the set of intervals of grazing days. ...
Thesis
Full-text available
La modélisation dynamique des systèmes écologiques constitue une méthode incontournable pour comprendre, prédire et contrôler la dynamique des écosystèmes semi-naturels, qui fait intervenir des processus complexes. Le principal objectif de cette thèse est de développer un modèle permettant de simuler la dynamique à moyen terme de la végétation herbacée dans les prairies permanentes, en tenant compte à la fois de la productivité et de la biodiversité. Les prairies sont des réservoirs présentant une forte biodiversité végétale, qui soutiennent de nombreux services écosystémiques. Sur le plan agricole, cette importante diversité contribue à la qualité de la production fourragère, et de plus, elle permet une plus grande résistance de la végétation face à des changements climatiques (réchauffement moyen, vagues de chaleur et de sécheresse).Pourtant, cette notion clé de biodiversité n'est que faiblement prise en considération dans la modélisation de l'écosystème prairial : elle est souvent absente ou alors présente sous une forme très simplifiée. En réponse à ces considérations, ces travaux de thèse présentent la construction d'un modèle de succession basé sur des processus, décrit par un système d'équations différentielles ordinaires, qui représente la dynamique de la végétation aérienne des prairies tempérées. Ce modèle intègre les principaux facteurs écologiques impactant la croissance et la compétition des espèces herbacées, et peut s'ajuster à n'importe quel niveau de diversité, par le choix du nombre et de l'identité des espèces initialement présentes dans l'assemblage. Ce formalisme mécaniste de modélisation nous permet alors d'analyser les relations qui lient diversité, productivité et stabilité, en réponse à différentes conditions climatiques et différents modes de gestion agricole.Ce modèle mathématique représente la composition du couvert végétal par plusieurs variables d'état, qui décrivent les valeurs de biomasse d'espèces dominantes ou de type fonctionnel de plantes. Or la taille du réservoir initial d'espèces considérée peut avoir des conséquences sur les résultats de la dynamique simulée de l'écosystème, en terme de productivité, de diversité et de stabilité. Ce choix peut également influencer la sensibilité du modèle à différents paramètres de forçage qui le composent. Pour traiter cette question, nous développons une méthode basée sur les outils d'analyse de sensibilité, pour comparer les comportements de versions alternatives du modèle, qui se distinguent par leur niveau de diversité qu'elles considèrent. Soulignons que cette méthodologie présente un aspect novateur, en effectuant l'analyse de sensibilité du modèle par l'utilisation d'arbres de régression multivariée. Nous évaluons et comparons la sensibilité de chacune de ces versions alternatives du modèle aux paramètres de contrôle clés du modèle, qui sont liés à la fertilité du sol, au climat et à la gestion agricole. Nous établissons que la sensibilité de la structure de la communauté et de l'homogénéité de la répartition des espèces au sein de l'assemblage aux paramètres de contrôle diffère considérablement selon le niveau de diversité considéré. Nous montrons un glissement, en réponse à l'augmentation de la taille du réservoir d'espèces, depuis une forte importance de la fertilité du sol vers une forte importance d'intensité du traitement agricole. Ces résultats soulignent alors le besoin de prendre en compte le rôle clé joué par la biodiversité dans les modèles de l'écosystème prairial, de par son impact sur le comportement des dynamiques simulées. De plus, pour rendre correctement compte des interactions au sein de la végétation, le nombre d'espèces considéré dans le modèle doit être suffisamment important. Enfin, nous comparons les simulations de végétation de ce modèle à des mesures issues de deux sites expérimentaux, la prairie de fauche d'Oensingen, et le pâturage de Laqueuille. Les résultats de ces comparaisons sont encourageants et soulignent la pertinence du choix et de la représentation des processus écologiques clés qui composent ce modèle mécaniste. Ce travail de thèse propose donc un modèle, en total adéquation avec les besoins actuels en terme de modélisation de l'écosystème prairial, qui permet de mieux comprendre la dynamique de la végétation herbacée et les interactions entre productivité, diversité et stabilité.
... This latter question has been tackled in [5] where the authors focused on the transmission of the parasite in Eastern Europe, where the DHs are the red foxes (Vulpes vulpes) and the IHs are two small mammals, the common vole (Microtus arvalis) and the water vole (Arvicola scherman). Following a preliminary ecological modeling of the trophic relationships in [4], where it was shown that the property of prey switching, i.e a change in the preference of the predator to a prey species with a variation of its relative density, was a characteristic of the studied predator-prey interactions, the transmission of the Em parasite has then been described using the epidemiological diagram of Figure 8 (where i = 1, 2 denotes a type of prey, S, resp I, refers to suceptible populations, resp. infected), and translated through the ODEs system (4). ...
... Following a preliminary ecological modeling of the trophic relationships in [4], where it was shown that the property of prey switching, i.e a change in the preference of the predator to a prey species with a variation of its relative density, was a characteristic of the studied predator-prey interactions, the transmission of the Em parasite has then been described using the epidemiological diagram of Figure 8 (where i = 1, 2 denotes a type of prey, S, resp I, refers to suceptible populations, resp. infected), and translated through the ODEs system (4). ...
... Such a function, called functional response, is a modeling characteristics of predator-prey interactions that represents the intake rate of the predator as a function of prey densities. The most common shapes of functional responses are Holling type I (linear), Holling type II (first order rational) and Holling type III (second order rational), see [4,15,35] for a review about all the existing current shapes. ...
Article
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This article introduces the notion of basic reproduction number R 0 in mathematical epi-demiology. After an historic reminder describing the steps leading to the statement of its mathematical definition, we explain the next-generation matrix method allowing its calculation in the case of epidemic models described by ordinary differential equations (ODEs). The article then focuses, through four ODEs examples and an infection load structured PDE model, on the usefulness of the R 0 to address biological as well mathematical issues.
... Raptors and owls show both numerical and functional responses depending on the variation of their food supply, particularly the density fluctuation of their main prey (Korpimäki & Norrdahl 1989, 1991, Salamolard et al. 2000, Tome 2003, Reif et al. 2004, Millon & Bretagnolle 2008, Tóth 2014, Baudrot et al. 2016. The reproductive output and population dynamics of these avian predators are strongly affected by multi-annual periodic (cyclic) or irregular fluctuation of small mammals, especially herbivorous voles (Korpimäki et al. 2002, Klok & de Roos 2007, Pavluvčík et al. 2015, Zárybnická et al. 2015, Fay et al. 2020. ...
... However, Barn Owls frequently select a given prey species and/or group, and based on their functional response, switch easily between prey items in their foraging strategy (Yom-Tov & Wool 1997, Tores et al. 2005, Romano et al. 2020. According to the 'alternative prey hypothesis', if the main prey species declines in the given year, generalist predators can show dietary shifts and switch to alternative prey (Angelstam et al. 1984), which was detected in case of raptors (Reif et al. 2001, Riegert et al. 2009, Kreiderits et al. 2016, Dementavičius et al. 2020) and different owls (Korpimäki et al. 1990, Jędrzejewski et al. 1994, Sasvári et al. 2000, Riegert et al. 2009), including also the Common Barn-owl (Roulin 2004a, Tores et al. 2005, Charter et al. 2015, Baudrot et al. 2016. ...
... Considering the potential alternative prey of Common Barn-owl, we did not find significant relationship between the proportion of red-toothed shrews (Sorex genus) and reproductive parameters, which could be caused by this group of shrews being a subordinate prey category in the diet of owls in our study area and the examined period. Conversely, other studies found higher consumption rate of Sorex species (at the species or genus level) (Benedek et al. 2007, Bernard et al. 2010, Szűcs et al. 2014, Baudrot et al. 2016. Bene dek et al. (2007) reported a higher consumption frequency of Soricidae, which increased the diversity of diet and reflected a low abundance of rodents, particularly that of the Common Vole, although it was characteristic of only one of the two studied areas. ...
Article
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In the present study, we analysed the variation of breeding parameters and the diet composition of the Common Barn-owl (Tyto alba) in three different demographic phases of the Common Vole (Microtus arvalis) in a complete population cycle between two outbreaks. The study was conducted in the south-eastern part of the Transdanubian region in South Hungary. For the analysis, we used data of 81 randomly selected first clutches from 2015 to 2019, a time period which represented a full demographic cycle of the Common Vole after the 2014 outbreak with an exceptionally high peak. We tested the impact of prey abundance and diversity of diet composition as continuous predictors as well as the demographic phase of Common Vole and the mesoregion as categorical explanatory variables on the measured reproductive outputs as response variables using Generalized Linear Models (GLM). Considering the breeding parameters, the number of fledglings, and fledging and reproductive success were significantly higher in the increase phase than during the vole crash phase. Based on GLM models, our results demonstrated that the clutch size of the Common Barn-owl is determined ultimately by the availability and consumption rate of the Common Vole as main prey, while other small mammal prey categories did not affect the clutch size. These results support the finding that the clutch size of vole-eating raptors and owls, which begin breeding periods in early spring predicts the vole abundance in this early spring period. Considering the other investigated small mammal prey groups, the alternative prey role was confirmed only in case of the Murid rodent prey categories ( Apodemus spp., Muridae).
... Second, when prey are mobile, predator diet is more strongly determined by variation in vulnerability among prey than by active choice 13 . Interestingly, prey selectivity can also vary with the total prey available (i.e., 'rank switching' 33 ). One proposed explanation for this is that predators target easy-to-capture prey when overall prey density is low, but switch to targeting more profitable prey types at higher total prey densities 33,34 . ...
... Interestingly, prey selectivity can also vary with the total prey available (i.e., 'rank switching' 33 ). One proposed explanation for this is that predators target easy-to-capture prey when overall prey density is low, but switch to targeting more profitable prey types at higher total prey densities 33,34 . In such cases, the pattern of lethal predation should be governed by prey vulnerability at low total prey density, but by predator preference when total prey density is high, irrespective of their relative abundances. ...
... Instead, prey selection shifted from a significant preference for mobile unpalatable prey at low total prey density to a significant preference for less active palatable prey at high total prey density. A shift in prey selection resulting from changes in total prey density (i.e., "rank switching") has been observed in other generalist predators 33 , but its general importance has been largely overlooked. Our profitability trials indicate that toad tadpoles are easier for dragonfly nymphs to obtain (lower time to capture), but that a greater proportion of each leopard frog tadpole captured was consumed. ...
Article
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Understanding the factors governing predation remains a top priority in ecology. Using a dragonfly nymph-tadpole system, we experimentally varied predator density, prey density, and prey species ratio to investigate: (i) whether predator interference varies between prey types that differ in palatability, (ii) whether adding alternate prey influences the magnitude of predator interference, and (iii) whether patterns of prey selection vary according to the predictions of optimal diet theory. In single-prey foraging trials, predation of palatable leopard frog tadpoles was limited by prey availability and predator interference, whereas predation of unpalatable toad tadpoles was limited by handling time. Adding unpalatable prey did not affect the predator’s kill rate of palatable prey, but the presence of palatable prey increased the influence of predator density on the kill rate of unpalatable prey and reduced unpalatable prey handling time. Prey selection did not change with shifts in the relative abundance of prey types. Instead, predators selected easy-to-capture unpalatable prey at low total densities and harder-to-capture palatable prey at high densities. These results improve our understanding of generalist predation in communities with mobile prey, and illustrate that characteristics of the prey types involved govern the extent to which alternate prey influence the predator’s kill rate.
... Since we treated small mustelids as vole specialist predators, we assumed a Holling Type II functional response with attack rate a M and handling time h M (Equation 2). We then represented foxes feeding on voles and mustelids by a multi-species functional response derived from Holling Type III, referring to generalist feeding behaviour (Baudrot, Perasso, Fritsch, Giraudoux, & Raoul, 2016). For that, we denoted a VF and a MF the fox attack rate on voles and mustelids respectively. ...
... We assumed that AR in dead voles disappeared from the system when voles decomposed (assumed in one week: d = 1/7 per day). Mustelids could feed on live voles V, or non-decomposed dead voles V d and we assumed a Type II functional response adapted for a multi-species functional response (Baudrot et al., 2016). Mustelids ingested AR with absorption rate η M (ratio between biomasses of voles, B V , and mustelids, B M ) and the total of ingested voles (alive V and dead V d ) was defined by function Θ M (V, V d ) (see Table 1). ...
Article
1. Understanding pesticide impacts on populations of target/non‐target species and communities is a challenge to applied ecology. When predators that otherwise regulate pest densities ingest prey contaminated with pesticides, this can suppress predator populations by secondary poisoning. It is, however, unknown how species relationships and protocols of treatments (e.g. anticoagulant rodenticide (AR)) interact to affect pest regulation. 2. To tackle this issue, we modelled a heuristic non‐spatialized system including montane water voles, specialist vole predators (stoats, weasels), and a generalist predator (red fox) which consume voles, mustelids and other prey. By carrying out a broad‐range sensitivity analysis on poorly known toxicological parameters, we explored the impact of 5 farmer functional responses (defined by both AR quantity and threshold vole density above which AR spreading is prohibited) on predator‐prey interactions, AR transfer across the trophic chain and population effects. 3. Spreading AR to maintain low vole densities suppressed mustelid and fox populations, leading to vole population dynamics being entirely regulated by AR use. Such vole‐suppression treatment regimes inhibited predation ecosystem services and promoted pesticide dependence. 4. Keeping vole density below acceptable bounds by spreading AR while maintaining sufficient voles as prey resources led to less AR being applied and extended periods without AR in the environment, benefiting predators while avoiding episodes with high vole density. This may meet farm production interests while minimizing the impact on mustelid and fox populations and associated ecosystem processes. These alternating phases of mustelids and farmer regulation highlight the consequence of intraguild relationship where mustelids may rescue foxes from poisoning. Both global and wide‐range sensitivity analysis illustrate the tightrope between predator‐prey regulation and pesticide‐pest regulation. 5. Synthesis and applications Different pesticide protocols lead to a rich variety of predator prey dynamics in agro‐ecosystems. Our model reveals the need to maintain refuges with sufficient non‐poisoned voles for sustaining specialist mustelids, to conserve the predator community given the potential of secondary poisoning with rodenticides. We suggest that long periods without pesticide treatment are essential to maintain predator populations, and that practices of pesticides use that attempt to permanently suppress a pest over a large scale are counterproductive.
... where γ ki and a ki are the discovery rates of prey k by predator i, and h i the handling time assuming it mostly depends on the predator physiological needs (Baudrot et al., 2016). ...
... Herein, we use Baudrot et al. (2016)'s approach to describe the processes underlying predation governed by a type II functional response. α i denotes the rate of prey accessibility for predator i, p ki the preference of predator i for prey k, and h ki the handling time of prey k by predator i once killed. ...
Article
Dynamic food web models describe how species abundances change over time as a function of trophic and life‐history parameters. They are essential to predicting the response of ecosystems to perturbations. However, they are notoriously difficult to parameterise, so that most models rely heavily either on allometric scaling of parameters or inverse estimation of biomass flows. The allometric approach makes species of comparable body mass have near‐identical parameters which can generate extinctions within a trophic level. The biomass flow approach is more precise, but is restricted to steady‐states, which is not appropriate for time‐varying environments. Adequately parameterising large food webs of temperate and arctic environments requires to deal both with many species of similar sizes and a strongly seasonal environment. Inspired by the rich empirical knowledge on the vertebrate food web of the Bialowieza forest, we parameterize a bipartite food web model comprising 21 predators and 124 prey species. Our model is a non‐autonomous coupled ODE system that allows for seasonality in life‐history and predation parameters. Birth and death rates, seasonal descriptions of diet for each species, food requirements and biomass information are combined into a seasonal parameterisation of a dynamic food web model. Food web seasonality is implemented with time‐varying intrinsic growth rate and interaction parameters, while predation is modelled with both type I and type II functional responses. All our model variants allow for >80 % persistence in spite of massive apparent competition, and a quantitative match to observed (seasonal) biomasses. We also identify trade‐offs between maximising persistence, reproducing observed biomasses, and ensuring model robustness to sampling errors. Although multi‐annual cycles are expected with type II functional responses, they are here prevented by a strong predator self‐regulation. We discuss these results and possible improvements of the model. We provide a general workflow to parameterise dynamic food web models in seasonal environments, based on a real case study. This may help to better predict how biodiverse food webs respond to changing environments.
... Despite this, overall CPUE varied little between seasons, suggesting that penguins were able to maintain stable foraging effort and success despite marked changes in diet (Baudrot, Perasso, Fritsch, Giraudoux, & Raoul, 2016;Holling, 1959). ...
... Prey availability to predators may be considered a proxy for abundance (Velarde et al., 2013), but there are behavioural and environmental factors that can confound interpretation. Generalists may disproportionately feed on the most abundant prey (Jaworski, Bompard, Genies, Amiens-Desneux, & Desneux, 2013), and, when overall prey abundance is low, they may choose to target the most easily caught prey ('rank switching': Baudrot et al., 2016). If pCPUE analysis indicates that species A has declined, it may actually be that species B has become more available. ...
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Detecting changes in marine food webs is challenging, but top predators can provide information on lower trophic levels. However, many commonly measured predator responses can be decoupled from prey availability by plasticity in predator foraging effort. This can be overcome by directly measuring foraging effort and success and integrating these into a measure of foraging efficiency analogous to the catch per unit effort (CPUE) index employed by fisheries. We extended existing CPUE methods so that they would be applicable to the study of generalist foragers, which introduce another layer of complexity through dietary plasticity. Using this method, we inferred species‐specific patterns in prey availability and estimated taxon‐specific biomass consumption. We recorded foraging trip duration and body mass change of breeding little penguins Eudyptula minor and combined these with diet composition identified via non‐invasive faecal DNA metabarcoding to derive CPUE indices for individual prey taxa. We captured weekly patterns of availability of key fish prey in the penguins’ diet and identified a major prey shift from sardine Sardinops sagax to red cod Pseudophycis bachus between years. In each year, predation on a dominant fish species (~150 g/day) was replaced by greater diversity of fish in the diet as the breeding season progressed. We estimated that the colony extracted ~1,300 tonnes of biomass from their coastal ecosystem over two breeding seasons, including 219 tonnes of the commercially important sardine and 215 tonnes of red cod. This enhanced pCPUE is applicable to most central‐placed foragers and offers a valuable alternative to existing metrics. Informed prey‐species biomass estimates extracted by apex and meso predators will be a useful input for mass‐balance ecosystem models and for informing ecosystem‐based management. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article
... Then, lynx switch to caribou calves (Rangifer tarandus), and the cycle continues (Bergerud, 1983). As a whole, those multiple and complex interactions can hardly be investigated in depth by simple modeling (Baudrot et al., 2016) or by small-scale experiments that cannot technically take into account all the relevant space-time scales and species communities involved in the real world and, thus, be generalized. ...
... The description of the dietary response in this context where the two main prey abundances varied among several other alternative food resources is quite complex (Bernard et al., 2010;Dupuy et al., 2009;Giraudoux, 1991;Weber & Aubry, 1993). Comparisons of multispecies functional response (MSFR) models with empirical data on the red fox and barn owl showed that switching between prey depends on the proportion of the prey available among other prey (frequency dependence), as commonly thought, but also on the total amount of prey (density dependence), with a nonlinear frequency and density-dependent interactions (Baudrot et al., 2016). ...
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Voles can reach high densities with multiannual population fluctuations of large amplitude, and they are at the base of predator communities in Northern Eurasia and Northern America. This status places them at the heart of management conflicts wherein crop protection and health concerns are often raised against conservation issues. Here, a 20‐year survey describes the effects of large variations in grassland vole populations on the densities and the daily theoretical food intakes (TFI) of vole predators based on roadside counts. Our results show how the predator community responded to prey variations of large amplitude and how it reorganized with the increase in a dominant predator, here the red fox, which likely negatively impacted hare, European wildcat, and domestic cat populations. This population increase did not lead to an increase in the average number of predators present in the study area, suggesting compensations among resident species due to intraguild predation or competition. Large variations in vole predator number could be clearly attributed to the temporary increase in the populations of mobile birds of prey in response to grassland vole outbreaks. Our study provides empirical support for more timely and better focused actions in wildlife management and vole population control, and it supports an evidence‐based and constructive dialogue about management targets and options between all stakeholders of such socio‐ecosystems.
... Although a tremendous amount remains to be learned about consumer functional responses (e.g. Koen-Alonso, 2007;Baudrot et al., 2016;Novak et al., 2017;Uiterwaal and DeLong, 2020), the long-standing debate regarding the relative merits of prey-versus ratio-dependent models in particular is now largely considered by many to be pragmatically resolved: the most recent synthetic assessments of published experiments conclude that most consumer feeding rates respond to both prey and consumer densities, and that they do so in a more general manner than described by exact ratio dependence (Osenberg et al., 1999;. More specifically, interference among consumers is considered common, variable in strength and tending to magnitudes that are 'intermediate' to exact prey-and ratio-dependence (Osenberg et al., 1999;Arditi and Ginzburg, 2014). ...
... Bias is similarly probable and strong among published estimates of body mass scaling exponents and the Hill exponent in the respective contexts of allometric scaling theory and the density-dependent per capita attack rates of Type-III functional responses (e.g. Rall et al., 2012;Baudrot et al., 2016;. Few datasets in our compilation evidenced over-prediction at low prey densities by the models we considered (which could indicate density-dependent attack rates) and too few included information on consumer and prey body masses, hence the extent of the issue in these contexts deserves further investigation. ...
Article
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Functional responses are a cornerstone to our understanding of consumer–resource interactions, so how to best describe them using models has been actively debated. Here we focus on the consumer dependence of functional responses to evidence systematic bias in the statistical comparison of functional‐response models and the estimation of their parameters. Both forms of bias are universal to nonlinear models (irrespective of consumer dependence) and are rooted in a lack of sufficient replication. Using a large compilation of published datasets, we show that – due to the prevalence of low sample size studies – neither the overall frequency by which alternative models achieve top rank nor the frequency distribution of parameter point estimates should be treated as providing insight into the general form or central tendency of consumer interference. We call for renewed clarity in the varied purposes that motivate the study of functional responses, purposes that can compete with each other in dictating the design, analysis and interpretation of functional‐response experiments.
... Most studies of trophic ecology focus on a specific geographic area (e.g., Jensen et al. 2008;Trystram et al. 2017;Mumby et al. 2018), whereas studies that integrate multiple factors such as climatic conditions and geographic regions to assess biogeographic (spatial sensu lato) feeding patterns on global scales are rare (e.g., Clavero et al. 2003;Lozano et al. 2006;Rheingantz et al. 2017). Because both temporal and spatial variations in site-specific prey communities likely shape foraging and diet composition of aquatic predators (e.g., Rader 1997;Zhou et al. 2011;Baudrot et al. 2016; but see Van Ginderdeuren et al. 2014), biogeographic feeding patterns of animals can be strongly shaped by bottom-up mechanisms (i.e., through geographical differences in prey availability). Climatic conditions also have important influences on prey communities and predator-prey dynamics (e.g., Wilmers et al. 2007;Arbeiter et al. 2016). ...
... The identification of such patterns will allow us to address the relationship between diet composition and environmental variables from a global biogeographical perspective. Based on the above considerations, we hypothesized that (H1) the diet composition will be more similar among similar geographic areas (here freshwater ecoregions as defined by Abell et al. 2008), such as Mediterranean ecoregions located in different parts of the world, whereas larger differences should occur among nonsimilar regions or between native and exotic territories; and (H2) sitespecific prey communities will be associated with foraging and diet composition (Baudrot et al. 2016) and, consequently, biogeographic patterns in feeding. Also, spatial differences in inherent food preferences of species can be expected to lead patterns in feeding (e.g., Sanford et al. 2003). ...
Article
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We analysed data of a globally distributed model organism (brown trout) in an attempt to understand relationships among biogeography, prey communities and climate on diet composition at regional spatial scales (Scandinavia), and thereafter explored whether diet patterns remained the same at global scales. At regional scales, we uncovered comprehensive patterns in diet composition among neighbouring freshwater ecoregions, with site-specific prey communities as the best predictor of the observed prey utilisation patterns. Thus, we posit that environmental gradients altering site-specific prey communities and consequently the trophic niche of the predator through bottom-up mechanisms are key in understanding spatial dietary patterns. Proximity was also important for the revealed biogeographic patterns at global scales. We suggest that geographic location (latitude and elevation) as a proxy of environmental heterogeneity is key at small spatial scales, and climate at global extents, to understand spatial dietary patterns. Our findings support the hypothesis that future shifts in prey communities due to climate change will strengthen biographical patterns in feeding of freshwater fishes, with consequences for invasiveness assessment and nature management and conservation.
... To improve the modeling process, several collections of criteria capturing consistency were suggested [26][27][28][29][30][31][32][33][34]. While many of these are specific to the ecological scenario considered, e.g., predation, the following invariance is a recurring theme [28][29][30][31][32][33][34][35][36][37][38]: If two populations have identical parameter values, they contain identical individuals (clones) within a general model. ...
... Our framework also informs the form of more general models by outlining the space of possible models for ecosystems and enables new research directions in this field. Finally, our approach could be extended to implement criteria for specific ecological scenarios such as predation [27][28][29][30]33]. Overall, the framework presented here provides a systematic way to understand models and can form the backbone for a wide range of ecological modeling studies. ...
Article
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Many ecological studies employ general models that can feature an arbitrary number of populations. A critical requirement imposed on such models is clone consistency: If the individuals from two populations are indistinguishable, joining these populations into one shall not affect the outcome of the model. Otherwise a model produces different outcomes for the same scenario. Using functional analysis, we comprehensively characterize all clone-consistent models: We prove that they are necessarily composed from basic building blocks, namely linear combinations of parameters and abundances. These strong constraints enable a straightforward validation of model consistency. Although clone consistency can always be achieved with sufficient assumptions, we argue that it is important to explicitly name and consider the assumptions made: They may not be justified or limit the applicability of models and the generality of the results obtained with them. Moreover, our insights facilitate building new clone-consistent models, which we illustrate for a data-driven model of microbial communities. Finally, our insights point to new relevant forms of general models for theoretical ecology. Our framework thus provides a systematic way of comprehending ecological models, which can guide a wide range of studies.
... Cette dernière question a été traitée dans [2] où les auteurs se sont concentrés sur la transmission du parasite en Europe de l'Est, où les HD sont des renards roux et les IH deux petits mammifères, le campagnol commun et le campagnol aquatique. En suivant un modèle écologique préliminaire des chaînes alimentaires dans [1], où il a été démontré que la propriété des proies change, c'est-à-dire un changement dans la préférence du prédateur pour une espèce de proie avec une variation de sa densité relative, était une caractéristique des interactions étudiées entre le prédateur et la proie, la transmission du parasite Em a ensuite été décrite à l'aide du diagramme épidémiologique de la Figure 3.6 (où i " 1, 2 désigne un type de proie, S, resp I, fait référence aux populations susceptibles d'être capturées, resp infectées), et a été traduite par le système d'équations. ...
... Vérifions que la méthode de la prochaine génération nous permet obtenir pour le modèle SEIT R c " κpβ 1`p r 2 q pµ`r 2 qpµ`κ`r 1 q Rc = with ( paras , ( beta 1 * k + p * r 2 * k )/(( mu + k + r 1 )*( mu + r 2 ))) [ 1 ] 0 . 0 7 6 5 9 5 7 4 ...
Technical Report
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The purpose of this document is to first make a short study of some basic tools of the qualitative analysis of ODE's, such as analysis of ODE's, such as stability, Lyapunov's theorem and LaSalle's invariance principle, to then apply these tools to the then apply these tools to the study of the stability of ODE's systems for epidemiology through the study of the next generation matrix method (NGM), and thus define the base reproduction number as the spectral radius of the NGM.
... The composition of prey communities is expected to influence the diet of predators (e.g. Sinclair et al. 2003;Garrott et al. 2007;Baudrot et al. 2016). In turn, large carnivores play a pivotal role in ecosystems, as their action may generate cascading effects on lower trophic groups (e.g. ...
... Feeding habits have evolved to maximise fitness and subject to constraints imposed by availability of food resources (MacArthur and Pianka 1966). Generalist predators are expected to shape their diet according to the local availability of prey species (Terraube et al. 2014;Baudrot et al. 2016). ...
Article
Generalist predators are expected to shape their diets according to the local availability of prey species. In turn, the extent of consumption of a prey would be influenced by the number of alternative prey species. We have tested this prediction by considering the wild boar and the grey wolf: two widespread species whose distribution ranges overlap largely in Southern Europe, e.g. in Italy. We have reviewed 16 studies from a total of 21 study areas, to assess whether the absolute frequency of occurrence of wild boar in the wolf diet was influenced by (i) occurrence of the other ungulate species in diet and (ii) the number of available ungulate species. Wild boar turned out to be the main prey of the wolf (49% occurrence, on average), followed by roe deer (24%) and livestock (18%). Occurrence of wild boar in the wolf diet decreased with increasing usage of roe deer, livestock, and to a lower extent, chamois and red deer. The number of prey species did not influence the occurrence of wild boar in the wolf diet. The wild boar is a gregarious, noisy and often locally abundant ungulate, thus easily detectable, to a predator. In turn, the extent of predation on this ungulate may not be influenced so much by the availability of other potential prey. Heavy artificial reductions of wild boar numbers, e.g. through numerical control, may concentrate predation by wolves on alternative prey (e.g. roe deer) and/or livestock, thus increasing conflicts with human activities.
... However, functional 22 responses that include multiple resources are more complicated because the relationship 23 between consumption rate and resource density may be different for different resources. 24 These relationships may be further complicated by the fact that the consumption rate 25 of one resource may be affected by the abundance of other available resources [14,15]. 26 Gentleman et al. [16] provide a review of functional responses that have been used in 27 the literature to describe zooplankton grazing on multiple phytoplankton types. ...
... To avoid antagonistic feeding, Vallina et al. [20] developed an alternative 51 formulation, the Kill-the-Winner (KTW) functional response. Since its publication, the 52 KTW functional response has become a popular way to include switching behavior in a 53 variety of models [22][23][24][25][26][27][28][29][30][31][32]. 54 Vallina et al. [20] used one case of the KTW functional response to study how grazer 55 switching promotes diversity on a global scale in a size-structured phytoplankton 56 community model. ...
Preprint
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Grazing by zooplankton can maintain diversity in phytoplankton communities by allowing coexistence between competitors in situations that would otherwise lead to competitive exclusion. In mathematical models, grazing is represented by a functional response that describes the consumption rate by an individual zooplankter as a function of phytoplankton concentration. Since its initial description, the Kill-the-Winner functional response has been increasingly adopted for large-scale biogeochemical modeling. Here, we analyze how two properties of the Kill-the-Winner functional response - preference and switching - interact to promote coexistence and increase diversity in two simple models: a diamond-shaped nutrient-phytoplankton-zooplankton model and a size-structured phytoplankton community model. We found that, compared to preference, switching leads to coexistence and increased diversity over a much wider range of environmental conditions (nutrient supply and mixing rate). In the absence of switching, preference only allows for coexistence within the narrow range of environmental conditions where the preference is precisely balanced against the competitive difference between phytoplankton types. We also explored a counterintuitive aspect of the Kill-the-Winner functional response that we have termed "synergistic grazing". Synergistic grazing occurs when the grazing rate on one phytoplankton type increases as the biomass of an alternative phytoplankton type increases. This unrealistic effect is most evident when switching is strong and when zooplankton have a preference for the weaker competitor.
... Yet, a variation in the diet of a species is likely to change the exposure of that species to contaminants. The direct next step is therefore the inclusion of multiprey predation to explore the influence of the adaptive foraging behavior of the predator (Baudrot et al., 2016) on similar ecotoxicological systems, and the role of biodiversity in prey community on shaping the responses of food-webs to environmental disturbances such as environmental pollution. Among many complexification of the models, since collection of data have been thought into a landscape approach, we suggest to take this spatial heterogeneity of habitats into account (Fritsch et al., 2012). ...
... Under field conditions, predators commonly foraging in complex patches with multiple prey species, and could exhibit type 3 functional response caused by prey switching (Schenk and Bacher, 2002). In addition, functional response of a predator could be altered by host plant species (Messina and Hanks, 1998), the presence of an intraguild predator (Martinou et al., 2010), number of co-existed prey species (Schenk and Bacher, 2002;Baudrot et al., 2016), type of prey species (Luo, 1987;Seko and Miura, 2008), and environmental complexity (Hoddle, 2003). Therefore, accurately predicting the type of functional response is key to evaluate the performance of a predator. ...
Article
The effects of prey distribution and digestion on the functional response of an invertebrate predator Harmonia axyridis (Pallas) to varying densities of Aphis citricola (van der Goot) were investigated. Experiments were conducted in petri dish and wind tunnels with multiple plants to present conditions in which the predator could behave more naturally. To discriminate if the functional response of H. axyridis is digestion or handling limited, numbers of aphids consumed were measured at five time-points during a 24 h period in all assays. In the wind tunnel, aphid consumption was measured with two types of prey distributions (aggregate and uniform). Type 2 functional responses were observed in petri dish and three wind tunnel assays with aphid uniformly distributed (6, 12 and 24 h). Based on the Akaike Information Criterion (AIC) value, type 1 response was most appropriate for two assays (1 and 2 h) with aphid uniformly distributed and all assays with aphid aggregate in wind tunnels. There was a significant effect of aphid distribution and its interactions with experiment duration and prey density on the number of aphids consumed in wind tunnel. The functional responses between uniform and aggregate treatments were mostly overlapped except when prey densities were above 90. This indicates that prey distribution could affect H. axyridis foraging under relative high prey densities. Prey risk raised as the increase of experiment duration for all treatments, while attack rates and handling times differed significantly among the assays with different experimental lengths, thus digestion process could limit predation process of H. axyridis. Our results indicate that prey distribution and predator digestion could alter predator-prey interactions and thus the capacity of this generalist predator to suppress aphids.
... Fewer limitations to discriminate feeding exist when prey are abundant, but when faced with overall food scarcity, generalist diets have been shown to be more indiscriminate to meet energetic needs (Agosta et al. 2003, Clare et al. 2014). Due to elevated hunger levels at low prey densities, a frequency-dependent foraging strategy can be optimal (Baudrot et al., 2016). ...
Article
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Generalist predators are capable of selective foraging, but are predicted to feed in close proportion to prey availability to maximize energetic intake especially when overall prey availability is low. By extension, they are also expected to feed in a more frequency-dependent manner during winter compared to the more favorable foraging conditions during spring, summer and fall seasons. For 18 months, we observed the foraging patterns of forest-dwelling wolf spiders from the genus Schizocosa (Araneae: Lycosidae) using PCR-based gut-content analysis and simultaneously monitored the activity-densities of two common prey: springtails (Collembola) and flies (Diptera). Rates of prey detection within spider guts relative to rates of prey collected in traps were estimated using Roualdes’ cst model and compared using various linear contrasts to make inferences pertaining to seasonal prey selectivity. Results indicated spiders foraged selectively over the course of the study, contrary to predictions derived from optimal foraging theory. Even during winter, with overall low prey densities, the relative rates of predation compared to available prey differed significantly over time and by prey group. Moreover, these spiders appeared to diversify their diets; the least abundant prey group was consistently overrepresented in the diet within a given season. We suggest that foraging in generalist predators is not necessarily restricted to frequency-dependency during winter. In fact, foraging motives other than energy maximization, such as a more nutrient-focused strategy, may also be optimal for generalist predators during prey-scarce winters.
... A fundamental question in behavioral ecology is how generalist animals forage efficiently on diverse resources (Loeuille 2010;Wright et al. 2010;Baudrot et al. 2016). This question has been extensively addressed for generalist pollinators foraging on diverse plant species that vary greatly in floral morphology. ...
Article
Full-text available
Bees foraging for floral rewards are one of our most thoroughly studied examples of generalist foraging ecology. Generalist bees rely considerably on instrumental (associative) learning to acquire routines that allow them to collect nectar efficiently from diverse plant species. Although such bees must also collect pollen from diverse species, few studies have examined if and how high efficiency is achieved. We characterized how generalist bumble bees (Bombus impatiens) foraged effectively for pollen from diverse floral resources, by manipulating the presence of pollen and anther cues, in a series of experiments using pollen-bearing live flowers, flowers of a sterile pollen-less horticultural hybrid, and artificial flowers. We show that generalist bumble bees exhibit flexible and effective pollen collection by switching between 2 routines: " scrabbling " when pollen is abundant and " sonicating " when pollen is scarce. Efficient switching between these behaviors is regulated by the interplay of 2 ubiquitous floral cues: chemical anther cues stimulating pollen collection behavior and mechanical pollen cues suppressing sonication (and eliciting scrabbling). Flexible pollen collection behavior is functional: When pollen on anthers was scarce, bees collected it at a greater rate by sonicating than scrabbling. This mechanism of behavioral flexibility likely allows generalist bees to handle diverse anther morphologies efficiently and may have facilitated the recurrent evolution of plant species that conceal pollen rewards via pored floral morphology. Whereas effective nectar foraging relies heavily on associative learning of unique routines for each flower type, a weighing of 2 types of cues regulates the flexible pollen collection mechanism we describe.
... Many more such models, including those that consider allometric constraints and those that more generally relax the assumptions of predator homogeneity and the constancy of attack rates and handling times (e.g. Murdoch & Oaten 1975;Abrams 2010;Okuyama 2012;Rall et al. 2012;Baudrot et al. 2016;Kalinoski & DeLong 2016), should become empirically accessible with the observational framework, particularly when applied in combination with experimental manipulations. Whether the inferences of our study on whelks will conform to generalizable theory or will instead represent insightful outliers will be unknowable until more field-based studies of generalist predators are performed. ...
Article
Full-text available
A long-standing debate concerns how functional responses are best described. Theory suggests that ratio dependence is consistent with many food web patterns left unexplained by the simplest prey-dependent models. However, for logistical reasons, ratio dependence and predator dependence more generally have seen infrequent empirical evaluation and then only so in specialist predators, which are rare in nature. Here we develop an approach to simultaneously estimate the prey-specific attack rates and predator-specific interference (facilitation) rates of predators interacting with arbitrary numbers of prey and predator species in the field. We apply the approach to surveys and experiments involving two intertidal whelks and their full suite of potential prey. Our study provides strong evidence for predator dependence that is poorly described by the ratio dependent model over manipulated and natural ranges of species abundances. It also indicates how, for generalist predators, even the qualitative nature of predator dependence can be prey-specific.
... Our model has obvious limitations to have accurate predictive abilities. For instance, we do not consider the dynamics of prey resources, or other feeding interactions of the barn owl, which is well-known to be a generalist predator with multi-prey ( Baudrot et al., 2016a). ...
Thesis
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La structure et l’intensité des interactions ressources-consommateurs qui forment les réseaux trophiques régulent une très grande partie des transferts de biomasse mais aussi de contaminants biologiques et chimiques dans les écosystèmes. L’objectif de la thèse est de développer des modèles permettant d’étudier les mécanismes de transport des contaminants et d’évaluer ainsi d’une part la dynamique des maladies infectieuses et des pollutions chimiques, et d’autre part les réponses des réseaux trophiques soumis à ces contaminations.[...] À l’issue de ces travaux, une quatrième étape de la thèse a été d’intégrer les interactions trophiques, les dynamiques des parasites et les impacts des pollutions dans des méta-écosystèmes (i.e. avec dispersions d’individus entre écosystèmes). En utilisant la théorie des matrices aléatoires nous avons établi des mesures des risques d’émergence de parasites que nous avons évalués en fonction des perturbations extérieures.L’étude a ainsi montré que ces perturbations augmentent les risques épidémiques, mais que ces risques pouvaient être réduits par la dispersion des individus (sains et infectés) sous certaines conditions qui sont,par exemple pour les TTP, un nombre d’espèces plus grand que le nombre d’écosystèmes connectés, et un taux de virulence plus faible que le taux de contagion.Ainsi, dans un contexte planétaire d’augmentation des pressions anthropiques sur les écosystèmes,cette thèse de modélisation apporte un ensemble d’outils et de développements conceptuels permettant d’analyser quantitativement et qualitativement les transferts et les impacts des contaminants sur les écosystèmes.
... Although once viewed as static, niche space is no longer seen as a fixed property, but one that can change as a function of intraspecific variation (Baudrot, Perasso, Fritsch, Giraudoux, & Raoul, 2016;Ingram, Costa-Pereira, & Araujo, 2018;Lafferty, Belant, & Phillips, 2015;Newsome et al., 2015). Factors such as life stage and habitat use (Polis, 1984), intraspecific competition , and sex (Shine, 1989) all affect niche variation within species or populations. ...
Article
Full-text available
Predators exert strong effects on ecological communities, particularly when they re‐occupy areas after decades of extirpation. Within species, such effects can vary over time and by sex and cascade across trophic levels. We used a space‐for‐time substitution to make foraging observations of sea otters (Enhydra lutris) across a gradient of reoccupation time (1–30 years), and nonmetric multidimensional scaling (nMDS) analysis to ask whether (a) sea otter niche space varies as a function of occupation time and (b) whether niche space varies by sex. We found that niche space varied among areas of different occupation times. Dietary niches at short occupation times were dominated by urchins (Mesocentrotus and Strongylocentrotus spp; >60% of diets) in open habitats at 10–40 m depths. At longer occupation times, niches were dominated by small clams (Veneroida; >30% diet), mussels (Mytilus spp; >20% diet), and crab (Decapoda; >10% diet) in shallow (<10 m) kelp habitats. Diet diversity was lowest (H′ = 1.46) but energy rich (~37 kcal/min) at the earliest occupied area and highest, but energy poor (H′ = 2.63, ~9 kcal/min) at the longest occupied area. A similar transition occurred through time at a recently occupied area. We found that niche space also differed between sexes, with bachelor males consuming large clams (>60%), and urchins (~25%) from deep waters (>40 m), and females and territorial males consuming smaller, varied prey from shallow waters (<10 m). Bachelor male diets were less diverse (H′ = 2.21) but more energy rich (~27 kcal/min) than territorial males (H′ = 2.54, ~13 kcal/min) and females (H′ = 2.74, ~11 kcal/min). Given recovering predators require adequate food and space, and the ecological interactions they elicit, we emphasize the importance of investigating niche space over the duration of recovery and considering sex‐based differences in these interactions.
... It might be related to abundant food sources contributing to consumers, and consumers then have more choices to balance their diets. Predators need to adjust the diet choices to accommodate the variations of species composition and dominance in different habitats (Baudrot et al. 2016). Because of the spatial heterogeneity of ecological conditions and pollution loads, the food webs of the two studied zones showed distinct characteristics and processes. ...
Article
Full-text available
The knowledge of food web spatial heterogeneity is important for ecologists and lake managers to understand ecosystem complexity and lake management. Lake Taihu, a large shallow eutrophic lake in China, has two distinct zones: algae- and macrophyte-dominated. In this study, we assessed the spatial heterogeneity of food webs in the two lake zones using stable isotope analysis and isotope mixing model. The basal sources and consumers showed significant differences in δ¹³C and δ¹⁵N ratios between the two lake zones, except for the filter-feeding fishes. Overall, more δ¹³C-depleted and δ¹⁵N-enriched ratios were found in the algae- than the macrophyte-dominated zones for basal sources and consumers. Although the consumers in the algae-dominant zone had higher average δ¹⁵N values, the food web of the macrophyte-dominated zone had longer food chain length and more diverse trophic linkages. These spatial differences may have resulted from resource availability and environmental stress of Lake Taihu ecosystem. Factors associated with spatial trophic heterogeneity should be considered for the management and restoration of this shallow eutrophic lake.
... Interannual variation in prey availability (i.e., temporal variations in prey communities) has frequently been observed in aquatic systems (e.g., Løvik and Kjellberg 2003;Hämäläinen et al. 2003;Frainer et al. 2016;Prati et al. 2021), likely shaping foraging and diet composition of predators (e.g., Ringler 1985;Baudrot et al. 2016). In the present study, even though most interannual variation observed with the singleand two-year time scales could be ascribed to bias from low sample sizes of certain ontogenetic stages, there were a few dietary changes that were consistent also for the five-and ten-year time scale approaches, supporting that these represent valid temporal variation. ...
Article
Full-text available
Disentangling the causes and consequences of ontogenetic niche shifts has been a pivotal challenge in ecology, aiming to enhance the understanding of biological processes that function at the individual, population, and community levels. Studies on ontogenetic dietary shifts have traditionally focused on short time scales, mostly including sampling covering just one or a few consecutive years, thus neglecting possible aspects of temporal variation and ecosystem stability that can only be revealed on long-term scales. We address ontogenetic dietary shifts of two fish predators in an intraguild system (Arctic charr and brown trout) using a long-term dataset spanning 20 consecutive years. Our study revealed distinct ontogenetic niche shifts of the two intraguild predators and demonstrated that these patterns were stable over time, suggesting large stability in prey acquisition and resource partitioning despite changes in their abundances and relative species composition. Some interannual variation was observed, but this was primarily due to sampling bias from low observation numbers for some ontogenetic stages, reflecting a common methodical challenge for ontogenetic niche shift studies. The persistent patterns in the trophic ontogeny of intraguild predators likely facilitate population and community stability by reducing inter- and/or intraspecific competition, thereby having important consequences for ecosystem functioning and resilience. Our study provides a strong rationale for performing ontogenetic niche shift studies over several consecutive years, enabling important insights into temporal variation, enhancement of observation numbers by merging data from multiple years, and the facilitation of a less intrusive sampling scheme for more vulnerable populations.
... The question thus arises whether the findings can be generalized to more complex food webs (Millon et al. 2009) in other areas. In particular, how generalist predators will respond to changes in their prey community is not predicted by current theoretical models (but see Baudrot et al. 2016), despite generalist predators probably constituting the majority of avian predators (review in Valkama et al. 2005). However, a generalist predator may be partly sensitive to changes in diversity or composition of prey communities. ...
Chapter
Climate change is likely to impact all trophic levels, although the response of communities and ecosystems to it has only recently received considerable attention. Further, it is expected to affect the magnitude of species interactions themselves. In this chapter, we summarize why and how climate change could affect predator–prey interactions, then review the literature about its impact on predator–prey relationships in birds, and provide prospects for future studies. Expected effects on prey or predators may include changes in the following: distribution, phenology, population density, behaviour, morphology, or physiology. We review the currently available information concerning particular key topics: top-down versus bottom-up control, specialist versus generalist predators, functional versus numerical responses, trophic cascades and regime shifts, and lastly adaptation and selection. Finally, we focus our review on two well-studied bird examples: seabirds and raptors. Key future topics include long-term studies, modelling and experimental studies, evolutionary questions, and conservation issues.
... Although the assumption that all time durations are exponentially distributed may be questionable, from the theoretical point of view this assumption can be considered as a simplifying one (e.g., Ruxton and Gurney 1994). I note that Kohlmann et al. (1999) Baudrot et al. (2016) for a generalist optimal forager investigated a multi-species functional response. Kannan (1983) used Markov chains for the predator's learning. ...
... For generalist predators, prey preferences can influence functional responses (sensu Holling, 1959aHolling, ,1959b, although the relationship between prey consumption and prey availability may not necessarily resemble classic response types (Murdoch & Oaten, 1975;Oksanen et al., 2001). For example, generalist predators foraging in multiprey systems have been shown to consume prey irrespective of changing availability or even reduce the consumption of increasing prey as a result of preferences related to nutritional demands, energy requirements or ease of prey capture (Baudrot et al., 2016;Chesson, 1984;Dale et al., 1994). Therefore, the relationship between prey consumption and quantitative availability in generalist predators can be highly context-dependent (Novak et al., 2017;Preston et al., 2018;Symondson et al., 2002). ...
Article
Although most predators are generalists, the majority of studies on the association between prey availability and prey consumption have focused on specialist predators. To investigate the role of highly generalist predators in a complex food web, we measured the relationships between prey consumption and prey availability in two common arthropodivorous bats. Specifically, we used high‐throughput amplicon sequencing coupled with a known mock community to characterize seasonal changes in little brown and big brown bat diets. We then linked spatio‐temporal variation in prey consumption with quantitative prey availability estimated from intensive prey community sampling. We found that although quantitative prey availability fluctuated substantially over space and time, the most commonly consumed prey items were consistently detected in bat diets independently of their respective abundance. Positive relationships between prey abundance and probability of consumption were found only among prey groups that were less frequently detected in bat diets. While the probability of prey consumption was largely unrelated to abundance, the community structure of prey detected in bat diets was influenced by the local or regional abundance of prey. Observed patterns suggest that while little brown and big brown bats maintain preferences for particular prey independently of quantitative prey availability, total dietary composition may reflect some degree of opportunistic foraging. Overall, our findings suggest that generalist predators can display strong prey preferences that persist despite quantitative changes in prey availability.
... Since its publication, the KTW functional response has become a popular way to include switching behavior in a variety of models (Baudrot et al., 2016;Cadier et al., 2017;Chen et al., 2019;Egilmez and Morozov, 2016;Guyennon et al., 2015;Nissen et al., 2018;Smith et al., 2016;Tanioka and Matsumoto, 2018;Vallina et al., 2017;Ward and Follows, 2016). ...
... In what has come to be termed multilayer networks [7][8][9][10] , where ecological networks are clustered into separate but interlinked network layers by their functional properties, the complex structuring of species nodes, links and node switching across different network layers is hypothesised to govern the delivery, stability and balance of functions in an ecological community 6,11 . Within this framework, key predator species that contribute to the service of weed-seed regulation by feeding on weed seeds in one layer, might also disrupt this function by switching to the consumption of alternative prey species 12,13 , such as gastropods, in another layer where the amount of alternative prey increases. In switching between prey, and therefore functions, the predators move between the layers of the full ecological network. ...
Article
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Agriculture is under pressure to achieve sustainable development goals for biodiversity and ecosystem services. Services in agro-ecosystems are typically driven by key species, and changes in the community composition and species abundance can have multifaceted effects. Assessment of individual services overlooks co-variance between different, but related, services coupled by a common group of species. This partial view ignores how effects propagate through an ecosystem. We conduct an analysis of 374 agricultural multilayer networks of two related services of weed seed regulation and gastropod mollusc predation delivered by carabid beetles. We found that weed seed regulation increased with the her-bivore predation interaction frequency, computed from the network of trophic links between carabids and weed seeds in the herbivore layer. Weed seed regulation and herbivore interaction frequencies declined as the interaction frequencies between carabids and molluscs in the carnivore layer increased. This suggests that carabids can switch to gastropod predation with community change, and that link turnover rewires the herbivore and carnivore network layers affecting seed regulation. Our study reveals that ecosystem services are governed by ecological plasticity in structurally complex, multi-layer networks. Sustainable management therefore needs to go beyond the autecological approaches to ecosystem services that predominate, particularly in agriculture.
... In such cases, the killing probability may be driven by the encounter probability (i.e. the probability that a mesopredator will enter the area where the top-predator is able to detect the mesopredator) and thus increase with the mobility of both the top predator and the mesopredator (Wise 2006, Pawar et al. 2012. The interaction between hunting strategies of predators may further be modified by habitat properties because habitats alter the composition of hunting strategies in local predator communities (Birkhofer et al. 2015) and affect the diet of generalist predators through effects on available prey (Birkhofer and Wolters 2012, Baudrot et al. 2016, Arvidsson et al. 2020. ...
Article
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... In generalist predators, such as feral cats, the most simplistic models of diet suggest that the relative frequency of each prey type in the diet is positively correlated with the local abundance of the prey [51,52]. More complicated models support this basic hypothesis but incorporate some additional variation from foraging success, nutrient requirements and prey switching, and ultimately mean that when cats are hungry, they eat what is available; when they are less hungry, they are likely to be more choosy [53,54]. ...
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Environmental damage caused by the intensification of agriculture may be compensated by implementing conservation projects directed towards reducing threatening processes and conserving threatened native species. In Australia, feral cats (Felis catus) have been a ubiquitous threatening process to Australian fauna since European colonisation. On Shamrock Station, in the north-west of Western Australia, the Argyle Cattle Company has proposed intensifying agriculture through the installation of irrigation pivots. There is concern that irrigating land and storing agricultural produce may indirectly increase the abundance of feral cats and European red foxes (Vulpes vulpes) on the property, which in turn may negatively impact threatened bilbies (Macrotis lagotis) that also inhabit the property. Feral cat control is required under the approved management plan for this project to mitigate this potential impact. Our baseline study revealed a high density of feral cats on Shamrock Station (0.87 cats km−2) and dietary data that suggest the current native mammal assemblage on Shamrock Station is depauperate. Given the high density of feral cats in this area, the effective control of this introduced predator is likely to confer benefits to the bilby and other native species susceptible to cat predation. We recommend ongoing monitoring of both native species and feral cats to determine if there is a benefit in implementing feral cat control around areas of intensive agriculture and associated cattle production.
... Interactions between predator and prey in natural communities are difficult to describe quantitatively. Various mathematical models have been used to quantify prey acquisition by the predator and to investigate the nature and the strength of species interactions within food webs (Abrams et al., 1998;Baudrot et al., 2016;Chan et al., 2017;Pawar et al., 2012). Several studies have compared how a predator acquisition rate varies with prey density using statistical approaches (reviewed by Novak and Stouffer 2020), but few of them explicitly tackled the underlying mechanisms. ...
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Prey handling processes are considered a dominant mechanism leading to short‐term positive indirect effects between prey that share a predator. However, a growing body of research indicates that predators are not necessarily limited by such processes in the wild. Density‐dependent changes in predator foraging behavior can also generate positive indirect effects but they are rarely included as explicit functions of prey densities in functional response models. With the aim of untangling proximate mechanisms of species interactions in natural communities and improving our ability to quantify interaction strength, we extended the multi‐prey version of the Holling disk equation by including density‐dependent changes in predator foraging behavior. Our model, based on species traits and behavior, was inspired by the vertebrate community of the arctic tundra, where the main predator (the arctic fox) is an active forager feeding primarily on cyclic small rodent (lemming) and eggs of various tundra‐nesting bird species. Short‐term positive indirect effects of lemmings on birds have been documented over the circumpolar Arctic but the underlying mechanisms remain poorly understood. We used a unique data set, containing high‐frequency GPS tracking, accelerometer, behavioral, and experimental data to parameterize the multi‐prey model, and a 15‐year time series of prey densities and bird nesting success to evaluate interaction strength between species. We found that: (i) prey handling processes play a minor role in our system and (ii) changes in arctic fox daily activity budget and distance traveled can partly explain the predation release on birds observed during lemming peaks. These adjustments in predator foraging behavior with respect to the main prey density thus appear as the dominant mechanism leading to positive indirect effects commonly reported among arctic tundra prey. Density‐dependent changes in functional response components have been little studied in natural vertebrate communities and deserve more attention to improve our ability to quantify the strength of species interactions.
... Fewer limitations to discrim- inate feeding exist when prey are abundant, but when faced with overall food scarcity, generalist diets have been shown to be more indiscriminate to meet energetic needs (Agosta, Morton, & Kuhn, 2003;Clare et al. 2014). Due to elevated hunger levels at low prey densities, a frequency-dependent foraging strategy can be optimal (Baudrot, Perasso, Fritsch, Giraudoux, & Raoul, 2016). ...
Conference Paper
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Background/Question/Methods Forest-dwelling spiders can profoundly impact the decomposer food web because of their prevalence in the leaf litter and their voracious appetite for detritivores. They are frequently food limited in terrestrial environments, however, causing them to forage simply according to availability of prey. This is complicated by the fact that prey populations show considerable spatio-temporal variation and many of these prey items are of poor nutritional quality. The primary objective of this research was to identify seasonal spider predation patterns in response to fluctuations in prey availability, focusing on shifts in foraging dynamics during the autumn and winter, where there is the greatest paucity of information. Within an eastern deciduous forest ecosystem, prey availability was monitored and, in parallel, spiders were collected for molecular gut-content analysis in order to delineate predation strength throughout the season. Prey availability and predation were correlated to ultimately identify reliance and food preference patterns of these predators. Results/Conclusions Extensive monitoring throughout the winter revealed that spiders were the dominant predators in the forest floor food web. While intraguild competitors from Carabidae, Staphylinidae, and Formicidae were virtually absent by November, spider activity remained high from autumn through the winter. Over 500 spiders were collected for molecular gut-content analysis and showed that dietary diversity shifted during winter, as prey availability changed. Tomoceridae (Collembola), an important prey item for eastern forest spiders, remained active but decreased throughout the winter. In contrast, dipterans fluctuated in activity and increased significantly during February thus providing a critical pulse resource for these predators as alternative food items decreased in abundance. Molecular gut-content analysis revealed less selectivity in spider feeding when the breadth of prey available to spiders narrowed. Given that detritivores have a direct impact on forest decomposition rates through their grazing activities, arachnid predators have cascading effects on these ecosystem processes. Tracking seasonal feeding dynamics between spiders and their prey therefore provides valuable insights into their functional role in forest floor food webs.
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A bstract The rise of the Asian chestnut gall wasp Dryocosmus kuriphilus in France has benefited the native community of parasitoids originally associated with oak gall wasps by becoming an additional trophic subsidy and therefore perturbing population dynamics of local parasitoids. However, the successful biological control of this pest has then led to significant decreases in its population densities. Here we investigate how the invasion of the Asian chestnut gall wasp Dryocosmus kuriphilus in France and its subsequent control by the exotic parasitoid Torymus sinensis has impacted the local community of native parasitoids. We explored 5 years of native community dynamics within 26 locations during the rise and fall of the invasive pest. In an attempt to understand how mechanisms such as local extinction or competition come into play, we analyzed how the patterns of co-occurrence between the different native parasitoid species changed through time. Our results demonstrate that native parasitoid communities experienced increased competition as the D. kuriphilus levels of infestation decreased. During the last year of the survey, two alternative patterns were observed depending on the sampled location: either native parasitoid communities were represented by an extremely limited number of species occurring at low densities, in some cases no native parasitoid species at all, or they were dominated by one main parasitoid: Mesopolobus sericeus . These two patterns seemed to correlate with the habitat type, M. sericeus being more abundant in semi-natural habitats compared to agricultural lands, the former known to be natural reservoirs for native parasitoids. These results highlight how the “boom-and-bust” dynamics of an invasive pest followed by successful biological control can deeply alter the structure of native communities of natural enemies. This article has been peer-reviewed and recommended by Peer Community in Zoology https://doi.org/10.24072/pci.zool.100004
Chapter
Rodent outbreaks have, in historical memory and at more or less regular intervals, massively affected crops and stored goods locally and sometimes even regionally. The Jura Massif is known, among other things, for its cheese specialties with several emblematic protected designations of origin (PDO), such as Comté, Morbier, Mont‐d'or and Bleu de Gex. In the 1950s, in this region of medium‐altitude mountains, grassland covered between 20% and almost 75% of farmland, regardless of altitude. From the early 1980s to the mid‐1990s, population demographic monitoring of small mammals was carried out in the Septfontaines and Le Souillot area, covering nearly 20,000 hectares. It has been suggested that predation is a major driver of fluctuations in rodent populations. It has taken about 30 years to describe and understand the factors that determine vole outbreaks in the Jura Massif in PDO grassland areas and to establish the basis for controlling them.
Article
Understanding predator–prey interactions is critical for marine fisheries and ecosystem management as they shape community structure, regulate prey populations and present energy demands critical for community sustainability. We examined multispecies functional responses of 17 fishes (48 predator‐size combinations) spanning piscivores, planktivores and benthivores for the northeast US continental shelf. Similar to previous work, linear relationships between predation and prey density (Holling type I response) were not supported, since model estimates of handling time were greater than zero for the prey considered. Instead, a clear majority of the predators sampled were Holling type III feeders (sigmoidal; prey switching or learning). For piscivores, nearly all responses were Holling type III with the exception of one being Holling type II (hyperbolic; satiation). Planktivores and benthivores exhibited a combination of type IV (feeding confusion at high prey density) and Holling type III responses. The relationships were predator‐ and prey‐dependent, which is counter to assumptions that are often made of trophic groups. Decreased predation at high prey densities (type IV response) present among planktivores and benthivores suggests an overestimation of predation can occur if ignored. This contrasts with fish and squid prey which primarily invoked a Holling type III response. Functional responses are key to modelling trophic interactions for multispecies and ecosystem models. By refining these inputs in a multispecies context with empirical data, we can advance our understanding of whole‐shelf ecology and improve decision‐making tools for resource management.
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Immense effort has been devoted to mitigating the negative effect of deforestation, one of the main factors causing global change. However, the effect of reforestation management on food-webs has been rarely studied and no study so far has investigated the effect on predator–prey interactions in forest understories. We studied predator–prey interactions in forest understories using web-building spiders in four forest types: dry evergreen forest representing a natural control and three 20–30-year-old reforestation types, namely secondary naturally regenerating dry evergreen forest, monoculture reforestation dominated by Eucalyptus camaldulensis, and mixture reforestation dominated by Acacia mangium and E. camaldulensis. We collected spiders with their prey and measured the availability of potential prey. We also measured different spider traits (web type, body size) that can be selected by various forest types and consequently affect the predator–prey interactions. The forest type influenced the predator–prey interaction in a complex way, interactively affecting spider density and prey-specific capture efficacy of spider community. The forest type also influenced the web-type and body-size distributions of spiders. Surprisingly, the prey composition caught by spider webs was related only to the web-type but not to the spider mean body size. None of the studied reforestations have yet restored the natural predator–prey interactions, which indicates that conservation management in the tropics should focus on establishing protected areas in pristine regions instead of relying on reforestation. Moreover, the food-web models need to incorporate not only body sizes but also hunting strategies of predators to improve their predictive abilities.
Thesis
Biological control (or biocontrol) is the use of living organisms to suppress the population density or impact of a specific pest organism, making it less abundant or less damaging than it would otherwise be. The biological control agent may directly or indirectly interact with more than just the target pest and vice versa. Therefore, monitoring its populations, in conjunction toother ecological factors, may allow to confirm or discard ecology theories or unveil brand new interactions with both abiotic and biotic facets of the recipient ecosystem. Moreover, the methodological aspects of the post release monitoring phase and those of ecological experimentations sometimes do share similarities. In this work I explore how both disciplines are reconciled and how the resulting data from biocontrol could be optimized for its use in ecology.I use data from biological control programs to address questions related to invasion dynamics, community ecology and landscape ecology.In chapter 1, I detail the case studies: (i) the introduction of the parasitoid Torymus sinensis (Hymenoptera: Torymidae) against the Asian chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae) ; (ii) the introduction of the ectoparasitoid Mastrus ridens (Hymenoptera: Ichneumonidae) against the codling moth Cydia pomonella (Lepidoptera: Tortricidae) ; (iii) a nation-wide survey of Trichogramma species in France in order to characterize the ecological ranges of each species; (iv) the description of egg parasitoid species associated with Iphiclides podalirius (Lepidoptera: Papilionidae) at a fine temporal scale.Chapter 2 is focused on understanding the dispersal of T. sinensis at the scale of several chestnut producing areas. In this chapter, I use monitoring data from release sites to fit a growth model for populations of T. sinensis in order to infer the time since colonization in naturally colonized sites. In chapter 3 I investigate the impacts of the successful control of D. kuriphilus by T.sinensis on the structure of native parasitoid community that recently became associated with the pest. Chapter 4 is focused on cases where scientific valorization ranges from a complete failure (primo-introduction of M. ridens), the diffusion of naturalist knowledge (survey of I. podalirius and related oophagous parasitoids) and/or the identification of some patterns using specific statistics (national survey of Trichogramma species).Finally, by compiling knowledge from the extensive literature on biological control and field experience I then discuss on the potentials and limits of biological control programs for experimental ecology. I conclude that although biological control gives an ecological context to experimentation by allowing to manipulate a wide variety of factors, the context and the organisms at play may not be compatible with any ecological issue. For example, the obvious parallel between classical biological control and invasion biology makes the former extremely useful to study ecological processes that drive the success of invasions. This in turn could yield knowledge that may have implication in other disciplines such as the preservation of endangered species. However, factors like the low detectability of a biological control agent at low densities (coupled with varying sensibility of monitoring methods) may render the study of early stages dynamics and interactions too much of a daunting endeavor.
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The rise of the Asian chestnut gall wasp Dryocosmus kuriphilus in France has benefited the native community of parasitoids originally associated with oak gall wasps by becoming an additional trophic subsidy and therefore perturbing population dynamics of local parasitoids. However, the successful biological control of this pest has then led to significant decreases in its population densities. Here we investigate how the invasion of the Asian chestnut gall wasp Dryocosmus kuriphilus in France and its subsequent control by the exotic parasitoid Torymus sinensis has impacted the local community of native parasitoids. We explored 5 years of native community dynamics within 26 locations during the rise and fall of the invasive pest. In an attempt to understand how mechanisms such as local extinction or competition come into play, we analyzed how the patterns of co-occurrence between the different native parasitoid species changed through time. Our results demonstrate that native parasitoid communities experienced increased competition as the D. kuriphilus levels of infestation decreased. During the last year of the survey, two alternative patterns were observed depending on the sampled location: either native parasitoid communities were represented by an extremely limited number of species occurring at low densities, in some cases no native parasitoid species at all, or they were dominated by one main parasitoid: Mesopolobus sericeus. These two patterns seemed to correlate with the habitat type, M. sericeus being more abundant in semi-natural habitats compared to agricultural lands, the former known to be natural reservoirs for native parasitoids. These results highlight how the boom-and-bust dynamics of an invasive pest followed by successful biological control can deeply alter the structure of native communities of natural enemies.
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This study aims at estimating the effect of landscape composition on the availability of small mammal preys (in terms of biomass) to predators on a sectorial scale (n × 1 km2). Four study sites, representative of different stages of agriculture intensification, were selected in eastern France according to landscape composition. The population dynamics of Microtus arvalis, Arvicola terrestris, Clethrionomys glareolus and Apodemus sp. were monitored from 1992 to 1996 by using index methods and trapping. M. arvalis and A. terrestris population biomasses were stable in landscapes with low percentage of permanent grassland. M. arvalis populations displayed greater biomass variations with sharp declines in the sites where the proportion of permanent grassland to farmland was greater than 50 %. A. terrestris populations were very unstable in one study site where the proportion of permanent grassland to farmland was greater than 85 %. Synchronic patterns between M. arvalis populations and the populations of hedgerow rodents were suspected at sites with large fluctuations of M. arvalis: Every decline of the populations of hedgerow rodents was concomitant with the M. arvalis decline. These results suggest that two kinds of ecological systems in terms of prey-resource variations for mammalian predators can be distinguished: (i) stable in landscapes with lower proportion of permanent grassland, and (ii) unstable, with grassland species crashes and synchronous declines of the rodent community, in landscapes with higher proportion of permanent grassland. Moreover, the population dynamics of small mammals were asynchronous between the four sites situated at relatively short distance (some tens kilometres).
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The functional response is a key element of predator-prey interactions. Basic functional response theory explains foraging behavior of individual predators, but many empirical studies of free-ranging predators have estimated functional responses by using population-averaged data. We used a novel approach to investigate functional responses of an avian predator (the rough legged-buzzard Buteo lagopus Pontoppidan, 1763) to intra-annual spatial variation in rodent density in subarctic Sweden, using breeding pairs as the sampling unit. The rough-legged buzzards responded functionally to Norwegian lemmings (Lemmus lemmus L. 1758), grey-sided voles (Myodes rufocanus Sundevall, 1846) and field voles (Microtus agrestis L. 1761), but different rodent prey were not utilised according to relative abundance. The functional response to Norwegian lemmings was a steep type II curve and a more shallow type III response to grey-sided voles. The different shapes of these two functional responses were likely due to combined effects of differences between lemmings and grey-sided voles in habitat utilisation, anti-predator behaviour and size-dependent vulnerability to predation. Diet composition changed less than changes in relative prey abundance, indicating negative switching, with high disproportional use of especially lemmings at low relative densities. Our results suggest that lemmings and voles should be treated separately in future empirical and theoretical studies in order to better understand the role of predation in this study system.
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Understanding of complex trophic interactions in ecosystems requires correct descriptions of the rate at which predators consume a variety of different prey species. Field and laboratory data on multispecies communities are rarely sufficient and usually cannot provide an unambiguous test for the theory. As a result, the conventional way of constructing a multi-prey functional response is speculative, and often based on assumptions that are difficult to verify. Predator responses allowing for prey selectivity and active switching are thought to be more biologically relevant compared to the standard proportion-based consumption. However, here we argue that the functional responses with switching may not be applicable to communities with a broad spectrum of resource types. We formulate a set of general rules that a biologically sound parameterization of a predator functional response should satisfy, and show that all existing formulations for the multispecies response with prey selectivity and switching fail to do so. Finally, we propose a universal framework for parameterization of a multi-prey functional response by combining patterns of food selectivity and proportion-based feeding.
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Many issues in fundamental and applied ecology require the use of sampling protocols at the sectoral or even regional scales at which many important ecological mechanisms occur. The lack of workable sampling methods at these scales is a major obstacle to the analysis and understanding of these mechanisms. We test the validity of an index method of estimating relative population densities, applicable along transects of several kilometers in length, for a population of Common Voles (Microtus arvalis). The results show that the index method of estimating relative density is well adapted for monitoring variations in the abundance and spatial distribution of Common Vole populations and authorizes studies for a wide range of objectives and spatial scales.
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A method to estimate the abundance of the fossorial form of the water vole Arvicola terrestris scherman (Shaw, 1801) has been developed, by using surface indices. Results are compared to the standard method of estimation using trap lines. These results show quantitatively that it is possible to differentiate reliably mole indices from water vole indices. Moreover, the two species are inclined to exclude each other. Even though water voles share the same galleries as moles, specific surface indices of the water vole occur for any density exceeding 2 ind/trap line (over 20 ind/ha). Several models of abundance estimation are put forward, all of them using linear multiple regressions. Correlations between the estimations from indices and the estimations from trap lines exceed 0.8 and the limits of using abundance classes are tested. Other limits are developed in the discussion. One of them is that the sampling intervals are saturated for densities exceeding 400 ind/ha. The index method, which is easy to carry out, offers the definite advantage of being suitable to space and time scales otherwise incompatible with estimations from trap lines. For instance, it allows distribution maps from wide transects about areas of more than 25 km(2) to be drawn, in less than two days.
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Predator-Prey switching may stabilise predator-prey interactions, promote co-existence of prey that share a common predator, and increase the overall stability of homogeneous systems of interacting species. This study presents an investigation of prey switching of 2 major North Sea fish predators, cod Gadus morhua and whiting Merlangius merlangus. Relative food composition derived from analysis of more than 36 000 stomachs is compared to the relative density of fish prey reflected by trawl survey catches, and generalised linear models are used to examine how prey switching is affected by predator length and prey species and length. Possible effects of stomach sample size and predator density are also investigated. Prey preference is a decreasing function of the relative density of the prey (negative prey switching), in particular for large cod (40 to 100 cm). This was neither the result of variations in stomach sample size, nor of changes in local predator abundance. If not counteracted by compensatory changes in spatial overlap or total food intake, negative switching is likely to destabilise the interactions between cod and whiting and their fish prey.
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Seabirds that consume more than one prey type may adjust their foraging to maintain provisioning rates for their chicks. How energetically effective are these strategies, and what are the implications for the management of seabirds and their marine habitat? A multi-species functional response links consumption rates to the availability of multiple prey types, but fitting multi-species functional responses to field data can be difficult, requiring consumption measurements over a range of different prey abundances. Such detailed data may be especially difficult to obtain in marine ecosystems. We used annual time-series data on chick provisioning for the common guillemot Uria aalge together with abundance indices for its two main prey (lesser sandeel Ammodytes marinus and sprat Sprattus sprattus) to parameterize a multi-species functional response for parents provisioning chicks at a major North Sea colony from 1992 to 2005. The fitted model reproduced changes in diet and consumption rate which were consistent with changes in local prey abundance including a long-term decline in sandeels. The model predicted that energy intake by chicks would be more sensitive to changes in sprat abundance than sandeel abundance. Guillemots appeared able to adjust their foraging tactics over a wide range of prey abundances to maintain a consistent energetic intake rate for chicks. Synthesis and applications. Our results suggest guillemot chicks obtain adequate calorific intake from their parents despite fluctuating prey abundances, conferring some resilience in the face of environmental variation. The parameterized multi-species functional response model can be used to estimate levels of severe prey shortage that compromise provisioning. It also enables us to interpret predator consumption rates so that these can be used as a metric of prey availability. Further, quantifying trophic links between marine prey and apex predators is needed to support the development of multi-species models in which the predators can be included. Such models are needed as tools to effectively manage the marine ecosystem, taking into account the objectives of fishing, conservation and the need to maintain Good Environmental Status. © 2013 British Ecological Society.
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The diet of the Barn Owl (Tyto alba (Scopoli, 1769)) was studied over an 8-year period in the Jura mountains of France, during two population surges of its main rodent prey (common voles, Microtus arvalis (Pallas, 1778), and European water voles, Arvicola terrestris (L.,1758)), allowing us to test whether T. alba is an opportunistic predator as is often cited in the literature or exhibits more complex patterns of prey selection as is reported in arid environments. Small mammals were sampled by trapping and index methods. We observed (i) significant correlations between the proportions of A. terrestris, M. arvalis, and woodland rodents in the diet and their respective densities in the field; (ii) interactions between populations of A. terrestris and M. arvalis, indicating that the proportion of each species in diet was affected by the density of the other; (iii) proportions of red-toothed shrews (genus Sorex (L., 1758)) in the diet did not correlate with their abundance in the field, indicating that those species were likely to be preyed upon when others were no longer available. This confirms that T. alba is generally opportunistic; however, prey selection of a focal species (e.g., Sorex spp., grassland species) can be affected by the density or availability of the other prey species.
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1. Predator conservation management requires detailed understanding of the ecological circumstances associated with predation, especially that on economically valuable prey. We examined the mechanisms behind Bonelli’s eagle Hieraaetus fasciatus predation on prey of domestic origin, using dietary data from 22 pairs breeding in south-west Portugal (1992–2001) together with information on landscape composition and prey availability. 2. Numerically, 42·7% (37·7% in biomass) of eagle prey comprised domestic species, about 70% of which were rural pigeons Columba livia and the remainder were racing pigeons Columba livia and domestic fowl Gallus gallus. Rabbits Oryctolagus cuniculus, red-legged partridges Alectoris rufa and jays Garrulus glandarius were the most frequent wild prey (43·1%; 50·8% in biomass). This dietary pattern was remarkably stable over a decade, but within each year the intake of pigeons almost halved over the course of the breeding season. 3. Landscape composition significantly affected the dietary proportion of wild and domestic prey items. This was particularly evident in territories dominated by eucalyptus Eucalyptus globulus plantations, where there was reduced consumption of rural pigeons and partridges, an increased intake of minor avian prey items and greater diversity in the diet overall. 4. Bonelli’s eagles showed type II functional responses while preying on the most important wild (rabbit) and domestic (rural pigeon) prey, although the former was much stronger. Eagle predation on rabbits declined with increasing abundance of pigeons, and vice versa, but there was no switching in the traditional sense, as selection between these two species was inversely frequency dependent. 5. Synthesis and applications. Predation by Bonelli’s eagle on domestic pigeons results from a combination of high vulnerability of the pigeons to eagles and a shortage of key wild prey such as rabbits and partridges, especially during the early breeding season. Given the relatively low economic value of rural pigeons and their importance in the diet of Bonelli’s eagles, they could probably be used as a conservation tool to enhance food resources in breeding territories and to deflect predation from more valuable prey such as partridges and racing pigeons.
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Modelers often need to quantify the rates at which zooplankton consume a variety of species, size classes and trophic types. Implicit in the equations used to describe the multiple resource functional response (i.e. how nutritional intake varies with resource densities) are assumptions that are not often stated, let alone tested. This is problematic because models are sensitive to the details of these formulations. Here, we enable modelers to make more informed decisions by providing them with a new framework for considering zooplankton feeding on multiple resources. We define a new classification of multiple resource responses that is based on preference, selection and switching, and we develop a set of mathematical diagnostics that elucidate model assumptions. We use these tools to evaluate the assumptions and biological dynamics inherent in published multiple resource responses. These models are shown to simulate different resource preferences, implied single resource responses, changes in intake with changing resource densities, nutritional benefits of generalism, and nutritional costs of selection. Certain formulations are further shown to exhibit anomalous dynamics such as negative switching and sub-optimal feeding. Such varied responses can have vastly different ecological consequences for both zooplankton and their resources; inappropriate choices may incorrectly quantify biologically-mediated fluxes and predict spurious dynamics. We discuss how our classes and diagnostics can help constrain parameters, interpret behaviors, and identify limitations to a formulation's applicability for both regional (e.g. High-Nitrate-Low-Chlorophyll regions comprising large areas of the Pacific) and large-scale applications (e.g. global biogeochemical or climate change models). Strategies for assessing uncertainty and for using the mathematics to guide future experimental investigations are also discussed.
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Over the last three decades, many studies have attempted to explain forager diets by using optimal diet theory (ODT). Despite some obvious successes, the utility of this theory remains controversial. We reviewed the results of 134 studies of optimal diet theory to test hypotheses on factors that can explain variation in the ability of ODT to predict diets and diet shifts in response to changes in prey availability. Our major conclusion is that while ODT has generally worked well for foragers that feed on immobile prey, the theory often failed to predict the diets of foragers that attack mobile prey. We found only mixed support for the hypothesis that the theory works better when the study scenario more closely fits the assumptions of the model. Contrary to our a priori predictions, forager types (invertebrate versus ectothermic vertebrate versus endothermic vertebrate) did not differ in their likelihood of corroborating ODT. Two explanations for why optimal diet theory does not work well with mobile prey are that studies on mobile prey often lack information on key parameters that are required to rigorously test ODT, and that with mobile prey, variations among prey in vulnerability (encounter rate and capture success) are often more important than variation in predator active choice in determining predator diets.
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Predators can have profound impacts on the dynamics of their prey that depend on how predator consumption is affected by prey density (the predator's functional response). Consumption by a generalist predator is expected to depend on the densities of all its major prey species (its multispecies functional response, or MSFR), but most studies of generalists have focussed on their functional response to only one prey species. Using Bayesian methods, we fit an MSFR to field data from an avian predator (the hen harrier Circus cyaneus) feeding on three different prey species. We use a simple graphical approach to show that ignoring the effects of alternative prey can give a misleading impression of the predator's effect on the prey of interest. For example, in our system, a "predator pit" for one prey species only occurs when the availability of other prey species is low. The Bayesian approach is effective in fitting the MSFR model to field data. It allows flexibility in modelling over-dispersion, incorporates additional biological information into the parameter priors, and generates estimates of uncertainty in the model's predictions. These features of robustness and data efficiency make our approach ideal for the study of long-lived predators, for which data may be sparse and management/conservation priorities pressing.
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The functional response of predators to prey density variations has previously been investigated in order to understand predation patterns. However, the consequences of functional response on parasite transmission remain largely unexplored. The rodents Microtus arvalis and Arvicola terrestris are the main prey of the red fox Vulpes vulpes in eastern France. These species are intermediate and definitive hosts of the cestode Echinococcus multilocularis. We explored the dietary and contamination responses of the red fox to variations in prey density. The dietary response differed between the two prey species: no response for M. arvalis and a type III-like (sigmoidal) response for A. terrestris that shows possible interference with M. arvalis. The fox contamination response followed a type II shape (asymptotic) for both species. We conclude that fox predation is species specific and E. multilocularis transmission is likely to be regulated by a complex combination of predation and immunologic factors. These results should provide a better understanding of the biological and ecological mechanisms involved in the transmission dynamics of trophically transmitted parasites when multiple hosts are involved. The relevance of the models of parasite transmission should be enhanced if non-linear patterns are taken into account.
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We consider a model for the functional response of a predator feeding on two species of prey. We assume that the predator searches randomly, at constant speed, for randomly distributed prey, but that whether it attacks a contacted prey will depend on the species of the prey, the species of the last meal, and the time since the last meal. We establish a formula for the expected time between meals on species 1, and take the functional response on species 1, the number of species 1 eaten per unit time by a single predator, to be the reciprocal of this. The general formulae are somewhat complicated, but if it is assumed that the probability of attack is independent of time, it is possible to obtain a fairly simple expression for functional response. This functional response is not necessarily stabilizing; it will be if there is a sufficiently strong (relative to the handling times) tendency for the predator to be more likely to attack a contacted prey if it is the species that was eaten last. (More detail is ...
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A model which relates optimal food preference relationships and caloric yield per unit time of potential food sources is derived. It is suggested, on the basis of this model, that: 1) Food preferences can be adequately described only if a number of factors other than relative frequencies in the diet and relative abundances of the food types are known. 2) Animals should be more selective in their choice of foods when satiated or when food is common, more indiscriminate when starved or when food is scarce. 3) Animals may eat one food type with greater frequency, relative to its abundance, than another even if the other food is richer and more efficiently exploited. This occurs in situations of high relative abundance of the first food type. 4) The extent to which predators tend to pass by potential food items may be used to evaluate the role of food in the population limitation of a predator species. 5) Food preferences appear to change readily and appropriately to changes in the environment. preferences a ...
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The growth response of a population to the resources in a particular environment is used to classify pairs of resources as being either (1) essential, (2) hemi-essential, (3) complementary, (4) perfectly substitutable, (5) antagonistic, or (6) switching. Although nutrition is one important factor determining resource type, the growth response of a population to resources also depends on the interaction between a species' foraging methods and the spatial distribution of the resources. For example, two resources which are nutritionally perfectly substitutable may be operationally switching, antagonistic, or complementary because of spatial heterogeneity. A graphical, equilibrium theory of resource competition allows prediction of the outcome of interactions between several consumers for the various classes of resources. The technique requires information on (1) resource type (growth isoclines), (2) resource preference, (3) resource supply processes, and (4) mortality rates for all species. For all resource types, the major criterion for stable coexistence is that each species consume relatively more of the one resource which more limits its own growth rate.
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This paper summarizes models of estimation and analysis for the measure of consumer food preferences originally derived by Manly et al. (1972) and further developed by Chesson (1978). Unlike many alternative measure this measure of preference does not change with changes in food densities unless consumer behavior also changes. This measure is shown to relate in a simple way to parameters, such as clearance and attack rates, which appear in certain commonly used models of foraging behavior.
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The functional response of a consumer is the relationship between its consumption rate and the abundance of its food. A functional response is said to be of type I if consumption rate increases linearly with food abundance up to a threshold level at which it remains constant. According to conventional wisdom, such type I responses are more frequent among filter feeders than among other consumers. However, the validity of this claim has never been tested. We review 814 functional responses from 235 studies, thereby showing that type I responses are not only exceptionally frequent among filter feeders but that they have only been reported from these consumers.
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The dietary structure and distribution patterns of red foxes Vulpes vulpes in situations of different food supply in the coniferous-deciduous (mostly small-leaved) woodlands of northern Belarus were investigated. A total of 1526 scats of red foxes was analysed, and snowtracking of the species was performed each winter. Abundance of the main prey (small rodents, perching birds and hares) and wild ungulates supplying carrion for red foxes in the cold season were monitored. The results suggest that in northern Belarus red foxes had a diversified diet, consisting basically of different combinations of bank votes, Microtus votes, and wild ungulate carrion. The importance of carrion much increased in winter, while the proportions of birds and fruits grew during the warm season. In the ecologically rich woodland harbouring on clay soil, red foxes relied more on small rodents, white carrion and fruits appeared to be more important food item of the predator in the barren forested terrain dwelling on poor sandy deposits. During Microtus population outbreaks, red foxes more frequently fed on this prey. One-sixth Lower density of red foxes was attributable to the forested terrain on sandy deposits compared to the woodland on clay soil, and a pronounced Landscape-related difference in the habitat selection by the predator was found. (c) 2005 Deutsche Gesellschaft fur Sugetierkunde. Published by Elsevier GmbH. All rights reserved.
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1. Selective pressures acting on foraging activities constrain the strength of interaction, hence the stability and energetic availability in food webs. 2. Because such selective pressures are usually measured at the individual level and because most experimental and theoretical works focus on simple settings, linking adaptive foraging with community scale patterns is still a far stretch. 3. Some recent models incorporate foraging adaptation in diverse communities. The models vary in the way they incorporate adaptation, via evolutionary or behavioural changes, and define individual fitness in various ways. 4. In spite of these differences, some general results linking adaptation to community structure and functioning emerge. In the present article, I introduce these different models and highlight their common results. 5. Adaptive foraging provides stability to large food web models and predicts successfully interaction patterns within food webs as well as other topological features such as food chain length. 6. The relationships between adaptive foraging and other structuring factors particularly depend on how well connected the local community is with surrounding communities (metacommunity aspect).
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We compare the results of four experiments, conducted at different times and with different protocols, that explored the relationship between frequency-dependent selection and prey density in wild birds feeding on artificial populations of coloured baits. One (experiment 4) used pastry baits that differed only in the presence or absence of a red stripe, and this experiment provided no evidence for any kind of selective behaviour. The other three experiments used green and brown baits, and they all provided evidence for a trend towards increasing anti-apostatic selection with high densities (>100 baits m–2). However, one of these (experiment 3) provided no evidence for frequency-dependent selection at low densities (0.5–20 baits m–2), while the other two experiments concurred in suggesting a trend towards increasing apostatic selection with low densities (down to 2 baits m–2). Together, these experiments both support and qualify the published findings of experiment 1 that frequency- dependent selection by wild birds on bait populations is modified by density. Experiment 4 indicates that frequency-dependent selection may break down entirely if bait types are too similar, while experiment 3 indicates that some details of this trend with density will depend either on the protocol used or on exogenous changes in the birds’ feeding behaviour.
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Models are developed in which prey preferences vary between individual predators but the preference of an individual does not change with prey relative density. These two properties generally lead to the surprising conclusion that the aggregate preference of a population of predators does change with prey relative density. This phenomenon may result in negative or positive switching, depending on the circumstances, with negative switching being the more likely result. Such population negative switching is found in previously published experimental data. Implications are given for the analysis of ecological data, and some implications for the stability of field populations are suggested.
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Food-web population models are rather sensitive to parameterization of functional response in predation terms. Theoretical studies predict enhancing of ecosystems' stability for a functional response of sigmoid type (Holling type III). The choice of a correct type of response is especially important for modelling outcome of grazing control of algal blooms by zooplankton in nutrient-rich ecosystems. Extensive experiments on zooplankton feeding in laboratories show non-sigmoid nature of response for most herbivorous zooplankton species. As a consequence, there is a strong opinion in literature that the implementation of Holling III type grazing in plankton models is biologically meaningless. I argue, however, that such an 'evident' claim might be wrong and sigmoid functional responses in real plankton communities would emerge more often than was suggested earlier. Especially, this concerns plankton models without vertical resolution, which ignore heterogeneity in vertical distribution of species. Having conducted extensive literature search of data on zooplankton feeding in situ, I show that vertical heterogeneity in food distribution as well as active food searching behaviour of zooplankton can modify the type of functional response. In particular, the rate of food intake by the whole zooplankton population in the column, as a function of total amount of food, often exhibits a sigmoid behaviour, instead of a non-sigmoid one postulated previously based on laboratory experiments. This conceptual discrepancy is due to the ability of zooplankton to feed mostly in layers with high algal density. I propose a generic model explaining the observed alteration of type between overall and local functional responses. I show that emergence of Holling type III in plankton systems is due to mechanisms different from those well known in the ecological literature (e.g. food search learning, existence of alternative food, refuge for prey).
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Multi-species Lotka-Volterra models exhibit greater instability with an increase in diversity and/or connectance. These model systems, however, lack the likely behavior that a predator will prey more heavily on some species if other prey species decline in relative abundance. We find that stability does not depend on diversity and/or connectance in multi-species Lotka-Volterra models with this 'predator switching'. This conclusion is more consistent with several empirical observations than the classic conclusion, suggesting that large complex ecosystems in nature may be more stable than previously supposed.
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The functional response of a consumer is the relationship between its consumption rate and the abundance of its food. A functional response is said to be of type I if consumption rate increases linearly with food abundance up to a threshold level at which it remains constant. According to conventional wisdom, such type I responses are more frequent among filter feeders than among other consumers. However, the validity of this claim has never been tested. We review 814 functional responses from 235 studies, thereby showing that type I responses are not only exceptionally frequent among filter feeders but that they have only been reported from these consumers. These findings can be understood by considering the conditions that a consumer must fulfil in order to show a type I response. First, the handling condition: the consumer must have a negligibly small handling time (i.e. the time needed for capturing and eating a food item), or it must be able to search for and to capture food while handling other food. Second, the satiation condition: unless its gut is completely filled and gut passage time is minimal, the consumer must search for food at a maximal rate with maximal effort. It thus has to spend much time on foraging (i.e. searching for food and handling it). Our functional response review suggests that only filter feeders sometimes meet both of these conditions. This suggestion is reasonable because filter feeders typically fulfil the handling condition and can meet the satiation condition without losing time, for they are, by contrast to non-filter feeders, able simultaneously to perform foraging and non-foraging activities, such as migration or reproduction.
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We investigate the long-term web structure emerging in evolutionary food web models when different types of functional responses are used. We find that large and complex webs with several trophic layers arise only if the population dynamics is such that it allows predators to focus on their best prey species. This can be achieved using modified Lotka-Volterra or Holling/Beddington functional responses with effective couplings that depend on the predator's efficiency at exploiting the