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1. In community and population ecology, there is a chronic gap between the classic Eltonian ecology describing patterns in abundance and body mass across species and ecosystems and the more process oriented foraging ecology addressing interactions and quantitative population dynamics. However, this dichotomy is arbitrary, because body mass also determines most species traits affecting foraging interactions and population dynamics. 2. In this review, allometric (body-mass dependent) scaling of handling times and attack rates are documented, whereas body-mass effects on Hill exponents (varying between hyperbolic type II and sigmoid type III functional responses) and predator interference coefficients are lacking. This review describes how these allometric relationships define a biological plausible parameter space for population dynamic models. 3. Consistent with the classic Eltonian description, species co-existence in consumer-resource models and tri-trophic food chains is restricted to intermediate consumer-resource body-mass ratios. Allometric population dynamic models allow understanding the processes of energy limitation and unstable dynamics leading to this restriction. Complex food webs are stabilized by high predator-prey body-mass ratios, which are consistent with those found in natural ecosystems. These high body-mass ratios yield positive diversity-stability and complexity-stability relationships thus supporting the classic picture of ecosystem stability. 4. Allometric-trophic network models, based on body mass and trophic information from ecosystems, bridge the gap between Eltonian community patterns and process-oriented foraging ecology and provide a new means to describe the dynamics and functioning of natural ecosystems.

The potential for climate change and temperature shifts to affect community stability remains relatively unknown. One mechanism by which temperature may affect stability is by altering trophic interactions. The functional response quantifies the per capita resource consumption by the consumer as a function of resource abundance and is a suitable framework for the description of nonlinear trophic interactions. We studied the effect of temperature on a ciliate predator–prey pair (Spathidium sp. and Dexiostoma campylum) by estimating warming effects on the functional response and on the associated conversion efficiency of the predator. We recorded prey and predator dynamics over 24 hr and at three temperature levels (15, 20 and 25°C). To these data, we fitted a population dynamic model including the predator functional response, such that the functional response parameters (space clearance rate, handling time and density dependence of space clearance rate) were estimated for each temperature separately. To evaluate the ecological significance of temperature effects on the functional response parameters, we simulated predator–prey population dynamics. We considered the predator–prey system to be destabilized, if the prey was driven extinct by the predator. Effects of increased temperature included a transition of the functional response from a Type III to a Type II and an increase of the conversion efficiency of the predator. The simulated population dynamics showed a destabilization of the system with warming, with greater risk of prey extinction at higher temperatures likely caused by the transition from a Type III to a Type II functional response. Warming‐induced shifts from a Type III to II are not commonly considered in modelling studies that investigate how population dynamics respond to warming. Future studies should investigate the mechanism and generality of the effect we observed and simulate temperature effects in complex food webs including shifts in the type of the functional response as well as consider the possibility of a temperature‐dependent conversion efficiency. The authors study highlights that warming can induce shifts in the functional response type of a predator–prey system by lowering the scaling exponent q. In contrast, modelling studies exploring the consequences of warming often rely on a single fixed functional response type and hence overlook a potential destabilization of a system due to changes in the functional response type.

We consider functional linear regression models with a functional response and multiple functional predictors, with the goal of finding the best finite-dimensional approximation to the signal part of the response function. Defining the integrated squared correlation coefficient between a random variable and a random function, we propose to solve a penalized generalized functional eigenvalue problem, whose solutions satisfy that projections on the original predictors generate new scalar uncorrelated variables and these variables have the largest integrated squared correlation coefficient with the signal function. With these new variables, we transform the original function-on-function regression model to a function-on-scalar regression model whose predictors are uncorrelated, and estimate the model by penalized least-square method. This method is also extended to models with both multiple functional and scalar predictors. We provide the asymptotic consistency and the corresponding convergence rates for our estimates. Simulation studies in various settings and for both one and multiple functional predictors demonstrate that our approach has good predictive performance and is very computational efficient. Supplementary materials for this article are available online.

Describing the mechanisms that drive variation in species interaction strengths is central to understanding, predicting, and managing community dynamics. Multiple factors have been linked to trophic interaction strength variation, including species densities, species traits, and abiotic factors. Yet most empirical tests of the relative roles of multiple mechanisms that drive variation have been limited to simplified experiments that may diverge from the dynamics of natural food webs. Here, we used a field-based observational approach to quantify the roles of prey density, predator density, predator-prey body-mass ratios, prey identity, and abiotic factors in driving variation in feeding rates of reticulate sculpin (Cottus perplexus). We combined data on over 6,000 predator-prey observations with prey identification time functions to estimate 289 prey-specific feeding rates at nine stream sites in Oregon. Feeding rates on 57 prey types showed an approximately log-normal distribution, with few strong and many weak interactions. Model selection indicated that prey density, followed by prey identity, were the two most important predictors of prey-specific sculpin feeding rates. Feeding rates showed a positive relationship with prey taxon densities that was inconsistent with predator saturation predicted by current functional response models. Feeding rates also exhibited four orders-of-magnitude in variation across prey taxonomic orders, with the lowest feeding rates observed on prey with significant anti-predator defenses. Body-mass ratios were the third most important predictor variable, showing a hump-shaped relationship with the highest feeding rates at intermediate ratios. Sculpin density was negatively correlated with feeding rates, consistent with the presence of intraspecific predator interference. Our results highlight how multiple co-occurring drivers shape trophic interactions in nature and underscore ways in which simplified experiments or reliance on scaling laws alone may lead to biased inferences about the structure and dynamics of species-rich food webs.

The curvature of generalized Holling type functional response curves is controlled by a shape parameter b yielding hyperbolic type II (b = 1) to increasingly sigmoid type III (b > 1) responses. Empirical estimates of b vary considerably across taxa. Larger consumer–resource body mass ratios have been suggested to generate more pronounced type III responses and therefore to promote dynamic stability. The dependence of consumer–resource stability on b has, however, not been systematically explored, and the accurate empirical determination of b is challenging. Specifically, the shape of the functional response of the pelagic grazer Daphnia feeding on phytoplankton, and its consequences for stability, remain controversial. We derive a novel analytical condition relating b to local stability of consumer–resource interactions and use it to predict stability of empirically parameterized models of Daphnia and phytoplankton under enrichment. Functional response parameters were experimentally derived for two species of Daphnia feeding separately on single cultures of two different phytoplankton species. All experimentally studied Daphnia–algae systems exhibited type III responses. Parameterized type III responses are predicted to stabilize the modeled Daphnia–phytoplankton dynamics in some species pairs but not in others. Remarkably, stability predictions differ depending on whether functional response parameters are derived from clearance vs. ingestion rates. Accurate parameter estimation may therefore require fitting to both rates. In addition, our estimates of b for filter‐feeding Daphnia are much smaller than predicted for actively hunting predators at similar consumer–resource body mass ratios. This suggests that the relationship between functional response shape and body mass ratios may vary with predation mode.

Nitrogen (N) fertilization is a common agricultural practice, which, by increasing the quality of plants, also enhances their nutritional suitability for insect herbivores, creating the possibility of a cascade of N across trophic levels, from plant to herbivore to predator. We manipulated the quality of cucumber plants by fertilizing them with three different N rates (110, 160, and 210 ppm), which represented low, medium, and high N levels, respectively. Colonies of Aphis gossypii Glover (Hemiptera: Aphididae) were then reared on these plants and used as prey for adult Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae) in experiments that characterized the predator's foraging behavior and functional response to different aphid densities. The nutritional content of plants and aphids was also measured. As N fertilization increased, so did the nutrient content (total energy) of aphids and this resulted in declining rates of aphid consumption by beetles at higher aphid densities. Females in the 110 N treatment, and males in all treatments, responded to aphids with a type II functional response (decelerating consumption at higher densities), but females in the 160 and 210 ppm N treatments exhibited a type III response (consuming a declining proportion of available aphids at high densities). Beetles fed aphids from the 110 N treatment consumed more prey in both assays than did those fed aphids from the 210 N treatment. Beetle searching time, handling time, and duration of digestive pauses all increased at high levels of N fertilization, especially for females.The results indicate that heavy N fertilization can increase prey nutritional quality to the point where it alters predator foraging and feeding behavior, resulting in slower rates of prey consumption and longer prey handling times.

Long-term feeding effects of the almond pollen on the life table parameters of Neoseiulus californicus McGregor were assessed after 5, 10, and 20 generations after introduction in the rearing arena. Furthermore, to evaluate behavioral characteristics of the mass-reared predator (strain A) in face with the real prey, functional and numerical responses of the predator to different densities of the twospotted spider mite nymphs were determined, and the obtained data were compared with those reared on twospotted spider mite (strain T). Long-term rearing did not significantly affect total fecundity of N. californicus (ranged from 37.79 to 41.91 eggs). Nevertheless, preadult duration in the 5th generation was significantly longer than the 10th and 20th generations. The intrinsic rate of increase (r) in the 10th (0.2056 d–1) and 20th (0.2201 d–1) generations had not significant difference together. However, the r value slightly dropped in the 5th generation (0.1706 d–1) because of the irregular offering of fresh pollen to the rearing colonies before that. Both strains of N. californicus exhibited a type II functional response; however, the N. californicus reared on the almond pollen (strain A) had a higher attack rate (a) and shorter handling time (Th). The individuals reared on the almond pollen had a greater size than those reared on twospotted spider mite; its higher predation potential is probably due to this characteristic. Consequently, the rearing of N. californicus on the almond pollen positively affected its attributes including high survivorship, body size, and fecundity, and subsequently higher potential to control twospotted spider mite.

Host–parasite interactions are shaped by the broader web of community interactions, from interspecific competition to predator–prey dynamics. Heterospecific scavengers might also affect parasite transmission from infectious carcasses, which can be an important source of infections for some wildlife diseases. A robust scavenger community can quickly remove carcasses and tissue and thus prevent secondary transmission by necrophagy or contact with infectious carcasses. Alternatively, by spreading infectious particles and tissues throughout the environment, scavengers may increase rates of casual contact with pathogens and thus overall transmission. However, there has been little empirical consideration of the contrasting roles that scavengers might play in infectious disease dynamics. We carried out a series of studies to determine the efficiency with which scavenging invertebrates remove carcasses of Long‐toed Salamander (Ambystoma macrodactylum) larvae and their role in the transmission of frog virus 3 (Genus: Ranavirus, Family: Iridoviridae) from carcasses. We then estimated the functional response of one efficient invertebrate scavenger (Family: Dytiscidae) to increasing carcass densities in field conditions in order to determine the capacity of scavenging invertebrates to consume large amounts of carcass tissue, as may be present at high prevalence sites. We found that removal of infectious carcasses by scavengers strongly reduced transmission to naïve larvae. Scavengers were as effective at reducing transmission from a carcass as a physical barrier preventing contact with the carcass. There was little evidence that scavenging released sufficient infectious tissues into the water column to rival direct contact as a route of infection. Moreover, while scavenging rates saturated at increasing carcass densities, consistent with a type II functional response, there were sufficient densities of dytiscid larvae, not to mention other scavenging invertebrates, in a surveyed pond to theoretically prevent transmission from carcasses. Our results suggest that at least in systems in which conspecific necrophagy is common, the scavenger community can play an important role in reducing transmission. A plain language summary is available for this article. Plain Language Summary

A predator's per capita feeding rate on prey, or its functional response, provides a foundation for predator-prey theory. Since 1959, Holling's prey-dependent Type II functional response, a model that is a function of prey abundance only, has served as the basis for a large literature on predator-prey theory. We present statistical evidence from 19 predator-prey systems that three predator-dependent functional responses (Beddington-DeAngelis, Crowley-Martin, and Hassell-Varley), i.e., models that are functions of both prey and predator abundance because of predator interference, can provide better descriptions of predator feeding over a range of predator-prey abundances. No single functional response best describes all of the data sets. Given these functional forms, we suggest use of the Beddington-DeAngelis or Hassell-Varley model when predator feeding rate becomes independent of predator density at high prey density and use of the Crowley-Martin model when predator feeding rate is decreased by higher predator density even when prey density is high.

Summary Despite their importance in determining the rate of both energy gain and expenditure, how the fine‐scale kinematics of foraging are modified in response to changes in prey abundance and distribution remain poorly understood in many animal ecosystems. In the marine environment, bulk‐filter feeders rely on dense aggregations of prey for energetically efficient foraging. Rorqual whales (Balaenopteridae) exhibit a unique form of filter feeding called lunge feeding, a process whereby discrete volumes of prey‐laden water are intermittently engulfed and filtered. In many large rorqual species the size of engulfed water mass is commensurate with the whale's body size, yet is engulfed in just a few seconds. This filter‐feeding mode thus requires precise coordination of the body and enlarged engulfment apparatus to maximize capture efficiency. Previous studies from whale‐borne tags revealed that many rorqual species perform rolling behaviours when foraging. It has been hypothesized that such acrobatic manoeuvres may be required for efficient prey capture when prey manifest in small discrete patches, but to date there has been no comprehensive analysis of prey patch characteristics during lunge feeding events. We developed a null hypothesis that blue whale kinematics are independent of prey patch characteristics. To test this hypothesis, we investigated the foraging performance of blue whales, the largest filter‐feeding predator and their functional response to variability in their sole prey source, krill using a generalized additive mixed model framework. We used a combination of animal‐borne movement sensors and hydroacoustic prey mapping to simultaneously quantify the three‐dimensional foraging kinematics of blue whales (Balaenoptera musculus) and the characteristics of targeted krill patches. Our analyses rejected our null hypothesis, showing that blue whales performed more acrobatic manoeuvres, including 180° and 360° rolling lunges, when foraging on low‐density krill patches. In contrast, whales targeting high‐density krill patches involved less manoeuvring during lunges and higher lunge feeding rates. These data demonstrate that blue whales exhibit a range of adaptive foraging strategies that maximize prey capture in different ecological contexts. Because first principles indicate that manoeuvres require more energy compared with straight trajectories, our data reveal a previously unrecognized level of complexity in predator–prey interactions that are not accounted for in optimal foraging and energetic efficiency models. Lay Summary