Risk of predation makes foragers less choosy about their food

Nutritional needs and mortality risk combine to shape foraging decisions in ants

When foraging, internal needs for particular nutrients might affect food choice, and external constraints, such as predation risk, might impact trade-offs between foraging and risk avoidance. Examining both internal and external constraints simultaneously can provide important insights into how animals make decisions. We examined how internal nutritional needs and external cues of mortality risk jointly impact the foraging behavior of ants. Ant colonies require carbohydrates to support workers energetically and proteins to raise brood. Furthermore, colonies adjust their foraging activity in response to the environment, such as food availability and the presence of predators or heterospecifics. Here we examine the foraging decisions of groups of Argentine ants Linepithema humile, which differ in their nutritional needs in high-risk environments. We starved groups of ants for either proteins or carbohydrates and determined the foraging choices that ants made when cues of heterospecifics were present. We found that ants preferentially forage for carbohydrates in high-risk conditions. Furthermore, starvation for carbohydrates increased the ants' preference for carbohydrates, even when cues of heterospecifics were present at both carbohydrates and protein resources. Starvation for protein also resulted in preferential foraging for carbohydrates, but it increased visitation to a protein food source in high-risk environments compared to when ants were starved for carbohydrates or for both resources. Examining the effect of both nutrition and mortality risk on foraging simultaneously provides insights about state-dependent risk-taking behavior that may have important implications for predicting the invasion of species into novel habitats.

Consumer identity but not food availability affects carabid diet in cereal crops

Understanding trophic interactions in agroecosystems is crucial for harnessing ecosystem services such as pest control, thus enabling a reduction in pesticide use. Carabid beetles (Coleoptera: Carabidae) have the potential to regulate not only insect pests but also weed seeds and slugs. The aim of this study was to investigate the food choice of different carabid species in the experimental setting of a cereal field with varying seed and slug prey availability during the season. In addition to varying food availability, the effects of species identity and season on carabid food choice should also be closely examined. Therefore, the gut contents of 1,120 beetles of eight carabid species were screened for the DNA of plants, aphids, springtails, earthworms and slugs via diagnostic multiplex PCR and a nested metabarcoding approach for plant species identification. Plant DNA was detected far more often (72%) than the various animal prey types (less than 12.5% each). Within the plant detections, 80 weed species were identified in the metabarcoding, with Galinsoga parviflora/quadriradiata (Galinsoga spp.-quickweeds) as the most frequently detected species. Carabid food choice was driven by their species identity and seasonality, while no effect of increased availability of seeds and slugs on their food choice was detected. While weed seeds seem to be an important food source for carabids, their availability does not directly affect the carabid diet. The importance of consumer identity and seasonality highlight the need for a diverse carabid species community for resilient pest control services.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10340-023-01620-w.

The Ecological View of Selective Attention

Accumulating evidence is supporting the hypothesis that our selective attention is a manifestation of mechanisms that evolved early in evolution and are shared by many organisms from different taxa. This surge of new data calls for the re-examination of our notions about attention, which have been dominated mostly by human psychology. Here, we present an hypothesis that challenges, based on evolutionary grounds, a common view of attention as a means to manage limited brain resources. We begin by arguing that evolutionary considerations do not favor the basic proposition of the limited brain resources view of attention, namely, that the capacity of the sensory organs to provide information exceeds the capacity of the brain to process this information. Moreover, physiological studies in animals and humans show that mechanisms of selective attention are highly demanding of brain resources, making it paradoxical to see attention as a means to release brain resources. Next, we build on the above arguments to address the question why attention evolved in evolution. We hypothesize that, to a certain extent, limiting sensory processing is adaptive irrespective of brain capacity. We call this hypothesis the ecological view of attention (EVA) because it is centered on interactions of an animal with its environment rather than on internal brain resources. In its essence is the notion that inherently noisy and degraded sensory inputs serve the animal’s adaptive, dynamic interactions with its environment. Attention primarily functions to resolve behavioral conflicts and false distractions. Hence, we evolved to focus on a particular target at the expense of others, not because of internal limitations, but to ensure that behavior is properly oriented and committed to its goals. Here, we expand on this notion and review evidence supporting it. We show how common results in human psychophysics and physiology can be reconciled with an EVA and discuss possible implications of the notion for interpreting current results and guiding future research.

Consistent variations in personality traits and their potential for genetic improvement of biocontrol agents: Trichogramma evanescens as a case study

Improvements in the biological control of agricultural pests require improvements in the phenotyping methods used by practitioners to select efficient biological control agent (BCA) populations in industrial rearing or field conditions. Consistent inter‐individual variations in behaviour (i.e. animal personality) probably affect BCA efficiency, but have never been taken into account in the development of phenotyping methods, despite having characteristics useful for phenotyping: repeatable (by definition), often heritable, etc. We developed a video‐tracking method targeting animal personality traits and evaluated the feasibility of its use for genetic improvement in the BCA Trichogramma evanescens, by phenotyping 1,049 individuals from 24 isogenic lines. We found consistent individual variations in boldness, activity and exploration. Personality differences between the 24 isogenic lines suggested a genetic origin of the variations in activity and exploration (broad‐sense heritability estimates of 0.06 to 0.11) and revealed a trade‐off between exploration and fecundity.

The legacy of predator threat shapes prey foraging behaviour

Predators exert strong selection on prey foraging behaviour such that prey responses may reflect a combination of ancestral effects of predators (genetic and nongenetic transgenerational effects), past individual experience with predators (phenotypic plasticity), and current exposure to predators (behavioural response). However, the importance of these factors in shaping prey foraging behaviour is not well understood. To test the relative effects of ancestry, prior experience, and current exposure, we measured foraging rates and food size preference of different ancestry and exposure groups of Western mosquitofish in the presence and absence of immediate threat from predatory largemouth bass. Our results confirm that mosquitofish had lower foraging rate in the immediate presence of predator threat. Mosquitofish also foraged at a lower rate if they had ancestry with predators, regardless of immediate threat. In contrast, individual prior experience with predators only caused reduced foraging rates in the immediate presence of a predator. This suggests that phenotypic plasticity could carry a lower risk of maladaptive antipredator responses-i.e., reduced food intake-in the complete absence of a predator. Finally, in the presence of a predator, mosquitofish with both ancestry and experience with predators consumed larger, presumably more energetically valuable, food items. Overall, our results show that non-consumptive effects of predators on prey behaviour can persist within and across generations, such that the legacy of past predator exposure-or "the ghost of predation past"-may continue to shape prey behaviour even when predators are no longer around.

Inferring species interactions from ecological survey data: A mechanistic approach to predict quantitative food webs of seed feeding by carabid beetles

Ecological networks are valuable for ecosystem analysis but their use is often limited by a lack of data because many types of ecological interaction, for example, predation, are short-lived and difficult to observe or detect. While there are different methods for inferring the presence of interactions, they have rarely been used to predict the interaction strengths that are required to construct weighted, or quantitative, ecological networks.Here, we develop a trait-based approach suitable for inferring weighted networks, that is, with varying interaction strengths. We developed the method for seed-feeding carabid ground beetles (Coleoptera: Carabidae) although the principles can be applied to other species and types of interaction.Using existing literature data from experimental seed-feeding trials, we predicted a per-individual interaction cost index based on carabid and seed size. This was scaled up to the population level to create inferred weighted networks using the abundance of carabids and seeds from empirical samples and energetic intake rates of carabids from the literature. From these weighted networks, we also derived a novel measure of expected predation pressure per seed type per network.This method was applied to existing ecological survey data from 255 arable fields with carabid data from pitfall traps and plant seeds from seed rain traps. Analysis of these inferred networks led to testable hypotheses about how network structure and predation pressure varied among fields.Inferred networks are valuable because (a) they provide null models for the structuring of food webs to test against empirical species interaction data, for example, DNA analysis of carabid gut regurgitates and (b) they allow weighted networks to be constructed whenever we can estimate interactions between species and have ecological census data available. This permits ecological network analysis even at times and in places when interactions were not directly assessed.

A hypothalamic-thalamostriatal circuit that controls approach-avoidance conflict in rats

Survival depends on a balance between seeking rewards and avoiding potential threats, but the neural circuits that regulate this motivational conflict remain largely unknown. Using an approach-food vs. avoid-predator threat conflict test in rats, we identified a subpopulation of neurons in the anterior portion of the paraventricular thalamic nucleus (aPVT) which express corticotrophin-releasing factor (CRF) and are preferentially recruited during conflict. Inactivation of aPVT^CRF neurons during conflict biases animal's response toward food, whereas activation of these cells recapitulates the food-seeking suppression observed during conflict. aPVT^CRF neurons project densely to the nucleus accumbens (NAc), and activity in this pathway reduces food seeking and increases avoidance. In addition, we identified the ventromedial hypothalamus (VMH) as a critical input to aPVT^CRF neurons, and demonstrated that VMH-aPVT neurons mediate defensive behaviors exclusively during conflict. Together, our findings describe a hypothalamic-thalamostriatal circuit that suppresses reward-seeking behavior under the competing demands of avoiding threats.

Ecological plasticity governs ecosystem services in multilayer networks

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 herbivore 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.

Connected Carabids: Network Interactions and Their Impact on Biocontrol by Carabid Beetles

Carabid beetles can greatly contribute to biocontrol in agroecosystems, reducing both insect pests and weed seeds. However, insect foraging and feeding behavior can be highly dependent on the interaction network and spatial structure of the environment, which can make their biocontrol contributions variable. In the present article, we explore how the interaction network of carabids can affect their behavior and how spatial vegetation structure and specific agronomy practices can, in turn, affect the strength of interactions in their network. We suggest that research on carabid biocontrol should move toward an approach in which the network of interactions among pests, carabids, and other organisms within its spatial structure is evaluated, with equal focus on direct and indirect interactions, and provide examples of tools to do so. Overall, we believe this approach will improve our knowledge of carabid networks, help to elucidate the underlying mechanisms of biocontrol, and lay the foundation for future biocontrol strategies.

Predator-induced stress responses in insects: A review

Predators can induce extreme stress and profound physiological responses in prey. Insects are the most dominant animal group on Earth and serve as prey for many different predators. Although insects have an extraordinary diversity of anti-predator behavioral and physiological responses, predator-induced stress has not been studied extensively in insects, especially at the molecular level. Here, we review the existing literature on physiological predator-induced stress responses in insects and compare what is known about insect stress to vertebrate stress systems. We conclude that many unrelated insects share a baseline pathway of predator-induced stress responses that we refer to as the octopamine-adipokinetic hormone (OAH) axis. We also present best practices for studying predator-induced stress responses in prey insects. We encourage investigators to compare neurophysiological responses to predator-related stress at the organismal, neurohormonal, tissue, and cellular levels within and across taxonomic groups. Studying stress-response variation between ecological contexts and across taxonomic levels will enable the field to build a holistic understanding of, and distinction between, taxon- and stimulus-specific responses relative to universal stress responses.

Spatial and temporal patterns of a pulsed resource dynamically drive the distribution of specialist herbivores

Patterns and drivers of the spatio-temporal distribution of herbivores are key elements of their ecological and evolutionary impacts on plant populations. Herbivore spatial distributions may be influenced by increased (RCH: resource concentration hypothesis) or decreased (RDH: resource dilution hypothesis) resource densities, but the effect of temporal variations in resource densities on such distributions remains poorly documented. We used a survey of a masting tree species and its seed predators in Southeastern France to address the effect of a host’s pulsed resource on the spatio-temporal distributions of highly specialized insect herbivores feeding on seeds. Variations in both resource and seed predator densities were assessed by estimating seed production and seed infestation rates in focus trees during 10 consecutive years. We found increasing seed infestation rates with decreasing host tree densities in years of low seed production, indicating a RDH pattern of seed predators. However, such pattern was not persistent in years of high seed production during which seed infestation rates did not depend on host tree densities. We showed that temporal variations in resource density can lead to transience of seed predator spatial distribution. This study highlights how predictions of plant-herbivore interactions in natural ecosystems may rely on temporal components underlying RCH and RDH hypotheses.

Causes and Consequences of Phenotypic Plasticity in Complex Environments

Phenotypic plasticity is a ubiquitous and necessary adaptation of organisms to variable environments, but most environments have multiple dimensions that vary. Many studies have documented plasticity of a trait with respect to variation in multiple environmental factors. Such multidimensional phenotypic plasticity (MDPP) exists at all levels of organismal organization, from the whole organism to within cells. This complexity in plasticity cannot be explained solely by scaling up ideas from models of unidimensional plasticity. MDPP generates new questions about the mechanism and function of plasticity and its role in speciation and population persistence. Here we review empirical and theoretical approaches to plasticity in response to multidimensional environments and we outline new opportunities along with some difficulties facing future research.