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Foraging Theory

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... In reality, cockatoos will travel up to 20 km over multiple trips per day from their nests in search of food and water (R. Johnstone et al., 2013). Though this is not a requirement of our approach, specifying a foraging range will usually be important as animals are more likely to access resources within close proximity to maximise net energy gains (i.e., optimal foraging theory; Pyke, 1984;Stephens and Krebs, 2019). ...
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Across the world, wildlife must coexist with humans in modified and increasingly fragmented landscapes but balancing the competing land use objectives of economic production and conservation is challenging. Multi-objective optimisation and spatial conservation prioritisation can inform land use planning but have not yet explicitly accounted for the way species access multiple resources at different locations in a landscape. Here, we demonstrate a novel approach for conservation prioritisation that accounts for the spatial distribution of different resources as well as a species' movements. This suite of tools and models identifies Pareto-optimal solutions to competing objectives of economic production on the one hand, with conserving a species’ food, drink and shelter requirements and movement corridors on the other. We demonstrate the broader functionality of these tools using a case study with competing objectives of clearing land for mining versus conservation of the listed vulnerable endemic species.
... Optimal foraging theory (OFT) (Stephens & Krebs, 1986) and patterns presented by other seascape ecology studies offer a useful framework to explain the larger trophic niche and lower trophic level observed in fragmented F I G U R E 2 Pinfish trophic hypervolumes in the continuous (dark blue) and fragmented (light green) seascapes in (a) high and stable salinity zone and (b) low and variable salinity zone. Note the points in the pair plots are random points generated within the hypervolume. ...
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Habitat fragmentation of submerged aquatic vegetation (SAV) transforms the spatial pattern of seascapes by changing both the total area and spatial configuration of the habitat patches. The ecological effects of SAV seascapes are most often assessed using metrics of biological community composition (e.g., species and assemblage changes). We know considerably less about the effects of seascape structure on ecological processes such as food web function and energy flow. Here, we assess the difference in the trophic niche of Pinfish (Lagodon rhomboides, a generalist omnivore) across a spatial gradient of SAV from continuous to highly fragmented seascapes in Biscayne Bay (Miami, Florida, USA). The Bay seascapes are influenced by freshwater management practices that alter the distribution of SAV habitat and fish species abundance, diversity, and community assemblage. We combined SAV seascape maps with stable isotope and hypervolume analyses to determine how trophic niche size and overlap varied with changes in the seascape. We observed similar resource use across the seascape, but trophic niche size increased in more fragmented SAV seascapes, suggesting diversification of trophic roles and energy flow pathways. Pinfish collected from more continuous SAV habitats had smaller trophic niche size and higher trophic levels. Both trophic response metrics manifested a threshold response that depended on distinct SAV spatial characteristics (amount vs. spatial configuration) and environmental conditions. Our results suggest that habitat fragmentation of SAV seascape structure has ecological implications that could affect energy flow with cascading consequences for food web stability and ecosystem functioning.
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Optimality theory is useful for modeling habitat use in animals, although many models have not been rigorously tested. We evaluated the ability of the Grossman et al. net‐energy‐intake (NEI) optimal foraging model for drift‐feeding stream fishes, to predict the holding velocity (microhabitat) of native brook charr (BC; Salvelinus fontinalis) inhabiting a southern Appalachian stream. This model postulates that fish choose holding velocities that maximize their NEI, and is broadly applicable to stream fishes, many of which are drift‐feeders. We used laboratory prey capture success versus water velocity data to quantify the relationship between prey capture success, water velocity, and holding velocity of BC (N = 21, mean standard length = 147 mm ± 14 sd). Parameterization of the Grossman et al. model yielded an optimal holding velocity prediction of 18.5 cm·s−1. Based on fitting criteria from previous work, the model prediction was successful because it fell within the 95% confidence interval (13.5–20.5 cm·s−1) of mean holding velocities (17.0 cm·s−1, N = 26) of BC in Lynn Camp Prong, Tennessee. Consequently, NEI maximization likely is a causal factor affecting BC habitat choice. Our result argues strongly for the general usefulness of this model. We tested the Grossman et al. energy intake‐based microhabitat model using native southern brook charr. The model successfully predicted the holding positions occupied in a stream by this species. Consequently, net‐energy‐intake maximization likely is a causal factor affecting BC habitat choice. Our result argues strongly for the general usefulness of this model.
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Large mammalian carnivores have undergone catastrophic declines during the Anthropocene across the world. Despite their pivotal roles as apex predators in food webs and ecosystem dynamics, few detailed dietary datasets of large carnivores exist, prohibiting deep understanding of their coexistence and persistence in human-dominated landscapes. Here, we present fine-scaled, quantitative trophic interactions among sympatric carnivores from three assemblages in the Mountains of Southwest China, a global biodiversity hotspot harboring the world's richest large-carnivore diversity, derived from DNA metabarcoding of 1,097 fecal samples. These assemblages comprise a large-carnivore guild ranging from zero to five species along with two mesocarnivore species. We constructed predator-prey food webs for each assemblage and identified 95 vertebrate prey taxa and 260 feeding interactions in sum. Each carnivore species consumed 6-39 prey taxa, and dietary diversity decreased with increased carnivore body mass across guilds. Dietary partitioning was more evident between large-carnivore and mesocarnivore guilds, yet different large carnivores showed divergent proportional utilization of different-sized prey correlating with their own body masses. Large carnivores particularly selected livestock in Tibetan-dominated regions, where the indigenous people show high tolerance toward wild predators. Our results suggest that dietary niche partitioning and livestock subsidies facilitate large-carnivore sympatry and persistence and have key implications for sustainable conservation promoting human-carnivore coexistence.
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The effects of ovipositing female body size on the survival of the first and second offspring under self and conspecific superparasitism have not been determined. Here, we report the importance of the body size of ovipositing females for three intervals (0, 1, and 24 h) between first and second ovipositions using a semi-solitary ectoparasitoid, Echthrodelphax fairchildii, and fourth-instar nymphs of its host, the planthopper Laodelphax striatellus. We addressed the case in which the first and second parasitoid eggs were laid on different sides of the same host. The second ovipositing female killed the previous offspring using the sting, but when the oviposition intervals were 0 and 1 h, the elimination was unprofitable because both offspring often emerged under non-probing superparasitism. The survival rate of the second offspring decreased with increasing oviposition intervals under non-probing superparasitism, whereas that of the first offspring was independent of oviposition intervals. Under non-probing superparasitism, the survival rates of the first and second offspring were higher under conspecific superparasitism than under self superparasitism, especially when the first and/or second ovipositing females were small. Large mothers ensured high survival rates of their offspring under non-probing superparasitism, except the survival rate of the second offspring under conspecific superparasitism, which was negatively associated with the first female's size. Thus, the first offspring from small mothers were likely to lose the competition to the second offspring. Under probing superparasitism, the second offspring survival rate was positively associated with the mother's size, suggesting that offspring, not ovipositing females, release agents affecting the mother-size effect.
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Natural observations suggest that in safe environments, organisms avoid competition to maximize gain, while in hazardous environments the most effective survival strategy is to congregate with competition to reduce the likelihood of predatory attack. We probed the extent to which survival decisions in humans follow these patterns, and examined the factors that determined individual-level decision-making. In a virtual foraging task containing changing levels of competition in safe and hazardous patches with virtual predators, we demonstrate that human participants inversely select competition avoidant and risk diluting strategies depending on perceived patch value (PPV), a computation dependent on reward, threat, and competition. We formulate a mathematically grounded quantification of PPV in social foraging environments and show using multivariate fMRI analyses that PPV is encoded by mid-cingulate cortex (MCC) and ventromedial prefrontal cortices (vMPFC), regions that integrate action and value signals. Together, these results suggest humans utilize and integrate multidimensional information to adaptively select patches highest in PPV, and that MCC and vMPFC play a role in adapting to both competitive and predatory threats in a virtual foraging setting. Humans adapt decision strategies in response to environmental demands. Here the authors show that decisions in a virtual foraging task can be modelled based on perceived patch value, which includes reward, competition and threat, and is associated with activity in ventromedial prefrontal and medial cingulate cortices.
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Religions “in the wild” are the varied set of religious activities that occurred before the emergence of organized religions with doctrines, or that persist at the margins of those organized traditions. These religious activities mostly focus on misfortune; on how to remedy specific cases of illness, accidents, failures; and on how to prevent them. I present a general model to account for the cross-cultural recurrence of these particular themes. The model is based on (independently established) features of human psychology—namely, (a) epistemic vigilance, the set of systems whereby we evaluate the quality of information and of sources of information, and (b) threat-detection psychology, the set of evolved systems geared at detecting potential danger in the environment. Given these two sets of systems, the dynamics of communication will favor particular types of messages about misfortune. This makes it possible to predict recurrent features of religious systems, such as the focus on nonphysical agents, the focus on particular cases rather than general aspects of misfortune, and the emergence of specialists. The model could illuminate not just why such representations are culturally successful, but also why people are motivated to formulate them in the first place.
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1. Many animals can actively redress nutrient imbalances in their diet to maximise performance. However, food items are commonly patchily distributed in nature, thus, animals often need to commute between prey patches to mix their diet. 2. We previously found that females of two species of predatory mites showed a higher oviposition rate when feeding on a mixture of eggs of co-occurring phytophagous mites than on each prey separately. Besides, they searched for such a prey mixture on artificial arenas. 3. In nature, however, the two prey species are found on different parts of their host plant; hence, the predators need to commute between plant parts to obtain a mixed diet. 4. Here, we show that the reproduction of one of these predators was highest on mixtures consisting of various proportions of these prey, and was lower on single diets and on a mixture with a high proportion of one of the two prey. The predators consumed prey eggs in proportions differing from those offered, suggesting that they actively selected prey to obtain a mixed diet. 5. We found that the oviposition of the predator was lower on plants inoculated with either of the two prey species alone than on plants on which the eggs of the two prey species occurred on separate leaves of the same plant, forcing the predators to commute between the two prey. 6. We conclude that the predators actively searched for a mixed diet consisting of prey that were spatially separated on a plant.
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en • Mammalian carnivores (order Carnivora) perform important regulatory functions in terrestrial food webs. Building a comprehensive knowledge of the dietary patterns of carnivorans and the factors determining such patterns is essential for improving our understanding of the role of carnivorans in ecosystem functioning. • In the Neotropics, there are 64 extant species of terrestrial Carnivora, but information on their trophic ecology is diffuse. We compiled and analysed the available quantitative dietary data for Neotropical carnivorans, aiming to detect patterns of intraspecific and interspecific dietary variation at a large geographical scale. • The resulting database encompasses information on trophic interactions of 37 native carnivoran species from six families across 14 countries. There are clear geographical biases towards southern Brazil, Chile, and Argentina, and a noticeable knowledge gap within the Amazon. Also, most studies are focused on canids and felids, especially Puma concolor, Panthera onca, Cerdocyon thous, Leopardus pardalis, and Chrysocyon brachyurus, whereas for 27 native species, we found no quantitative dietary information. • Neotropical carnivorans consume species from at least 651 genera of vertebrates, invertebrates, and plants. We found clear species-specific dietary patterns and marked differences between Neotropical felids and canids. Although predators generally exhibit high levels of consistency in their diets regarding prey body mass, we detected significant intraspecific variation for all species analysed across study sites. • Body mass imposes strong constraints on prey use, but biogeographical differences in prey availability and human influence may drive the geographical variation we found. Overall, observed patterns show not only similarities with resource-use patterns found for carnivorans in other continents, such as nestedness driven by body mass, but also differences, such as high levels of frugivory and consumption of invertebrates by canids. Assessing resource-use patterns is the first step towards a better understanding of processes underlying the organisation of trophic interactions, and is imperative for addressing impacts of defaunation on ecosystems and for informing conservation efforts. RESUMO EM PORTUGUÊS es • Carnivoros mamíferos (ordem Carnivora) são responsáveis por manter funções regulatórias importantes em redes tróficas terrestres. Para que possamos entender o papel desempenhado por esses animais no funcionamento dos ecossistemas, é essencial construir um conhecimento abrangente no que diz respeito aos padrões de dieta e aos fatores que determinam esses padrões. • Na região neotropical, há 64 espécies nativas de Carnivora terrestres, mas as informações relativas à ecologia trófica dessas espécies são bastante difusas na literatura. Nós compilamos e analisamos dados quantitativos de dieta disponíveis para carnívoros neotropicais, com o objetivo de detectar padrões intraespecíficos e interespecíficos na dieta, além de variações numa escala geográfica extensa. • A base de dados resultante contém informações provenientes de estudos realizados em 14 países, acerca de interações tróficas de 37 espécies nativas de carnívoros de seis famílias diferentes. Há um viés geográfico evidente: as regiões Sul e Sudeste do Brasil, Chile e Argentina foram consideravelmente mais amostradas, enquanto há um vazio amostral na região da Amazônia, por exemplo. Além disso, a maioria dos estudos foca na dieta de canídeos e felídeos, principalmente Puma concolor, Panthera onca, Cerdocyon thous, Leopardus pardalis and Chrysocyon brachyurus, enquanto para 27 espécies, não encontramos dados quantitativos de dieta. • Carnívoros neotropicais consumem pelo menos 651 gêneros diferentes, entre vertebrados, invertebrados e plantas. Há um claro padrão de dieta espécie-específico e diferenças marcantes entre felídeos e canídeos neotropicais. Apesar de esses predadores geralmente exibirem altos níveis de consistência em suas dietas em termos da massa corpórea das presas, nós identificamos variações intraespecíficas significativas entre sítios para todas as espécies analisadas. • O tamanho corpóreo impõe limitações consideráveis aos padrões de uso de recursos, mas diferenças biogeográficas na disponibilidade de presas e influências antrópicas possivelmente levam às variações encontradas. De maneira geral, os padrões observados evidenciam similaridades com padrões de uso de recurso encontrados para carnívoros em outros continentes, como aninhamento relacionado a tamanho corpóreo, mas também divergências, como altos níveis de frugivoria e consumo de invertebrados por canídeos. Avaliar padrões de uso de recursos é o primeiro passo em direção a um entendimento mais completo dos processos que organizam interações tróficas, além de ser imprescindível para estimar os impactos da defaunação e orientar medidas de conservação.
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Arctic sea ice loss has direct consequences for predators. Climate-driven distribution shifts of native and invasive prey species may exacerbate these consequences. We assessed potential changes by modelling the prey base of a widely distributed Arctic predator (ringed seal; Pusa hispida) in a sentinel area for change (Hudson Bay) under high- and low-greenhouse gas emission scenarios from 1950 to 2100. All changes were relatively negligible under the low-emission scenario, but under the high-emission scenario, we projected a 50% decline in the abundance of the well-distributed, ice-adapted and energy-rich Arctic cod (Boreogadus saida) and an increase in the abundance of smaller temperate-associated fish in southern and coastal areas. Furthermore, our model predicted that all fish species declined in mean body size, but a 29% increase in total prey biomass. Declines in energy-rich prey and restrictions in their spatial range are likely to have cascading effects on Arctic predators.
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Island radiations represent unique evolutionary histories in unique ecological contexts. These radiations provide opportunities to investigate ecological diversification in groups that typically exhibit niche partitioning among their constituents, including partitioning of food resources. DNA metabarcoding produces finer levels of diet identification than traditional methods, allowing us to examine dietary niche partitioning in communities or clades in which species share superficially similar diets. Here we use DNA metabarcoding to investigate dietary niche partitioning in an endemic radiation of mammals in the Philippines. Our data reveal niche partitioning as well as phylogenetically-uncorrelated adaptive evolution in this small mammal community. Because 70% of the focal species belong to the tribe Chrotomyini, an endemic Philippine radiation of murid rodents that feed extensively on earthworms, this study sheds light on dietary adaptation and its role in the co-occurrence of closely related species. Our results reveal fine-scale resource partitioning within this community; our data provide compelling evidence for niche partitioning of diet that was masked by previous diet categories and will help in further dissecting the model adaptive radiation of endemic small mammals on Luzon. This study reinforces the notion that DNA metabarcoding can be a valuable tool for investigating both ecological relationships and evolutionary ecology at the community and phylogenetic level, respectively.
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Foraging trails of leafcutter colonies are iconic scenes in the Neotropics, with ants collecting freshly cut plant fragments to provision a fungal food crop. We hypothesised that the fungus‐cultivar's requirements for macronutrients and minerals govern the foraging niche breadth of Atta colombica leafcutter ants. Analyses of plant fragments carried by foragers showed how nutrients from fruits, flowers and leaves combine to maximise cultivar performance. While the most commonly foraged leaves delivered excess protein relative to the cultivar's needs, in vitro experiments showed that the minerals P, Al and Fe may expand the leafcutter foraging niche by enhancing the cultivar's tolerance to protein‐biased substrates. A suite of other minerals reduces cultivar performance in ways that may render plant fragments with optimal macronutrient blends unsuitable for provisioning. Our approach highlights how the nutritional challenges of provisioning a mutualist can govern the multidimensional realised niche available to a generalist insect herbivore. Free‐ranging leafcutter ants forage nutritionally and chemically diverse plant fragments to fit the requirements of their fungal food crop. However, these foraged plant fragments can also contain nutrients in excess of the cultivar's tolerance, which can limit fungal production. Results obtained from in vitro cultures suggest that the mineral composition of plant fragments might influence the suitability of the nutrient blends provided to the fungal culture, thus allowing the cultivar to exploit apparently toxic blends of nutrients.
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Sensory regulation, the ability to select and process sensory information to plan and perform appropriate behaviours, provides a foundation for learning. From early in development, infants manifest differences in the strategies used for sensory regulation. Here, we discuss the nature and characteristics of sensory seeking, a key behavioural strategy for sensory regulation often described as atypical in children with Neurodevelopmental Disorders. We evaluate theoretical models proposed to clarify mechanisms underlying individual differences in sensory seeking and discuss evidence for/against each of these models. We conclude by arguing that the information prioritization hypothesis holds the greatest promise to illuminate the nature of individual differences in sensory seeking across participant cohorts. This proposal aligns to molecular genetic animal and human evidence, provides a coherent explanation for developmental findings, and generates testable hypotheses for future research.
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Background Apathy, a disabling and poorly understood neuropsychiatric symptom, is characterised by impaired self-initiated behaviour. It has been hypothesised that the opportunity cost of time (OCT) may be a key computational variable linking self-initiated behaviour with motivational status. OCT represents the amount of reward which is foregone per second if no action is taken. Using a novel behavioural task and computational modelling, we investigated the relationship between OCT, self-initiation and apathy. We predicted that higher OCT would engender shorter action latencies, and that individuals with greater sensitivity to OCT would have higher behavioural apathy. Methods We modulated the OCT in a novel task called the ‘Fisherman Game’, Participants freely chose when to self-initiate actions to either collect rewards, or on occasion, to complete non-rewarding actions. We measured the relationship between action latencies, OCT and apathy for each participant across two independent non-clinical studies, one under laboratory conditions ( n = 21) and one online ( n = 90). ‘Average-reward’ reinforcement learning was used to model our data. We replicated our findings across both studies. Results We show that the latency of self-initiation is driven by changes in the OCT. Furthermore, we demonstrate, for the first time, that participants with higher apathy showed greater sensitivity to changes in OCT in younger adults. Our model shows that apathetic individuals experienced greatest change in subjective OCT during our task as a consequence of being more sensitive to rewards. Conclusions Our results suggest that OCT is an important variable for determining free-operant action initiation and understanding apathy.
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Explaining variation in hunter-gatherer livelihoods hinges on our ability to predict the tradeoffs and opportunities of pursuing different kinds of prey. Central to this problem is the commonly held assumption that larger animals provide higher returns upon encounter than smaller ones. However, to test this assumption, actualistic observations of hunting payoffs must be comparable across different social, technological, and ecological contexts. In this meta-analysis, we revisit published and unpublished estimates of prey return rates (n = 217 from 181 prey types) to assess, first, whether they are methodologically comparable, and second, whether they correlate with body size. We find systematic inter-study differences in how carcass yield, energetic content, and foraging returns are calculated. We correct for these inconsistencies first by calculating new estimates of energetic yield (kcals per kg live weight) and processing costs for over 300 species of terrestrial and avian game. We then recalculate on-encounter returns using a standardized formula. We find that body size is a poor predictor of on-encounter return rate, while prey characteristics and behavior, mode of procurement, and hunting technology are better predictors. Although prey body size correlates well with processing costs and edibility, relationships with pursuit time and energetic value per kilogram are relatively weak.
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Intrinsic to several hypotheses explaining the evolution of foraging behavior complexity, such as proto-tool use, is the assumption that more complex ingestive behaviors are adaptations allowing individuals to access difficult to procure but nutritionally or energetically rewarding foods. However, nutritional approaches to understanding this complexity have been underutilized. The goal of this study was to evaluate potential nutritional determinants of two unusual foraging behaviors, fruit cracking with anvils and seed reingestion, by adult male western chimpanzees (Pan troglodytes verus) at Fongoli, Senegal during the baobab (Adansonia digitata) fruit season. We examined these behaviors in relation to nutrient and energy intake, and compared macronutrient and energy concentrations found in baobab fruits to other plant foods. Adult males ingested at least 31 distinct foods from 23 plant species. Baobab fruit comprised the majority of daily energy intake (68 ± 34%, range: 0%-98%). The energetic concentration of baobab fruit varied by phenophase and part ingested, with ripe and semi-ripe fruit ranking high in energy return rate. Males preferred ripe and semi-ripe baobab fruit but unripe fruit intake was higher overall. The seed kernels were high in protein and fat relative to fruit pulp, and these kernels were easier to access during the unripe stage. During the ripe stage, seed kernels were accessible by reingestion, after the seed coat was softened during gut passage. In addition to providing macronutrients and energy, baobab fruit was a relatively abundant food source. We conclude that baobab pulp and seed are high quality foods at Fongoli during the baobab season because they are nutritionally balanced, high in energy, and relatively abundant in the environment. These nutritional and abundance characteristics may explain, in part, why these chimpanzees use anvils and reingestion to access a mechanically challenging food.
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Since its creation, considerable effort has been given to improving the utility of the consumer functional response. To date, the majority of efforts have focused on improving mathematical formulation in order to include additional ecological processes and constraints, or have focused on improving the statistical analysis of the functional response to enhance rigor and to more accurately match experimental designs used to measure the functional response. In contrast, relatively little attention has been given to improving the interpretation of functional response empirical results, or to clarifying the implementation and extrapolation of empirical measurements to more realistic field conditions. In this paper I explore three concepts related to the interpretation and extrapolation of empirically measured functional responses. First, I highlight the need for a mechanistic understanding when interpreting foraging patterns and highlight pitfalls that can occur when we lack understanding between the shape of the functional response curve and the mechanisms that give rise to that shape. Second, I discuss differences between experimental and real-world field conditions that must be considered when trying to extrapolate measured functional responses to more natural conditions. Third, I examine the importance of the time scale of empirical measurements, and the need to consider tradeoffs that alter or limit foraging decisions under natural conditions. Clearly accounting for these three conceptual areas when measuring functional responses and when interpreting and attempting to extrapolate empirically measured functional responses will lead to more accurate estimates of consumer impacts under natural field conditions, and will improve the utility of the functional response as a heuristic tool in ecology.
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Neoclassical and behavioral economics disagree over the human consumption of dietary fat, a pervasive behavior that increases morbidity and mortality. Neoclassical economics assumes that people are choosing optimal diets, trading off utility and money today in return for disease and early death. In contrast, behavioral economics argues people are making poor dietary decisions. Evolutionary biology suggests that, for our human ancestors, dietary choices were optimal, in a constrained manner consistent with the neoclassical economic model. In the modern environment, which has more and different foods, biology provides no support for the neoclassical view.
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Integrating diverse concepts from animal behavior, movement ecology, and machine learning, we develop an overview of the ecology of learning and animal movement. Learning-based movement is clearly relevant to ecological problems, but the subject is rooted firmly in psychology, including a distinct terminology. We contrast this psychological origin of learning with the task-oriented perspective on learning that has emerged from the field of machine learning. We review conceptual frameworks that characterize the role of learning in movement, discuss emerging trends, and summarize recent developments in the analysis of movement data. We also discuss the relative advantages of different modeling approaches for exploring the learning-movement interface. We explore in depth how individual and social modalities of learning can matter to the ecology of animal movement, and highlight how diverse kinds of field studies, ranging from translocation efforts to manipulative experiments, can provide critical insight into the learning process in animal movement.
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Aim Exotic species invasion often leads to declines in local and regional biodiversity, particularly in freshwater ecosystems. This biodiversity loss is generally facilitated by human activities such as land cover change and hydrological alternation. Recent advances in stable isotope analysis (SIA) have been highlighted in many studies addressing fundamental issues in invasion ecology, especially in quantifying competition for resources between native and exotic species. However, how anthropogenic disturbance influences trophic relationships among invasive and native species remains poorly understood. Location Middle-lower Yangtze River Region, China. Methods To investigate the effects of human disturbance on interspecific trophic interactions, this study compared isotopic niche space and overlap of the introduced red swamp crayfish (Procambarus clarkii) and the native oriental river shrimp (Macrobrachium nipponense) and freshwater snail (Bellamya aeruginosa) in natural and modified wetlands. Results Based on carbon and nitrogen SIA, we found ubiquitous niche shifts in macroinvertebrates with increased competition, which might lead to significant niche contraction in modified habitats at both community and population scales. Moreover, the isotopic niche width of the exotic crayfish was twice as larger as that of natives at both habitats, suggesting that the exotic P. clarkii had great competitive superiority over the native species. However, the effects of habitat modification on niche overlap were inconsistent. While the niche overlap between crayfish and shrimp was significantly higher in modified habitats than in natural open waters, niche overlap between crayfish and the snail was significantly reduced. Main conclusions Collectively, our findings highlight that the competitive outcomes of interspecific trophic interactions can be dependent on the prey availability and diversity, which embraces both the classic optimal foraging theory and competition theory to understand how environmental change, such as habitat alternation, affects the biological invasion processes.
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en Provisioning behavior can have cascading effects on nest survival, juvenile recruitment, and parental fitness. Provisioning behavior may be influenced by temporal variables, such as nestling age, or habitat variables, such as food availability and landscape disturbance. Black-backed Woodpeckers (Picoides arcticus) are associated with burned forests, where they nest in stands of fire-killed trees. Our objectives were to determine if their nestling provisioning behavior is influenced by the characteristics of fires and post-fire management, and if provisioning behavior differs with sex and varies across the breeding season. We recorded provisioning rates and the size of prey deliveries at 21 nests of Black-backed Woodpeckers in a burned area of northern California in 2014–2015 and examined the possible effects of habitat, temporal variables, and parental sex on provisioning rates and prey delivery size using mixed-effects models. Provisioning rates were higher for early season nests than late-season nests, and provisioning rates increased with nestling age. The size of prey provided to nestlings increased with nestling age, and prey delivery size was also larger for nests near areas where post-fire logging had occurred. Parental sex had no effect on either provisioning rates or prey delivery size. Our results suggest that, in burned forests in our study area, Black-backed Woodpeckers provisioning nestlings respond more strongly to temporal variables than habitat variables, and both sexes contribute equally to feeding young. Temporal variation in provisioning rates and prey delivery size likely reflect variation in the energetic demands of nestlings. RESUMEN es Comportamiento de aprovisionamiento de pichones en Picoides arcticus en el bosque posterior al incendio El comportamiento de aprovisionamiento puede tener un efecto cascada sobre la supervivencia de los nidos, reclutamiento de los juveniles y aptitud de los parentales. El comportamiento de aprovisionamiento puede estar influenciado por variables temporales, como la edad de los pichones, o variables del hábitat, como la disponibilidad de alimento y el disturbio en el paisaje. Picoides arcticus están asociados a bosques propensos a incendios, donde los nidos son ubicados en arboles afectados por el fuego. Nuestros objetivos fueron los de determinar si el comportamiento de aprovisionamiento de los pichones esta influenciado por las características de los incendios y el manejo posterior al incendio, y si el comportamiento de aprovisionamiento difiere con el sexo y varia a través de la temporada de reproducción. Colectamos información sobre tasas de aprovisionamiento y el tamaño de las presas entregadas en 21 nidos de Picoides arcticus en un área incendiada del norte de California en 2014–2015 y examinamos los posibles efectos del hábitat, las variables temporales y el comportamiento parental de cada sexo sobre las tasas de aprovisionamiento y el tamaño de las presas entregadas usando modelos de efectos mixtos. Las tasas de aprovisionamiento fueron mayores para nidos construidos temprano en la temporada que en nidos construidos tarde en la temporada, y las tasas de aprovisionamiento incrementaron con la edad de los pichones. El tamaño de la presa entregado a los pichones incrementó con la edad de los pichones, y el tamaño de la presa entregada también fue mayor para nidos cerca de áreas donde existió tala posterior al incendio. Nuestro resultados sugieren que en bosques incendiados, en nuestra área de estudio, el aprovisionamiento de pichones en Picoides arcticus responde más fuertemente a variables temporales que a variables de hábitat, y que ambos sexos contribuyen igualmente a la alimentación de los polluelos. La variación temporal en tasas de aprovisionamiento y el tamaño de presa entregada posiblemente refleja la variación en las demandas energéticas de los pichones.
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Foraging animals have to locate food sources that are usually patchily distributed and subject to competition. Deciding when to leave a food patch is challenging and requires the animal to integrate information about food availability with cues signaling the presence of other individuals (e.g., pheromones). To study how social information transmitted via pheromones can aid foraging decisions, we investigated the behavioral responses of the model animal Caenorhabditis elegans to food depletion and pheromone accumulation in food patches. We experimentally show that animals consuming a food patch leave it at different times and that the leaving time affects the animal preference for its pheromones. In particular, worms leaving early are attracted to their pheromones, while worms leaving later are repelled by them. We further demonstrate that the inversion from attraction to repulsion depends on associative learning and, by implementing a simple model, we highlight that it is an adaptive solution to optimize food intake during foraging.
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Prey defensive traits against predators can be categorized into primary defense (avoiding detection) and secondary defense (avoiding attack after detection). There are trade-offs between these two defensive traits, which consider the cost of defense. To quantify the predation avoidance efficacy of both defensive traits against common predators, we compared bird predation pressures and the corresponding avoidance measures of cocoons of two nettle moth species, which utilize contrasting avoidance strategies: Parasa lepida (investing predominantly in primary defense) and Monema flavescens (investing predominantly in secondary defense). Field censuses revealed that bird predation was the most significant mortality factor for both species. The survival rate of cocoons was significantly higher for M. flavescens than for P. lepida, although M. flavescens were more conspicuous than P. lepida. Measurement of prepupae (cocoon content) mass, and experiments on the feeding preferences of the prepupae of both species using chicks, confirmed a similar quantity and quality of both speciesʼ prepupae as prey items. Our results were explained by the advantage of cocoon hardness outweighing the disadvantage of cocoon conspicuousness. The predation behavior of wild birds suggested that they spent considerably longer handling than searching for cocoons, which accounted for their cocoon preference for P. lepida over M. flavescens in the context of optimal foraging theory. Our results suggested that secondary defense was more effective in reducing bird predation than primary defense in limacodid cocoons.
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Predatory mites have an incredible role in the suppression of spider mites in modern agriculture. The present study compared some behavioral traits of two predatory mites, namely Neoseiulus californicus McGregor and Amblyseius swirskii Athias-Henriot in response to different life stages of two-spotted spider mite, Tetranychus urticae Koch. In no-choice predation test, both predators had a higher predation rate on larval than other developmental stages of the prey. In this assay, the lower predation rate of A. swirskii was recorded on the egg stage, which was observed on the adult female for N. californicus. With one exception, the results obtained from the predation test in choice conditions confirmed these observations. In the choice test, both predators had a lower consumption rate on different stages of prey than no-choice ones. To investigate the predation preference of predatory mites, Manly's preference index (β) was used. With respect to this index, both predators significantly preferred the larval stage than other developmental stages of T. urticae. Although N. californicus exhibited a lower preference to the female prey, in the case of A. swirskii, the lower preference to deutonymph and female was observed. Our findings also revealed that both predatory mites had no switching behavior from preferred stages to non-preferred ones, indicating that reducing the ratio of preferred stage in the experimental arena has no detectable effect on the predation preference of both predators.
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Rapid alternations between exploration and defensive reactions require ongoing risk assessment. How visual cues and internal states flexibly modulate the selection of behaviors remains incompletely understood. Here, we show that the ventral lateral geniculate nucleus (vLGN)—a major retinorecipient structure—is a critical node in the network controlling defensive behaviors to visual threats. We find that vLGNGABA neuron activity scales with the intensity of environmental illumination and is modulated by behavioral state. Chemogenetic activation of vLGNGABA neurons reduces freezing, whereas inactivation dramatically extends the duration of freezing to visual threats. Perturbations of vLGN activity disrupt exploration in brightly illuminated environments. We describe both a vLGN→nucleus reuniens (Re) circuit and a vLGN→superior colliculus (SC) circuit, which exert opposite influences on defensive responses. These findings reveal roles for genetic- and projection-defined vLGN subpopulations in modulating the expression of behavioral threat responses according to internal state.
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Decisions are based on the subjective values of choice options. However, subjective value is a theoretical construct and not directly observable. Strikingly, distinct theoretical models competing to explain how subjective values are assigned to choice options often make very similar behavioral predictions, which poses a major difficulty for establishing a mechanistic, biologically plausible explanation of decision-making based on behavior alone. Here, we demonstrate that model comparison at the neural level provides insights into model implementation during subjective value computation even though the distinct models parametrically identify common brain regions as computing subjective value. We show that frontal cortical regions implement a model based on the statistical distributions of available rewards, whereas intraparietal cortex and striatum compute subjective value signals according to a model based on distortions in the representations of probabilities. Thus, better mechanistic understanding of how cognitive processes are implemented arises from model comparisons at the neural level, over and above the traditional approach of comparing models at the behavioral level alone.
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Organisms are constantly under selection to respond effectively to diverse, sometimes rapid, changes in their environment, but not all individuals are equally plastic in their behaviour. Although cognitive processes and personality are expected to influence individual behavioural plasticity, the effects reported are highly inconsistent, which we hypothesise is because ecological context is usually not considered. We explored how one type of behavioural plasticity, foraging flexibility, was associated with inhibitory control (assayed using a detour‐reaching task) and exploration behaviour in a novel environment (a trait closely linked to the fast–slow personality axis). We investigated how these effects varied across two experimentally manipulated ecological contexts—food value and predation risk. In the first phase of the experiment, we trained great tits Parus major to retrieve high value (preferred) food that was hidden in sand so that this became the familiar food source. In the second phase, we offered them the same familiar hidden food at the same time as a new alternative option that was visible on the surface, which was either high or low value, and under either high or low perceived predation risk. Foraging flexibility was defined as the proportion of choices made during 4‐min trials that were for the new alternative food source. Our assays captured consistent differences among individuals in foraging flexibility. Inhibitory control was associated with foraging flexibility—birds with high inhibitory control were more flexible when the alternative food was of high value, suggesting they inhibited the urge to select the familiar food and instead selected the new food option. Exploration behaviour also predicted flexibility—fast explorers were more flexible, supporting the information‐gathering hypothesis. This tendency was especially strong under high predation risk, suggesting risk aversion also influenced the observed flexibility because fast explorers are risk prone and the new unfamiliar food was perceived to be the risky option. Thus, both behaviours predicted flexibility, and these links were at least partly dependent on ecological conditions. Our results demonstrate that an executive cognitive function (inhibitory control) and a behavioural assay of a well‐known personality axis are both associated with individual variation in the plasticity of a key functional behaviour. That their effects on foraging flexibility were primarily observed as interactions with food value or predation risk treatments also suggest that the population‐level consequences of some behavioural mechanisms may only be revealed across key ecological conditions. This work points to the complex nature of the mechanisms underlying behavioural plasticity. It shows that individual foraging flexibility is associated with cognitive and personality measures (inhibitory control and exploration behaviour) simultaneously, in a manner that is sensitive to the precise nature of the changing ecological conditions.
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In the past decade, decision neuroscience and neuroeconomics have developed many new insights in the study of decision making. This review provides an overarching update on how the field has advanced in this time period. Although our initial review a decade ago outlined several theoretical, conceptual, methodological, empirical, and practical challenges, there has only been limited progress in resolving these challenges. We summarize significant trends in decision neuroscience through the lens of the challenges outlined for the field and review examples where the field has had significant, direct, and applicable impacts across economics and psychology. First, we review progress on topics including reward learning, explore–exploit decisions, risk and ambiguity, intertemporal choice, and valuation. Next, we assess the impacts of emotion, social rewards, and social context on decision making. Then, we follow up with how individual differences impact choices and new exciting developments in the prediction and neuroforecasting of future decisions. Finally, we consider how trends in decision‐neuroscience research reflect progress toward resolving past challenges, discuss new and exciting applications of recent research, and identify new challenges for the field. This article is categorized under: Psychology > Reasoning and Decision Making Psychology > Emotion and Motivation This graphical abstract shows (1) progress made in the field of decision neuroscience over the past decade and (2) ongoing and future theoretical, methodological, practical, and empirical challenges affecting the field of decision neuroscience.
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Climate change and anthropological activities have led to an expansion of hypoxia into the natural habitat of Cancer irroratus. In this study, we examined the effects of hypoxia and food deprivation state on food intake and subsequent gastric processing. Three different techniques were used to measure food intake. The gravimetric analysis of dry food pellets was the most accurate method. In severe hypoxia (20% oxygen), rock crabs reduced food intake, and more crabs refused to eat. Compared with fasted crabs, more starved crabs tended to eat in severe hypoxia. Subsequently, prolonged gastric emptying times paralleled the previously measured postprandial oxygen consumption in hypoxia. Starved crabs also exhibited slightly longer transit times for digesta compared with fasted crabs. These results suggest that although a trade-off may occur in starved rock crabs between the need to procure nutrients and deal with hypoxic stress, impaired digestive processing may still deleteriously affect these animals.
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Foraging plays a vital role in animal life histories, and learning whether unfamiliar food items are palatable is a key part of this process. Animals that engage in extractive foraging must also learn how to overcome the protective measures of their prey. While otters (subfamily Lutrinae) are a taxon known for their extractive foraging behaviour, how they learn about prey palatability and acquire extractive foraging techniques remains poorly understood. Here we investigated (i) how captive Asian short-clawed otters ( Aonyx cinereus ) learned to interact with, and extract meat from, unfamiliar natural prey and (ii) how their exploitation of such prey compared to their ability to overcome artificial foraging tasks containing familiar food rewards. Network-based diffusion analysis showed that otters learned to interact with unfamiliar natural prey by observing their group mates. However, once interacting with the prey, they learned to extract the meat mainly asocially. In addition, otters took longer to overcome the protective measures of unfamiliar natural prey than those of extractive food puzzles. Asian short-clawed otter populations are declining in the wild. Increasing our understanding of how they learn to overcome novel foraging challenges could help develop pre-release training procedures as part of reintroduction programmes for otter conservation.
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Humans and other animals routinely make choices between goods of different values. Choices are often made within identifiable contexts, such that an efficient learner may represent values relative to their local context. However, if goods occur across multiple contexts, a relative value code can lead to irrational choices. In this case, an absolute context-independent value is preferable to a relative code. Here we test the hypothesis that value representation is not fixed but rationally adapted to context expectations. In two experiments, we manipulated participants’ expectations about whether item values learned within local contexts would need to be subsequently compared across contexts. Despite identical learning experiences, the group whose expectations included choices across local contexts went on to learn more absolute-like representation than the group whose expectations covered only fixed local contexts. Human value representation is thus neither relative nor absolute but efficiently and rationally tuned to task demands. Juechems et al. show that value encoding is flexible, not fixed. Coding adapts to expected task demands: when relative value coding is insufficient, humans use a more globally optimal absolute value code.
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Dietary selection and preference are poorly understood for the mountain bongo (Tragelaphus eurycerus isaaci Thomas, 1902). Focal animal sampling was used to determine seasonal food choice and preference for captive‐bred individuals at the Mount Kenya Wildlife Conservancy, in preparation for reintroduction into the wild at a proposed sanctuary within the surrounding forest reserve. Food availability was assessed using nested plot sampling. Plant life forms contributed differently to the diet (H[4] = 28.93, p < 0.01), with shrubs accounting for 55%. Relative abundance of the principal food plant species influenced their contribution to the diet in both wet and dry seasons (χ2 = 7.33, df = 1, p = 0.07; χ2 = 2.47, df = 1, p = 0.116 respectively). Despite having a high relative abundance (1.88%), Trichocladus ellipticus Eckl. & Zeyh. was less preferred during the wet season (E* = 0.20). It was however most preferred during the dry season (E* = 0.78), possibly reflecting relative nutritive value. The bongos included a large proportion of grass (27%) in their diet like other browsing herbivores that inhabit forest glades. Compared to the conservancy, plant foods were well represented at the proposed sanctuary with 72% and 80% similarity in both wet and dry seasons. This potentially enhances the likelihood of bongos adapting and establishing once reintroduced. La sélection et les préférences alimentaires sont mal comprises pour le bongo des montagnes (Tragelaphus eurycerus isaaci Thomas, 1902). Un échantillonnage focal d'animaux a été utilisé pour déterminer le choix alimentaire saisonnier et la préférence pour les individus élevés en captivité au Mount Kenya Wildlife Conservancy, en vue de la réintroduction dans la nature dans un sanctuaire proposé dans la réserve forestière environnante. La disponibilité de la nourriture a été évaluée à l'aide d'un échantillonnage de parcelles imbriquées. Les formes de vie végétales ont contribué différemment au régime alimentaire (H(4) = 28.93, p〈0.01), les arbustes représentant 55 %. L'abondance relative des principales espèces de plantes alimentaires a influé sur leur contribution au régime alimentaire en période humide ou sèche.saison (χ2 = 7.33, df = 1, p = 0.07 ; χ2 = 2.47, df = 1, p = 0.116 respectivement). Malgré une abondance relative élevée (1.88%), Trichocladus ellipticus Eckl. & Zeyh. était moins appréciée pendant la saison des pluies (E* = 0.20). Il était cependant le plus préféré pendant la saison sèche (E* = 0.78), reflétant peut‐être la valeur nutritive relative. Les bongos incluaient une grande proportion d'herbe (27%) dans leur alimentation comme les autres herbivores brouteurs qui habitent les clairières forestières. Par rapport à la réserve, les aliments végétaux étaient bien représentés dans le sanctuaire proposé avec une similitude de 72 % et 80 % à la fois en saison sèche et en saison humide. Cela augmente potentiellement la probabilité que les bongos s'adaptent et s'établissent une fois réintroduits.
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Human behavioral ecology has proven a valuable theoretical framework for evaluating the archaeological record of human population expansion the world over. To evaluate hypotheses for the late Pleistocene human colonization of the Americas, we need to address a typical assumption built into those models: static landscape knowledge. By taking landscape knowledge as the predicting variable, rather than a constant, we can explore the behavioral mechanisms involved in the interaction of humans with new and unfamiliar environments. Acknowledging the process of adaptation produces contrasting and readily testable hypotheses for human population expansion. As a case study, we use an ideal free distribution model to test competing hypotheses for the colonization of Southeast Alaska. Our results indicate that Southeast Alaska was likely colonized by humans prior to their appearance in the extant archaeological record in the early Holocene. The locations of our oldest archaeological sites in the early Holocene are best explained as the result of a well-established population matching their settlement locations to rising sea level.
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In most sex-changing fishes in coral reefs, a dominant male and multiple females form a mating group (harem). In a few species, the subordinates are simultaneous hermaphrodites that may act as sneakers. In this paper, we ask whether the subordinates in most sex changers choose to be female or whether they are forced to give up their male function to avoid eviction by the harem holder. We consider a game model in which (1) the dominant male evicts some hermaphroditic subordinates if the risk of sperm competition in regard to fertilizing eggs is high, and (2) each subordinate individual chooses its own sex allocation considering the risk of being evicted. In the evolutionarily stable state, the dominant male evicts subordinates only when the subordinates vary greatly in their reproductive resources. All the subordinate individuals are female if the summed male function of the subordinates is smaller than that of the dominant male. Otherwise, all the subordinates are hermaphrodites, and the large individuals have the same male investment but a greatly different female investment, while small individuals have a reduced male investment to avoid eviction risk. We conclude that situations in which the sex allocation of subordinates is affected by the possibility of eviction by the harem holder are rather limited Significance statement We studied the role of eviction in social evolution. In most sex-changing fishes in coral reefs, a dominant male and multiple females form a mating group. In a few species, subordinates are simultaneous hermaphrodites. We asked whether the subordinates are forced to give up their male function to avoid eviction by the harem holder. We examined a game model in which the dominant male evicts hermaphroditic subordinates with a high risk of sperm competition, and each subordinate chooses its own sex allocation considering the eviction risk. We derived mathematical conditions for when subordinates are females or hermaphrodites in the ESS. The model demonstrated that the control by the dominant over subordinate reproductive decisions is rather limited.
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Transgenerational effects abound in animals. While a great deal of research has been dedicated to the effects of maternal stressors such as diet deficiency, social deprivation or predation risk on offspring phenotypes, we have a poor understanding of the adaptive value of transgenerational effects spanning across multiple generations under benign conditions and the relative weight of multigenerational effects. Here we show that grandparental and parental diet experiences combine with personal early-life learning to form adaptive foraging phenotypes in adult plant-inhabiting predatory mites Amblyseius swirskii. Our findings provide insights into transgenerational plasticity caused by persistent versus varying conditions in multiple ancestral generations and show that transgenerational effects may be adaptive in non-matching ancestor and offspring environments.
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Fluxes of matter, energy and information over space and time contribute to ecosystems' functioning and stability. The meta‐ecosystem framework addresses the dynamics of ecosystems linked by these fluxes but, to date, has focused solely on energy and matter. Here, we synthesize existing knowledge of information's effects on local and connected ecosystems and demonstrate how new hypotheses emerge from the integration of ecological information into meta‐ecosystem theory. We begin by defining information and reviewing how it flows among ecosystems to affect connectivity, local ecosystem function and meta‐ecosystem dynamics. We focus on the role of semiotic information: that which can reduce an individual's – or a group's – uncertainty about the state of the world. Semiotic information elicits behavioral, developmental and life history responses from organisms, potentially leading to fitness consequences. Organisms' responses to information can ripple through trophic interactions to influence ecosystem processes, their local and regional dynamics, and the spatiotemporal flows of energy and matter, therefore information should affect meta‐ecosystem dynamics such as stability and productivity. While specific subdisciplines of ecology currently consider different types of information (e.g. social and cultural information, natural and artificial light or sound, body condition, genotype and phenotype), many ecological models currently account for neither the spatio–temporal distribution of information nor its perception by organisms. We identify the empirical, theoretical and philosophical challenges in developing a robust information meta‐ecology and offer ways to overcome them. Finally, we present new hypotheses for how accounting for realistic information perception and responses by organisms could impact processes such as home range formation and spatial insurance, and thus our understanding of ecological dynamics across spatial and temporal scales. Accounting for information will be essential to understanding how dynamics such as fitness, organismal movement and trophic interactions influence meta‐ecosystem functioning, and predicting how ecosystem processes are affected by anthropogenic pressures.
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Outbreaks of defoliating insects in low‐diversity tropical forests occur infrequently but provide valuable insights about outbreak ecology in temperate environments and in general. We investigated an extensive outbreak of the endemic koa moth (Scotorythra paludicola), which defoliated endemic koa trees (Acacia koa) over a third of their range on Hawai‘i Island during 2013 and 2014. At Hakalau Forest National Wildlife Refuge, we observed the dynamics of the outbreak and its effects on host trees, nutrient cycling, and insectivorous consumers in reforestation stands of densely planted koa and in natural forest stands of mixed koa and ‘ōhi‘a (Metrosideros polymorpha). Contrary to predictions of the resource concentration hypothesis, caterpillar biomass and defoliation severity were greater in the natural forest sites, where koa density was relatively low. Caterpillars preferentially consumed the most palatable koa foliage type (phyllodes), and koa initially refoliated with the least palatable foliage type (true leaves). Lightly defoliated small trees refoliated more quickly than did heavily defoliated ones but the opposite was true for large trees, which also produced a greater proportion of phyllodes. Mortality was greatest for heavily defoliated small koa. Caterpillar frass caused larger increases in soil nitrogen (N) than phosphorus (P) availability, with the greatest N increases in fine‐textured soils. Foliar N increased in alien grasses under koa canopies compared to grasses away from koa and to native woody understory species. Bird activity was influenced by ‘ōhi‘a flower abundance and the severity of koa defoliation; birds switched to outbreaking caterpillar prey, and they gained weight during the outbreak. Bat foraging times decreased during the outbreak, apparently because they became satiated quickly each night. Parasitoid wasps increased with caterpillar abundance but had little influence on outbreak dynamics. Reducing alien grass cover and increasing tree diversity would likely reduce the impacts of insect outbreaks and similar perturbations to native forests.
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The disappearance and deterioration of amphibian breeding habitats is a major cause of their global extinction. In Europe, this problem affects the yellow‐bellied toad Bombina variegata, which inhabits small ponds in the early stages of succession, where no predatory invertebrate species normally occur. Nonetheless, as habitats, small temporary ponds are highly endangered, a situation that is intensifying with urban spread. A system of 13 pairs of artificial ponds was constructed in 2012 for the breeding of B. variegata with the aim of reconnecting disjunct populations. During the 2 years of the study, one of the twin ponds was regularly cleared of emergent vegetation and invertebrates. The survival rates of the tadpoles released in the cleared and uncleared ponds were analysed. The survival rate of the tadpoles released into the cleared ponds was higher than of those introduced into the uncleared ones. Tadpole survival rates were also higher in new, single ponds, constructed in 2013. The lower survival rates of the introduced tadpoles are best explained by the presence of predatory aquatic invertebrates, particularly the large diving beetle Dytiscus marginalis. Experimentally obtained consumption rates indicate that one Dytiscus larva is capable of destroying a typical clutch of B. variegata tadpoles within a few hours, much faster than any of the other insect predators tested. The impact of freshwater invertebrates on tadpoles is frequently studied but rarely quantified. For conservation measures to be effective, quantitative standards need to be applied that describe the impact of predation in a predictable manner. Construction of artificial small ponds is broadly accepted as an important conservation measure compensating for the disappearance of natural amphibian breeding sites. This function of artificial ponds may be substantially enhanced by the periodic removal of invertebrate predators.
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Area‐restricted search is the capacity to change search effort adaptively in response to resource encounters or expectations, from directional exploration (global, extensive search) to focused exploitation (local, intensive search). This search pattern is used by numerous organisms, from worms and insects to humans, to find various targets, such as food, mates, nests, and other resources. Area‐restricted search has been studied for at least 80 years by ecologists, and more recently in the neurological and psychological literature. In general, the conditions promoting this search pattern are: (1) clustered resources; (2) active search (e.g. not a sit‐and‐wait predator); (3) searcher memory for recent target encounters or expectations; and (4) searcher ignorance about the exact location of targets. Because area‐restricted search adapts to resource encounters, the search can be performed at multiple spatial scales. Models and experiments have demonstrated that area‐restricted search is superior to alternative search patterns that do not involve a memory of the exact location of the target, such as correlated random walks or Lévy walks/flights. Area‐restricted search is triggered by sensory cues whereas concentrated search in the absence of sensory cues is associated with other forms of foraging. Some neural underpinnings of area‐restricted search are probably shared across metazoans, suggesting a shared ancestry and a shared solution to a common ecological problem of finding clustered resources. Area‐restricted search is also apparent in other domains, such as memory and visual search in humans, which may indicate an exaptation from spatial search to other forms of search. Here, we review these various aspects of area‐restricted search, as well as how to identify it, and point to open questions.
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Adverse childhood experiences (ACEs) are extreme stressors that lead to negative psychosocial outcomes in adulthood. Nonhuman animals explore less after exposure to early stress. Therefore, in this preregistered study, we hypothesized that reduced exploration following ACEs would also be evident in human adults. Further, we predicted that adults with ACEs, in a foraging task, would adopt a decision-making policy that relies on the most-recent reward feedback, a rational strategy for unstable environments. We analyzed data from 145 adult participants, 47 with four or more ACEs and 98 with fewer than four ACEs. In the foraging task, participants evaluated the trade-off between exploiting a known patch with diminishing rewards and exploring a novel one with a fresh distribution of rewards. Using computational modeling, we quantified the degree to which participants’ decisions weighted recent feedback. As predicted, participants with ACEs explored less. However, contrary to our hypothesis, they underweighted recent feedback. These unexpected findings indicate that early adversity may dampen reward sensitivity. Our results may help to identify cognitive mechanisms that link childhood trauma to the onset of psychopathology.
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Very little information is available to zoo managers on the nutritional preferences of the lesser anteater, a highly specialized predator. By studying lesser anteater feeding behavior, we expect to contribute to improved management decisions and individual welfare experiences. We studied the response of zoo-housed lesser anteaters (n = 7) to feeders with live ants (Acromyrmex lundi) and termites (Cortaritermes fulviceps), and we also evaluated the nutritional values of these prey. We individually evaluated each lesser anteater (3 sessions), recording activities by camera. We ground insect samples into a coarse meal and evaluated in vitro biochemical parameters (humidity, lipids proteins, ash, and carbohydrates). Lesser anteaters spent more time with termites than with ants and consumed more termites. Ant meal presented a higher protein and lipid content than termite meal (35.28 ± 0.18% vs. 18.19 ± 0.34% and 16.95 ± 0.13% vs. 6.54 ± 0.31%, respectively), and carbohydrate digestibility was higher in termites. These findings indicate an association between the level of insect consumption and nutritional and digestibility values. This is the first exploration of lesser anteater responses to the presence of social insects in feeders and may serve to guide the study of food preferences in captivity.
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In order to meet the increasing demands from an exploding human population, sustainable agriculture relies on the availability of crop varieties with high yields and optimal defenses to pests. However, ample work has suggested that domesticated plants could have reduced defenses at the expense of increased biomass or yield, and these potential trade-offs can vary among plant species and genotypes. Herbivory coping mechanisms such as tolerance and resistance can be expressed differently among plant genotypes, with variable relationships and inherent fitness costs. Knowledge of the connection between growth and defense mechanisms in cultivated plants is still limited, especially in tropical crops and is needed to guide theories on plant defenses and crop improvement efforts. Using twenty Sorghum bicolor landraces from the tropics, we evaluated genetic variation in growth and defense measures in response to herbivory from Chilo partellus, a major pest of S. bicolor. Specifically, we tested for trade-offs among tolerance and resistance and their association to growth traits. We found significant genetic differences among landraces in terms of their growth, tolerance, and constitutive resistance to herbivory. There was no apparent trade-off between tolerance and resistance, suggesting that it is possible to enhance both defense strategies in S. bicolor. There were contradictory results in terms of potential growth costs associated with constitutive and induced resistance, and tolerance to C. partellus. Landraces with higher resistance and tolerance had lower biomass, but at the same time had a higher number of stems. Future efforts should be directed at understanding the genetic source of resistance and tolerance, and their inclusion for crop improvement.
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Ants, mice, and dogs often use surface-bound scent trails to establish navigation routes or to find food and mates, yet their tracking strategies remain poorly understood. Chemotaxis-based strategies cannot explain casting, a characteristic sequence of wide oscillations with increasing amplitude performed upon sustained loss of contact with the trail. We propose that tracking animals have an intrinsic, geometric notion of continuity, allowing them to exploit past contacts with the trail to form an estimate of where it is headed. This estimate and its uncertainty form an angular sector, and the emergent search patterns resemble a “sector search.” Reinforcement learning agents trained to execute a sector search recapitulate the various phases of experimentally observed tracking behavior. We use ideas from polymer physics to formulate a statistical description of trails and show that search geometry imposes basic limits on how quickly animals can track trails. By formulating trail tracking as a Bellman-type sequential optimization problem, we quantify the geometric elements of optimal sector search strategy, effectively explaining why and when casting is necessary. We propose a set of experiments to infer how tracking animals acquire, integrate, and respond to past information on the tracked trail. More generally, we define navigational strategies relevant for animals and biomimetic robots and formulate trail tracking as a behavioral paradigm for learning, memory, and planning.
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Efficiency leads to leisure Humans are animals—merely another lineage of great apes. However, we have diverged in significant ways from our ape cousins and we are perennially interested in how this happened. Kraft et al . looked at energy intake and expenditure in modern hunter-gatherer societies and great apes. They found that we do not spend less energy while foraging or farming, but we do acquire more energy and at a faster rate than our ape cousins. This difference may have allowed our ancestors to spend more time in contexts that facilitated social learning and cultural development. —SNV
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Aim The evolution and maintenance of accurate Batesian mimicry has been explained by several hypotheses built upon relaxed selection. However, selection can be influenced by ecological factors, such as habitat type or geographical distribution, which have not been considered. Location Worldwide. Taxon Araneae. Methods I gathered data on body size, geographical area of distribution (temperate, subtropical, tropical), and habitat stratification (ground, low vegetation, bush, tree) from literature on more than 400 ant-mimicking (myrmecomorphic) spider species from 18 spider families. I ranked them into four accuracy levels based on morphology, from poor inaccurate mimics to very accurate ones. I used regression to study the effect of body size, distribution, and habitat on mimetic accuracy while controlling for phylogeny. Results Mimetic accuracy increased with spider body size but differently depending on habitat type. On the ground and in low vegetation, smaller species were inaccurate; whereas on shrubs and trees even smaller species were accurate. Accuracy increased from temperate to tropical locations, again differently depending on habitat. In the temperate zone, only species occurring on bushes were accurate, but in the tropical zone even ground-living species were accurate. Main conclusions Higher accuracy at lower latitudes is likely due to stronger predation pressure from visually hunting predators. Lower accuracy in species occurring near the ground is presumably due to predation pressure by non-visually hunting predators. Inaccurate myrmecomorphy in spiders appears to be further driven by smaller body size due to lower profitability to predators; and higher latitude due to increased occurrence of generalist predators.
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Cognitive and physical effort are typically regarded as costly, but demands for effort also seemingly boost the appeal of prospects under certain conditions. One contextual factor that might influence choices for or against effort is the mix of different types of demand a decision maker encounters in a given environment. In two foraging experiments, participants encountered prospective rewards that required equally long intervals of cognitive effort, physical effort, or unfilled delay. Monetary offers varied per trial, and the two experiments differed in whether the type of effort or delay cost was the same on every trial, or varied across trials. When each participant faced only one type of cost, cognitive effort persistently produced the highest acceptance rate compared to trials with an equivalent period of either physical effort or unfilled delay. We theorized that if cognitive effort were intrinsically rewarding, we would observe the same pattern of preferences when participants foraged for varying cost types in addition to rewards. Contrary to this prediction, in the second experiment, an initially higher acceptance rate for cognitive effort trials disappeared over time amid an overall decline in acceptance rates as participants gained experience with all three conditions. Our results indicate that cognitive demands may reduce the discounting effect of delays, but not because decision makers assign intrinsic value to cognitive effort. Rather, the results suggest that a cognitive effort requirement might influence contextual factors such as subjective delay duration estimates, which can be recalibrated if multiple forms of demand are interleaved.
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