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Defensive traits are hypothesized to benefit prey by reducing predation risk from a focal predator but come at a cost to the fitness of the prey. Variation in the expression of defensive traits is seen among individuals within the same population, and in the same individual in response to changes in the environment (i.e., phenotypically plastic responses). It is the relative magnitude of the cost and benefit of the defensive trait that underlies the defensive trait expression and its consequences to the community. However, whereas the cost has received much attention in ecological research, the benefit is seldom examined. Even in a defensive trait as extensively studied as vigilance, there are few studies of the purported benefit of the behavior, namely that vigilance enhances survival. We examined whether prey vigilance increased survival and quantified that benefit in a natural system, with white‐tailed deer (Odocoileus virginianus) experiencing unmanipulated levels of predation risk from Florida panther (Puma concolor coryi). Deer that spent more time vigilant (as measured by head position using camera trap data) had a higher probability of survival. Indeed, an individual deer that was vigilant 75% of the time was more than three times as likely to be killed by panthers over the course of a year than a deer that was vigilant 95% of the time. Our results therefore show that within‐population variation in the expression of a defensive trait has profound consequences for the benefit it confers. Our results provide empirical evidence supporting a long‐held but seldom‐tested hypothesis, that vigilance is a behavior that reduces the probability of predation and quantifies the benefit of this defensive trait. Our work furthers an understanding of the net effects of a trait on prey fitness and predator–prey interactions, within‐population variation in traits, and predation risk effects. [ABSTRACT FROM AUTHOR]

Animals representing a wide range of taxonomic groups are known to select specific food combinations to achieve a nutritionally balanced diet. The nutrient balancing hypothesis suggests that, when given the opportunity, animals select foods to achieve a particular target nutrient balance, and that balancing occurs between meals and between days. For wild ruminants who inhabit landscapes dominated by human land use, nutritionally imbalanced diets can result from ingesting agricultural crops rich in starch and sugar (nonstructural carbohydrates [NCs]), which can be provided to them by people as supplementary feeds. Here, we test the nutrient balancing hypothesis by assessing potential effects that the ingestion of such crops by Alces alces (moose) may have on forage intake. We predicted that moose compensate for an imbalanced intake of excess NC by selecting tree forage with macro‐nutritional content better suited for their rumen microbiome during wintertime. We applied DNA metabarcoding to identify plants in fecal and rumen content from the same moose during winter in Sweden. We found that the concentration of NC‐rich crops in feces predicted the presence of Picea abies (Norway spruce) in rumen samples. The finding is consistent with the prediction that moose use tree forage as a nutritionally complementary resource to balance their intake of NC‐rich foods, and that they ingested P. abies in particular (normally a forage rarely eaten by moose) because it was the most readily available tree. Our finding sheds new light on the foraging behavior of a model species in herbivore ecology, and on how habitat alterations by humans may change the behavior of wildlife. [ABSTRACT FROM AUTHOR]

Habitat loss and change are often implicated as the primary causes of species extinction. Although any population can be instantly imperiled by catastrophe, most habitat loss occurs gradually, thus enabling affected individuals an adaptive advantage to occupy the best of their dwindling opportunities. I demonstrate how to infer the advantage between two habitats for any density and frequency‐dependent strategy of habitat selection. I explore the concept of an Adaptive Dispersal Strategy Landscape to reveal the Evolutionarily Stable Strategy separately for ideal‐free and ideal preemptive habitat selectors. Both solutions reveal an initially counterintuitive expectation that individuals living at high density gain insufficient adaptive advantage to disperse from a deteriorating habitat. Adaptive dispersal is constrained at high density because habitats of better quality are fully occupied. I test the theory with measures of movement and foraging in crossover experiments on a seminatural population of meadow voles. The experiment allowed the voles to choose among patches and between enclosures in which I differentially manipulated food and shelter. Although photographs from an infrared camera documented voles venturing from one habitat to the other, none became resident. Voles preferentially foraged in the richer of the two enclosures, even when I reversed treatments, and they foraged more in patches protected by mulched straw. The adaptive advantage of dispersal using a surrogate fitness proxy based on the voles' giving‐up densities mirrored that generated by theory. The convergence between theory and experiment yields much‐needed insight into our ability to test, predict, and hopefully resolve, the ecological, evolutionary, and conservation consequences of habitat loss. [ABSTRACT FROM AUTHOR]

Animals are integrated into the wider ecosystem via their foraging and behavior. The compensation hypothesis predicts that animals target their foraging efforts (i) toward nutrients that are scarce in the environment and (ii) toward nutrients that are not present in the usual diet of species, which varies across trophic levels. Understanding how foraging for resources varies locally, such as across habitat strata, and trophic levels will help to elucidate the links between the local environment and communities to the ecological functions that animals mediate. We examined whether the relative resource use of ants varies consistently along a habitat strata gradient and across trophic levels across Neotropical biomes. We placed 4500 baited tubes, each containing one of five liquid resources (sugar, amino acid, lipid, sodium, and distilled water) in one of three habitat strata (subterranean, epigaeic, and arboreal) across 60 transects in Amazon, Atlantic Forest, Caatinga, Cerrado, Pampa, and Pantanal biomes. We assessed the relative resource use of all ants across the habitat strata and among two different trophic groups across biomes. The relative preference for sugar increased from subterranean to arboreal strata in all biomes, while the relative preference for lipids decreased at this gradient in five biomes. We also found that in general sugar‐consuming ants foraged more for sugar and less for lipids than predatory ants across biomes. Conversely, we found no consistency across biomes in nutrient preference of amino acid and sodium across habitat strata or trophic levels. Overall, our results indicate sugar limitation in the arboreal stratum and lipid limitation on the ground across biomes and that the trophic level of ants strongly determines their foraging efforts—possibly because ants try to fix their dietary nutrient imbalances. Hence, our findings suggest strong local niche partitioning of sugar and lipid use across habitat strata and trophic levels and that other large spatial scale processes influence the local amino acid and sodium dynamics. [ABSTRACT FROM AUTHOR]

Plants modulate multitrophic ecological interactions, and variation in plant traits can affect these interactions. Pollinators are exposed to pathogens at flowers and acquire or transmit pathogens at different rates on different plant species, but the traits mediating those interactions are almost entirely unknown. We experimentally manipulated five plant traits that span scales including flower, inflorescence, and plant, to determine their effects on pathogen transmission between foraging bees. Specifically, we manipulated two morphological traits (corolla lip length and flower orientation within an inflorescence) and three resource distribution traits (inflorescence nectar, plant patch nectar, and plant aggregation) in tents to test how plant traits affect bee pathogen transmission. We also quantified foraging behavior and fecal deposition patterns as potential mechanisms driving differences in transmission, and assessed trait manipulation consequences for bee reproduction. We found that pathogen transmission was reduced when we trimmed the corolla lip, evenly dispersed nectar distribution within an inflorescence, or aggregated plants in space. Some traits also affected bee reproduction; tents with trimmed corollas had more larval production than control tents, and tents with evenly distributed nectar across plant patches had more larval production than tents with clumped resources. Thus, some trait manipulations both reduced transmission and increased bee microcolony reproduction, although our design does not allow us to discern whether these are related or separate effects. Taken together, our results demonstrate causal effects of several floral traits on pathogen transmission and pollinator reproduction, indicating the importance of intraspecific plant trait variation for pollinator health and population dynamics. [ABSTRACT FROM AUTHOR]

The coexistence of competing species requires density feedbacks that have a larger effect on their own species' population growth than they do on others in the assembly. The feedbacks are often associated with behavioral tradeoffs that enable species to differentially exploit underlying axes of heterogeneity. Conjoining theories of species coexistence with foraging behavior and density‐dependent habitat selection reveals that such tradeoffs impinge on invasion probabilities and equilibrium dynamics emerging from species' differences in habitat use. The resulting habitat separation promotes coexistence by reducing the overall interaction among species. Differential habitat selection depends on the behavioral abilities of organisms to identify and exploit the most profitable habitats and resource patches. One might thus expect that each species will evolve behavioral types distinct from those of other potential competitors. Accordingly, we exposed four coexisting species in four genera of boreal rodents to open‐field tests. We used principal components (PC) to summarize their behaviors along three independent axes corresponding with clines of exploratory, vigilant, and apprehensive personalities. We confirmed that the axes represented repeatable behaviors (personalities) and assessed differences among species with a general linear model (GLM). The GLM revealed highly distinct differences among species, and between pairs of species, on each PC. Even so, it is difficult to infer the adaptive advantages of personality to the habitat segregation that reduces otherwise high interactions among species. Rather, personalities are best interpreted as co‐adaptive behaviors reflecting the complex of morphological, physiological and behavioral attributes that dictate tradeoffs and enable coexistence. [ABSTRACT FROM AUTHOR]

Understanding how megaherbivores incorporate habitat features into their foraging behavior is key toward understanding how herbivores shape the surrounding landscape. While the role of habitat structure has been studied within the context of predator–prey dynamics and grazing behavior in terrestrial systems, there is a limited understanding of how structure influences megaherbivore grazing in marine ecosystems. To investigate the response of megaherbivores (green turtles) to habitat features, we experimentally introduced structure at two spatial scales in a shallow seagrass meadow in The Bahamas. Turtle density increased 50‐fold (to 311 turtles ha−1) in response to the structures, and turtles were mainly grazing and resting (low vigilance behavior). This resulted in a grazing patch exceeding the size of the experimental setup (242 m2), with reduced seagrass shoot density and aboveground biomass. After structure removal, turtle density decreased and vigilance increased (more browsing and shorter surfacing times), while seagrass within the patch partly recovered. Even at a small scale (9 m2), artificial structures altered turtle grazing behavior, resulting in grazing patches in 60% of the plots. Our results demonstrate that marine megaherbivores select habitat features as foraging sites, likely to be a predator refuge, resulting in heterogeneity in seagrass bed structure at the landscape scale. [ABSTRACT FROM AUTHOR]

On the other hand, substrate-gleaning bats utilize a combination of echolocation, perhaps vision, and very often prey-generated sounds to detect, localize, and take prey from the ground, foliage, and other terrestrial surfaces (Norberg & Rayner, [29]; Razak, [34]). Keywords: aerial hawking bats; echolocation; insectivore; opportunistic behavior; quadruped locomotion; sensory mechanisms EN aerial hawking bats echolocation insectivore opportunistic behavior quadruped locomotion sensory mechanisms 1 6 6 01/04/23 20230101 NES 230101 Insects are the primary food of most bats, and insect-eating bats display a variety of foraging strategies molded by different sets of selective pressures on morphology, echolocation, vision, and nervous system to optimize prey capture in different habitats (Norberg & Rayner, [29]; Razak, [34]). Although some bats can switch their foraging strategies, and thereby exploit more than one foraging niche (Daniel, [14], [15]; Faure & Barclay, [17]; Ratcliffe & Dawson, [32]), reliable records of morphologically specialized aerial hawking bats adopting alternative foraging strategies in natural conditions are rare. [Extracted from the article]

Prey handling processes are considered a dominant mechanism leading to short‐term positive indirect effects between prey that share a predator. However, a growing body of research indicates that predators are not necessarily limited by such processes in the wild. Density‐dependent changes in predator foraging behavior can also generate positive indirect effects but they are rarely included as explicit functions of prey densities in functional response models. With the aim of untangling proximate mechanisms of species interactions in natural communities and improving our ability to quantify interaction strength, we extended the multi‐prey version of the Holling disk equation by including density‐dependent changes in predator foraging behavior. Our model, based on species traits and behavior, was inspired by the vertebrate community of the arctic tundra, where the main predator (the arctic fox) is an active forager feeding primarily on cyclic small rodent (lemming) and eggs of various tundra‐nesting bird species. Short‐term positive indirect effects of lemmings on birds have been documented over the circumpolar Arctic but the underlying mechanisms remain poorly understood. We used a unique data set, containing high‐frequency GPS tracking, accelerometer, behavioral, and experimental data to parameterize the multi‐prey model, and a 15‐year time series of prey densities and bird nesting success to evaluate interaction strength between species. We found that (1) prey handling processes play a minor role in our system and (2) changes in arctic fox daily activity budget and distance traveled can partly explain the predation release on birds observed during lemming peaks. These adjustments in predator foraging behavior with respect to the main prey density thus appear as the dominant mechanism leading to positive indirect effects commonly reported among arctic tundra prey. Density‐dependent changes in functional response components have been little studied in natural vertebrate communities and deserve more attention to improve our ability to quantify the strength of species interactions. [ABSTRACT FROM AUTHOR]

Indirect species interactions are ubiquitous in nature, often outnumbering direct species interactions. Yet despite evidence that indirect interactions have strong ecological effects, relatively little is known about whether they can shape adaptive evolution by altering the strength and/or direction of natural selection. We tested whether indirect interactions affect the strength and direction of pollinator‐mediated selection on floral traits of the bumble‐bee pollinated wildflower Lobelia siphilitica. We estimated the indirect effects of two pollinator predators with contrasting hunting modes: dragonflies (Aeshnidae and Corduliidae) and ambush bugs (Phymata americana, Reduviidae). Because dragonflies are active pursuit predators, we hypothesized that they would strengthen pollinator‐mediated selection by weakening plant–pollinator interactions (i.e., a density‐mediated indirect effect). In contrast, because ambush bugs are sit‐and‐wait predators, we hypothesized that they would weaken or reverse the direction of pollinator‐mediated selection by altering pollinator foraging behavior (i.e., a trait‐mediated indirect effect). Specifically, if ambush bugs hunt from plants with traits that attract pollinators (i.e., prey), then pollinators will spend less time visiting those plants, weakening or reversing the direction of selection on attractive floral traits. We did not find evidence that high dragonfly abundance strengthened selection on floral traits via a density‐mediated indirect effect: neither pollen limitation (a proxy for the strength of plant–pollinator interactions) nor directional selection on floral traits of L. siphilitica differed significantly between high‐ and low‐dragonfly abundance treatments. In contrast, we did find evidence that ambush bug presence affected selection on floral traits via a trait‐mediated indirect effect: ambush bugs hunted from L. siphilitica plants with larger daily floral displays, reversing the direction of pollinator‐mediated selection on daily display size. These results suggest that indirect species interactions have the potential to shape adaptive evolution by altering natural selection. [ABSTRACT FROM AUTHOR]

Trait variation can have important consequences for the outcomes of species interactions. Even though some traits vary as much within species as across related species, models and empirical studies typically do not consider the role of intraspecific trait variation for processes such as disease transmission. For example, many pollinator species are in decline because of a variety of stressors including pathogens, but the role of intraspecific trait variation in mediating disease dynamics is rarely considered. For example, pollinator body size could affect pathogen transmission via differences in resistance, foraging behavior and physiology. We tested effects of body size on pollinator pathogen transmission using the common eastern bumble bee Bombus impatiens in field tents, introducing an infected "donor" microcolony of large or small workers with an uninfected average‐sized "recipient" microcolony and allowing bees to forage for 9–16 d. Small donor bees had nearly 50% higher infection intensity (cells/0.02 μL) than large donor bees, but large donor bees were twice as likely to transmit Crithidia bombi to recipient bees. Both behavioral and physiological mechanisms may underlie this apparent paradox. Compared to small bees, large bees foraged more and produced more feces; simulations showed that foraging and defecation rates together had stronger effects on transmission than did donor infection intensity. Thus, effects of bee size on contact rates and pathogen supply may play significant roles in disease transmission, demonstrating the multifaceted impacts of traits on transmission dynamics. [ABSTRACT FROM AUTHOR]

The role of light in partitioning ecological niche space remains a frontier in understanding the assembly of terrestrial vertebrate communities and their response to global change. Leveraging recent advances in biologging technology and intensive field surveys of cloud forest bird communities across an agricultural land use gradient in the Peruvian Andes, we demonstrate that eye size predicts (1) the ambient light microenvironment used by free‐ranging birds, (2) their foraging niche, and (3) species‐specific sensitivity to agricultural land use change. For 15 species carrying light sensors (N = 71 individuals), light intensity levels were best explained by eye size and foraging behavior, with larger‐eyed species using darker microenvironments. Across the cloud forest bird community (N = 240 species), hyperopic ("far‐sighted") foragers, (e.g., flycatchers), had larger eyes compared to myopic ("near‐sighted") species (e.g., gleaners and frugivores); eye size was also larger for myopic insectivores that foraged in the forest understory. Eye size strongly predicted sensitivity to brightly lit habitats across an agricultural land use gradient. Species that increased in abundance in mixed intensity agriculture, including fencerows, silvopasture, and pasture, had smaller eyes, suggesting that light acts as an environmental filter when communities disassemble in a human‐disturbed landscape. We suggest that eye size represents a novel functional trait contributing to terrestrial vertebrate community assembly and sensitivity to habitat disturbance. [ABSTRACT FROM AUTHOR]

Behavioral niche partitioning is an important and widely assumed mechanism for the coexistence of ecologically similar species. Here we assessed this mechanism by testing its core assumption, that evolved differences in foraging behavior correspond with differences in resources consumed. We combined data on foraging behavior, available prey, and observed diets of five coexisting species of New World wood warblers (Parulidae), a system that has been foundational to our understanding of behavioral niche partitioning. Consistent with past work, we found that the five species differed markedly in their foraging behavior, enough that some species pairs hardly overlapped at all in foraging microhabitat. In contrast, the birds overlapped highly in diet, while exhibiting small, interpretable differences in resource use. The high overlap resulted mostly from all five species consuming numerous ants, a prey source that moves between microhabitats. To test the prediction that the large differences in foraging behavior explain the small dietary differences, we generated expected diets based on available prey and foraging microhabitat use. Consistent with niche partitioning as a coexistence mechanism, we found that the small dietary differences were explained by a combination of foraging microhabitat and available prey, but this pattern was driven by only a small number of prey taxa. Thus, we found mixed support for behavioral niche partitioning. Our results indicate that foraging behavior among these bird species helps explain subtle variation in diet, potentially facilitating coexistence. However, our results also revealed a weak relationship between foraging behavior and resource partitioning. Consequently, studies that rely solely on foraging behavior may greatly overestimate the degree of niche differentiation leading to erroneous conclusions. Overall, this study calls into question how and why these differences in foraging behavior evolved, and what role if any they play in facilitating coexistence. [ABSTRACT FROM AUTHOR]

Mark-recapture experiments reveal foraging behavior and plant fidelity of native bees in plant nurseries Keywords: agroecosystems; California; foraging fidelity; Halictus; native plants; ornamental plants EN agroecosystems California foraging fidelity Halictus native plants ornamental plants 1 4 4 06/04/20 20200601 NES 200601 Understanding the spatial and temporal foraging patterns of pollinators is essential to conserving these organisms in human-modified landscapes, such as agroecosystems (Cranmer et al. [3]). These bees not only foraged in the same general location the next day, but of the 106 recaptured bees, 102 (96.2%) foraged on the same plant species as the previous day despite the broad diversity of plants flowering in nurseries. Although more bees were recaptured on native plants overall, some bees still displayed relatively high rates of fidelity to nonnative plants, though we found no preference for or against any nonnative plant species. [Extracted from the article]

Resource availability in agricultural landscapes has been disturbed for many organisms, including pollinator species. Abundance and diversity in flower availability benefit bee populations; however, little is known about which of protein or carbohydrate resources may limit their growth and reproductive performance. Here, we test the hypothesis of complementary resource limitation using a supplemental feeding approach. We applied this assumption with bumble bees (Bombus terrestris), assuming that colony growth and reproductive performance should depend on the continuous supply of carbohydrates and proteins, through the foraging for nectar and pollen, respectively. We placed wild‐caught bumble bee colonies along a landscape gradient of seminatural habitats, and monitored the colonies' weight, foraging activity, and reproductive performance during the whole colony cycle. We performed supplemental feeding as an indicator of landscape resource limitation, using a factorial design consisting of the addition of sugar water (carbohydrate, supplemented or not) crossed by pollen (protein, supplemented or not). Bumble bee colony dynamics showed a clear seasonal pattern with a period of growth followed by a period of stagnation. Higher abundance of seminatural habitats resulted in reducing the proportion of pollen foragers relative to all foragers in both periods, and in improving the reproductive performance of bumble bees. Interestingly, the supplemental feeding of sugar water positively affected the colony weight during the stagnation period, and the supplemental feeding of pollen mitigated the landscape effect on pollen collection investment. Single and combined supplementation of sugar water and pollen increased the positive effect of seminatural habitats on reproductive performance. This study reveals a potential colimitation in pollen and nectar resources affecting foraging behavior and reproductive performance in bumble bees, and indicates that even in mixed agricultural landscapes with higher proportions of seminatural habitats, bumble bee populations face resource limitations. We conclude that the seasonal management of floral resources must be considered in conservation to support bumble bee populations and pollination services in farmlands. [ABSTRACT FROM AUTHOR]

Invasive ecosystem engineers both positively and negatively affect their recipient ecosystems by generating novel habitats. Many studies have focused on alterations to ecosystem properties and to native species diversity and abundance caused by invasive engineers. However, relatively few studies have documented the extent to which behaviors of native species are affected. The red seaweed Gracilaria vermiculophylla (Rhodophyta) invaded estuaries of the southeastern United States within the last few decades and now provides abundant aboveground vegetative cover on intertidal mudflats that were historically devoid of seaweeds. We hypothesized that G. vermiculophylla would affect the foraging behavior of native shorebirds positively for birds that target seaweed‐associated invertebrates or negatively for birds that target prey on or within the sediment now covered with seaweed. Visual surveys of mudflats >1 ha in size revealed that more shorebirds occurred on mudflats with G. vermiculophylla relative to mudflats without G. vermiculophylla. This increased density was consistent across 7 of 8 species, with the one exception being the semipalmated plover Charadrius semipalmatus. A regression‐based analysis indicated that while algal presence predicted shorebird density, densities of some bird species depended on sediment composition and infaunal invertebrate densities. At smaller spatial scales (200 m2 and <1 m2), experimental removals and additions of G. vermiculophylla and focal observations showed strong variation in behavioral response to G. vermiculophylla among bird species. Birds preferentially foraged in bare mud (e.g., C. semipalmatus), in G. vermiculophylla (e.g., Arenaria interpres), or displayed no preference for either habitat (e.g., Tringa semipalmata). Thus, while the presence of the invasive ecosystem engineer on a mudflat appeared to attract greater numbers of these predators, shorebird species differed in their behavioral responses at the smaller spatial scales that affect their foraging. Our research illuminates the need to account for species identity, individual behavior, and scale when predicting the impacts of invasive species on native communities. [ABSTRACT FROM AUTHOR]

Hotspots of disease transmission can strongly influence pathogen spread. Bee pathogens may be transmitted via shared floral use, but the role of plant species and floral trait variation in shaping transmission dynamics is almost entirely unexplored. Given the importance of pathogens for the decline of several bee species, understanding whether and how plant species and floral traits affect transmission could give us important tools for predicting which plant species may be hotspots for disease spread. We assessed variation in transmission via susceptibility (probability of infection) and mean intensity (cell count of infected bees) of the trypanosomatid gut pathogen Crithidia bombi to uninfected Bombus impatiens workers foraging on 14 plant species, and assessed the role of floral traits, bee size and foraging behavior on transmission. We also conducted a manipulative experiment to determine how the number of open flowers affected transmission on three plant species, Penstemon digitalis, Monarda didyma, and Lythrum salicaria. Plant species differed fourfold in the overall mean abundance of Crithidia in foraging bumble bees (mean including infected and uninfected bees). Across plant species, bee susceptibility and mean intensity increased with the number of reproductive structures per inflorescence (buds, flowers and fruits); smaller bees and those that foraged longer were also more susceptible. Trait‐based models were as good or better than species‐based models at predicting susceptibility and mean intensity based on AIC values. Surprisingly, floral size and morphology did not significantly predict transmission across species. In the manipulative experiment, more open flowers increased mean pathogen abundance fourfold in Monarda, but had no effect in the other two plant species. Our results suggest that variation among plant species, through their influence on pathogen transmission, may shape bee disease dynamics. Given widespread investment in pollinator‐friendly plantings to support pollinators, understanding how plant species affect disease transmission is important for recommending plant species that optimize pollinator health. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, it has been argued that the effect of predator fear exacts a greater demographic toll on prey populations than the direct killing of prey. However, efforts to quantify the effects of fear have primarily relied on experiments that replace predators with predator cues. Interpretation of these experiments must consider two important caveats: (1) the magnitude of experimenter‐induced predator cues may not be realistically comparable to those of the prey's natural sensory environment, and (2) given functional predators are removed from the treatments, the fear effect is measured in the absence of any consumptive effects, a situation which never occurs in nature. We contend that demographic consequences of fear in natural populations may have been overestimated because the intensity of predator cues applied by experimenters in the majority of studies has been unnaturally high, in some instances rarely occurring in nature without consumption. Furthermore, the removal of consumption from the treatments creates the potential situation that individual prey in poor condition (those most likely to contribute strongly to the observed fear effects via starvation or reduced reproductive output) may have been consumed by predators in nature prior to the expression of fear effects, thus confounding consumptive and fear effects. Here, we describe an alternative treatment design that does not utilize predator cues, and in so doing, better quantifies the demographic effect of fear on wild populations. This treatment substitutes the traditional cue experiment where consumptive effects are eliminated and fear is simulated with a design where fear is removed and consumptive effects are simulated through the experimental removal of prey. Comparison to a natural population would give a more robust estimate of the effect of fear in the presence of consumption on the demographic variable of interest. This approach represents a critical advance in quantifying the mechanistic pathways through which predation structures ecological communities. Discussing the merits of both treatments will motivate researchers to go beyond simply describing the existence of fear effects and focus on testing their true magnitude in wild populations and natural communities. [ABSTRACT FROM AUTHOR]

Numerous mechanisms may allow species to coexist. We tested for frequency-dependent predation, a mechanism predicted by theory and established as a foraging behavior for many types of animals. Our field test included multiple prey species exposed in situ to multiple predator species and individuals to determine whether the prey species experienced predation patterns that were frequency dependent. The prey were seeds of three species of Sonoran Desert winter annual plants while the predator species were a guild of nocturnal seed foraging heteromyid and murid rodents that co-occur naturally in the same community as the desert annuals at Tumamoc Hill near Tucson. Seeds of one species were much preferred over the other two. Nonetheless, we found the net effect of rodent foraging to be positively frequency dependent (the preference for each species is higher when it is common than when it is uncommon) as has been previously hypothesized. This frequency-dependent predation should function as a species coexistence promoting mechanism in concert with the storage effect that has been previously demonstrated for this system. [ABSTRACT FROM AUTHOR]

Many studies examine how body size mediates energy use, but few investigate how size simultaneously regulates energy acquisition. Furthermore, rarely energy fluxes are examined while accounting for the role of biotic and abiotic factors in which they are nested. These limitations contribute to an incomplete understanding of how size affects the transfer of energy through individuals, populations, and communities. Here we characterized photosynthesis-irradiance (P-I) curves and per-cell net-energy use for 21 phytoplankton species spanning across four orders of magnitude of size and seven phyla, each measured across six light intensities and four population densities. We then used phylogenetic mixed models to quantify how body size influences the energy turnover rates of a species, and how this changes across environments. Rate-parameters for the P-I curve and net-energy budgets were mostly highly correlated and consistent with an allometric size-scaling exponent of <1. The energy flux of a cell decreased with population density and increased with light intensity, but the effect of body size remained constant across all combinations of treatment levels (i.e. no [ABSTRACT FROM AUTHOR]

Many arboreal ants depend on myrmecophytic plants for both food and shelter; in return, these ants defend their host plants against herbivores, which are often insects. Ant-plant and other mutualisms do not necessarily involve the exchange of costly rewards or services; they may instead result from by-product benefits, or positive outcomes that do not entail a cost for one or both partners. Here, we examined whether the plant-ant Allomerus octoarticulatus pays a short-term cost to defend their host plants against herbivores, or whether plant defense is a by-product benefit of ant foraging for insect prey. Because the food offered by ant-plants is usually nitrogen-poor, arboreal ants may balance their diets by consuming insect prey or associating with microbial symbionts to acquire nitrogen, potentially shifting the costs and benefits of plant defense for the ant partner. To determine the effect of ant diet on an ant-plant mutualism, we compared the behavior, morphology, fitness, stable isotope signatures, and gaster microbiomes of A. octoarticulatus ants nesting in Cordia nodosa trees maintained for nearly a year with or without insect herbivores. At the end of the experiment, ants from herbivore exclosures preferred protein-rich baits more than ants in the control (i.e., herbivores present) treatment. Furthermore, workers in the control treatment were heavier than in the herbivore-exclusion treatment, and worker mass predicted reproductive output, suggesting that foraging for insect prey directly increased ant colony fitness. The gaster microbiome of ants was not significantly affected by the herbivore exclusion treatment. We conclude that the defensive behavior of some phytoecious ants is a by-product of their need for external protein sources; thus, the consumption of insect herbivores by ants benefits both the ant colony and the host plant. [ABSTRACT FROM AUTHOR]

Seed removal can influence plant community dynamics, composition, and resulting vegetation characteristics. In the African savanna, termites and large herbivores influence vegetation in various ways, likely including indirect effects on seed predators and secondary dispersers. However, the intensity and variation of seed removal rates in African savannas has seldom been studied. We experimentally investigated whether termites and large herbivores were important factors in the mechanisms contributing to observed patterns in tree species composition on and off mounds, in Lake Mburo National Park, Uganda. Within fenced (excluding large herbivores) and unfenced termite mound and adjacent savanna plots, we placed seeds of nine native tree species within small open 'cages,' accessed by all animals, roofed cages that only allowed access to small vertebrates and invertebrates, and closed cages that permitted access by smaller invertebrates only (5 mm wire mesh). We found that mean seed removal rate was high (up to 87.3% per 3 d). Mound habitats experienced significantly higher removal rates than off-mound habitats. The mean removal rate of native seeds from closed cages was 11.1% per 3 d compared with 19.4% and 23.3% removed per 3 d in the roofed and open cages, respectively. Smaller seeds experienced higher removal rates than larger seeds. Large herbivore exclusion on mounds reduced native seed removal rates by a mean of 8.8% in the open cages, but increased removal rates by 1.7% in the open cages when off-mound habitats were fenced. While removal rates from open cages were higher on active mounds (30.9%) than on inactive mounds (26.7%), the removal rates from closed cages were lower on active vs. inactive mounds (6.1% vs. 11.6%, respectively). Thus, we conclude that large herbivores and Macrotermes mounds influence seed removal rates, though these effects appear indirect. [ABSTRACT FROM AUTHOR]

Changes in the time available for organisms to maintain physiologically preferred temperatures (thermal opportunity) is a primary mechanism by which climate change impacts the fitness and population dynamics of organisms. Yet, it is unclear whether losses or gains in thermal opportunity result in proportional changes in rates of energy procurement and use. We experimentally quantified lizard food consumption and energy assimilation at different durations of thermal opportunity. We incorporated these data in an individual-based model of foraging and digestion in lizards to explore the implications of nonlinear responses to shifts in thermal opportunity across a wide geographic range. Our model predicts that shifts in thermal opportunities resulting from climate change alter energy intake primarily through digestion rather than feeding, because simulated lizards were able to fill their gut faster than they can digest their food. Moreover, since rates of energy assimilation decelerate with increasing thermal opportunity, shifts in daily energetic assimilation would depend on the previous opportunity for thermoregulation. In particular, the same changes in thermal opportunity will have little impact on lizards from warm locations, while having a large impact on lizards from cold locations where thermoregulation is possible for only a few hours each day. Energy expenditure followed spatial patterns in thermal opportunity, with greater annual energy expenditure occurring at warmer locations. Our model predicts that lizards will spend more energy under climate change by maintaining higher body temperatures and remaining active longer. However, the predicted changes in energy assimilation following climate change greatly exceeded the predicted increases in energy expenditure. Simple models, which assume constant rates of energy gain during activity, will potentially mislead efforts to understand and predict the biological impacts of climate change. [ABSTRACT FROM AUTHOR]

Transmission is central to our understanding and efforts to control the spread of infectious diseases. Because transmission generally requires close contact, host movements and behaviors can shape transmission dynamics: random and complete mixing leads to the classic density-dependent model, but if hosts primarily interact locally (e.g., aggregate) or within groups, transmission may saturate. Manipulating host behavior may thus change both the rate and functional form of transmission. We used the ranavirus-wood frog ( Lithobates sylvaticus) tadpole system to test whether transmission rates reflect contacts, and whether the functional form of transmission can be influenced by the distribution of food in mesocosms (widely dispersed, promoting random movement and mixing vs. a central pile, promoting aggregations). Contact rates increased with density, as expected, but transmission rapidly saturated. Observed rates of transmission were not explained by observed contact rates or the density-dependent model, but instead transmission in both treatments followed models allowing for heterogeneities in the transmission process. We argue that contacts were not generally limiting, but instead that our results are better explained by heterogeneities in host susceptibility. Moreover, manipulating host behavior to manage the spread of infectious disease may prove difficult to implement. [ABSTRACT FROM AUTHOR]

Prey often retreat into the safety of refuges for protection from predators. This shift into refuge can reduce foraging opportunities, escalating the costs of risk and the strength of nonconsumptive effects. Such costs, however, may be shaped by the variation in resources that refuges harbor for prey foraging (i.e., refuge quality), and change dynamically via impacts on prey state. Despite its potential importance, we lack an explicit understanding of how refuge quality impacts prey performance under risk. Using a rocky intertidal food chain, we examined the interaction between predation risk and the amount of resources available for prey in refuge. We found that refuges with more resources greatly reduce the costs of refuge use, and that nonconsumptive effects are thereby weakened by as much as one-half, with especially strong impacts on prey growth and growth efficiency. These results suggest that failure to consider refuge quality could result in overestimation of the negative effects associated with prey refuge use. [ABSTRACT FROM AUTHOR]

Warm temperatures are required for insect flight. Consequently, warming could benefit many high-latitude and high-altitude insects by increasing opportunities for foraging or oviposition. However, warming can also alter species interactions, including interactions with natural enemies, making the net effect of rising temperatures on population growth rate difficult to predict. We investigated the temperature-dependence of nesting activity and lifetime reproductive output over 3 yr in subalpine populations of a pollen-specialist bee, Osmia iridis. Rates of nest provisioning increased with ambient temperatures and with availability of floral resources, as expected. However, warmer conditions did not increase lifetime reproductive output. Lifetime offspring production was best explained by rates of brood parasitism (by the wasp Sapyga), which increased with temperature. Direct observations of bee and parasite activity suggest that although activity of both species is favored by warmer temperatures, bees can be active at lower ambient temperatures, while wasps are active only at higher temperatures. Thus, direct benefits to the bees of warmer temperatures were nullified by indirect costs associated with increased parasite activity. To date, most studies of climate-change effects on pollinators have focused on changing interactions between pollinators and their floral host-plants (i.e., bottom-up processes). Our results suggest that natural enemies (i.e., top-down forces) can play a key role in pollinator population regulation and should not be overlooked in forecasts of pollinator responses to climate change. [ABSTRACT FROM AUTHOR]

Pollination syndromes are suites of floral traits presumed to reflect adaptations to attract and utilize a 'primary' type of animal pollinator. However, syndrome traits may also function to deter 'secondary' flower visitors that reduce plant fitness through their foraging activities. Here we use the hummingbird-pollinated plant species Mimulus cardinalis as a model to investigate the potential deterrent effects of classic bird syndrome traits on bumble bee foragers. To establish that M. cardinalis flowers elicit an avoidance response in bees, we assessed the choice behavior of individual foragers on a mixed experimental array of M. cardinalis and its bee-pollinated sister species M. lewisii. As expected, bees showed a strong preference against M. cardinalis flowers (only 22% of total bee visits were to M. cardinalis), but surprisingly also showed a high degree of individual specialization (95.2% of total plant transitions were between conspecifics). To determine M. cardinalis floral traits that discourage bee visitation, we then assessed foraging responses of individuals to M. cardinalis-like and M. lewisii-like floral models differing in color, orientation, reward, and combinations thereof. Across experiments, M. cardinalis-like trait combinations consistently produced a higher degree of flower avoidance behavior and individual specialization than expected based on bee responses to each trait in isolation. We then conducted a series of flower discrimination experiments to assess the ability of bees to utilize traits and trait combinations associated with each species. Relative to M. lewisii-like alternatives, M. cardinalis-like traits alone had a minimal effect on bee foraging proficiency but together increased the time bees spent searching for rewarding flowers from 1.49 to 2.65 s per visit. Collectively, our results show that M. cardinalis flowers impose foraging costs on bumble bees sufficient to discourage visitation and remarkably, generate such costs through synergistic color-orientation and color-reward trait interactions. Floral syndromes therefore represent complex adaptations to multiple pollinator groups, rather than simply the primary pollinator. [ABSTRACT FROM AUTHOR]

Rodent preference for scatter-hoarding large seeds has been widely considered to favor the evolution of large seeds. Previous studies supporting this conclusion were primarily based on observations at earlier stages of seed dispersal, or on a limited sample of successfully established seedlings. Because seed dispersal comprises multiple dispersal stages, we hypothesized that differential foraging preference on seed size by animal dispersers at different dispersal stages would ultimately result in medium-sized seeds having the highest dispersal success rates. In this study, by tracking a large number of seeds for 5 yr, we investigated the effects of seed size on seed fates from seed removal to seedling establishment of a dominant plant Pittosporopsis kerrii (Icacinaceae) dispersed by scatter-hoarding rodents in tropical forest in southwest China. We found that small seeds had a lower survival rate at the early dispersal stage where more small seeds were predated at seed stations and after removal; large seeds had a lower survival rate at the late dispersal stage, more large seeds were recovered, predated after being cached, or larder-hoarded. Medium-sized seeds experienced the highest dispersal success. Our study suggests that differential foraging preferences by scatter-hoarding rodents at different stages of seed dispersal could result in conflicting selective pressures on seed size and higher dispersal success of medium-sized seeds. [ABSTRACT FROM AUTHOR]

Animal pollinators mediate reproduction of many plant species. Foraging theory suggests that animal pollinators exhibit preferences for common plant species in natural communities (positive frequency-dependent foraging) and temporary single-species specialization (flower constancy) during foraging bouts. Positive frequency dependence may favor common plant species; flower constancy may enhance conspecific pollen transfer particularly in rare plant species. Previous experimental studies suggest that avian pollinators are unlikely to exhibit these behaviors. We studied foraging behavior of Cape Sugarbirds ( Promerops cafer), the main avian pollinator of many Protea species, using focal-plant and focal-bird sampling, assisted by high-resolution maps of the spatiotemporal distribution of Protea individuals and their flowering status. We found that Sugarbird's visitation preference increased with species' relative floral abundance, and that individual Sugarbirds tended to visit single species in sequence. Flower constancy during foraging bouts was significantly higher than expected from random plant-animal encounters at the scale of pollinator movements. Positive frequency dependence may favor the reproduction of abundant plant species while flower constancy may be particularly important for rare plant species. This first simultaneous study of both behaviors in a natural plant-pollinator system shows that bird pollinators exhibit both types of behavior and, in this way, possibly influence plant community structure. [ABSTRACT FROM AUTHOR]

Cross-habitat foraging movements of predators can have widespread implications for predator and prey populations, community structure, nutrient transfer, and ecosystem function. Although central-place foraging models and other aspects of optimal foraging theory focus on individual predator behavior, they also provide useful frameworks for understanding the effects of predators on prey populations across multiple habitats. However, few studies have examined both the foraging behavior and ecological effects of nonnative predators across multiple habitats, and none has tested whether nonnative predators deplete prey in a manner predicted by these foraging models. I conducted behavioral observations of invasive lionfish ( Pterois volitans) to determine whether they exhibit foraging movements similar to other central-place consumers. Then, I used a manipulative field experiment to test whether their effects on prey populations are consistent with three qualitative predictions from optimal foraging models. Specifically, I predicted that the effects of invasive lionfish on native prey will (1) occur at central sites first and then in surrounding habitats, (2) decrease with increasing distance away from their shelter site, and (3) extend to greater distances when prey patches are spaced closer together. Approximately 40% of lionfish exhibited short-term crepuscular foraging movements into surrounding habitats from the coral patch reefs where they shelter during daylight hours. Over the course of 7 weeks, lionfish depleted native fish populations on the coral patch reefs where they reside, and subsequently on small structures in the surrounding habitat. However, their effects did not decrease with increasing distance from the central shelter site and the influence of patch spacing was opposite the prediction. Instead, lionfish always had the greatest effects in areas with the highest prey densities. The differences between the predicted and observed effects of lionfish foraging are likely due to different constraints faced by invasive predators compared to native predators, namely that lionfish do not face increased predation risk with increased movement away from shelter sites. By foraging at greater distances from patch reefs than native predators, lionfish eliminated a spatial refuge from predation used by juveniles of many commercially and ecologically important reef fishes. [ABSTRACT FROM AUTHOR]

The roots of the majority of tree species are associated with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi. The absorptive roots of tree species also vary widely in their diameter. The linkages between root thickness, mycorrhiza type and nutrient foraging are poorly understood. We conducted a large root ingrowth experiment in the field to investigate how absorptive roots of varying thickness and their associated fungi (AM vs. EM) exploit different nutrient patches (inorganic and organic) in a common garden. In nutrient-rich patches, thin-root tree species more effectively proliferated absorptive roots than thick-root tree species, whereas thick-root tree species proliferated more mycorrhizal fungal biomass than thin-root tree species. Moreover, nutrient patches enriched with organic materials resulted in greater root and mycorrhizal fungal proliferation compared to those enriched with inorganic nutrients. Irrespective of root morphology, AM tree species had higher root foraging precision than mycorrhizal hyphae foraging precision within organic patches, whereas EM tree species exhibited the opposite. Our findings that roots and mycorrhizal fungi are complementary in foraging within nutrient patches provide new insights into species coexistence and element cycling in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Encounter competition is interference competition in which animals directly contend for resources. Ecological theory predicts the trait that determines the resource holding potential ( RHP), and hence the winner of encounter competition, is most often body size or mass. The difficulties of observing encounter competition in complex organisms in natural environments, however, has limited opportunities to test this theory across diverse species. We studied the outcome of encounter competition contests among mesocarnivores at deer carcasses in California to determine the most important variables for winning these contests. We found some support for current theory in that body mass is important in determining the winner of encounter competition, but we found that other factors including hunger and species-specific traits were also important. In particular, our top models were 'strength and hunger' and 'size and hunger,' with models emphasizing the complexity of variables influencing outcomes of encounter competition. In addition, our wins above predicted ( WAP) statistic suggests that an important aspect that determines the winner of encounter competition is species-specific advantages that increase their RHP, as bobcats ( Lynx rufus) and spotted skunks ( Spilogale gracilis) won more often than predicted based on mass. In complex organisms, such as mesocarnivores, species-specific adaptations, including strategic behaviors, aggressiveness, and weapons, contribute to competitive advantages and may allow certain species to take control or defend resources better than others. Our results help explain how interspecific competition shapes the occurrence patterns of species in ecological communities. [ABSTRACT FROM AUTHOR]

Despite increasing evidence that herbivory on a focal plant may hinge upon the identity of its neighbors, it is not clear whether predictable mechanisms govern the nature and magnitude of such associational effects. Using a factorial field experiment replicated at 14 sites across 80,000 hectares, we evaluated the mechanisms driving associational effects between two plant species mediated by grasshopper herbivores. Our experiment manipulated local neighborhood plant density (two levels) and frequency (three levels), nested within two larger-scale habitat contexts (habitats that did or did not have past agricultural land use). We found that the more palatable plant species, Solidago nemoralis, experienced reduced herbivory (associational resistance) when rare due mainly to reduced grasshopper foraging activity. Damage to the less palatable plant species, S. odora, was affected by the interaction between plant frequency and the land-use history of the site: it experienced increased damage (associational susceptibility) in even-frequency neighborhoods, but only in sites with a history of agricultural use. Behavioral assays generally corroborated the results from the field, further supporting the importance of foraging behavior in generating associational effects. In finding that associational effects are contingent upon relative palatability among plants and events in the distant past that modify contemporary habitat structure (i.e., past agricultural land use), our work suggests that foraging decisions made at the neighborhood level are important for generating associational effects and that in some cases these neighborhood interactions also depend on the larger-scale environmental context resulting from legacies of past land-use events. [ABSTRACT FROM AUTHOR]

A challenge in community ecology is connecting biogeographic patterns with local scale observations. In Neotropical hummingbirds, closely related species often co-occur less frequently than expected (overdispersion) when compared to a regional species pool. While this pattern has been attributed to interspecific competition, it is important to connect these findings with local scale mechanisms of coexistence. We measured the importance of the presence of competitors and the availability of resources on selectivity at experimental feeders for Andean hummingbirds along a wide elevation gradient. Selectivity was measured as the time a bird fed at a feeder with a high sucrose concentration when presented with feeders of both low and high sucrose concentrations. Resource selection was measured using time-lapse cameras to identity which floral resources were used by each hummingbird species. We found that the increased abundance of preferred resources surrounding the feeder best explained increased species selectivity, and that related hummingbirds with similar morphology chose similar floral resources. We did not find strong support for direct agonism based on differences in body size or phylogenetic relatedness in predicting selectivity. These results suggest closely related hummingbird species have overlapping resource niches, and that the intensity of interspecific competition is related to the abundance of those preferred resources. If these competitive interactions have negative demographic effects, our results could help explain the pattern of phylogenetic overdispersion observed at regional scales. [ABSTRACT FROM AUTHOR]

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

Bigeye tuna are known for remarkable daytime vertical migrations between deep water, where food is abundant but the water is cold, and the surface, where water is warm but food is relatively scarce. Here we investigate if these dive patterns can be explained by dynamic optimal foraging theory, where the tuna maximizes its energy harvest rate. We assume that foraging efficiency increases with body temperature, so that the vertical migrations are thermoregulatory. The tuna's state is characterized by its mean body temperature and depth, and we solve the optimization problem numerically using dynamic programming. With little calibration of model parameters, our results are consistent with observed data on vertical movement: we find that small tuna should display constant-depth strategies while large tuna should display vertical migrations. The analysis supports the hypothesis that the tuna behaves such as to maximize its energy gains. The model therefore provides insight into the processes underlying observed behavioral patterns and allows generating predictions of foraging behavior in unobserved environments. [ABSTRACT FROM AUTHOR]

Interactions between predator and prey, or parasitoid and host, are shaped by trait- and density-mediated processes involving other community members. Parasitoids that lay their eggs in herbivorous insects locate their hosts through infochemicals such as herbivore-induced plant volatiles ( HIPVs) and host-produced kairomones. Hosts are frequently accompanied by non-host herbivores that are unsuitable for the parasitoid. These non-hosts may interfere with host location primarily through trait-mediated processes, by their own infochemicals, and their induction of the emission of plant volatiles. Although it is known that single non-hosts can interfere with parasitoid host location, it is still unknown whether the observed effects are due to species specific characteristics or to the feeding habits of the non-host herbivores. Here we addressed whether the feeding guild of non-host herbivores differentially affects foraging of the parasitoid Cotesia glomerata for its common host, caterpillars of Pieris brassicae feeding on Brassica oleracea plants. We used different phloem-feeding and leaf-chewing non-hosts to study their effects on host location by the parasitoid when searching for host-infested plants based on HIPVs and when searching for hosts on the plant using infochemicals. To evaluate the ultimate effect of these two phases in host location, we studied parasitism efficiency of parasitoids in small plant communities under field-tent conditions. We show that leaf-chewing non-hosts primarily affected host location through trait-mediated effects via plant volatiles, whereas phloem-feeding non-hosts exerted trait-mediated effects by affecting foraging efficiency of the parasitoid on the plant. These trait-mediated effects resulted in associational susceptibility of hosts in environments with phloem feeders and associational resistance in environments with non-host leaf chewers. [ABSTRACT FROM AUTHOR]

In plant-pollinator networks, foraging choices by pollinators help form the connecting links between species. Flexible foraging should therefore play an important role in defining network topology. Factors such as morphological trait complementarity limit a pollinator's pool of potential floral resources, but which potential resource species are actually utilized at a location depends on local environmental and ecological context. Pollinators can be highly flexible foragers, but the effect of this flexibility on network topology remains unclear. To understand how flexible foraging affects network topology, we examined differences between sets of locally realized interactions and corresponding sets of potential interactions within 25 weighted plant-pollinator networks in two different regions of the United States. We examined two possible mechanisms for flexible foraging effects on realized networks: (1) preferential targeting of higher-density plant resources, which should increase network nestedness, and (2) context-dependent resource partitioning driven by interspecific competition, which should increase modularity and complementary specialization. We found that flexible foraging has strong effects on realized network topology. Realized connectance was much lower than connectance based on potential interactions, indicating a local narrowing of diet breadth. Moreover, the foraging choices pollinators made, which particular plant species to visit and at what rates, resulted in networks that were significantly less nested and significantly more modular and specialized than their corresponding networks of potential interactions. Preferentially foraging on locally abundant resources was not a strong driver of the realization of potential interactions. However, the degree of modularity and complementary specialization both increased with the number of competing pollinator species and with niche availability. We therefore conclude that flexible foraging affects realized network topology more strongly through resource partitioning than through focusing on high-density resources. [ABSTRACT FROM AUTHOR]

Temporal variability in the distribution of feeding links in a food web can be an important stabilizing factor for these complex systems. Adaptive foraging and prey choice have been hypothesized to cause this link flexibility as organisms adjust their behavior to variation in the prey community. Here, we analyze a 10-yr time series of monthly aphid-parasitoid-secondary-parasitoid networks and show that interaction strengths for polyphagous secondary parasitoids are generally biased toward the larger host species within their fundamental niche; however, in months of higher competition for hosts, size-based biases are reduced. The results corroborate a previous hypothesis stating that host selectivity of parasitoids should be correlated to the relative likelihood of egg limitation vs. time limitation. Our results evince adaptation of foraging behavior to varying conditions affects the distribution of host-parasitoid link strengths, where link-rewiring may be integral to stability in complex communities. [ABSTRACT FROM AUTHOR]

Plant species can influence the pollination and reproductive success of coflowering neighbors that share pollinators. Because some individual pollinators habitually forage in particular areas, it is also possible that plant species could influence the pollination of neighbors that bloom later. When flowers of a preferred forage plant decline in an area, site-fidelity may cause individual flower feeders to stay in an area and switch plant species rather than search for preferred plants in a new location. A newly blooming plant species may quickly inherit a set of visitors from a prior plant species, and therefore experience higher pollination success than it would in an area where the first species never bloomed. To test this, we manipulated the placement and timing of two plant species, Delphinium barbeyi and later-blooming Gentiana parryi. We recorded the responses of individually marked bumble bee pollinators. About 63% of marked individuals returned repeatedly to the same areas to forage on Delphinium. When Delphinium was experimentally taken out of bloom, most of those site-faithful individuals (78%) stayed and switched to Gentiana. Consequently, Gentiana flowers received more visits in areas where Delphinium had previously flowered, compared to areas where Delphinium was still flowering or never occurred. Gentiana stigmas received more pollen in areas where Delphinium disappeared than where it never bloomed, indicating that Delphinium increases the pollination of Gentiana when they are separated in time. Overall, we show that individual bumble bees are often site-faithful, causing one plant species to increase the pollination of another even when separated in time, which is a novel mechanism of pollination facilitation. [ABSTRACT FROM AUTHOR]

A key constraint faced by consumers is achieving a positive energy balance in the face of temporal variation in foraging opportunities. Recent work has shown that spatial heterogeneity in resource phenology can buffer mobile consumers from this constraint by allowing them to track changes in resource availability across space. For example, salmon populations spawn asynchronously across watersheds, causing high-quality foraging opportunities to propagate across the landscape, prolonging the availability of salmon at the regional scale. However, we know little about how individual consumers integrate across phenological variation or the benefits they receive by doing so. Here, we present direct evidence that individual brown bears track spatial variation in salmon phenology. Data from 40 GPS collared brown bears show that bears visited multiple spawning sites in synchrony with the order of spawning phenology. The number of sites used was correlated with the number of days a bear exploited salmon, suggesting the phenological variation in the study area influenced bear access to salmon, a resource which strongly influences bear fitness. Fisheries managers attempting to maximize harvest while maintaining ecosystem function should strive to protect the population diversity that underlies the phenological variation used by wildlife consumers. [ABSTRACT FROM AUTHOR]

Predators play a key role in shaping natural ecosystems, and understanding the factors that influence a predator's kill rate is central to predicting predator-prey dynamics. While prey density has a well-established effect on predation, it is increasingly apparent that predator density also can critically influence predator kill rates. The effects of both prey and predator density on the functional response will, however, be determined in part by their distribution on the landscape. To examine this complex relationship we experimentally manipulated prey density, predator density, and prey distribution using a tadpole (prey)-dragonfly nymph (predator) system. Predation was strongly ratio-dependent irrespective of prey distribution, but the shape of the functional response changed from hyperbolic to sigmoidal when prey were clumped in space. This sigmoidal functional response reflected a relatively strong negative effect of predator interference on kill rates at low prey: predator ratios when prey were clumped. Prey aggregation also appeared to promote stabilizing density-dependent intraguild predation in our system. We conclude that systems with highly antagonistic predators and patchily distributed prey are more likely to experience stable dynamics, and that our understanding of the functional response will be improved by research that examines directly the mechanisms generating interference. [ABSTRACT FROM AUTHOR]

Population consequences of endangered species interacting as predators and prey have been considered theoretically and legally, but rarely investigated in the field. We examined relationships between spatially variable populations of a predator, the California sea otter, Enhydra lutris nereis, and a prey species, the black abalone, Haliotis cracherodii. Both species are federally listed under the Endangered Species Act and co-occur along the coast of California. We compared the local abundance and habitat distribution of black abalone at 12 sites with varying densities of sea otters. All of the populations of abalone we examined were in the geographic area currently unaffected by withering disease, which has decimated populations south of the study area. Surprisingly, our findings indicate that sea otter density is positively associated with increased black abalone density. The presence of sea otters also correlated with a shift in black abalone to habitat conferring greater refuge, which could decrease illegal human harvest. These results highlight the need for a multi-species approach to conservation management of the two species, and demonstrate the importance of using fieldcollected data rather than simple trophic assumptions to understand relationships between jointly vulnerable predator and prey populations. [ABSTRACT FROM AUTHOR]

Many established models of animal foraging assume that individuals are ecologically equivalent. However, it is increasingly recognized that populations may comprise individuals who differ consistently in their diets and foraging behaviors. For example, recent studies have shown that individual foraging site fidelity (IFSF, when individuals consistently forage in only a small part of their population's home range) occurs in some colonial breeders. Short-term IFSF could result from animals using a win--stay, lose--shift foraging strategy. Alternatively, it may be a consequence of individual specialization. Pelagic seabirds are colonial central-place foragers, classically assumed to use flexible foraging strategies to target widely dispersed, spatiotemporally patchy prey. However, tracking has shown that IFSF occurs in many seabirds, although it is not known whether this persists across years. To test for long-term IFSF and to examine alternative hypotheses concerning its cause, we repeatedly tracked 55 Northern Gannets (Morus bassanus) from a large colony in the North Sea within and across three successive breeding seasons. Gannets foraged in neritic waters, predictably structured by tidal mixing and thermal stratification, but subject to stochastic, wind-induced overturning. Both within and across years, coarse to mesoscale (tens of kilometers) IFSF was significant but not absolute, and foraging birds departed the colony in individually consistent directions. Carbon stable isotope ratios in gannet blood tissues were repeatable within years and nitrogen ratios were also repeatable across years, suggesting long-term individual dietary specialization. Individuals were also consistent across years in habitat use with respect to relative sea surface temperature and in some dive metrics, yet none of these factors accounted for IFSF. Moreover, at the scale of weeks, IFSF did not decay over time and the magnitude of IFSF across years was similar to that within years, suggesting that IFSF is not primarily the result of win--stay, lose--shift foraging. Rather, we hypothesize that site familiarity, accrued early in life, causes IFSF by canalizing subsequent foraging decisions. Evidence from this and other studies suggests that IFSF may be common in colonial central-place foragers, with farreaching consequences for our attempts to understand and conserve these animals in a rapidly changing environment. [ABSTRACT FROM AUTHOR]

The major factors explaining ecological variation in plants have been widely discussed over the last decade thanks to numerous studies that have examined the covariation that exists between pairs of traits. However, multivariate relationships among traits remain poorly characterized in animals. In this study, we aimed to identify the main multivariate trait dimensions that explain variance in important functional traits related to resource exploitation in ants. To this end, we created a large ant trait database. This database includes information on 11 traits that are important in ant resource exploitation; data were obtained for 150 European species found in different biomes. First, we examined the pairwise correlations between the traits included in the database. Second, we used multivariate analyses to identify potential trait dimensions. Our study shows that, to a great extent, resource exploitation strategies align along two main trait dimensions. The first dimension emerged in both the overall and group-specific analyses, where it accounted for the same pairwise trait correlations. The second dimension was more variable, as species were grouped by levels of taxonomy, habitat, and climate. These two dimensions included most of the significant pairwise trait correlations, thus highlighting that complementarity, but also redundancy, exists among different pairs of traits. The first dimension was associated with behavioral dominance: dominance was associated with large colony size, presence of multiple nests per colony, worker polymorphism, and a collective foraging strategy. The second dimension was associated with resource partitioning along dietary and microhabitat lines: it ranged from species that consume liquid foods, engage in group foraging, and mainly nest in the vegetation to species that consume insects and seeds, engage in individual foraging, and demonstrate strictly diurnal activity. Our findings establish a proficient ecological trait-based animal research that minimizes the number of traits to be measured while maximizing the number of relevant trait dimensions. Overall, resource exploitation in animals might be framed by behavioral dominance, foraging strategy, diet, and nesting habitat; the position of animal species within this trait space could provide relevant information about their distribution and abundance, for today as well as under future global change scenarios. [ABSTRACT FROM AUTHOR]

Large-mammal herbivore populations are subject to the interaction of internal density-dependent processes and external environmental stochasticity. We disentangle these processes by linking consumer population dynamics, in a highly stochastic environment, to the availability of their key forage resource via effects on body condition and subsequent fecundity and mortality rates. Body condition and demographic rate data were obtained by monitoring 500 tagged female goats in the Richtersveld National Park, South Africa, over a three-year period. Identifying the key resource and pathway to density dependence for a population allows environmental stochasticity to be partitioned into that which has strong feedbacks to population stability, and that which does not. Our data reveal a densitydependent seasonal decline in goat body condition in response to concomitant densitydependent depletion of the dry-season forage resource. The loss in body condition reduced density-dependent pregnancy rates, litter sizes, and pre-weaning survival. Survival was lowest following the most severe dry season and for juveniles. Adult survival in the late-dry season depended on body condition in the mid-dry season. Population growth was determined by the length of the dry season and the population size in the previous year. The RNP goat population is thereby dynamically coupled primarily to its dry-season forage resource. Extreme environmental variability thus does not decouple consumer resource dynamics, in contrast to the views of nonequilibrium protagonists. [ABSTRACT FROM AUTHOR]

Ecological stoichiometry (ES) uses elemental ratios and mass balance to explain organismal growth, an important parameter in ecological systems. In this study, we tested quantitative predictions of the ES ''minimal model'' for the growth rates of two tadpole species (wood frogs, Lithobates sylvaticus and American toads, Anaxyrus americanus), by manipulating light and the quality of a leaf litter mixture in a seminatural mesocosm experiment. We predicted that wood frogs, which consume leaf litter as a resource, would respond more strongly to leaf litter quality than toads, which forage on periphyton and algae. The ES minimal model, parameterized from literature values, provided strikingly accurate quantitative predictions of nonlinear wood frog growth patterns across gradients of leaf litter quality, both in this experiment and when applied to previously published data on wood frog growth responses to various leaf litter species. In contrast, toad growth was best explained by the biomass of periphyton, which was driven primarily by light availability and only indirectly influenced by litter-derived soluble polyphenols. This study demonstrates the power of ES to predict organism growth rates, and highlights potential applications of this theory to predicting population- and communitylevel responses to changing forest environments. [ABSTRACT FROM AUTHOR]

Predation risk can strongly influence community dynamics through its effects on prey foraging decisions that often involve habitat shifts (i.e., from risky to refuge habitats). Although the within-generation effects of risk on prey are well appreciated, the effects of parental experience with risk on offspring decision-making and growth are poorly understood. The capacity of parents to prepare their offspring for potential risk exposure may be adaptive when the likelihood of eventual risk exposure is high and be instrumental in shaping how offspring allocate their foraging effort and habitat use. Using a simple rocky intertidal food chain, we examined the influence of parental exposure to predator risk cues on the behavior, foraging, and tissue maintenance of offspring exposed to the presence and absence of risk. We found that offspring of risk-experienced parents were bolder. When confronted with risk, these offspring spent more time out of refuge habitat, foraged more, and maintained more tissue than offspring of risk-free parents. Thus, parental experience with risk was most important when offspring were exposed to risk. These results suggest that the effects of parental experience with predation risk on offspring traits strongly shape the transmission of risk effects in ecological communities. [ABSTRACT FROM AUTHOR]

Across animal taxa, migration allows individuals to exploit habitats and resources that predictably vary seasonally in suitability. Theory predicts that the ''decision'' to migrate or not is shaped by the relative fitness costs and benefits of exhibiting a given life history. Adoption of a migratory strategy is widely thought to reflect a dichotomous outcome; individuals are either resident or migratory, and continue to exhibit this life history until death. In fishes, anadromy and freshwater residency represents a well-studied life history dichotomy. Resident individuals may adopt a migratory life history later in life, but migratory individuals are not known to abandon this pattern. Here, we investigated the fitness benefits, as measured by body size, of residency and anadromy in a salmonid fish, Dolly Varden, Salvelinus malma, in Alaska, and reveal a novel life history: cessation of migration by older, larger individuals. Otolith microchemical analysis of Dolly Varden showed that while most fish migrated to sea at least once in their lives, lifelong resident fish exist in streams with close proximity to the ocean. Moreover, the probability of seaward migration in any year of life decreased annually after an individual's fourth year, and no fish migrated after their eighth year, while the oldest fish were captured in their 11th year. Migration conferred a size advantage in young fish, but the size benefits of marine foraging declined in older fish, at which time fish increasingly ''retired from anadromy.'' Additionally, measurement of both natal otolith chemistry and the gonadosomatic index indicated a continued contribution to lifetime fitness, rather than senescence, in retired individuals. We suggest that the novel life history of reversion to residency by older fish is viable because foraging opportunities are subsidized by the predictable annual supply of energy-rich eggs and carcasses of spawning Pacific salmon. [ABSTRACT FROM AUTHOR]

Selective predation can lead to natural selection in prey populations and may alleviate competition among surviving individuals. The processes of selection and competition can have substantial effects on prey population dynamics, but are rarely studied simultaneously. Moreover, field studies of predator-induced short-term selection pressures on prey populations are scarce. Here we report measurements of density dependence in body composition in a bivalve prey (edible cockle, Cerastoderma edule) during bouts of intense predation by an avian predator (Red Knot, Calidris canutus). We measured densities, patchiness, morphology, and body composition (shell and flesh mass) of cockles in a quasiexperimental setting, i.e., before and after predation in three similar plots of 1 ha each, two of which experienced predation, and one of which remained unvisited in the course of the short study period and served as a reference. An individual's shell and flesh mass declined with cockle density (negative density dependence). Before predation, cockles were patchily distributed. After predation, during which densities were reduced by 78% (from 232 to 50 cockles/m²), the patchiness was substantially reduced, i.e., the spatial distribution was homogenized. Red Knots selected juvenile cockles with an average length of 6.9 6 1.0 mm (mean 6 SD). Cockles surviving predation had heavier shells than before predation (an increase of 21.5 percentage points), but similar flesh masses. By contrast, in the reference plot shell mass did not differ statistically between initial and final sampling occasions, while flesh mass was larger (an increase of 13.2 percentage points). In this field study, we show that Red Knots imposed a strong selection pressure on cockles to grow fast with thick shells and little flesh mass, with selection gradients among the highest reported in the literature. [ABSTRACT FROM AUTHOR]