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Changes to the community ecology of hosts for zoonotic pathogens, particularly rodents, are likely to influence the emergence and prevalence of zoonotic diseases worldwide. However, the complex interactions between abiotic factors, pathogens, vectors, hosts, and both food resources and predators of hosts are difficult to disentangle. Here we (1) use 19 yr of data from six large field plots in southeastern New York to compare the effects of hypothesized drivers of interannual variation in Lyme disease risk, including the abundance of acorns, rodents, and deer, as well as a series of climate variables; and (2) employ landscape epidemiology to explore how variation in predator community structure and forest cover influences spatial variation in the infection prevalence of ticks for the Lyme disease bacterium, Borrelia burgdorferi, and two other important tick-borne pathogens, Anaplasma phagocytophilum and Babesia microti. Acorn-driven increases in the abundance of mice were correlated with a lagged increase in the abundance of questing nymph-stage Ixodes scapularis ticks infected with Lyme disease bacteria. Abundance of white-tailed deer 2 yr prior also correlated with increased density of infected nymphal ticks, although the effect was weak. Density of rodents in the current year was a strong negative predictor of nymph density, apparently because high current abundance of these hosts can remove nymphs from the host-seeking population. Warm, dry spring or winter weather was associated with reduced density of infected nymphs. At the landscape scale, the presence of functionally diverse predator communities or of bobcats, the only obligate carnivore, was associated with reduced infection prevalence of I. scapularis nymphs with all three zoonotic pathogens. In the case of Lyme disease, infection prevalence increased where coyotes were present but smaller predators were displaced or otherwise absent. For all pathogens, infection prevalence was lowest when forest cover within a 1 km radius was high. Taken together, our results suggest that a food web perspective including bottom-up and top-down forcing is needed to understand drivers of tick-borne disease risk, a result that may also apply to other rodent-borne zoonoses. Prevention of exposure based on ecological indicators of heightened risk should help protect public health.

Lakes and ponds harbour a high number of diverse planktonic microorganisms that are centrally involved in biochemical cycles and aquatic food webs. Although the open water body (pelagial) seems to be a uniform and unstructured environment, ecological niche separation of coexisting microbial taxa might be triggered by limiting resources (bottom-up control) and mortality factors (top-down control), leading to distinct spatial and temporal distribution patterns of different microbes. This review gives an overview of the most abundant prokaryotic populations by grouping them in specific ecological guilds based on their life strategies. Defense specialists such as very small Actinobacteria or big filamentous bacteria mostly occur at times of highest grazing pressure by heterotrophic nanoflagellates, the main consumers of bacteria. Oligotrophic ultramicrobacteria, on the other hand, seem to be mostly adapted to nutrient depleted water layers during summer stratification, while opportunistic bacteria profit from material released during short-living algal blooms. Seasonal changes in abiotic and biotic factors may be the main causes for periodic reoccurring density maxima of different prokaryotes populations in the pelagial of temperate lakes, reflected in a distinct seasonality of the freshwater bacterioplankton.

Theory on intraguild killing (IGK) is central to mammalian carnivore community ecology and top-down ecosystem regulation. Yet, the cryptic nature of IGK hinders empirical evaluations. Using a novel data source – online photographs of interspecific aggression between African carnivores – we revisited existing predictions about the extent and drivers of IGK. Compared with seminal reviews, our constructed IGK network yielded 10 more species and nearly twice as many interactions. The extent of interactions increased 37% when considering intraguild aggression (direct attack) as a precursor of killing events. We show that IGKoccurs over a wider range of body-mass ratios than predicted by standing competition-based views, with highly asymmetrical interactions being pervasive. Evidence that large species, particularly hypercarnivore felids, target sympatric carnivores with a wide range of body sizes suggests that current IGK theory is incomplete, underestimating alternative competition pathways and the role of predatory and incidental killing. Our findings reinforce the potential for IGK-mediated cascades in species-rich assemblages and community-wide suppressive effects of large carnivores.

Feature-based attention (FBA) enhances the representation of image characteristics throughout the visual field, a mechanism that is particularly useful when searching for a specific stimulus feature. Even though most theories of visual search implicitly or explicitly assume that FBA is under top-down control, we argue that the role of top-down processing in FBA may be limited. Our review of the literature indicates that all behavioural and neuro-imaging studies investigating FBA suffer from the shortcoming that they cannot rule out an effect of priming. The mere attending to a feature enhances the mandatory processing of that feature across the visual field, an effect that is likely to occur in an automatic, bottom-up way. Studies that have investigated the feasibility of FBA by means of cueing paradigms suggest that the role of top-down processing in FBA is limited (e.g. prepare for red). Instead, the actual processing of the stimulus is needed to cause the mandatory tuning of responses throughout the visual field. We conclude that it is likely that all FBA effects reported previously are the result of bottom-up priming.

Predators exert a strong influence on ecological communities by reducing the abundance of prey (consumptive effects) and shaping their foraging behavior (non-consumptive effects). Although the prevalence of trophic cascades triggered by non-consumptive effects is increasingly recognized in a wide range of ecosystems, how its relative strength changes as prey individuals grow in size along various life stages remains poorly resolved. We investigated how the effects of predators vary with the ontogeny of a key herbivorous sea urchin, which is responsible for transforming diverse macroalgal forests to a barren state dominated by bare rock and encrusting coralline algae. We conducted a series of field and laboratory experiments to determine how susceptibility to predation, prey behavioral responses, and grazing impact on algal cover vary with sea urchin size. The consumptive effects of predators were greater on smaller sea urchin size classes, which were more susceptible to predation. Unexpectedly however, predator non-consumptive effects acted only on larger sea urchins, significantly reducing their grazing activity in the presence of predator cues. Crucially, only these larger sea urchins were capable of overgrazing macroalgae in the field, with non-consumptive effects reducing sea urchin foraging activity and macroalgal grazing impact by 60%. The decoupling between risk and fear as prey grow indicates that the strength of consumptive and non-consumptive trophic cascades may act differently at different ontogenetic stages of prey. While the consumptive effects of predators directly influence population numbers, the consequences of non-consumptive effects may far outlive consumptive effects as prey grow, finding refuge in size, but not from fear.

The impact of grazing pressure on ammonia oxidizers (AO) has never been quantified in the field. Here we develop a new method to quantify the grazing rates on AO in aquatic systems. We introduce 15NH4+ tracer into the traditional dilution experiments to measure AO's apparent growth rates by using the end‐product of 15NH4+ oxidation, that is, 15NOx−. Field studies in the North Pacific revealed that 15NOx− in the end‐product was sensitive enough to detect AO's grazing rates. Experiments from the lower euphotic zone showed NH4+ replete growth rates of 0.40 d−1 and 0.77 d−1 of AO and in situ grazing rates on AO of 0.41 d−1 and 0.45 d−1, respectively, indicating a strong top‐down control by grazing on AO. Compiled data show a vertical decoupling between ammonia oxidation rates and AO abundance within the euphotic zone, indicating that strong grazing may have affected the distribution of AO in the global ocean. Plain Language Summary Grazing by zooplankton exerts important control on microbes in the aquatic systems. Ammonia oxidizers (AO) are chemoautotrophic microorganisms that utilize most of their substrate as a source of energy rather than biomass (low biomass yield but high transformation efficiency) and mediate nitrification, a critical process in biogeochemical cycles. Due to the technical difficulty of differentiating AO from other microbes and calculating their change in abundance, the influence of grazing on the AO population in the field has never been quantified. Here we develop a new method that introduces a highly sensitive isotope‐tracing technique into traditional dilution experiments to focus on functional chemoautotrophic AO and quantify their NH4+‐replete growth rates and rates of grazing on them. We found our method to be effective, and for the first time, we revealed that grazing induced a strong top‐down control on AO at the base of the euphotic zone in the North Pacific Ocean. This influence could also be the reason for the vertical decoupling of the ammonia oxidation rate and AO abundance globally. We therefore suggest a wider exploration of grazing influence on AO in field experiments for a deeper understanding of the role of grazing in the marine nitrogen cycle. Key Points A method that introduced 15NH4+ isotope tracers into dilution experiments is developed to quantify the grazing rate on ammonia oxidizers Field experiments showed that grazing consumed more than half of ammonia oxidizer daily growth at the base of the euphotic zone in the North Pacific The strong top‐down control may be widespread to shape the distributions of ammonia oxidizers in the global ocean

Defenses that target particular consumers often influence community organization, ecosystem function, and diversity maintenance. In coral reef, mangrove, and seagrass ecosystems, sponges affect substratum stability, water clarity, diversity of associated species, and survival of habitat-providing organisms, key roles not duplicated by other organisms. Whether and how predators control sponges are much disputed. Substantial ecosystem consequences of losing or gaining sponges motivated definitive experiments on how predators control sponge distribution and abundance. Caribbean sponges of 94 species representing 13 taxonomic orders and three linked habitats (coral reefs, mangroves, and seagrass meadows) were exposed to seven predator species representing different habitats and degrees of spongivory in 4,493 in situ trials. The resulting data force reassessment of popular interpretations of several patterns and processes. Contrary to extract pellet assays that declare most sponges deterrent, 78% of these 94 species were eaten by at least one predator. But \"palatability\" is consumer dependent: a sponge species eaten by one predator can be rejected by other predators, and predator species differed in what sponges they ate in 55.4% (214/392) of pairwise comparisons between predators. Because spongivore species are usually restricted to particular habitats, they impose abrupt boundaries on sponges' habitat distributions, reflecting inverse relationships between accessibility and palatability to each predator. Thus a seagrass-dwelling starfish eats only 9% of seagrass sponge species, but 70% of coral reef species, and 78% of mangrove species. Reef-dwelling angelfishes completely consume only 13% of reef species, but 29% of seagrass species, and 63% of mangrove species. Defenses that target specific predators reveal that spongivore influence on community organization cannot be inferred from extract pellet/omnivore assays that assume defenses target all predators equally. In fact, pellet data wrongly predicted actual consumption of living sponges of that pellet's species in 43% of field experiments with spongivores. In contrast with herbivore–plant interactions, opportunistic spongivory is at least as important as routine spongivory for community organization and ecosystem function. Potential for loss of key functional roles of sponges, if opportunistic predators gain access to sponge species that lack defenses against them, must inform conservation plans for coral reef, mangrove, and seagrass ecosystems.

Forest loss threatens biodiversity, but its potential effects on multitrophic ecological interactions are poorly understood. Insect herbivory depends on complex bottomup (e.g., resource availability and plant antiherbivore defenses) and top-down forces (e.g., abundance of predators and herbivorous), but its determinants in human-altered tropical landscapes are largely unknown. Using structural equation models, we assessed the direct and indirect effects of forest loss on insect herbivory in 40 landscapes (115 ha each) from two regions with contrasting land-use change trajectories in the Brazilian Atlantic rainforest. We considered landscape forest cover as an exogenous predictor and (1) forest structure, (2) abundance of predators (birds and arthropods), and (3) abundance of herbivorous arthropods as endogenous predictors of insect leaf damage. From 12 predicted pathways, 11 were significant and showed that (1) leaf damage increases with forest loss (direct effect); (2) leaf damage increases with forest loss . through the simplification of vegetation structure and its associated dominance of herbivorous insects (indirect effect); and further demonstrate (3) a lack of top-down control of herbivores by predators (birds and arthropods). We conclude that forest loss favors insect herbivory by undermining the bottom-up control (presumably reduced plant antiherbivore defense mechanisms) in forests dominated by fast-growing pioneer plant species, and by improving the conditions required for herbivores proliferation.

1. There is a growing theoretical basis for the role of predation risk as a driver of trophic interactions, conceptualized as the 'ecology of fear'. However, current ungulate management ignores the role of nonlethal risk effects of predation. 2. We introduce the concept of 'hunting for fear' as an extension of the more classical 'hunting to kill' that is typically used in large herbivore management. Hunting for fear aims to induce a behavioural response in ungulates, for example, as a way of diverting them from areas where their impact is undesired. 3. Synthesis and applications. Hunting for fear asks for novel, potentially controversial, ways of hunting to induce strong enough risk effects, including more hunting on foot and with dogs, extended hunting seasons (ideally year-round) and increased hunting of calves. Hunting for fear may offer novel opportunities to help manage the growing human–wildlife conflicts that we experience globally.

Understanding the mechanisms contributing to positive relationships between predator diversity and natural pest control is fundamental to inform more effective management practices to support sustainable crop production. Predator body size can provide important insights to better understand and predict such predator-pest interactions. Yet, most studies exploring the link between predator body size and pest control have been conducted in species-poor communities under controlled environmental conditions, limiting our ability to generalize this relationship across heterogeneous landscapes. Using the community of naturally occurring ground beetles in cabbage fields, we examined how landscape composition (percent cropland) influences the size structure (mean, variance, and skewness of body size distribution) of predator communities and the subsequent effects on pest control. We found that predator communities shifted their size distribution toward larger body sizes in agriculturally dominated landscapes. This pattern arose from increasing numerical dominance of a few large-bodied species rather than an aggregated response across the community. Such landscape-driven changes in community size structure led to concomitant impacts on pest control, as the mean body size of predators was positively related to predation rates. Notably, the magnitude of pest control depended not only on the size of the dominant predators but was also strongly determined by the relative proportion of small vs. large-bodied species (i.e., skewness). Predation rates were higher in predator assemblages with even representation of small and large-bodied species relative to communities dominated by either large or small-bodied predators. Landscape composition may therefore modulate the relationship between predator body size and pest control by influencing the body size distribution of co-occurring species. Our study highlights the need to consider agricultural practices that not only boost effective predators, but also sustain a predator assemblage with a diverse set of traits to maximize overall pest control.