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1. Globally, large carnivores are declining due to direct persecution, habitat loss, and prey depletion. The effects of prey depletion could be amplified by changes in the composition of the herbivore (prey) community that provoke changes in carnivore diets, but this possibility has received little attention. 2. We tested for changes over the past half-century in prey selection by the large carnivore guild in Zambia's Kafue National Park (KNP). 3. Across 52 predator-prey dyads, 71% of the observed changes showed that large prey have become less important and small prey have become more important. Consequently, dietary niche breadth has decreased for KNP carnivores and niche overlap has increased. 4. We tested whether changes in the importance of prey species are related to their current abundance and uniformly found that prey that have increased in importance are now relatively common, while those that have decreased in importance are now relatively rare. We identify four potential effects of these changes for conservation (through intraguild competition, group size, the energetics of hunting, and vulnerability to snaring) that warrant investigation. 5. Synthesis and applications. Patterns of prey selection by the large carnivores in Kafue National Park (KNP) have changed appreciably over the past half-century. Decreased predation on large prey, which are now relatively rare, has caused niche compression and increased overlap in carnivore diets. Predation by all KNP large carnivores now concentrates on four small prey species that remain relatively abundant (impala, puku, lechwe, and warthog). Methods to detect such changes in interactions between species are well-established, but are rarely applied to large carnivore-ungulate systems. To guide conservation of ecosystem function, monitoring programmes should consider whether prey depletion alters the patterns of predation or competition within the predator guild because these interactions strongly affect the distribution and abundance of both predators and prey. If the patterns seen in KNP are general, then where carnivores are limited by prey depletion, conservation efforts will be most effective if they focus on mitigating the loss of large prey. In KNP, targeted efforts to protect prey larger than 200 kg, particularly buffalo, should be a priority.

Smaller predators may overcome body size restrictions on their prey base by selecting for juveniles of larger prey species. However, traditional prey selection models ignore demographic classes within prey species. We refined these models for two predators with contrasting body sizes and hunting strategies, by including seasonal consumption and availability of prey demographic classes. We predicted that cheetahs would select for smaller neonate and juvenile prey especially of larger species, while lions would select for larger, adult prey. We further predicted seasonal diet shifts in cheetah, but not lion. We recorded species-specific demographic class prey use (kills) via direct observation and GPS cluster of cheetahs and lions fitted with GPS collars. Species-specific demographic class prey availability was estimated from monthly driven transects, and species-specific demographic class prey preferences were estimated. The availability of prey demographic classes varied seasonally. Cheetahs preferred neonates, juveniles, and sub-adults during the wet season, but adults and juveniles during the dry season. Lions preferred adult prey irrespective of season, with sub-adults, juveniles, and neonates killed relative to their abundance. This confirms that traditional prey preference models do not adequately account for demographic-specific prey preference. This is particularly important for smaller predators, like cheetahs, that focus on smaller prey but can expand their prey base by killing juveniles of larger species. For these smaller predators, prey availability will vary strongly seasonally, making them more vulnerable to processes that influence prey reproduction, like global change.

Top carnivores play an important role in maintaining energy flow and functioning of the ecosystem, and a clear understanding of their diets and foraging strategies is essential for developing effective conservation strategies. In this paper, we compared diets and prey selection of snow leopards and wolves based on analyses of genotyped scats (snow leopards n = 182, wolves n = 57), collected within 26 sampling grid cells (5×5 km) that were distributed across a vast landscape of ca 5000 km2 in the Central Himalayas, Nepal. Within the grid cells, we sampled prey abundances using the double observer method. We found that interspecific differences in diet composition and prey selection reflected their respective habitat preferences, i.e. snow leopards significantly preferred cliff-dwelling wild ungulates (mainly bharal, 57% of identified material in scat samples), whereas wolves preferred typically plain-dwellers (Tibetan gazelle, kiang and argali, 31%). Livestock was consumed less frequently than their proportional availability by both predators (snow leopard = 27%; wolf = 24%), but significant avoidance was only detected among snow leopards. Among livestock species, snow leopards significantly preferred horses and goats, avoided yaks, and used sheep as available. We identified factors influencing diet composition using Generalized Linear Mixed Models. Wolves showed seasonal differences in the occurrence of small mammals/birds, probably due to the winter hibernation of an important prey, marmots. For snow leopard, occurrence of both wild ungulates and livestock in scats depended on sex and latitude. Wild ungulates occurrence increased while livestock decreased from south to north, probably due to a latitudinal gradient in prey availability. Livestock occurred more frequently in scats from male snow leopards (males: 47%, females: 21%), and wild ungulates more frequently in scats from females (males: 48%, females: 70%). The sexual difference agrees with previous telemetry studies on snow leopards and other large carnivores, and may reflect a high-risk high-gain strategy among males.

1. Artificial night-lighting threatens to disrupt strongly conserved light-dependent processes in animals and may have cascading effects on ecosystems as species interactions become altered. Insectivorous bats and their prey have been involved in a nocturnal, coevolutionary arms race for millions of years. Lights may interfere with anti-bat defensive behaviours in moths, and disrupt a complex and globally ubiquitous interaction between bats and insects, ultimately leading to detrimental consequences for ecosystems on a global scale. 2. We combined experimental and mathematical approaches to determine effects of light pollution on a free-living bat–insect community. We compared prey selection by Cape serotine bats Neoromicia capensis in naturally unlit and artificially lit conditions using a manipulative field experiment, and developed a probabilistic model based on a suite of prey-selection factors to explain differences in observed diet. 3. Moth consumption by N. capensis was low under unlit conditions (mean percentage volume ± SD: 5.91 ± 6.25%), while moth consumption increased six-fold (mean percentage volume ± SD: 35.42 ± 17.90%) under lit conditions despite a decrease in relative moth abundance. Predictive prey-selection models which included high-efficacy estimates for eared-moth defensive behaviour found most support given diet data for bats in unlit conditions. Conversely, models which estimated eared-moth defensive behaviour as absent or low, found more support given diet data for bats in lit conditions. Our models therefore suggest the increase in moth consumption was a result of light-induced, decreased eared-moth defensive behaviour. 4. Policy implications. In the current context of unyielding growth in global light pollution, we predict that specialist moth-eating bats and eared-moths will face ever-increasing challenges to survival through increased resource competition and predation risk, respectively. Lights should be developed to be less attractive to moths, with the goal of reducing effects on moth behaviour. Unfortunately, market preference for broad-spectrum lighting and possible effects on other taxa make development of moth-friendly lighting improbable. Mitigation should therefore focus on the reduction of temporal, spatial, and luminance redundancy in outdoor lighting. Restriction of light inside nature reserves and urban greenbelts can serve as dark refugia for moth-eating bats and moths, and may become important for their persistence.

Entomopathogenic fungi are sprayed commercially for aphid control in greenhouses. Recently, their ability to grow endophytically within plants was discovered, offering the opportunity for systemic biological control. Endophytic colonization of host plants could also influence life-table parameters and behavior of herbivores. We investigated lethal and pre-mortality effects of Beauveria bassiana and Metarhizium brunneum on Aphis gossypii; aphids either received inoculum while feeding on recently sprayed leaves (surface inoculum and endophytically-colonized) or while feeding on unsprayed but endophytically-colonized leaves. We used choice assays to identify any preferences for endophytically-colonized or control plants. Volatile emissions from endophytically-colonized plants and control plants were also compared. Aphid mortality rates ranged between 48.2 and 56.9% on sprayed leaves, and between 37.7 and 50.0 on endophytically-colonized leaves. There was a significant effect of endophytic colonization on the rate of nymph production, but this did not result in an overall increase in the aphid population. Endophytic colonization did not influence host-plant selection even though there were qualitative and quantitative differences in the blend of volatiles released by endophytically-colonized and control plants. Although endophytic colonization did not change herbivore behavior, plants still benefit via indirect defense, resistance to plant pathogens or abiotic stress tolerance.

Aerial insectivores are highly mobile predators that feed on diverse prey items that have highly variable distributions. As such, investigating the diet, prey selection and prey availability of aerial insectivores can be challenging. In this study, we used an integrated DNA barcoding method to investigate the diet and food supply of Barn Swallows, an aerial insectivore whose North American population has declined over the past 40 yr. We tested the hypotheses that Barn Swallows are generalist insectivores when provisioning their young and select prey based on size. We predicted that the diets of nestlings would contain a range of insect taxa but would be biased towards large prey items and that the diet of nestlings would change as prey availability changed. We collected insects using Malaise traps at 10 breeding sites and identified specimens using standard DNA barcoding. The sequences from these insect specimens were used to create a custom reference database of prey species and their relative sizes for our study area. We identified insect prey items from nestling fecal samples by using high-throughput DNA sequencing and comparing the sequences to our custom reference database. Barn Swallows fed nestlings prey items from 130 families representing 13 orders but showed selection for larger prey items that were predominantly from 7 dipteran families. Nestling diet varied both within and between breeding seasons as well as between breeding sites. This dietary flexibility suggests that Barn Swallows are able to adjust their provisioning to changing prey availability on the breeding grounds when feeding their nestlings. Our study demonstrates the utility of custom reference databases for linking the abundance and size of insect prey in the habitat with prey consumed when employing molecular methods for dietary analysis.

Deciding which options to engage, and which to forego, requires developing accurate beliefs about the overall distribution of prospects. Here we adapt a classic prey selection task from foraging theory to examine how individuals keep track of an environment’s reward rate and adjust choices in response to its fluctuations. Preference shifts were most pronounced when the environment improved compared to when it deteriorated. This is best explained by a trial-by-trial learning model in which participants estimate the reward rate with upward vs. downward changes controlled by separate learning rates. A failure to adjust expectations sufficiently when an environment becomes worse leads to suboptimal choices: options that are valuable given the environmental conditions are rejected in the false expectation that better options will materialize. These findings offer a previously unappreciated parallel in the serial choice setting of observations of asymmetric updating and resulting biased (often overoptimistic) estimates in other domains. In some types of decision-making, people must accept or forego an option without knowing what prospects might later be available. Here, the authors reveal how a key bias– asymmetric learning from negative versus positive outcomes – emerges in this type of decision.

Knowledge of the foraging ecology of fishes is fundamental both to understanding the processes that function at the individual, population and community levels, and for the management and conservation of their populations and habitats. Furthermore, the factors that influence the acquisition and assimilation of food can have significant consequences for the condition, growth, survival and recruitment of fishes. The majority of marine and freshwater fish species are planktivorous at the onset of exogenous nutrition and have a limited ability to detect, capture, ingest and digest prey. Improvements in vision, development of fins and associated improvements in swimming performance, increases in gape size and development of the alimentary tract during ontogeny often lead to shifts in diet composition. Prey size, morphology, behaviour and abundance can all influence the prey selection of larval and juvenile fishes. Differences in feeding behaviour between fish species, individuals or during ontogeny can also be important, as can inter- and intraspecific interactions (competition, predation risk). Temporal (diel, seasonal, annual) and spatial (microhabitat, mesohabitat, macrohabitat, regional) variations in prey availability can have important implications for the prey selection, diet composition, growth, survival, condition and, ultimately, recruitment success of fishes. For fish populations to persist, habitat must be available in sufficient quality and quantity for the range of activities undertaken during all periods of development. Habitats that enhance the diversity, size ranges and abundance of zooplankton should ensure that sufficient food resources are available to larval and juvenile fishes.

The wolf is a generalist-opportunistic predator that displays diverse and remarkably adaptable feeding strategies across its range with local adaptations to certain prey species depending on their availability and vulnerability. The multi-prey system of the Slovak Carpathians supports important portion of the European wolf population; however, it has been markedly understudied. We evaluated winter diet composition and prey selection of Slovak wolves based on 321 scat samples collected between September–April within four different study areas during 2015–2017. The winter diet of wolves in the Slovak Carpathians was characterized by a 98% occurrence of wild large-sized and medium-sized ungulates with red deer occurring in wolf scats most often, consistent with their highest density among other wild ungulates. However, by comparing the consumption with availability of wild prey, we found that wolves in fact selected for wild boar especially in areas with higher altitudinal range, while selected for red deer in areas with low altitudinal range where this prey species was more spatially predictable. Although wolves showed the potential to switch between red deer and wild boar when their density increases, we found that this variation can be rather linked to changing prey vulnerability, which is dependent on particular environmental conditions at local scale such as topography and snow accumulation. The present study provides valuable insights into the winter foraging ecology of Slovak wolves in a multi-prey system of the Carpathians and allows for practical implications in the management of the rapidly increasing populations of wild ungulates across Europe.

Small pelagic fish (SPF) play a vital role in marine ecosystems, transferring energy from plankton to higher trophic levels. However, SPF dynamics in shallow coastal areas are often under-studied, despite their importance as crucial prey near breeding sites of fish-eating birds such as common terns ( Sterna hirundo ). This study had two connected objectives: to map the pelagic fish food landscape in the inlets of the Dutch Wadden Sea and to describe its use by common terns. Two hydro-acoustic fish surveys were conducted in May and October 2022, while tern distribution was assessed using aerial counts and GPS tracking. Prey selection was analyzed through camera traps and DNA analysis of faeces. Herring and sprat were the predominant species in the SPF community, with sandeel also abundant in May. Smelt was most common in freshwater-influenced areas. Most fish were below 12 cm, fitting the preferred size range for common terns. SPF energy density ranged from 20.1 to 22.1 kJ/g dry weight, with sprat having the highest values. SPF biomass showed significant spatiotemporal variability across transects, inlets, and seasons. Common terns foraged frequently around the gullies, feeding mostly on herring. A significant correlation was found between fish biomass and common tern density, indicating food landscape may be a good predictor of tern distribution and vice versa. This study presents the first integrated biomass estimates of SPF in the subtidal areas of Dutch Wadden Sea for both spring and autumn, providing essential data for future energy budget models and management strategies.