Predator Diet Research Articles

Accumulation of chemical elements and occurrence of microplastics in small pelagic fish from a neritic environment

The assessment of contaminant exposure in marine organisms often focuses on the most toxic chemical elements from upper trophic level species. Information on mid-trophic level species and particularly on potentially less harmful elements is lacking. Additionally, microplastics have been considered emergent contaminants in aquatic environments which have not been extensively studied in species from mid-trophic levels in food chains. This study aims to contribute to an overall assessment of environmental impacts of such chemicals in a community of small pelagic fish in the North Atlantic. The concentrations of 16 chemical elements, rarely simultaneously quantified (including minerals, trace elements and heavy metals), and the presence of microplastics were analysed in sardines (Sardina pilchardus) and mackerels (Scomber spp. and Trachurus trachurus) sampled along the Portuguese coast. Biochemical stress assessments and stable isotope analyses were also performed. The chemical element concentrations in S. pilchardus, T. trachurus, and Scomber spp. were relatively low and lower than the levels reported for the same species in the North Atlantic and adjacent areas. No clear relationships were found between chemical elements and oxidative damage in fish. However, the concentration of several chemical elements showed differences among species, being related with the species’ habitat use, trophic niches, and specific feeding strategies. The presence of plastic pieces in the stomachs of 29% of the sampled fishes is particularly concerning, as these small pelagic fish from mid-trophic levels compose a significant part of the diet of humans and other top predators. This study highlights the importance of multidisciplinary approaches focusing on the individual, including position data, stable isotopes, and oxidative stress biomarkers as complementary tools in contamination assessment of the marine mid-trophic levels in food chains.

Assessing the reliability of raptor pellets in recording local small mammal diversity

AbstractUnderstanding how raptors select prey is important to determine taphonomic biases both in modern and paleo pellet assemblages. We tested whether pellets more closely represent raptor dietary specialization or local small mammal diversity by sampling pellets from seven raptor species across four study sites in Yellowstone National Park, Wyoming, USA. We identified small mammal craniodental elements from each pellet and tested for differences among small mammal assemblages for each raptor species and study site. We found that reconstructed avian predator diets clustered significantly by site but not by predator species. Bray-Curtis diet dissimilarities were also significantly lower when comparing different raptor species within a site than when comparing the same raptor species across different sites. Our results suggest that raptors choose to eat a diversity of small mammal species close to their roosts rather than fly long distances to specialize on a particular prey species. Neontologists and paleoecologists alike can therefore be confident that raptor pellets faithfully represent local small mammal diversity.

Trophodynamics of the jumbo squid Dosidicus gigas during winter in the Southeast Pacific Ocean off the coast of Chile: Diet analyses and fatty acid profile

Marine trophodynamic studies have been developed mainly through the evaluation of stomach contents. However, these studies only reflect the feeding of a few days, showing a "snapshot" of the food consumed for a short time. Currently, new complementary techniques have been developed to evaluate the diet of predators using biochemical markers (fatty acids, FAs) and can, in turn, consider the rate of renewal of these biochemical constituents in body tissues. In the jumbo squid Dosidicus gigas, an important fishery resource in the Humboldt Current System, we identified and analyzed the stomach contents (prey) of D. gigas collected along the coasts of Chile in order to compare the FA profiles of its prey with those of three of its principal tissues and/or organs (digestive gland, gonad and mantle muscle). The analyses of the stomach contents indicate that D. gigas feeds on fish, crustaceans and squids, as previously have been reported. Regarding the FAs, the digestive gland presented the highest concentration and diversity of FAs, followed by the gonad and then the mantle. In turn, when comparing the FAs of the digestive gland of D. gigas with the FA profiles of its preys, the crustacean Pleuroncodes monodon and the fish Lampanyctus sp. presented the closest similarity, especially with a high contribution of essential FAs and PUFAs. Our findings indicate that during the cold season (austral winter), individuals of D. gigas may present an energy optimization strategy, characterized by the intake of prey with a high energy content rich in PUFAs, such as crustaceans and small fishes. This study not only contributes to the understanding of the squid biology and their trophodynamic, but also has important implications to improve fishery management within an ecosystem approach. This is relevant because D. gigas and its prey have suffered heavy exploitation, with a significant reduction in their biomass.

Sick of eating: Eco-evo-immuno dynamics of predators and their trophically acquired parasites.

When predators consume prey, they risk becoming infected with their prey's parasites, which can then establish the predator as a secondary host. A predator population's diet therefore influences what parasites it is exposed to, as has been repeatedly shown in many species such as threespine stickleback (Gasterosteus aculeatus) (more benthic‐feeding individuals obtain nematodes from oligocheate prey, whereas limnetic‐feeding individuals catch cestodes from copepod prey). These differing parasite encounters, in turn, determine how natural selection acts on the predator's immune system. We might therefore expect that ecoevolutionary dynamics of a predator's diet (as determined by its ecomorphology) should drive correlated evolution of its immune traits. Conversely, the predator's immunity to certain parasites might alter the relative costs and benefits of different prey, driving evolution of its ecomorphology. To evaluate the potential for ecological morphology to drive evolution of immunity, and vice versa, we use a quantitative genetics framework coupled with an ecological model of a predator and two prey species (the diet options). Our analysis reveals fundamental asymmetries in the evolution of ecomorphology and immunity. When ecomorphology rapidly evolves, it determines how immunity evolves, but not vice versa. Weak trade‐offs in ecological morphology select for diet generalists despite strong immunological trade‐offs, but not vice versa. Only weak immunological trade‐offs can explain negative diet‐infection correlations across populations. The analysis also reveals that eco‐evo‐immuno feedbacks destabilize population dynamics when trade‐offs are sufficiently weak and heritability is sufficiently high. Collectively, these results highlight the delicate interplay between multivariate trait evolution and the dynamics of ecological communities.

Polar bear diet composition reveals spatiotemporal distribution of Arctic marine mammals across Nunavut, Canada

Climate warming and associated physical and biological changes will likely force widespread species redistribution, particularly in polar environments. However, tracking such distributional shifts is difficult. The dietary habits of apex predators, like polar bears (Ursus maritimus), may provide early signals of distributional change in prey populations. We used harvest-based sampling to investigate the spatial feeding patterns of polar bears across Nunavut from 2010 to 2018 (n = 1570) and identify spatiotemporal clusters of different prey based on predator diet estimates. Quantitative fatty acid signature analysis and the Getis-Ord Gi* statistic identified spatial clusters of high or low dietary proportions (i.e., “hot spots” and “cold spots”) reflecting seasonal and spatial availability of prey. Ringed seal (Pusa hispida) was the primary prey of bears throughout Nunavut followed by bearded seal (Erignathus barbatus), although proportional consumption varied spatially. A consistent ringed seal consumption hot spot was found in Gulf of Boothia indicating the importance of year-round availability of ringed seals. Spatial clusters of bearded seal and Atlantic walrus (Odobenus rosmarus rosmarus) throughout Foxe Basin suggested overlapping seasonal distributions and high regional abundance. Bears had consistently high dietary levels of harbour seal (Phoca vitulina) around Southampton Island and along the western coast of Hudson Bay suggesting a possible year-round concentration of this prey. Hot spots of harp seal (Pagophilus groenlandicus) consumption were evident throughout Davis Strait and a spring-summer hot spot around Jones Sound was consistent with harp seal migratory patterns. Year-round beluga whale (Delphinapterus leucas) hot spots were found along eastern Baffin Island and southern Viscount Melville Sound providing new knowledge of local conditions that promote polar bear predation or scavenging. Narwhal (Monodon monoceros) were less susceptible to predation with only one spatial cluster of high consumption appearing during spring-summer in Barrow Strait. Bowhead whale (Balaena mysticetus) hot spots occurred around south-western Foxe Basin and seasonally in southern Viscount Melville Sound suggesting carcasses are locally accessible to bears and may act as a supplemental food source in particular areas and seasons. The congruence of polar bear feeding habits and known prey distribution suggests polar bears serve as ecological indicators and ongoing monitoring of their diets may reveal regional and broad-scale changes in prey population distributions and Arctic ecosystem functioning.

Predator life history and prey ontogeny limit natural selection on the major armour gene,Eda, in threespine stickleback

AbstractNatural selection shapes the evolution of antipredator traits in prey. However, selection in the wild depends on ecological context, including features of predator and prey populations, making field studies of selection critical to understanding how predators shape selection on prey defences. Threespine stickleback (Gasterosteus aculeatus) is a classic system to study the effects of predators on the natural selection of prey. In lakes and rivers, fish predators have been shown to impose selection against low plated adult stickleback phenotypes and genotypes. We directly measured selection by predatory salmonids on theEctodysplasin‐A(Eda) gene in estuary stickleback from California. Despite previous studies showing a positive correlation between predator presence and frequency of theEda“complete” allele in estuary populations, we found thatEda“low” genotypes were not significantly more frequent in salmonid predator diets. Further, we found no evidence of changes inEdagenotype frequencies across generations that would suggest directional selection driven by predators. Prior selection studies have examined the effects of large resident trout on adult stickleback. In contrast, predators in this study were juvenile anadromous salmonids, which only ate juvenile stickleback whose plate phenotypes had not fully developed. Thus, in this case, predator life history and stickleback ontogeny may preclude strong selection on stickleback armour. Our results underscore the importance of selection studies in the wild for understanding the context‐dependent nature of selection in natural populations.

Temporal variation in the niche partitioning of Lake Michigan salmonines as it relates to alewife abundance and size structure

Stable isotope analyses offer a useful means for quantifying ecological niche dimensions, though few studies have examined isotopic response of an ecological community with respect to resource gradients such as fluctuations in prey availability. Stable carbon and nitrogen isotopes were measured for Lake Michigan salmonines and their prey collected from 2014 to 2016. Bayesian ellipse and mixing model analyses were used to quantify isotopic niche characteristics and diets, respectively, among species and years. During the 3-year study period, abundance and size structure of preferred alewife (Alosa pseudoharengus) prey changed substantially and offered an opportunity to explore predator isotopic niche response and diet shifts along a prey resource gradient. Results suggested increased reliance on alewives, especially small alewives, over the study period and were consistent with greater availability of this prey. However, differential use of alewife size classes and alternative prey sources by salmonine predators was apparent, which suggested possible resource partitioning. Characterization of ecological niche overlap using stable isotopes likely requires consideration of shared resource availability as well as specific prey and habitat preferences.

Metabarcoding confirms the opportunistic foraging behaviour of Atlantic bluefin tuna and reveals the importance of gelatinous prey.

Studies of the diet, feeding habits and trophic activity of top marine predators are essential for understanding their trophodynamics. The main direct method used for such studies thus far has been morphological inventories of stomach contents. This approach presents limitations such as missing gelatinous prey, which are usually digested too quickly to be detectable. Here, we analysed the stomachs of 48 Atlantic bluefin tuna (Thunnus thynnus, approximately 15 to 60 kg, including juveniles and adult fishes) collected from the Mediterranean Sea through the metabarcoding of two gene regions (cytochrome c oxidase subunit I (COI) and the ribosomal 18S-V1V2 region). The identified prey taxa and their relative read abundances (RRAs) estimated using COI results were in line with the findings of morphologically based inventories simultaneously performed on the same set of tuna samples. In both cases (and with the same rankings), the prey taxa included anchovy (Engraulis encrasicolus, here detected in more than 80% of samples, RRA = 43%), sardine (Sardina pilchardus, also approximately 80%, RRA = 30%), sprat (Sprattus sprattus, approximately 66%, RRA = 8%), mackerel (Scomber colias, approximately 44%, RRA = 7%) and cephalopods (approximately 15%, RRA = 1.4%). Another striking result was the detection, based on 18S (with which vertebrates were detected as the most abundant group, RRA = 61.6%), of a high prevalence and diversity of gelatinous organisms (RRA = 27.1%), including cnidarians (6.7%), salps (11.7%), and ctenophores (8.7%), the latter increasing with the size of the predator. These results thus support the hypothesis of the role of gelatinous prey in the diet of Atlantic bluefin tuna, suggesting that this species is even more generalist and opportunistic than previously thought. This study further confirms that DNA metabarcoding can be a powerful tool for assessing the diet and trophodynamics of top marine predators.

Multiple species-specific molecular markers using nanofluidic array as a tool to detect prey DNA from carnivore scats.

Large carnivore feeding ecology plays a crucial role for management and conservation for predators and their prey. One of the keys to this kind of research is to identify the species composition in the predator diet, for example, prey determination from scat content. DNA‐based methods applied to detect prey in predators’ scats are viable alternatives to traditional macroscopic approaches, showing an increased reliability and higher prey detection rate. Here, we developed a molecular method for prey species identification in wolf (Canis lupus) scats using multiple species‐specific marker loci on the cytochrome b gene for 18 target species. The final panel consisted of 80 assays, with a minimum of four markers per target species, and that amplified specifically when using a high‐throughput Nanofluidic array technology (Fluidigm Inc.). As a practical example, we applied the method to identify target prey species DNA in 80 wolf scats collected in Sweden. Depending on the number of amplifying markers required to obtain a positive species call in a scat, the success in determining at least one prey species from the scats ranged from 44% to 92%. Although we highlight the need to evaluate the optimal number of markers for sensitive target species detection, the developed method is a fast and cost‐efficient tool for prey identification in wolf scats and it also has the potential to be further developed and applied to other areas and large carnivores as well.

Variation in Diet Patterns of the Invasive Top Predator Sander lucioperca (Linnaeus, 1758) across Portuguese Basins

The introduction of non-native species is recognized as a major threat to biodiversity, particularly in freshwater ecosystems. Pikeperch Sander lucioperca, is a recent invader to Portugal, primarily providing commercial and angling interest. The aim of this work was to study the diet of this top predator across Portuguese basins and to evaluate its potential impact on recipient ecosystems. In total, 256 pikeperch stomachs from seven basins were examined, of which 88 (n = 34%) were empty. Pikeperch diet was dominated by R. rutilus, M. salmoides and Diptera in northern populations, while A. alburnus, P. clarkii and Atyidae were important prey in more humid highlands. Variation in diet was most strongly linked to latitude and ontogeny, with both size classes showing signs of cannibalism. The population niche breadth remained low and was accompanied by higher individual diet specialization, particularly in northern populations. Pikeperch dietary patterns denoted an opportunistic ability to use locally abundant prey in each ecosystem, and was size dependent, with larger individuals becoming more piscivores, causing a higher impact in the lotic systems. This first perspective about the pikeperch diet presents a very broad view of the feeding traits of this non-native predator across Portugal, being very important to deepen our knowledge about the impact of these introduced piscivores.

The diet of dingoes, feral cats and eastern barn owl on Pullen Pullen Reserve, southwest Queensland

Predator diet can provide important data to inform management actions as well as an enhanced understanding of the fauna of a region. The diet of dingo (Canis lupus dingo), feral cat (Felis catus) and eastern barn owl (Tyto delicatula) were compared using scat, stomach and pellets from a significant conservation reserve in southwest Queensland. Dingo diet was dominated by macropods, while the diet of feral cat and barn owl was dominated by small mammals. We found no remains of threatened species but recommend continued monitoring of predator diet as a tool to assist management.

Порівняльний аналіз раціону представників родин Mustelidae та Canidae

The article analyzes 151 food samples of carnivoran mammals of two families. It was found that the diet includes 49 food items in the studied species of the family Canidae and 42 items in species of the family Mustelidae, of both plant and animal origin. It was revealed that plant food is an important component of the diet of predators, since the frequency of registration of these objects is 46.4%. Most often, it is the remains of cereals and plant seeds. Rodents are the main food for both families (19% in Canidae, 21% in Mustelidae). A seasonal change in diet for both families was noted. Members of the family Mustelidae consume plants more often in summer and winter, while in in spring and autumn mammals prevail in their diet when the share of juicy fruits is the lowest. Rodents are consumed throughout the year, but their largest share was noted in spring, when this family is characterized by the greatest variety of food (Shannon's index is 2.0). For members of the family Canidae, the most important component of the diet in winter is dry fruits. The number of rodents in their diet also increases in spring. The summer period is characterized by the consumption of invertebrates and the absence of animal carcasses in the diet. In autumn, the share of juicy fruits increases and during this period the diet of Canidae is the most diverse (1.9). The lowest variety of food in species of the two families was registered in summer. Competition between the studied families may increase in spring when the most important food for the representatives of both Canidae and Mustelidae is rodents. There are some sex-related trophic preferences in both families. In particular, males of the family Mustelidae consume rodents more often (68.7%), while females more often feed on plants (56.1%). As for the family Canidae, the analysis was carried out on the example of the red fox. It was found that females of this species prefer plant foods and there are no ungulates in their diet. Males consume fewer plants (41.4%) and often forage in cattle burial grounds and landfills. Accordingly, the diet of males is more diverse compared to that in females. The Shannon index is 3.3 and 2.5, respectively.

Using mark-recapture techniques to assess factors affecting survival of fall stocked walleye Sander vitreus in two Iowa lakes

Stocking walleye Sander virteus is a common management technique to supplement populations where natural reproduction is limited. However, numerous factors can influence the survival of fall stocked walleye including environmental conditions, predation, and stocked walleye total length (TL), condition, and foraging ability. The relative effects of these factors on survival of stocked walleye are challenging to evaluate and rarely assessed simultaneously. Our objective was to determine factors that influence survival rates of stocked fingerling walleye (98−287 mm TL) from stocking until ice cover in two Iowa systems (East Okoboji and West Okoboji) during fall 2015, 2016, and 2017 using mark-recapture techniques. Each fall, roughly 4000 stocked walleye were implanted with passive integrated transponder tags, stocked across both systems, and recaptured via boat electrofishing. Cormack-Jolly-Seber recapture models estimated walleye weekly apparent survival was negatively related to the weekly average proportion of walleye recovered from predator diets (β = −0.89; 95 % credibility interval = −1.74 to −0.03) and positively related to weekly average water temperatures (β = 2.62; 95 % credibility interval = 1.04–4.21). At an average fall water temperature (13.2 ℃), mean walleye apparent survival was 0.83 (95 % credibility interval = 0.75–0.91) when no walleye were recovered from predator diets and declined to 0.54 (95 % credibility interval = 0.28–0.84) when walleye comprised 60 % of predator diets. Between 41–97 % of stocked walleye were lost to apparent mortality from stocking through ice-up and survival was influenced by post-stocking predation rather than walleye body size or condition. Thus, strategies that minimize predation following stocking may result in the greatest improvements in walleye stocking success.

Macrozooplankton and micronekton community structure and diel vertical migration in the Heard Island Region, Central Kerguelen Plateau

The Kerguelen Plateau is the largest topographic barrier to the eastward flowing Antarctic Circumpolar Current (ACC) in the Indian Sector of the Southern Ocean. The plateau is separated into a northern and southern plateau by the Fawn Trough. The northern plateau has a shallow bathymetry (<700 m) with two prominent island systems, the Kerguelen Islands on the northern end and Heard and McDonald Islands on the southern end. The interaction of the northern and southern branches of the Polar Front with the northern plateau results in a complex oceanographic environment, with potential for dynamic mixing of sub-Antarctic and Antarctic fauna. Furthermore, the High Nutrient Low Chlorophyll (HNLC) water that flows over the northern plateau is subject to natural iron fertilization from the shallow bathymetry (< 700 m), leading to extensive phytoplankton blooms each summer, particularly to the southeast of the Kerguelen Islands. The Heard Island region on the central plateau has been relatively underexplored. In January 2004, the Heard Island Predator-Prey Investigation and Ecosystem Study (HIPPIES) conducted macrozooplankton (RMT-8 trawl) and micronekton (IYGPT trawl) sampling in foraging areas used by top predators in the vicinity of the island. Macrozooplankton and micronekton were sampled day and night from three depth strata (0–100 m, 100–300 m and 300–600 m). In the area south and east of Heard Island, over bathymetry ≥1000 m depth, the water column had characteristics of the southern branch of the Polar Front (S-PF) and the macrozooplankton and micronekton were dominated by Antarctic Zone fauna (e.g., the euphausiids Euphausia triacantha and Euphausia frigida, and the myctophids Krefftichthys anderssoni, Electrona antarctica, Gymnoscopelus braueri and Gymnoscopelus nicholsi). Shallow slope and shelf stations were located north of the S-PF and the macrozooplankton assemblages were influenced by Polar Frontal Zone species (e.g., Euphausia vallentini), while the shelf micronekton were dominated by the bentho-pelagic channichthyids Champsocephalus gunnari and Channichthys rhinoceratus, together with G. nicholsi. Most macrozooplankton migrated from the deep epipelagic (100–300 m) into the surface epipelagic (<100 m) at night, although some macrozooplankton occurred at high densities in the surface epipelagic during the day (e.g., Rhincalanus gigas, Themisto gaudichaudii). Most micronekton species occurred in the mesopelagic layers (300–600 m) during the day, and migrated into the deep and surface epipelagic at night. Only the small but very abundant K. anderssoni utilized the top 300 m during the day. The vertical distributions of macrozooplankton and micronekton are discussed with respect to the foraging behavior and diets of top predators.

Predation has small, short-term, and in certain conditions random effects on the evolution of aging

BackgroundThe pace of aging varies considerably in nature. The best-known explanation of the evolution of specific rates of aging is the Williams’ hypothesis suggesting that the aging rate should correlate with the level of extrinsic mortality. However, the current evidence is inconclusive with various examples where the Williams' hypothesis seems to be correct and where it doesn’t. Here we explore the relationship between extrinsic mortality and aging rate by developing a simulation model of the evolution of aging rate in prey subject to predation.ResultsOur results suggest that more intense predation leads to the evolution of faster pace of aging in prey. However, this effect slowly vanishes when the predator diet breadth is allowed to evolve, too. Furthermore, in our model, the evolution of a specific aging rate is driven mainly by a single parameter, the strength of a trade-off between aging and fecundity. Indeed, in the absence of this trade-off the evolutionary impacts of predation on the prey aging rate appear random.ConclusionsWe show that the William’s hypothesis appears valid when there is a trade-off between aging and fecundity and predators and prey do not coevolve. However, we also show that when the prey and predators coevolve or if there is no trade-off between aging and fecundity the William`s hypothesis is no longer applicable.

Variation in predator diet and prey size affects perceived impacts to salmon species of high conservation concern

Management of protected species is difficult when objectives include the recovery of both predator and its prey. Ideally, identifying trade-offs between competing objectives involves evaluating management alternatives with a quantitative model that integrates information on both species, but data are often limited. We used new predator diet data and simulation modeling to update our understanding of seal predation on juvenile Chinook (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) in the Puget Sound. Under prey size assumptions used by previous studies, estimates suggest predation could be a significant source of mortality for Chinook salmon (mean: 37% of ocean age-0 juveniles), but varied considerably among years (range of median estimates: 22%–49%). However, when we estimated prey size from otoliths recovered from seal scats, the impact (numbers of fish consumed) decreased by 71%. Predation on coho salmon was estimated to be relatively low under both scenarios (6%–8% of ocean age-0 juveniles) with a 21% decrease in consumption using otolith-derived prey size. Our analysis highlights the importance of updating model inputs and re-evaluating assumptions of multi-species models used for ecosystem-based fisheries management.

Contextual behavioural plasticity in Italian agile frog (Rana latastei) tadpoles exposed to native and alien predator cues.

Predation is a strong driver for the evolution of prey behaviour. To properly assess the actual risk of predation, anuran tadpoles mostly rely on water-borne chemical cues, and their ability to evaluate environmental information is even more crucial when potential predators consist of unknown alien species. Behavioural plasticity - that is, the capacity to express changes in behaviour in response to different environmental stimuli - is crucial to cope with predation risk. We explored the defensive behaviour of Italian agile frog (Rana latastei) tadpoles when exposed to the chemical cues of two predator species, one native (dragonfly larvae) and one alien (red swamp crayfish). Firstly, we observed whether a plastic life history trait (i.e. hatching time) might be affected by native predatory cues. Secondly, we recorded a suite of behavioural responses (activity level, lateralization and sinuosity) to each cue. For assessing lateralization and sinuosity, we developed a C++ code for the automatic analysis of digitally recorded tadpole tracks. Hatching time seemed not to be affected by the potential risk of predation, while both predator species and diet affected tadpoles' defensive behaviour. Tadpoles responded to a predator threat by two main defensive strategies: freezing and 'zig-zagging'. While the first behaviour had previously been reported, the analysis of individual trajectories indicated that tadpoles can also increase path complexity, probably to prevent predators from anticipating their location. We also recorded a decrease in lateralization intensity, which suggests that under predation risk, tadpoles tend to scrutinize the surrounding environment equally on both sides.

Feeding Ecology of Elusive Caribbean Killer Whales Inferred From Bayesian Stable Isotope Mixing Models and Whalers’ Ecological Knowledge

Investigating the feeding ecology of marine predators is critical for understanding their roles and functional importance in ecosystems. However, assessing the diet of large and wide-ranging predators can be challenging, particularly in the case of rare and elusive species. Killer whales (Orcinus orca) are large apex predators in global oceans, but very little is known about their feeding ecology in tropical ecosystems, particularly in the Caribbean Sea. Killer whales are distributed throughout the Caribbean, and are a regular target of artisanal whalers in St. Vincent and the Grenadines (West Indies). Here we investigate the feeding ecology of Caribbean killer whales using a combination of stable isotope analysis (δ15N, δ13C) and traditional ecological knowledge (TEK) data from whalers operating from St. Vincent. Potential prey data from the Caribbean region included large pelagic teleosts, sea turtles, oceanic sharks, cetaceans, and oceanic cephalopods. Mixing models suggest that the contribution of odontocete cetaceans to the diet of killer whales is the most important (overall mean contribution: 60.4%), particularly mesopelagic delphinids (Lagenodelphis hosei; 26.4%, SD = 0.14), large teuthophageous odontocetes (Physeter macrocephalus,Globicephala macrorhynchus; 20.0%, SD = 0.14), and epipelagic delphinids (Stenella attenuata; 14%, SD = 0.14). Oceanic sharks (Carcharhinus longimanus) had a contribution of 17.0% of the diet of killer whales (SD = 0.13), and other potential prey had a relatively marginal contribution. TEK data suggest that whalers believe killer whales feed almost exclusively on cetaceans, particularly odontocete species that they hunt (e.g.,G. macrorhynchus). Stable isotope and TEK data were consistent to some extent, although TEK data are qualitative and based on a limited number of observations. Despite some limitations (including sample size for both methods), this study highlights the value of combining independent data sources and methodologies to investigate the ecological roles of marine predators in data-poor regions.

Zebra jumping spiders opportunistically forage on different sized midges

Prey preferences influence predator diets and therefore the structure and function of food webs. Yet preferences may arise for several reasons, including the maximization of energy gain or the acquisition of specific nutrients. Detecting prey preferences requires a robust estimation of foraging rates from the functional response, but these are unavailable in most prey preference studies. Here we assess preference for small or large midges (Chironomidae) by zebra jumping spiders (Salticus scenicus). We conducted functional response experiments for both small and large midges to determine expectations for foraging rates on each. We then conducted foraging trials to assess preferences, predicting that jumping spiders would have a preference for large midges because of their greater energy content. We found that zebra jumping spiders had a higher functional response when foraging on small midges than when foraging on large midges. Rather than indicating a preference for small midges, this difference sets the correct null expectation for choice experiments, and when offered a choice of prey types, spiders showed no preference for large or small midges. In contrast, the Manly's α choice metric suggested a preference for small midges, and we therefore argue that this approach provides a distorted depiction of prey preferences in this spider.

Emergent Freshwater Insects Serve as Subsidies of Methylmercury and Beneficial Fatty Acids for Riparian Predators Across an Agricultural Gradient.

Aquatic-to-terrestrial subsidies have the potential to provide riparian consumers with benefits in terms of physiologically important organic compounds like omega-3 long-chain polyunsaturated fatty acids (n-3 LCPUFAs). However, they also have a "dark side" in the form of exposure to toxicants such as mercury. Human land use intensity may also determine whether subsidies provide benefits or come at a cost for riparian predators. We sampled insects as well as Eastern Phoebe (Sayornis phoebe) chicks in 2015-2016 within the southern Finger Lakes region to understand how food quality, in terms of n-3 LCPUFAs and methylmercury (MeHg), of emergent freshwater insects compared with that of terrestrial insects and how land use affected the quality of prey, predator diet composition, and MeHg exposure. Across the landscape, freshwater insects had a significantly higher percentage of the n-3 LCPUFA eicosapentaenoic acid (EPA) compared to terrestrial insects and contained significantly more MeHg than terrestrial insects did. In spite of differences in MeHg concentrations between aquatic and terrestrial insects, chick MeHg concentrations were not related to diet composition. Instead, chick MeHg concentrations increased with several metrics of human land use intensity, including percent agriculture. Our findings suggest that freshwater subsidies provide predators with both risks and benefits, but that predator MeHg exposure can vary with human land use intensity.