Variation In Prey Availability Research Articles

Sex-specific foraging behaviour in a long-lived seabird

Sex-specific foraging behaviour may lead to differences between the sexes in both resource acquisition and exposure to threats and thereby contribute to sex-specific reproductive roles or mortality. As such, it is important to identify in which species sex-specific foraging behaviour occurs. We deployed GPS devices to incubating common terns (Sterna hirundo) from a German breeding population to study how sex and spatial or temporal extrinsic factors influence the daily activity budget, foraging distribution, and trip characteristics of this slightly sexually size dimorphic seabird. Birds of both sexes only foraged during the day, showing peaks of activity after sunrise and before sunset, perhaps in response to temporal variation in prey availability and/or as a strategy to overcome or prepare for nocturnal fasting. Furthermore, foraging was more frequent around low tide and at the beginning of the flood tide and mainly occurred in shallow (< 5 m depth) and coastal waters (< 2 km from coastline) up to 20 km from the colony. Females rested less, foraged closer to the colony in more coastal waters, and showed a lower maximum flight speed than males. Males foraged more outside protected areas than females and showed higher variability in their foraging distribution throughout the tide cycle. As such, our study provides evidence for sex-specific aspects of foraging behaviour in common terns and underlines the importance of considering sex-specific foraging distributions when assessing the impact of at-sea threats on seabirds, knowledge of which should be incorporated when developing conservation management strategies.

Canada lynx foraging strategies: Facultative specialists become obligate generalists toward the distribution edge

AbstractSpatial and temporal variation in prey availability can affect predator foraging strategies, but it is unclear how large‐scale gradients in prey availability shape predator diets in space and time. The facultative specialist hypothesis predicts that niche expansion by specialist predators is advantageous when preferred prey are limited and alternate prey are available, as might be expected following the collapse of primary prey populations in species‐poor environments or at range margins where species assemblages shift. Canada lynx (Lynx canadensis) are broadly distributed and prey predominantly on snowshoe hares (Lepus americanus), with other species serving as alternate prey when hares are limited. We used stable isotope analysis of lynx, snowshoe hare, and red squirrel hair during periods of high/low snowshoe hare availability from five regions throughout their distribution, to measure spatiotemporal changes in diet and test the facultative specialist hypothesis. Hares were the primary food item in all lynx diets, irrespective of space and time. Core lynx populations consumed the greatest proportion of hares overall and increased the use of alternate prey when hares were limited. Despite fluctuations in hare availability, lynx toward the southeastern extent of their distribution invariably consumed alternate prey in similar proportions to those exhibited by core populations during hare lows. The temporal consistency of lynx diets in these regions indicates that broader diets are obligate along this distribution edge. Our results provide new evidence for the facultative specialist hypothesis across a broad spatial scale and emphasize that, as specialist–generalist paradigms operate along a continuum, so too can obligate–facultative strategies depending on environmental context.

Insectivorous bat foraging tracks the availability of aquatic flies (Diptera)

AbstractRivers and their adjacent riparian zones are model ecosystems for observing cross‐ecosystem energy transfers. Aquatic insects emerging from streams, for example, are resource subsidies that support riparian consumers such as birds, spiders, lizards, and bats. We collaborated with recreational river runners in Grand Canyon, Arizona, USA, to record acoustic bat activity and sample riparian insects using light traps at dusk from April through October 2017–2020. River runners collected these data on 1,428 events over 611 sampling nights at 410 sites throughout a 470‐km segment of the Colorado River. We documented 71 insect taxa in light traps and recorded 19 bat species with acoustic detectors. We hypothesized that bat activity along this highly regulated river segment would be influenced primarily by variation in prey availability, as compared to other habitat descriptors. We predicted that bat activity would be positively related to aquatic insect catch rates and unrelated to terrestrial insect abundance. We fit Bayesian regression models to test these hypotheses and to quantify the relationship between bat activity and a suite of environmental variables: time of year, time of day, distance from perennial tributaries, distance from rapids, channel width, geomorphic reach, tall vegetation cover, air temperature, and lunar phase. Bat activity was positively related to the abundance of aquatic flies (Diptera), which outcompeted all other prey categories and structural habitat descriptors in our models. Within our dusk sampling period, activity of small myotis (California myotis [Myotis californicus] and Yuma myotis [M. yumanensis]) was high late in the evening and canyon bats (Parastrellus hesperus), conversely, were more active early in the evening. Activity of canyon bats varied seasonally, with peak activity in August. Our results support the hypothesis that aquatic prey, specifically aquatic flies, are key predictors of bat activity along a large, regulated river corridor and demonstrate the power of community science as a tool for ecosystem monitoring.

Stable Isotope Differences among Species, Sexes, and Breeding Stages of Laysan and Black-Footed Albatrosses in the Western North Pacific

In order to understand the diet of Laysan Albatross Phoebastria immutabilis and Black-footed Albatross P. nigripes in western North Pacific waters, we investigated isotopic differences between species, sexes and breeding stages. We measured carbon and nitrogen isotope ratios in the muscles and livers of albatrosses (caught during Japanese pelagic longline fishing) and in their potential prey. Both δ 13C and δ15N of Black-footed Albatross were higher than those of Laysan Albatross. Delta13C of both species differed seasonally and δ13C was lower during the incubation period than during the chick-provisioning and non-breeding periods. The δ 13C and δ15N levels of males did not differ from those of females in either species. Our results suggest that Black-footed Albatross forages on higher isotope prey items and/or Laysan Albatross forages on lower isotope prey items other than squid and fish and that δ13C varies in response to seasonal variation in prey availability. This implies that Black-footed Albatross forages more on discard from the fishing industry than does Laysan Albatross; this in turn may be related to the areas of operation sea area of the longline fisheries in the western North Pacific. In conclusion, it is important for conservation of these two albatross species to monitor their diets and foraging areas and to identify the species-specific high-risk areas where albatross bycatch is most likely.

A surplus no more? Variation in krill availability impacts reproductive rates of Antarctic baleen whales.

The krill surplus hypothesis of unlimited prey resources available for Antarctic predators due to commercial whaling in the 20th century has remained largely untested since the 1970s. Rapid warming of the Western Antarctic Peninsula (WAP) over the past 50 years has resulted in decreased seasonal ice cover and a reduction of krill. The latter is being exacerbated by a commercial krill fishery in the region. Despite this, humpback whale populations have increased but may be at a threshold for growth based on these human-induced changes. Understanding how climate-mediated variation in prey availability influences humpback whale population dynamics is critical for focused management and conservation actions. Using an 8-year dataset (2013-2020), we show that inter-annual humpback whale pregnancy rates, as determined from skin-blubber biopsy samples (n= 616), are positively correlated with krill availability and fluctuations in ice cover in the previous year. Pregnancy rates showed significant inter-annual variability, between 29% and 86%. Our results indicate that krill availability is in fact limiting and affecting reproductive rates, in contrast to the krill surplus hypothesis. This suggests that this population of humpback whales may be at a threshold for population growth due to prey limitations. As a result, continued warming and increased fishing along the WAP, which continue to reduce krill stocks, will likely impact this humpback whale population and other krill predators in the region. Humpback whales are sentinel species of ecosystem health, and changes in pregnancy rates can provide quantifiable signals of the impact of environmental change at the population level. Our findings must be considered paramount in developing new and more restrictive conservation and management plans for the Antarctic marine ecosystem and minimizing the negative impacts of human activities in the region.

Diet energy density estimated from isotopes in predator hair associated with survival, habitat, and population dynamics.

Sea ice loss is fundamentally altering the Arctic marine environment. Yet there is a paucity of data on the adaptability of food webs to ecosystem change, including predator-prey interactions. Polar bears (Ursus maritimus) are an important subsistence resource for Indigenous people and an apex predator that relies entirely on the under-ice food web to meet its energy needs. In this study, we assessed whether polar bears maintained dietary energy density by prey switching in response to spatiotemporal variation in prey availability. We compared the macronutrient composition of diets inferred from stable carbon and nitrogen isotopes in polar bear guard hair (primarily representing summer/fall diet) during periods when bears had low and high survival (2004-2016), between bears that summered on land versus pack ice, and between bears occupying different regions of the Alaskan and Canadian Beaufort Sea. Polar bears consumed diets with lower energy density during periods of low survival, suggesting that concurrent increased dietary proportions of beluga whales (Delphinapterus leucas) did not offset reduced proportions of ringed seals (Pusa hispida). Diets with the lowest energy density and proportions from ringed seal blubber were consumed by bears in the western Beaufort Sea (Alaska) during a period when polar bear abundance declined. Intake required to meet energy requirements of an average free-ranging adult female polar bear was 2.1 kg/day on diets consumed during years with high survival but rose to 3.0 kg/day when survival was low. Although bears that summered onshore in the Alaskan Beaufort Sea had higher-fat diets than bears that summered on the pack ice, access to the remains of subsistence-harvested bowhead whales (Balaena mysticetus) contributed little to improving diet energy density. Because most bears in this region remain with the sea ice year round, prey switching and consumption of whale carcasses onshore appear insufficient to augment diets when availability of their primary prey, ringed seals, is reduced. Our results show that a strong predator-prey relationship between polar bears and ringed seals continues in the Beaufort Sea. The method of estimating dietary blubber using predator hair, demonstrated here, provides a new metric to monitor predator-prey relationships that affect individual health and population demographics.

Dietary Variation Is Driven by Landscape Heterogeneity in an Insular Omnivorous Endemic Lizard, Revealed by DNA Metabarcoding

Living on islands entails numerous challenges for animals, among which population density approaching the carrying capacity of trophic resources stands out. To overcome this limitation, many insular lizards can supplement their insectivorous diet with increasing portions of plant material. The Madeira wall lizard, Teira dugesii, is a medium-sized lacertid, endemic to the Madeira and Selvagens archipelagos. As common in this family, adults are sexually dimorphic with males being bigger than females. Previous dietary studies on morphological scatology identified a higher proportion of plant over animal prey items, changing according to the location and sex. Here, we used DNA metabarcoding to examine the diet of this lizard species quantifying it at a higher taxonomical resolution and enhancing the detection of soft-body prey that often go undetected in morphology-based studies. In a sample of 151 faecal samples from eight populations including different habitats and altitudes in Madeira, we identified 289 prey items belonging to eight animal and three plant Classes, encompassing 58 distinct orders and 140 families. Of these, 63 were identified up to the species level. The results support a strong trend towards herbivory in this species with plants representing almost 74% of the diet occurrences in contrast to the 26% of animal prey. Remarkably, the plant fraction of the diet remained stable across localities but varied with size and mass in males. As males grew bigger and heavier, they significantly increased their plant matter intake. Likely, larger bodies and abdomens allowed allocating longer and more complex digestive tracts harbouring intestinal flora to better decompose plant organic compounds. This allowed heavier animals to have a richer diet regime. However, diet richness and composition were not affected by either sex or size, while the locality had a significant effect on both diet components likely in response to local variation in prey availability. By including an increasing plant fraction into a primarily insectivorous diet, this insular lizard has not only enlarged its trophic niche but is also able to exploit more efficiently the highly variable resources provided by insular environments.

The overlooked underground diversity: physical and chemical edaphic structure predict morphological variation in South American amphisbaenians (Squamata: Amphisbaenidae)

ABSTRACT Morphological patterns may vary spatially in response to adaptations to regional environmental conditions. In fossorial animals, edaphic gradients potentially predict intra and interspecific morphological variation because they can limit dispersal and select morphotypes. We measured morphological traits of South American worm lizards, including three Amphisbaena and two Leposternon species, to test whether inter- and intraspecific morphological variation and morphotype distribution are predicted by edaphic gradients measured at different soil profiles. Interspecifically, we found that the variation in head length is mainly predicted by the chemical edaphic structure, which can be explained by spatial variation in prey availability. The variation in the width of the prefrontal and frontal shields was mainly predicted by clay and sand-soil contents, which can be explained by relationships of force and friction associated with digging. Intraspecifically, we found that the effects of edaphic gradients on morphological variation reflects the level of specialization to dig, since the most adapted species were mainly affected by variables measured in deeper soil profiles. We also show that soil-mediated intraspecific morphological variation shape morphotype distribution across different biomes that form the South American dry diagonal, which are discussed in light of biological, ecological, and biogeographic premises.

Understanding the effects of seasonal variation in prey availability on prey switching by large carnivores

AbstractOptimal foraging theory predicts that carnivores select prey species based on intrinsic factors, such as body size, vulnerability, and abundance. Prey abundance can vary significantly, especially when prey species move in and out of an area en masse in search of food. However, little is known about how these resource pulses influence the prey profiles of large carnivores. Using data on lion (Panthera leo) and cheetah (Acinonyx jubatus) kills in the Maasai Mara in Kenya, we investigate whether changes in prey abundance, as a result of a mass annual migration of herbivores, influence the prey profiles of these two carnivore species. Furthermore, for cheetah we investigate whether there are sex‐specific differences in prey profiles in response to changes in prey abundance. Using data from 387 lion kills and 220 cheetah kills (160 female and 60 male), we found that changes in prey abundance had a strong influence on prey profiles, but that for cheetahs this varied by sex and social grouping. More specifically, during the migration, when there is an influx of wildebeest (Connochaetes taurinus), lions and male cheetah (particularly those in coalitions) were more likely to feed on wildebeest than out of the migration. In addition, when wildebeest were less abundant, lions switched to buffalo (Syncerus caffer). Overall, the breadth of the prey profiles was narrower during the migration compared to out of the migration but this was most significant for lions and coalitions of male cheetahs. These changes in prey profiles could have an impact on herbivore dynamics, human‐wildlife conflict and ecological interactions more broadly. Through the detailed characterisation of prey profiles, we contribute to the understanding of predator–prey dynamics and trophic interactions in complex, multi‐species ecosystems and illustrate the importance of taking into account inter‐ and intraspecific variations in predators when modelling predator–prey dynamics.

Influence of Prey Availability in the Dissimilarity of Predator–Prey Interactions

Photo 1. Majority of anurans feed on arthropods, like the Oval Frog (Elachistocleis matogrosso), an ant specialist. Photo credit: Karoline Ceron. Photo 2. But there are some exceptions, such as the Cranwell's horned frog (Ceratophrys cranwelli), a voracious predator, attempting predation upon a Pigmy Toad (Rhinella bergi) in Brazilian Chaco. Photo credit: Karoline Ceron. Photo 3. Anuran diet can vary throughout space, for example, between ecoregions. Nhecolândia, a subregion of the Pantanal, is characterized by the coexistence of thousands of lakes called baías (freshwater) and salinas (waters of alkaline composition; upper panel), in contrast, the Chaco ecoregion has a flat topography, a semiarid climate, and distinct plant formations (lower panel). Photo credit: Karoline Ceron. Photo 4. Also, the anuran diet can vary throughout time, for example, between seasons. Brazilian Cerrado, a seasonal ecoregion, at the RPPN Estância Mimosa, Mato Grosso do Sul, Brazil, during the rainy season (upper panel) and the dry season (lower panel). Photo credit: Karoline Ceron. Photo 5. Studying these variations in time and space, we found that the dissimilarity of the anuran-prey network between ecoregions and seasons is primarily driven by interaction rewiring, which is determined by the variation in prey availability. A waxy monkey frog (Phyllomedusa sauvagii) in the RPPN Estância Mimosa, Mato Grosso do Sul, Brazil. Photo credit: Karoline Ceron. These photographs illustrate the article “Differences in prey availability across space and time lead to interaction rewiring and reshape a predator–prey metaweb” by Karoline Ceron, Diogo B. Provete, Mathias M. Pires, Andrea C. Araujo, Nico Blüthgen, and Diego J. Santana published in Ecology. https://doi.org/10.1002/ecy.3716

Growth variation in the endangered fish Zingel asper: Contribution of substrate quality, hydraulics, prey abundance, and water temperature

Abstract Intraspecific variation in life histories and its environmental correlates can indicate the degree of vulnerability to extinction of endangered taxa and guide conservation actions. Zingel asper (Percidae) is an endangered fish endemic to the Rhône catchment (France and Switzerland), where five populations subsist in separate river systems (Loue, Beaume, Durance, Verdon, and Doubs). Two populations of Z. asper differ in growth and longevity, but the existence of broader intraspecific differentiation in life histories and the environmental origins of this variation (if any) remain unknown. The age structure and growth profile of four populations of Z. asper (Loue, Beaume, Durance, and Verdon) and nine additional sub‐populations within the Durance system were determined by scale‐reading analysis, before evaluating the contribution of measured variation in substrate quality, hydraulics, prey availability, and water temperature to growth differentiation among and within populations. A trade‐off between early growth and longevity largely differentiated the populations of Z. asper along a slow (i.e. slower growth, smaller adult size, longevity of &gt;5 years) to fast (i.e. faster growth, larger adult size, longevity of &lt;4 years) continuum of life histories. This continuum differentiated populations from different river catchments along a south (Durance, Verdon) to north (Beaume, Loue) latitudinal gradient, and mapped onto an upstream–downstream gradient of sub‐populations within the Durance system. Differences in prey availability, hydraulics, and water temperature explained most of the growth variation among populations from different catchments, whereas local variation in prey availability, substrate quality, and water temperature mostly contributed to within‐river growth differentiation. These results indicate that short life cycles strongly expose all populations of Z. asper to extirpation and should motivate additional conservation actions. This study illustrates how quantifying intraspecific variation in life histories and its sensitivity to ecological context can reliably assess extinction risk and guide conservation actions by identifying endangered populations requiring priority management.

Two Decades of Match-Mismatch in Northeast Arctic Cod – Feeding Conditions and Survival

The successful recruitment of Northeast Arctic (NEA) cod is thought to depend on sufficient and suitable prey for the newly hatched larvae, in particular the nauplii stages of the lipid-rich calanoid copepod species Calanus finmarchicus. The role of spatial and temporal variations in prey availability in combination with temperature and other factors in influencing growth and survival of cod larvae is, however, incompletely understood. By combining an individual based model for NEA cod larvae at the Norwegian coast with a high-resolution ocean model and a nutrient-phytoplankton-zooplankton-detritus model providing 18 years of daily environmental conditions and prey availability we assessed larval growth and survival until they settle in their feeding habitat in the Barents Sea in early fall. We find on average a two-week delay from the peak timing of first-feeding cod larvae to the peak in prey availability. In warm years, more larvae experience food limitation than in normal years. The positive effects of high temperature on growth, survival and ultimately recruitment are nonetheless larger than the negative effects of food limitation. Food limitation mainly affects larvae spawned in southern areas or late in the spawning season as these larvae experience the highest temperatures and have the highest energy requirements. Our findings highlight the spatial and temporal differences in mechanisms that regulate growth and survival of early life stages of NEA cod and suggest that spatially resolved data may be essential for understanding match-mismatch dynamics.

Spatial Heterogeneity in Prey Availability, Feeding Success, and Dietary Selectivity for the Threatened Longfin Smelt

Food availability is a key determinant of the nursery value of a given habitat for larval and juvenile fishes. Growth, survival, and recruitment success are often inter-correlated and influenced by prey availability and associated feeding success. This is likely true for the threatened population of Longfin Smelt (Spirinchus thaleichthys) in the San Francisco Estuary (SFE) which has collapsed in recent decades along with its preferred prey. In years with high precipitation and freshwater outflow, larval Longfin Smelt are found in shallow wetland habitats throughout the SFE, but variation in the availability of food and feeding success in these habitats remains unexplored. To examine spatial variation in the trophic value of different rearing habitats, we quantified variation in prey availability, feeding success, and prey selection for larval and juvenile Longfin Smelt captured in restored tidal marshes, sloughs, and open-water habitats in the northern and southern SFE. Prey abundance varied spatially, with densities approximately tenfold greater in southern sloughs and restored tidal ponds relative to northern and open-water habitats. Feeding success of larval Longfin Smelt was positively correlated with both fish length and prey density. Larval Longfin Smelt fed selectively on the copepod Eurytemora affinis, with larger individuals (> 25 mm total length) exhibiting an ontogenetic diet shift to larger mysid shrimps. Our results suggest that wetland habitats across the SFE vary greatly in their trophic value, with previously unexplored habitats exhibiting the highest densities of prey and the highest foraging success for larval Longfin Smelt.

Intrapopulation variation in the diet of franciscana dolphin (Pontoporia blainvillei) off southern Brazil

AbstractThe franciscana dolphin (Pontoporia blainvillei) is a coastal dolphin endemic to the western South Atlantic Ocean. The dolphin is listed as vulnerable in the IUCN Red List, with incidental catches in gillnet fisheries the greatest conservation concern for this species. Insights into the feeding habits of this dolphin are essential to understand its distribution, movements and use of habitat, which are fundamental for effective management of the species. The feeding habits of franciscana dolphins were investigated from analyses of stomach contents of animals incidentally caught by two fishing operations from southern and northern regions of the southern Brazilian coast. In this study we investigate the existence of intrapopulation (sexual maturity and sex-related) variation in the diet of the franciscana dolphin, evaluating the spatial (northern and southern geographic areas) and seasonal influences. The analyses were based on Linear and Generalized Linear Models (LM and GLM). The majority of identified prey species were bottom-dwelling teleosts and the squidDoryteuthis sanpaulensis. The most important prey differed spatially and seasonally between northern and southern regions of the study area, and our results revealed significant differences between sexes and sexual maturity stages, mainly related to prey species sizes. This variation might indicate differences in prey selection, availability or habitat use patterns among these groups. In any case, these dietary differences are likely to minimize intraspecific competition for food resources, and/or indicate spatio-temporal variation in prey availability.

History of domestic cats on Pitcairn Island

This paper presents the first comprehensive history of Felis catus, the domestic cat, on Pitcairn Island. It includes detailed documentation of the cats and their status on the island, from settlement by H.M.A.V. Bounty mutineers in 1790 through the present time. The domestic cats of Pitcairn Island are worthy of study because they are inextricably linked to the island’s natural, cultural and maritime history. We present evidence that indicates domestic cats were introduced to Pitcairn Island by the Bounty mutineers in 1790. The cats have experienced cyclic periods of alternately being protected and culled due to variations in prey availability. There were at least two instances (c.1820 and in 1997) of nearly complete cat eradication. Some Pitcairn Islanders believe that ‘Bounty Cats’, which were descended from the cats that arrived with the Bounty mutineers, were poisoned or sterilized in 1997.

A molecular approach to study Hymenoptera diets using wasp nests

The study of animal diets has benefited from the rise of high-throughput DNA sequencing applied to stomach content or faecal samples. The latter can be fresh samples used to describe recent meals or older samples, which can provide information about past feeding activities. For most invertebrates, however, it is difficult to access ‘historical’ samples, due to the small size of the animals and the absence of permanent defecation sites. Therefore, sampling must be repeated to account for seasonal variation and to capture the overall diet of a species. This study develops a method to describe the overall diet of nest-building Hymenoptera, based on a single sampling event, by analysing prey DNA from faeces accumulated in brood cells. We collected 48 nests from two species of introduced paper wasps (Polistes chinensis Fabricius and P. humilis Fabricius) in the urban and peri-urban areas of Auckland, New Zealand and selected two samples per nest. One from brood cells in the outer layer of the nest to represent the most recent diet and one from brood cells in an inner layer to represent older diet. Diet differed between species, although both fed mainly on Thysanoptera, Lepidoptera and Acariformes. Prey taxa identified to species level included both agricultural pests and native species. Prey communities consumed were significantly different between inner and outer nest samples, suggesting seasonal variation in prey availability and/or a diversification of the wasps’ diet as the colony grows. We also show for the first time potential predation of marine organisms by Polistes wasps. Our study provides field evidence that Polistes wasps feed on agricultural pests, supporting the hypothesis that some social wasp species could have a suppressing effect on agricultural pests. The proposed methodology is readily applicable to other nest-building Hymenoptera and has the potential to provide comprehensive knowledge about their diet with minimum sampling effort. Such knowledge is essential to measure the ecological impact of invasive Vespidae and support the conservation of native invertebrate biodiversity.

Seasonal variation in the invertebrate community and diet of a top fish predator in a thermally stable spring

Many life-history events in aquatic invertebrates are triggered by seasonal changes in water temperature, but other ecological factors may be important as well. To rule out the confounding effects of changing water temperature, we studied the seasonal dynamics of an aquatic invertebrate community and their effect on a top fish predator in a thermally stable freshwater spring in South Iceland. We sampled benthic invertebrates five times over a year and conducted a mark-recapture study on the top predator in the system, small benthic Arctic charr, Salvelinus alpinus (L.). We assessed variation in diet composition and feeding preferences by calculating the electivity and individual specialisation of each fish at each sampling time. There was a clear separation of winter and summer communities for the benthic invertebrates. The variation in prey availability was also reflected in the fish diet, with higher feeding selectivity in summer than in winter for the highly abundant Chironomidae larvae. In contrast, individual specialisation as a measure of intrapopulation niche variation was higher in winter when prey availability was lower. We furthermore found that groundwater amphipods might play an important role in the winter diet of spring-dwelling Arctic charr. In conclusion, seasonal variation in the invertebrate community is an important factor to consider and has the potential to alter the phenotype (e.g. growth rates) and behaviour (e.g. feeding preferences) of higher trophic levels.

Drivers and consequences of apex predator diet composition in the Canadian Beaufort Sea.

Polar bears (Ursus maritimus) rely on annual sea ice as their primary habitat for hunting marine mammal prey. Given their long lifespan, wide geographic distribution, and position at the top of the Arctic marine food web, the diet composition of polar bears can provide insights into temporal and spatial ecosystem dynamics related to climate-mediated sea ice loss. Polar bears with the greatest ecological constraints on diet composition may be most vulnerable to climate-related changes in ice conditions and prey availability. We used quantitative fatty acid signature analysis (QFASA) to estimate the diets of polar bears (n = 419) in two western Canadian Arctic subpopulations (Northern Beaufort Sea and Southern Beaufort Sea) from 1999 to 2015. Polar bear diets were dominated by ringed seal (Pusa hispida), with interannual, seasonal, age- and sex-specific variation. Foraging area and sea ice conditions also affected polar bear diet composition. Most variation in bear diet was explained by longitude, reflecting spatial variation in prey availability. Sea ice conditions (extent, thickness, and seasonal duration) declined throughout the study period, and date of sea ice break-up in the preceding spring was positively correlated with female body condition and consumption of beluga whale (Delphinapterus leucas), suggesting that bears foraged on beluga whales during entrapment events. Female body condition was positively correlated with ringed seal consumption, and negatively correlated with bearded seal consumption. This study provides insights into the complex relationships between declining sea ice habitat and the diet composition and foraging success of a wide-ranging apex predator.

Prey Selection by Anurans in Subtemperate Swamps of the Extreme South of Brazil

Temporal habitat variations can affect the trophic relationships of amphibian species by changing either prey availability or predator selectivity. This study aimed to evaluate the influence of prey availability and temperature variation on the diet of three anuran species (Boana pulchella, Odontophrynus maisuma, and Leptodactylus latrans) in subtropical swamps. Coleoptera, Araneae, Diptera, and Hymenoptera were the most important prey. Trophic niche overlap was greatest between Odontophrynus maisuma and B. pulchella. In the warmer months, all three species narrowed their trophic niches by increasing the consumption of certain prey. The changes recorded in the diet might be related to variations in prey availability and other aspects of feeding ecology, such as adaptations in foraging activity, and show that these species have some plasticity regarding their feeding habits.

Niche dynamics of sympatric non‐breeding shearwaters under varying prey availability

Variation in prey availability can cause changes in species interactions among marine predators. Foraging theory predicts that niche breadth will expand when resources become limited, possibly leading to higher niche overlap among sympatric species; however, a species’ niche can become constrained by interactions with other similar species, resulting in an inability to shift niche breadth or position. In coastal Newfoundland, Capelin Mallotus villosus is the main forage fish species and its availability (i.e. biomass) during the summer has varied considerably following a population collapse in the 1990s. During the summer, non‐breeding Great and Sooty Shearwaters Ardenna gravis and A. grisea migrate and aggregate at annually persistent Capelin spawning sites. We used stable isotope ratios (δ13C, δ15N) of blood components (plasma, red blood cells) to investigate variation in isotopic niche breadth (95% prediction ellipse areas) and overlap of the two shearwater species during 2014, 2015 and 2016. Capelin availability varied among years, illustrated by lower peak biomass in 2015 (0.126 g/m²) and 2016 (0.027 g/m²) relative to 2014 (0.254 g/m²). The isotopic niche breadth (plasma) of both shearwater species expanded similarly from 2014 (0.65–0.66‰²) to 2015 (2.22–2.57‰²) and 2016 (1.15–1.42‰²), suggesting the incorporation of alternative prey types into their diet during years of lower prey availability. Isotopic niche overlap between Great and Sooty Shearwaters remained high across years (44–63%), however, providing little evidence for dietary niche partitioning during years of lower prey availability. Findings suggest that both shearwater species are flexible foragers and can modify their diet during the non‐breeding season to accommodate fluctuations in prey availability.