Key Prey Research Articles

Rodent population cycle as a determinant of gastrointestinal nematode abundance in a low-arctic population of the red fox.

We analyzed an 11-year time series (2005–2015) of parasite abundance for three intestinal nematode species in the red fox (Vulpes vulpes) as a function of the multi-annual rodent population cycle in low-arctic Norway, while correcting for other potential covariates that could influence prevalence and abundance. Rodents are paratenic and facultative intermediate hosts for the two Ascarididae species Toxascaris leonina and Toxocara canis, respectively and key prey for the red fox. Still the relative importance of indirect transmission through rodents and direct transmission through free-living stages is unclear. Abundance of these Ascarididae species in individual red foxes (N = 612) exhibited strongly cyclic dynamics that closely mirrored the 4-year rodent cycle. Negative binomial models provided evidence for a direct proportional increase in Ascarididae abundance with rodent density suggesting that predator functional response to rodent prey is the key transmission mechanism. In contrast, no cycles and constantly very low abundance were apparent for Uncinaria stenocephala – a third nematode species recorded without paratenic or intermediate stages.

Estimating Leopard Cat Prionailurus bengalensis Kerr, 1792 (Carnivora: Felidae) density in a degraded tropical forest fragment in northeastern Thailand

The Leopard Cat Prionailurus bengalensis is thought to be Asia’s most abundant wild cat. Yet, the species’ status is poorly known due to a lack of rigorous population estimates. Based on the few studies available, Leopard Cats appear to be more abundant in degraded forests, potentially due to increased prey availability. We conducted camera trap surveys, rodent live-trapping, and spatially-explicit capture-recapture analyses to estimate the density of Leopard Cats within a degraded tropical forest fragment (148km2) in northeastern Thailand. A total effort of 12,615 camera trap nights across 65km2 of trapping area resulted in at least 25 uniquely identified individuals. Average rodent biomass (the main prey of Leopard Cats) was highest in the dry evergreen forest (469.0g/ha), followed by dry dipterocarp forest (287.5g/ha) and reforested areas (174.2g/ha). Accordingly, Leopard Cat densities were highest in the dry evergreen forest with 21.42 individuals/100km2, followed by the reforested areas with 7.9 individuals/100km2. Only two detections came from the dry dipterocarp forest despite both an extensive survey effort (4,069 trap nights) and available prey. Although the dipterocarp supported the second highest average rodent biomass, it lacked a key prey species, Maxomys surifer, possibly explaining low encounter rates in that habitat. Our results provide important baseline information concerning the population status of Leopard Cat in southeastern Asia. Further, our findings corroborate with other studies that found a tolerance among Leopard Cats for degraded forests, highlighting the potential for forest fragments to serve as long-term conservation areas for the species.

Intraspecific variation in a dominant prey species can bias marine predator dietary estimates derived from stable isotope analysis

AbstractIt is often assumed that variation in consumer stable isotope values (δ15N and δ13C) reflect shifts in diet between isotopically distinct prey species. However, an alternate hypothesis is that such variation could be as a result of spatial, temporal, or ontogenetic variation in the stable isotope values of a key prey species that propagate up marine food chains. In the Southern Ocean, Antarctic krill (Euphausia superba) occupy a key position, linking primary production to secondary consumers including fish, squid, seabirds, and marine mammals. As such Antarctic krill represent an ideal prey species to test the critical assumptions behind what has become a common method of dietary analysis in marine predators. Similar to previous studies, we found that stable isotope values of Antarctic krill exhibit significant intraspecific variation associated with both ontogenetic (size) and oceanographic factors (chlorophyll a concentration). Our modeling results showed that intraspecific variation in the stable isotope values of Antarctic krill has the potential to force mean isotope values of krill predators by as much as 2.4‰, independent of changes in the species composition of diet. Our findings indicate that intraspecific variation in the stable isotope values of a single, dominate prey species, such as Antarctic krill, has the potential to bias both absolute and relative estimates of marine predator diets using stable isotope mixing models. Therefore, caution is warranted to avoid spatial, temporal, and ontogenetic mismatches between the stable isotope values of prey sources used in mixing models and the actual stable isotope values of prey consumed by marine predators.

Fish feeding groups, food selectivity, and diet shifts associated with environmental factors and prey availability along a large subtropical river, China

Understanding spatial variation in fish trophic structures along large river systems remains a challenge, and the influence of fish food selectivity and diet shifts on these structures remains unknown. In this study, the assemblage composition and stomach contents of fish in the subtropical East River of southern China were analyzed to determine their diet composition (DC) and identify prey-oriented feeding groups. Ten prey items were identified and used to cluster 106 fish species into 23 feeding groups. The number of groups increased longitudinally due to the accumulated emergence of site-specific prey sources in fish DC, although this number decreased sharply near the estuary due to the loss of insectivorous fish. The fish assemblages showed a longitudinal decrease in abundance and an increase in biomass, with higher values observed in the rainy season than the dry season. A downstream decrease in insectivores and epiphytivores and increase in detritivores and molluscivores represented the basic patterns observed along the river. Seven widespread fish species exhibited spatial dietary shifts, among which three generalist feeders with a high abundance notably influenced the fish trophic structures, and four specialist feeders with high food selectivity were significantly (P < 0.05) correlated with prey availability. Multivariate data analysis showed that the flow velocity, water depth, riffle areas, and nutrient concentrations were the key environmental factors that determined the distribution of fish feeding groups, while hydrophytes, plant debris, Ephemeroptera and Odonata insects, and Atyidae shrimp were the key prey sources.

Multi-locus DNA metabarcoding of zooplankton communities and scat reveal trophic interactions of a generalist predator

To understand the ecosystem dynamics that underpin the year-round presence of a large generalist consumer, the Bryde’s whale (Balaenoptera edeni brydei), we use a DNA metabarcoding approach and systematic zooplankton surveys to investigate seasonal and regional changes in zooplankton communities and if whale diet reflects such changes. Twenty-four zooplankton community samples were collected from three regions throughout the Hauraki Gulf, New Zealand, over two temperature regimes (warm and cool seasons), as well as 20 samples of opportunistically collected Bryde’s whale scat. Multi-locus DNA barcode libraries were constructed from 18S and COI gene fragments, representing a trade-off between identification and resolution of metazoan taxa. Zooplankton community OTU occurrence and relative read abundance showed regional and seasonal differences based on permutational analyses of variance in both DNA barcodes, with significant changes in biodiversity indices linked to season in COI only. In contrast, we did not find evidence that Bryde’s whale diet shows seasonal or regional trends, but instead indicated clear prey preferences for krill-like crustaceans, copepods, salps and ray-finned fishes independent of prey availability. The year-round presence of Bryde’s whales in the Hauraki Gulf is likely associated with the patterns of distribution and abundance of these key prey items.

Little to fear: largest lizard predator induces weak defense responses in ungulate prey

Nonconsumptive effects can strongly influence apex predator ecological function. These effects arise because prey often induce costly phenotypic responses to mitigate predation risk. Yet because predator–prey interactions are complex, prey defenses may vary considerably. We investigated if the Komodo dragon (Varanus komodoensis), a reptile apex predator, induced multiscale antipredator responses in key prey, the Rusa deer (Cervus timorensis) and the wild pig (Sus scrofa). To this end, we examined the temporal and spatial partitioning of habitats by predator and prey, determined the size of ungulate groups as a function of risk, and assessed changes in individual behavior of prey individuals exposed to predator kairomones at feeding stations. Komodo dragon, deer, and pig populations exhibited significant, but subtle differences in 3 habitat preferences that otherwise indicated high niche overlap. Komodo dragon predation risk, alongside other commonly considered predictor variables, did not affect deer or pig group size. With the exception of one individual-based vigilance-type behavior in pigs, no other antipredator behavior, including reduced food consumption, significantly varied in the presence of predator odor cue at feeding stations. Overall, our results indicated limited evidence for antipredator behavior and suggested Komodo dragons exert weak nonconsumptive effects of predation in ungulates. However, weak predatory interactions could be beneficial in island ecosystems as it could promote predator–prey coexistence that reduces extinction risk.

基于SURF指数识别海州湾食物网的关键饵料生物

PDF HTML阅读 XML下载 导出引用 引用提醒 基于SURF指数识别海州湾食物网的关键饵料生物 DOI: 10.5846/stxb201811012365 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31772852）；国家重点研发计划（2017YFE0104400）；山东省支持青岛海洋科学与技术试点国家实验室重大科技专项（2018SDKJ0501-2） Identification of keystone prey species in Haizhou Bay food web based on SURF index Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:关键种（keystone species）在生态系统中发挥着不可替代的重要作用，对于群落结构的稳定与演替起着决定性的作用。基于2011年3-12月在海州湾及其邻近海域进行的渔业资源底拖网调查资料以及胃含物分析数据和参考历史文献数据，以物种间的摄食关系作为基础，采用SURF（Supportive Role to Fishery ecosystems）指数识别海州湾食物网中的关键饵料生物。在矩阵中分析每个物种作为饵料生物为捕食者提供的摄食比例及捕食者数量，计算每个物种的关键指标（SURFi）的值，结果表明前五位数值较高的物种是细鳌虾（Leptochela gracilis）、毛虾（Acetes sp.）、疣背宽额虾（Latreutes planirostris）、日本鼓虾（Alpheus japonicus）和鳀鱼（Engraulis japonicus），它们是海州湾的关键饵料生物，在整个食物网中起到关键的控制作用，它们的数量波动会对海州湾其他物种产生直接或间接的影响。加强关键饵料生物的保护，对于维持海州湾生态系统的健康和稳定至关重要。 Abstract:Keystone species play an irreplaceable role in ecosystems and play a decisive role in the stability and succession of community structures. Based on the bottom trawl surveys from March to December in 2011 in Haizhou Bay and adjacent waters and reference historical literature, SURF (Supportive Role to Fishery ecosystems) index was calculated to identify keystone prey species in Haizhou Bay food web. In the matrix, we analyzed the ratio of food intake and predators for each species, and calculated the value of each species' key indicator (SURFi). The top five prey species were Leptochela gracilis, Acetes sp., Latreutes planirostris, Alpheus japonicus and Engraulis japonicus, which are keystone prey species in the Haizhou Bay ecosystem. As key prey species, they have relatively low trophic levels, which not only affect energy flow and mass transfer, but also control species diversity in the ecosystem. They play key roles in the control of the entire food web, and their fluctuations may have direct or indirect effects on other species in the Haizhou Bay food web. Therefore, it is critical to protect the key prey species for maintaining the health and stability of Haizhou Bay ecosystem. 参考文献 相似文献 引证文献

The diet of two opportunistic seabirds (Caspian and Royal Terns) confirms the importance of Sardinella spp. in West African coastal food webs

ABSTRACTDespite their importance for fisheries, livelihoods and biodiversity conservation, shelf ecosystems in West Africa are poorly known. Caspian Tern (Hydroprogne caspia) and Royal Tern (Thalasseus maximus) are two of the most numerous and widespread nesting seabirds in the region, and an understanding of the diet of these opportunistic predators may throw light on important elements of the local food webs. This study describes and compares the prey consumed by these two species in Guinea and Guinea-Bissau collected from 2013 to 2015. Our results show that both tern species feed mostly on pelagic fish from which Clupeidae (mostly Sardinella maderensis) dominated the diet at all locations and seasons. Pristigasteridae and Polynemidae were the next most frequent prey in the diet of these two tern species. Our findings strengthen the recent suggestion of a wasp-waist ecosystem for our study area, with sardinella as the key prey for several predators, including seabirds and pelagic fishes, and potentially influencing their distribution and abundance. Moreover, our results show a higher diversity in the diet of the Caspian Tern, with this species preying on a greater range of benthopelagic fishes (e.g. Gerreidae; Mugilidae) which fits with observations of inshore foraging that seems rarer in Royal Terns. We further show that prey identification based only on otoliths from pellets, as opposed to the use of all hard structures (e.g. otoliths, vertebrae, scales), seriously underestimates the occurrence of species with fragile and small otoliths, including clupeids and other small pelagics.

Could offspring predation offset the successful reproduction of the arctic copepod Calanus hyperboreus under reduced sea-ice cover conditions?

Life cycle and reproduction of Calanus hyperboreus were studied during a year of record low ice cover in the southeastern Beaufort Sea. Stages CIV, adult females and CV dominated the overwintering population, suggesting a 2- to 3-year life cycle. Within two spring-summer months in the upper water column females filled their energy reserves before initiating their downward seasonal migration. From February to March, vigorous reproduction (20–65 eggs f−1 d−1) delivered numerous eggs (29 000 eggs m−2) at depth and nauplii N1-N3 (17 000 ind. m−2) in the water column. However, CI copepodite recruitment in May, coincident with the phytoplankton bloom, was modest in Amundsen Gulf compared to sites outside the gulf. Consequently, C. hyperboreus abundance and biomass stagnated throughout summer in Amundsen Gulf. As a mismatch between the first-feeding stages and food was unlikely under the favourable feeding conditions of April-May 2008, predation on the egg and larval stages in late winter presumably limited subsequent recruitment and population growth. Particularly abundant in Amundsen Gulf, the copepods Metridia longa and C. glacialis were likely important consumers of C. hyperboreus eggs and nauplii. With the ongoing climate-driven lengthening of the ice-free season, intensification of top-down control of C. hyperboreus recruitment by thriving populations of mesopelagic omnivores and carnivores like M. longa may counteract the potential benefits of increased primary production over the Arctic shelves margins for this key prey of pelagic fish, seabirds and the bowhead whale.

Contrasting impact of diatoms on dominant calanoid and cyclopoid copepods in a temperate bay

The role of diatom dominance and phytoplankton concentration in determining the abundance of the dominant calanoid and cyclopoid copepod species in Port Phillip Bay, southern Australia, was investigated. Sampling for Chlorophyll-a, phytoplankton and zooplankton was conducted on 11 sampling trips between August 2016 and June 2017. The proportion of diatom cells was positively related to the total phytoplankton cell concentration but less related to the chlorophyll-a concentration. Abundance of the dominant calanoid copepod, a key prey item for larval fish, increased with water temperature but declined when the proportion of diatom cells increased, and was unrelated to chlorophyll-a concentration. In contrast, abundance of the dominant cyclopoid copepod was not related to the proportion of diatom cells but was positively related to water temperature and chlorophyll-a concentration. The results verify the assumptions previously made about the negative relationship between the proportion of diatoms and abundance of the dominant calanoid copepod Paracalanus indicus when modelling planktonic production and fish recruitment in Port Phillip Bay. In relation to the dominant cyclopoid copepod Oithona similis, the results indicate that this species was not affected by the proportion of diatoms. Instead, the results suggest that food-limitation may be a key factor determining the abundance of O. similis in Port Phillip Bay. Overall, variation in zooplankton composition and fish recruitment in Port Phillip Bay will depend not only on phytoplankton abundance but also on the composition in relation to the dominance of diatoms.

Vibrio cholerae motility exerts drag force to impede attack by the bacterial predator Bdellovibrio bacteriovorus

The bacterial predator Bdellovibrio bacteriovorus is evolved to attack and kill other bacteria, including the human intestinal pathogen Vibrio cholerae. Although B. bacteriovorus exhibit a broad prey range, little is known about the genetic determinants of prey resistance and sensitivity. Here we perform a genetic screen on V. cholerae and identify five pathways contributing to predation susceptibility. We find that the essential virulence regulators ToxR/S increase susceptibility to predation, as mutants of these genes are more resistant to predation. We observe by flow cytometry that lipopolysaccharide is a critical defense, as mutants lacking O-antigen are rapidly attacked by predatory B. bacteriovorus. Using polymer solutions to alter media viscosity, we find that when B. bacteriovorus attacks motile V. cholerae, increased drag forces slow its ability to prey. These results provide insights into key prey resistance mechanisms, and may be useful in the application of B. bacteriovorus in treating infections.

Forage fish fisheries management requires a tailored approach to balance trade‐offs

AbstractEcosystem‐based fishery management requires considering the effects of actions on social, natural and economic systems. These considerations are important for forage fish fisheries, because these species provide ecosystem services as a key prey in food webs and support valuable commercial fisheries. Forage fish stocks fluctuate naturally, and fishing may make these fluctuations more pronounced, yet harvest strategies intended to ameliorate these effects might adversely affect fisheries and communities. Here, we evaluate trade‐offs among a diverse suite of management objectives by simulating outcomes from several harvest strategies on forage fish species. We demonstrate that some trade‐offs (like those between catches and minimizing collapse length) were universal among forage species and could not be eliminated by the use of different control rules. We also demonstrate that trade‐offs vary among forage fish species, with strong trade‐offs between stable, high catches and high‐biomass periods (“bonanzas”) for menhaden‐ and anchovy‐like fish, and counterintuitive trade‐offs for sardine‐like fish between shorter collapses and longer bonanzas. We find that harvest strategies designed to maintain stability in catches will result in more severe collapses. Finally, we show that the ability of assessments to detect rapid changes in population status greatly affects control rule performance and the degree and type of trade‐offs, increasing the risk and severity of collapses and reducing catches. Together, these results demonstrate that while default harvest strategies are useful in data‐poor situations, management strategy evaluations that are tailored to specific forage fish may better balance trade‐offs.

Detection of Rabbit Hemorrhagic Disease Virus GI.2/RHDV2/b in the Mediterranean Pine Vole ( Microtus duodecimcostatus) and White-Toothed Shrew ( Crocidura russula).

The European wild rabbit ( Oryctolagus cuniculus) is a key prey species on the Iberian Peninsula, and several predator species that are at risk of extinction are dependent on them as prey. A new rabbit hemorrhagic disease (RHD) virus genotype (GI.2/RHDV2/b) emerged in 2010 and posed a threat to wild rabbit populations. During a survey aimed at investigating RHD epidemiology in wild rabbits, GI.2/RHDV2/b was detected by duplex real-time PCR in carcasses of one Mediterranean pine vole ( Microtus duodecimcostatus) and two white-toothed shrews ( Crocidura russula). Laboratory New Zealand white rabbits that were challenged with inocula obtained from the liver of the small mammals died showing RHD lesions, confirming the infectiousness of the isolates. Phylogenetic analysis of the VP60 gene nucleotide sequences showed complete homology between the isolates from the two small mammal species and a high degree of similarity, but not complete homology, to GI.2/RHDV2/b sequences from wild rabbits. The GI.2/RHDV2/b genotype has not been reported in species outside the order Lagomorpha.

Critical trophic links in southern Chukchi Sea lagoons

Arctic lagoons support a variety of fish, bird and marine mammal species, as well as subsistence fisheries that are critical to local food security along the Chukchi and Beaufort sea coasts. In summer 2015, diet samples from seven lagoon fishes were non-lethally collected in three lagoons along the Northwest Alaska coastline. Using these samples, we determined that the key prey species that supported these particular lagoon food webs were mysids, chironomids and Ninespine Stickleback. We identified the relative importance of freshwater/terrestrial and marine prey sources in lagoon fish diets and identified three key functional feeding groups of fishes: microbenthivore/zooplanktivores, macrobenthivore/piscivores, and piscivores. Several key predators were found in the microbenthivore/zooplanktivore group indicating a high degree of redundancy, which was lacking in the other functional feeding groups. This suggests that this group has the greatest resiliency, whereas other groups may be more vulnerable to changes in lagoon habitats. Functional groups with less redundancy, such as the upper trophic levels, may be good indicator species for identifying potential impacts to Arctic lagoons from climate change.

Population‐level effects of wind farms on a desert lizard

ABSTRACTRenewable forms of energy production can have major societal benefits including reduced carbon pollution and decreased dependence on fossil fuels but are not without associated costs. For example, habitat degradation at renewable energy production sites may affect the persistence of wildlife populations. We assessed the effects of wind farms in the San Gorgonio Wind Resource Area near Palm Springs, California, 2013–2015, on local populations of the side‐blotched lizard (Uta stansburiana). The side‐blotched lizard is a common and ubiquitous desert reptile that is a major consumer of invertebrates and, in turn, represents a key prey base for many avian, reptilian, and mammalian predators. We used spatially explicit capture‐recapture methods to compare a comprehensive set of population‐level vital signs (i.e., abundance, population growth rate, survival, recruitment, body condition, age structure, activity area size, movement rates) among populations at 4 wind farms and at 5 reference areas. Although our models indicate that wind facilities have a weak negative effect on side‐blotched lizard survival, our overall results suggest that wind farms do not substantially influence the demography or behavior of these small lizards. Population response to general anthropogenic disturbance (quantified as an index of road type and density) was more pronounced, with lower population growth rates, adult‐skewed age structure, and reduced body condition at highly disturbed wind farm and reference sites. We therefore conclude that wind‐power facilities can support healthy populations of side‐blotched lizards, indicating that wind energy development is compatible with a native Mojave Desert species. However, our results show that anthropogenic disturbance, as measured by the type and density of roadways, has a negative effect on lizard populations, and should be carefully planned whether associated with energy development or not. Our study demonstrates a methodological approach that can be applied to other species, including those with lower tolerances to disturbance, to measure their response to renewable energy development. © 2018 The Wildlife Society.

Conventional and molecular analysis of the diet of gentoo penguins: contributions to assess scats for non-invasive penguin diet monitoring

There is a growing search for less invasive methods while studying the diet of Antarctic animals in the wild. Therefore, we compared the diet of gentoo penguins from stomach contents (i.e. through visual identification of prey remains) and scats (i.e. faeces), and further compared prey DNA assay in fresh and old scats. Prey remains identified visually in stomach contents and scats were broadly comparable: the crustaceans and fish were the most important components, with Themisto gaudichaudii clearly being the most frequent and numerous prey species in both sampling methods. By mass, differences in species frequency were observed in stomach contents (Parachaenichthys georgianus) and scats (Champsocephalus gunnari), with the former fish species absent in scats. Differences were detected in the most frequent prey (T. gaudichaudii and Euphausia superba) and in various fish species, most with bigger sizes in scats. Allometric equations to estimate most crustacean’s sizes (i.e. relationships between carapace and mass/total length) are needed. For DNA studies, when comparing DNA from fresh and old scats, both provided similar results that, in general, were also similar to the visual analysis. In order to use penguin scats (along with the use of DNA analyses) for monitoring purposes, allometric equations to estimate mass and size of prey (most crustaceans) and better designed species-specific primers are needed for targeting key prey species (e.g. Euphausia superba, T. gaudichaudii). These DNA methodologies can complement other methods (i.e. visual analyses and stomach contents analyses) in monitoring programs of penguins.

Multi-Isotope investigations of ungulate bones and teeth from El Castillo and Covalejos caves (Cantabria, Spain): Implications for paleoenvironment reconstructions across the Middle-Upper Palaeolithic transition

The Cantabrian region of Northern Spain was an important area of human occupation during the Middle and Upper Palaeolithic as the rich archaeological record demonstrates. The environmental conditions experienced by late Neanderthals and Anatomically Modern Humans (AMH) in the region during MIS3 are still poorly known, but are crucial to understand the role climatic instability could have had on the adaptations of these populations. In this study, a series of archaeological levels with Mousterian and Aurignacian artefact assemblages, dating between 49 and 35 ka uncal. BP, from the sites of El Castillo and Covalejos caves in Cantabria were studied using multi-isotope techniques including bone collagen δ13C, δ15N and δ34S analysis and a pilot study based on tooth enamel δ18O and δ13C. Results at Covalejos indicate a large range in δ15N values observable within both Mousterian Level D and Aurignacian Level B, suggesting the presence of different micro-environments within the local area at certain times during each temporal period. Within Aurignacian Level C and Mousterian Level J, the δ15N values range is much smaller, but shows consistency in the parts of the landscape being exploited during both times. Neanderthals and AMH appear to have been procuring animals from isotopically similar zones (isozones) when they occupied Covalejos. The variations in δ34S values between levels analysed at Covalejos also implies the use of a variety of hunting locations by both late Neanderthals and AMH. At El Castillo, δ13C and δ15N values show great consistency between levels, indicating that animals were being hunted from the same isozones when the site was presumably occupied by the two human species. The mosaic landscapes of Cantabria may have buffered the sharp environmental fluctuations that occurred during late MIS3 throughout Europe, providing suitable habitats for the key prey ungulate species that were routinely exploited throughout the Middle and Early Upper Palaeolithic. This environmental buffering may explain why this southerly, oceanic region was consistently occupied throughout this time of bio-cultural transition.

Feeding of Greenland halibut (Reinhardtius hippoglossoides) in the Canadian Beaufort Sea

Abstract Trophic patterns for Greenland Halibut are reported for the first time in the Canadian Beaufort Sea and Amundsen Gulf (n = 269). Samples were collected from 2012 to 2014 on the upper (300–500 m) and lower continental slope (750–1500 m) and were analyzed for stomach contents, stable isotopes ratios and fatty acids (FA). Stomach contents indicated that Arctic Cod, Boreogadus saida, was the main prey ingested on the upper slope (50–94% of total biomass) whereas Gelatinous Snailfish (Liparis fabricii) and Zoarcids (Lycodes spp.) dominated diets on the lower slope (17–62% of total biomass). Stable isotope mixing models and FA analyses also identified benthopelagic fishes (i.e., Liparis spp., B. saida) as key prey and highlighted large dietary overlap among years and between the two depth categories. Greenland Halibut were characterized by relatively wide δ13C and narrow δ15N ranges that suggested use of both pelagic and benthic energy sources and a piscivorous diet. Calanus-type markers such as 20:1n9 dominated the FA (>20% of total FA) andemphasized the importance of pelagic-derived material in the diet. The contribution of pelagic and benthic-derived matter in the diet suggests that Greenland Halibut play a major role in the benthic-pelagic coupling for deep water communities (up to 1500 m) in the Canadian Beaufort Sea.

Reintroducing a keystone burrowing rodent to restore an arid North American grassland: challenges and successes

Prairie dogs (Cynomys spp.) are important ecosystem engineers in North America's central grasslands, and are a key prey base for numerous predators. Prairie dogs have declined dramatically across their former range, prompting reintroduction efforts to restore their populations and ecosystem functions, but the success of these reintroductions is rarely monitored rigorously. Here, we reintroduced 2,400 Gunnison's prairie dogs (C. gunnisoni) over a period of 6 years to the Sevilleta National Wildlife Refuge, in central New Mexico, U.S.A., a semi‐arid grassland ecosystem at the southern edge of their range. We evaluated the population dynamics of prairie dogs following their reintroduction, and their consequent effects on grassland vertebrates. We found postrelease survival of prairie dogs stabilized at levels typical for the species (ca. 50%) after approximately 1 month, while average annual recruitment was ca. 0.35 juveniles per female, well below what was required for a self‐sustaining, stable population. Extreme drought conditions during much of the study period may have contributed to low recruitment. However, recruitment increased steadily over time, indicating that the reintroduced colony may simply need more time to establish in this arid system. We also found well‐known associates of prairie dog colonies, such as American badgers (Taxidea taxus) and burrowing owls (Athene cunicularia), were significantly more common on the colonies than off. After 7 years, we have yet to meet our goal of establishing a self‐sustaining population of Gunnison's prairie dogs in this semi‐arid grassland. But despite the uncertainty and challenges, our work shows that reestablishing keystone species can promote ecosystem restoration.

Forage fish control population dynamics of North Sea whiting Merlangius merlangus

Predator populations are often affected by the abundance of their prey, but pronounced effects on predatory fish have mainly been demonstrated in ecosystems where a key predator depends largely on one key prey species. The North Sea food web has a comparatively high level of complexity with a high diversity of forage fish, and hence strong effects are less likely to occur. However, in the early 2000s within large parts of the North Sea, several forage fish stocks simultaneously suffered from successive years of recruitment failure together with decreasing stock abundances. Whiting Merlangius merlangus is a major fish predator in the North Sea ecosystem and is known to be almost exclusively piscivorous. We hypothesised that shortages in forage fish should lead to negative effects on growth or condition of a predator that relies on a few dominant prey fish species. In our study, we combined 6 different North Sea data sets on abundance of forage fish and length-at-age, condition and stomach contents of M. merlangus to analyse contrasting periods with high and low forage fish availability. We found a simultaneous decrease in forage fish availability and M. merlangus length-at-age in the period from 2000-2007 and a subsequent parallel increase in prey abundance and length-at-age after 2007. In the period of low forage fish availability, mean stomach content mass was on average 60% less than in the reference periods. Additionally, a bioenergetics calculation revealed that even smaller differences in the stomach contents than those observed would have been sufficient to explain the observed differences in length-at-age. Our findings emphasize the need to incorporate predator-prey interactions in assessment models and management strategies.