Variation In Prey Selection Research Articles

Temporal variation in prey selection by adult European sardine (Sardina pilchardus) in the NW Mediterranean Sea

In the North-Western Mediterranean Sea (NWMS), changes in size and taxonomic composition of zooplankton have been hypothesized to underlie observed changes in populations of Sardina pilchardus, one of the main small pelagic fish species. The present study was undertaken to better understand the link between the temporal variability of zooplankton and the diet of adult sardine in the Bay of Marseille over a period of 16 months by comparing the taxonomic and prey size composition of sardine stomach content with net-collected zooplankton samples from a fixed station. A greater similarity was found between sardine stomach content and 80-μm mesh size net samples than with the traditionally used 200-μm net samples. Sardine showed a high diet plasticity over the entire study period, covering a broad diversity of prey species and a wide prey size range (ranging from 400 to 1000 μm in measured total length), including a lot of small copepods (Microsetella/Macrosetella spp., Corycaeidae and Oncaeidae). The most consumed prey groups were not necessarily the most abundant in the zooplankton sampled with nets, suggesting potential prey selection. Sardine showed most often an opportunistic selective predation on larger individuals for most taxonomic prey groups. Results highlighted the diet flexibility of sardine between months and showed seasonal variation in prey size, suggesting a continuous filter-feeding mode on relatively small prey when prey densities were high and more frequent selective particulate-feeding on larger prey when prey densities were low. Sardines were able to feed on a wide diversity of prey and size range and thus to shift their diet between months. This ability probably allows them to adapt to high spatial and temporal variability of the zooplankton community in a context of both human-induced and climatic changes.

Isotopic niche partitioning between two small cetacean species

Commerson’s dolphin Cephalorhynchus commersonii and Peale’s dolphin Lagenorhynchus australis live in sympatry along the southwestern South Atlantic Ocean, suggesting the existence of some degree of habitat partitioning to reduce their competition for resources. Both species are usually associated with coastal environments, but information on their trophic ecology is scarce. Here we explored the existence of trophic resource partitioning between these 2 sympatric species using δ13C and δ15N. From 2007 to 2013, we analyzed a total of 14 Commerson’s dolphin and 34 Peale’s dolphin skin samples from a marine protected area in Argentina. Significant differences in δ13C values indicated intra- and interspecific spatial partitioning. Three different Peale’s dolphin feeding groups (FGs) were identified: FG1 exclusively exploited the pelagic habitat, FG2 occupied more pelagic/inshore habitats (similar to Commerson’s dolphins), and FG3 occupied more benthic/inshore habitats. Isotopic niche breadth varied between species and feeding groups, exhibiting less variation in prey selection among Commerson’s dolphins. According to Bayesian standard ellipse area analysis, isotopic niche overlap was found between FG2 and FG3 from 2007 to 2012, and between FG2 and Commerson’s dolphins. Mixing models suggest that FG3 has a diet mainly based in benthic fish, while FG2 and Commerson’s dolphins feed predominantly on pelagic fish. Overall, this study indicates segregation in the use of trophic resources between 2 sympatric dolphin species, showing different foraging strategies that promote coexistence and reduce intra- and interspecific competition. Furthermore, the presence of 3 Peale’s dolphin feeding groups segregated at a small geographic scale suggests a previously unknown ecological complexity.

Co-occurring predators increase biotic resistance against an invasive prey

The presence of multiple predators can lead to variation in predator behavior and ultimately altered risk for shared prey. This concept has seldom been accounted for in studies that consider predator-driven biotic resistance from native marine predators against invasive prey. This study compared the prey selection of whelks and rock lobsters when co-occurring and when foraging in isolation. When in isolation, both predators preferred the native mussel Choromytilus meridionalis, regardless of the abundance of alternative prey. However, when co-occurring, predation risk for all prey species, including the invasive mussel Semimytilus algosus, increased. This was largely driven by greater variation in prey selection by rock lobsters in the presence of whelks. This indicates that predatory efforts from co-occurring predators can result in stronger predation pressure on invasive prey than would be recognized if predators were assessed in isolation.

Age‐specific foraging strategies among pumas, and its implications for aiding ungulate populations through carnivore control

Humans have been controlling carnivore numbers for centuries. Predator hunting, however, may indirectly influence predator‐prey dynamics unintentionally by influencing the age‐ and sex‐structure of predator populations that exhibit intraspecific (IS) variation in prey selection. We tested for IS in a small population of pumas in the Greater Yellowstone Ecosystem, United States, and identified foraging strategies shared by multiple individuals. Further, we tested extrinsic and intrinsic variables that explained differences in foraging strategy. Our top model was composed of a single intrinsic characteristic, Age. In short, the older the animal, the larger the prey it specialized upon. Our provocative results suggest that the current controversial strategy of increasing puma culling to aid mule deer, as currently underway in Colorado, may in fact exacerbate problems for mule deer by changing the age‐structure of the puma population to predominantly younger animals that are more likely to hunt deer over elk.

Variation in prey selection and foraging success associated with early‐life ontogeny and habitat use of American paddlefish (Polyodon spathula)

AbstractMany fishes are planktivorous during early life and switch to piscivory or consume larger food items as ontogeny progresses. In contrast, paddlefish start as particulate feeders and later become filter feeders. Few studies have identified food items essential for paddlefish growth, survival and recruitment surrounding this ontogenetic diet shift. The objectives of this study were to investigate (i) prey types consumed by paddlefish, (ii) variability in prey selection surrounding an ontogenetic diet shift and (iii) whether habitat affected paddlefish prey selection or foraging success. We analysed gut contents of 189 wild age‐0 paddlefish from the middle Mississippi River (MMR) and also conducted a laboratory experiment to address these objectives. We found that paddlefish primarily foraged on benthic macroinvertebrates in the MMR, which differed from previous studies in lentic systems, suggesting young paddlefish prey selection may be labile depending on habitat (i.e., lotic versus lentic). Dominant prey of wild‐caught and experimental age‐0 paddlefish were caddisfly larvae (Trichoptera), followed by hemipterans and amphipods. We found little evidence that habitat attributes affected foraging success, but the most common prey items consumed were associated with wing dike habitat and the upstream and downstream tips of alluvial islands. Our experimental study revealed that if provided a mixture of organisms, age‐0 paddlefish will primarily consume macroinvertebrates while age‐1 paddlefish will mainly filter zooplankton. Overall results suggest young paddlefish prey selection can be highly variable, but also heavily reliant on a narrow group of prey resources.

Incorporating preferential prey selection and stochastic predation into population viability analysis for rare prey species

There is increasing evidence that predation can cause the decline and extinction of small populations of prey, and that stochastic predation resulting from variation in prey selection by individual predators can have significant consequences for population persistence. Modelling approaches that ignore variation in prey selection exhibited by individual predators may inaccurately predict the effect of predation on prey populations, especially over longer time scales. We assess the impacts of variation in prey selection by building PVA models for endangered huemul deer Hippocamelus bisulcus that sequentially include and exclude observed stochasticity in predation among individual pumas Puma concolor. Our results indicated that huemul are at risk of extinction in all scenarios modelled, although the immediacy of this risk differed based on model structure and time period considered. Specifically, modelling predation as a random effect based on an interrupted Poisson process rather than as a directional and continuous change in survival rates, resulted in significantly longer estimates of time to extinction independent of the assumed intensity of predation. Our results highlight the importance of determining whether specialist predators are driving predation on rare prey, and when they are, incorporating said stochastic predation when attempting to predict persistence probabilities of rare prey using PVA models. Since results of PVA models are commonly used to develop conservation strategies, we advocate for the inclusion of stochastic predation in future PVA models where warranted to more accurately inform strategies for the conservation of rare prey and their predators.

Application Of Stable Isotope Analysis To Study Temporal Changes In Foraging Ecology In A Highly Endangered Amphibian

BackgroundUnderstanding dietary trends for endangered species may be essential to assessing the effects of ecological disturbances such as habitat modification, species introductions or global climate change. Documenting temporal variation in prey selection may also be crucial for understanding population dynamics. However, the rarity, secretive behaviours and obscure microhabitats of some endangered species can make direct foraging observations difficult or impossible. Furthermore, the lethality or invasiveness of some traditional methods of dietary analysis (e.g. gut contents analysis, gastric lavage) makes them inappropriate for such species. Stable isotope analysis facilitates non-lethal, indirect analysis of animal diet that has unrealized potential in the conservation of endangered organisms, particularly amphibians.Methodology/findingsI determined proportional contributions of aquatic macroinvertebrate prey to the diet of an endangered aquatic salamander Eurycea sosorum over a two-year period using stable isotope analysis of 13/12C and 15/14N and the Bayesian stable isotope mixing model SIAR. I calculated Strauss’ dietary electivity indices by comparing these proportions with changing relative abundance of potential prey species through time. Stable isotope analyses revealed that a previously unknown prey item (soft-bodied planarian flatworms in the genus Dugesia) made up the majority of E. sosorum diet. Results also demonstrate that E. sosorum is an opportunistic forager capable of diet switching to include a greater proportion of alternative prey when Dugesia populations decline. There is also evidence of intra-population dietary variation.Conclusions/significanceEffective application of stable isotope analysis can help circumvent two key limitations commonly experienced by researchers of endangered species: the inability to directly observe these species in nature and the invasiveness or lethality of traditional methods of dietary analysis. This study illustrates the feasibility of stable isotope analysis in identifying preferred prey species that can be used to guide conservation management of both wild and captive food sources for endangered species.

Intraspecific variability drives diversity in food webs

AbstractBiodiversity theories neglect individual-level variability in ecological interactions even though empirical work has revealed considerable genetic and phenotypic variation among individuals in natural populations. This impedes assessing the impact of individual-level variability on biodiversity in multi-trophic ecosystems. Here we use a density-dependent and individual-based food web model, tested against the largest individual-based food web to date, to show that non-random intraspecific variation in prey selection alters species diversity in food webs. Predators consuming many prey increase diversity by preferentially selecting common prey; predators consuming few prey inhibit diversity by preferentially selecting rare prey, putting them at risk of extinction. Thus species-level patterns cannot be explained by species-level averages, but instead must consider individual-level variation in prey selection. Individual-level variation occurs in many biological and social contexts, suggesting that analyses of individual-level interaction data will be relevant in a wide range of fields.

Mercury concentrations in Southern Beaufort Sea polar bears: Variation based on stable isotopes of carbon and nitrogen

Total Hg concentration was measured in hair and whole blood of 52 adult Southern Beaufort Sea polar bears (Ursus maritimus) captured in the spring of 2005. Stable isotopic signatures (i.e., 13C/12C, delta13C; 15N/14N, delta15N) in hair and two blood compartments (packed blood cells/clot and serum) were determined to assess the variation of Hg concentrations among polar bears in relation to their feeding ecology and other biological factors. Concentrations of Hg in hair and blood (2.2-23.9 microg/g dry wt and 0.007-0.213 microg/g wet wt, respectively) were within the range of values previously reported for polar bears in Canada and East Greenland. Mercury concentration in hair from females was higher than that in hair from males, and concentration was related to interactions between delta13C, delta15N, and longitude of capture location. Mercury concentrations in hair were inversely correlated to delta13C in hair and blood, suggesting that polar bears with greater total Hg concentrations fed more on pelagic prey, such as ringed seals or beluga whale, than on benthic prey. Variability in Hg concentrations in polar bear hair and blood may be the result of intraspecific or regional variation in prey selection rather than strictly trophic level interactions.

Variation in prey selection of a piscivorous fish after the impoundment of a neotropical reservoir: prey size and type

The relative abundance and size of prey fish in the stomachs of the predator Acestrorhynchus pantaneiro were compared with those recorded in the field to estimate prey selection. Fish samples were taken monthly in the Manso Reservoir (State of Mato Grosso, Brazil) immediately after the impoundment, from March 2000 to February 2001 (period I) and from March 2003 to February 2004 (period II). In period I, the small relative dominance of the prey in the environment seemed to have lead to random foraging. In period II, however, when the forage fish Moenkhausia dichroura was dominant in the environment, the predator shifted its diet, foraging mainly on this prey. Species with short relative body depth were positively selected. The prey size classes between 30 and 49 mm, and 50 and 69 mm standard length (L(S)) were the most abundant in the environment. Small prey were predominantly selected by A. pantaneiro. Even when a given prey or prey size was predominant in the environment, A. pantaneiro was a selective predator and maintained its preferences associated to prey type and L(S), although it consumed the most abundant resource.

Spatial and temporal variation in prey selection of brown trout in a cold Arkansas tailwater

Abstract – We examined prey utilisation patterns of brown trout (Salmo trutta Linnaeus) as related to available benthos in a cold tailwater (Little Red River, Arkansas) having low biodiversity of benthic macroinvertebrates and low availability of fish as prey. Benthic macroinvertebrates were sampled monthly in upstream and downstream sites over a 1‐year period. Stomach content analysis was also performed on 30 brown trout (10 each of three size classes) collected monthly from each site. Benthic and diet diversities were low at both sites, as isopods (Lirceus) accounted for 67% and 51% of the numerical abundance upstream and downstream, respectively, and 80% and 70% of all prey consumed by upstream and downstream brown trout. Physid snails (upstream) and chironomid larvae (downstream) accounted for most of the remaining prey taxa consumed. Piscivory and consumption of terrestrial invertebrates were rare. There was no clear relation between diet diversity and trout size. Densities of benthic macroinvertebrates and prey consumption were significantly greater upstream than downstream. Benthic macroinvertebrate assemblages and prey consumption were seasonally constant at both sites. Generally, prey consumption was consistent with availability of each prey in the benthos; the lack of benthic diversity and overwhelming abundance of one taxon (Lirceus) most likely contributed to food selection patterns. Although isopods are abundant within this tailwater to serve as a forage base, the displacement of native fish fauna because of the thermal regime of hypolimnetic release from Greers Ferry Reservoir probably serves as a major limitation to brown trout growth.

Royal Tern (Sterna maxima) Chick Diet at Fisherman Island National Wildlife Refuge, Virginia

Abstract Royal Tern (Sterna maxima) chick diet at Fisherman Island National Wildlife Refuge, Virginia, was investigated in 2003 and 2004. Primary objectives were to document common prey species, annual and seasonal variation in prey selection, and seasonal variation in prey size based on average bill length in this species. Over 2200 Royal Terns bred on this island each year of the study. Single items of prey species carried in the bill by adult terns feeding their chicks were identified using 8 × 42 binoculars. A total of 11,566 and 33,646 prey items were identified during 44 and 87.5 h of systematic observations in 2003 and 2004, respectively. Terns foraged largely on anchovy (Anchoa spp.) early in the season, then switched to herrings (Clupeidae); average prey size also increased seasonally each year. Prey switching was similar to that of Royal Terns in North Carolina (but with drum as well as herring), indicating regional adaptations to forage fish availability by this species along the mid-Atlantic s...

Selective foraging by fish-eating killer whales Orcinus orca in British Columbia

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 316:185-199 (2006) - doi:10.3354/meps316185 Selective foraging by fish-eating killer whales Orcinus orca in British Columbia John K. B. Ford*, Graeme M. Ellis Fisheries and Oceans Canada, Pacific Biological Station, 3190 Hammond Bay Road, Nanaimo, British Columbia V9T 6N7, Canada *Email: fordjo@pac.dfo-mpo.gc.ca ABSTRACT: As the apex non-human marine predator, the killer whale Orcinus orca feeds on a wide diversity of marine fauna. Different ecotypic forms of the species, which often exist in sympatry, may have distinct foraging specialisations. One form found in coastal waters of the temperate NE Pacific Ocean, known as the ‘resident’ ecotype, feeds predominantly on salmonid prey. An earlier study that used opportunistic collection of prey remains from kill sites as an indicator of predation rates suggested that resident killer whales may forage selectively for chinook salmon Oncorhynchus tshawytscha, the largest but one of the least abundant Pacific salmon species. Potential biases in the prey fragment sampling technique, however, made the validity of this finding uncertain. We undertook field studies of foraging behaviour of resident killer whales to resolve this uncertainty and to examine potential variation in prey selection by season, geographical area, group membership and prey availability. Foraging by resident killer whales was found to frequently involve sharing by 2 or more whales. Prey fragments left at kill sites resulted mostly from handling and breaking up of prey for sharing, and all species and sizes of salmonids were shared. Resident killer whale groups in all parts of the study area foraged selectively for chinook salmon, probably because of the species’ large size, high lipid content, and year-round availability in the whales’ range. Chum salmon Oncorhynchus keta, the second largest salmonid, were also taken when available, but smaller sockeye O. nerka and pink O. gorbuscha salmon were not significant prey despite far greater seasonal abundance. Strong selectivity for chinook salmon by resident killer whales probably has a significant influence on foraging tactics and seasonal movements, and also may have important implications for the conservation and management of both predator and prey. KEY WORDS: Prey choice · Food sharing · Foraging specialisation · Salmonid predation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 316. Online publication date: July 03, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Individual variation in prey selection by sea otters: patterns, causes and implications

SummaryLongitudinal records of prey selection by 10 adult female sea otters on the Monterey Peninsula, California, from 1983 to 1990 demonstrate extreme inter‐individual variation in diet. Variation in prey availability cannot explain these differences as the data were obtained from a common spatial‐temporal area.Individual dietary patterns persisted throughout our study, thus indicating that they are life‐long characteristics.Individual dietary patterns in sea otters appear to be transmitted along matrilines, probably by way of learning during the period of mother–young association.Efficient utilization of different prey types probably requires radically different sensory/motor skills, each of which is difficult to acquire and all of which may exceed the learning and performance capacities of any single individual. This would explain the absence of generalists and inertia against switching, but not the existence of alternative specialists.Such individual variation might arise in a constant environment from frequency‐dependent effects, whereby the relative benefit of a given prey specialization depends on the number of other individuals utilizing that prey. Additionally, many of the sea otter's prey fluctuate substantially in abundance through time. This temporal variation, in conjunction with matrilineal transmission of foraging skills, may act to mediate the temporal dynamics of prey specializations.Regardless of the exact cause, such extreme individual variation in diet has broad ramifications for population and community ecology.The published literature indicates that similar patterns occur in many other species.

The diet of shy albatrosses (Thalassarche cauta) at Albatross Island, Tasmania

AbstractThe diet of shy albatrosses Thalassarche cauta at Albatross Island, Tasmania, was examined quantitatively from 1995 to 1998. Two main sample types were examined: (1) whole stomach contents from chicks that had recently died of natural causes; (2) samples of fresh food delivered to chicks by their parents. Fresh food samples were considered most representative of the overall diet composition and, throughout the study, they were predominated by fish (89+ by wet mass). Cephalopods, tunicates and crustaceans contributed 10+, < 0.1+ and < 0.1+ by wet mass, respectively, to the diet. There was little indication of seasonal or inter‐annual variation in prey selection, as the composition of the diet was relatively constant through time. Fish from 16 species or families were identified, however, pelagic schooling Jack mackerel Trachurus declivis and redbait Emmelichthys nitidus together accounted for 57+ and 80+ (by number) of the fish identified in the stomach and fresh food samples, respectively. Cephalopods from 16 species or families were also identified, and here a single species (Gould's squid Nototodarus gouldi), accounted for 66+ and 84+ (by number) of the cephalopods identified. Both salps Pyrosoma spp. and crustaceans (largely Australian krill Nyctiphanes australis) contributed little by mass, but they occurred frequently and sometimes they accounted for a significant number of the prey items identified. Aspects of the biology and behaviour of the albatrosses and their main prey species combine to indicate that shy albatrosses have a largely predatory foraging nature. Much of their prey can be captured live, at the surface, during the day.

Feeding chronology and habits of Alosa spp. (Clupeidae) juveniles from the lower Hudson River estuary, New York

Feeding habits of juvenile alewife, A. pseudoharengus, blueback herring, A. aestivalis, and American shad, Alosa sapidissima, were examined over a 24 h period at an inshore location on the lower Hudson River. Feeding periodicity differed by species: alewives showed no diel differences, whereas shad fed least intensively near dawn and herring least intensively at night. Alewives fed primarily on chironomids and the amphipod Corophium lacustre, shad on Formicidae and larval chironomids, and herring on chironomids and copepods. Diel variation in prey selection was evident. Dietary overlap was generally greatest between alewife and herring and least between shad and herring.

Effects of Body Size on the Predator‐Prey Interaction Between Pumpkinseed Sunfish and Gastropods

Body size is known to play a critical role in determining patterns of prey selection. In this study, we examined the diets of pumpkinseed sunfish (Lepomis gibbosus) from three Michigan lakes. Pumpkinseeds have highly developed pharyngeal jaws specialized for crushing gastropods, and in our study lakes gastropods consistently contributed >80% of the prey mass in pumpkinseed diets. However, the average dietary composition and prey selection among snail taxa and size classes varied considerably among dates and sites. We hypothesized that this variation was influenced by changes in the size structure of the snail community. We used laboratory studies to quantify the effect of snail (and fish) size on three important components of the predator—prey interaction: encounter rates, attack probabilities, and capture successes. We then used these laboratory data to predict prey selection observed in the field. For most of our field situations, a simple model based on size—specific encouter rates only) explained a large percent (71%) of the observed variation in prey selection. However, in those cases where some of the snails were resistant to predation, due to crushing resistance or gape limitation, this simple model was a very poor predictor of prey selection. A more complex model (based on encounter rates and size refuges) successfully explained 46% of the variance in these cases where snails were relatively invulnerable. Finally, we compared estimates of attack probabilities with predictions from optimal foraging theory and found qualitative agreement in that fish ignored prey of low profitabilities and became more selective as the quality of the environment improved. however, the incorporation of variable attack probabilities into the foraging model resolved only a small part of the observed residual variation in selectivities because snails with low profitabilities were already underrepresented in the diet due to their low encounter rates or capture successes. This study demonstrates that predator—prey interactions in size—structured populations can create apparently complex variation in prey selection, but that this variation can be largely understood within a framework that simultaneously considers the dynamics of prey size distributions and how components of the foraging interaction scale with body size of the predator and prey.

Interindividual Variation in Prey Selection by the Snail Nucella (= Thais) Emarginata

Variation in diet among individuals of a population of carnivorous marine snails in a rocky intertidal environment of central California was analyzed. Nucella emarginata drills and eats barnacles, mussels, and limpets. Out of 128 marked snails, 104 were observed through two or more feeding attacks in the field during the 4—mo study. Fifty—one of these snails were observed through five or more sequential feeding attacks. Three major points are illustrated. (1) Within each study site, individuals close to the same size often chose strikingly different diets. (2) There was a range of dietary specialization and generalization among individuals foraging in the same habitat. Individuals showed a high degree of consistency in their diets. While the population of N. emarginata attacked seven prey species at site A and four prey species at site B, no individual snail observed in this study ate more than three species of prey. (3) Food choices made by each individual were not a simple reflection of the relative abundance of the surrounding prey species or the differences in microhabitat prey distribution that each predator encountered. These conclusions remained the same for several different methods of measuring prey availability. I suggest that Nucella emarginata diet patterns have a variety of causes, which may include ingestive conditioning, learning, and genetic variability.