Frequency Of Prey Research Articles

Long‐term changes in the feeding of Pollachius virens on the Scotian Shelf: responses to a dynamic ecosystem

The diet and feeding ecology of pollock Pollachius virens from the Scotian Shelf and Bay of Fundy in the north‐west Atlantic changed over the last few decades, which was associated with decreases in euphausiid abundance. Stomach contents data for 2078 pollock collected during the 1958–1967 period and for 1230 pollock collected during the 1996–2002 period indicated that pollock diet contained fewer euphausiids and feeding activity decreased. During the early period, euphausiids were present in 65% of the pollock stomachs that contained food and only 9% of these stomachs in the recent period. The decrease of euphausiids was not wholly offset by an increase in piscivory, since there was little increase in the frequency of fish prey in the diet or in the fullness index for this prey type. Empty stomachs were significantly more common in the recent period during both the winter and summer. The decreased occurrence of euphausiids in stomach samples coincided with a significantly decreased abundance of this prey, suggesting that the near‐absence of euphausiids in recently collected pollock stomachs reflected prey abundance. Concurrent with changes in diet and feeding intensity, the condition or ‘plumpness’ of pollock significantly declined from the early to the late sampling periods.

Analysis of prey size preference of North Sea whiting, saithe, and grey gurnard

Abstract Size preference for prey fish of North Sea whiting, saithe, and grey gurnard was analysed. The analysis combined size-specific prey abundance estimates derived from bottom-trawl surveys with size frequencies of prey in predator stomachs from the International North Sea Stomach Database. To estimate the abundance of all potential prey fish in the sea, predator-specific length-based number spectra were calculated. Prey spectra were weighted by local predator abundance to take the spatial–temporal overlap between predator and their prey into consideration. Species-specific prey size preference models are presented. Contrary to former results, the preferred predator–prey weight ratio of whiting and grey gurnard is an exponentially increasing function of predator size and an exponentially decreasing function of the slope of the number spectrum. When predators grow, they prefer larger prey in absolute units. However, from a species-specific body size onwards they increasingly shift their prey preference towards relatively smaller prey sizes. From a bioenergetic point of view, this behaviour most likely maximizes the predator's foraging efficiency by reducing the expenditure of costly, anaerobically generated energy expended during burst swimming.

Diet of Epipedobates flavopictus (Anura: Dendrobatidae) in a Neotropical Savanna

A central issue in comparative biology is identifying the relative importance of historical (phylogenetic) versus present-day (ecological) factors in shaping phenotypic traits of organisms. Herein, we investigate effects of sex, ontogeny, and season on diet of Epipedobates flavopictus, a species restricted to open landscapes in central Brazil. Based on prey frequency, number, and volume, the most important prey categories were ants, termites, beetles, spiders, and orthopterans. Prey number and volume increased significantly with snout-vent length (SVL), and the consumption of termites also increased with SVL. There were few effects of sex and season upon diet composition, average prey number, or average prey volume, all independent of SVL. Reproductive females consumed larger prey, in great numbers, likely to increase energy uptake. As is true for most congeners, as well as species of closely related genera, ants are an important component in the diet of E. flavopictus. However, in contrast to its forest relatives, E. flavopictus consumes large amounts of termites, revealing the influence of prevailing ecological conditions. The small volume of ants in the diet of E. flavopictus and the high toxicity of its skin are not in agreement with the hypothesis of a causal relationship between skin toxicity and ant consumption.

Prey density, prey detectability and food habits: the case of Bonelli’s eagle and the conservation measures

In the diet of raptors the presence of prey-species is influenced by their abundance and the ground-level vegetation in territories, this situation being analysed for the Bonelli’s eagle ( Hieraaetus fasciatus) in south-eastern Spain. First, the minimum number of prey-items for the reliability of results was tested, obtaining between 15 and 30 prey-items depending of pair. Second, differences in prey frequency and productivity among pairs was analysed, finding an interpair shift in both variables, but there was no relationship between the frequency of prey-species in the diet and productivity. Third, it was found that the percentage of European wild rabbit in the diet was less correlated with its abundance in territories than with the surface of open land in the same. This suggests that accessibility to rabbits would be more important for the Bonelli’s eagle that the absolute abundance of this prey type. Thus, open land is the single variable selected by a multiple multiple-regression analysis explaining the frequency of rabbits in this raptor’s diet. Birds as prey complemented the diet when open-land scarcity in the territories implies low rabbit detectability and consumption. Conservation measures proposed concerning the increase of prey availability in this declining population should consider both the absolute prey density and prey detectability, avoiding extensive reforestation in territories and favouring vegetation structure suitable for prey detection by eagles.

Impact of spatial heterogeneity on a predator–prey system dynamics

This paper deals with the study of a predator–prey model in a patchy environment. Prey individuals moves on two patches, one is a refuge and the second one contains predator individuals. The movements are assumed to be faster than growth and predator–prey interaction processes. Each patch is assumed to be homogeneous. The spatial heterogeneity is obtained by assuming that the demographic parameters (growth rates, predation rates and mortality rates) depend on the patches. On the predation patch, we use a Lotka–Volterra model. Since the movements are faster that the other processes, we may assume that the frequency of prey and predators become constant and we would get a global predator–prey model, which is shown to be a Lotka–Volterra one. However, this simplified model at the population level does not match the dynamics obtained with the complete initial model. We explain this phenomenom and we continue the analysis in order to give a two-dimensional predator–prey model that gives the same dynamics as that provided by the complete initial one. We use this simplified model to study the impact of spatial heterogeneity and movements on the system stability. This analysis shows that there is a globally asymptotically stable equilibrium in the positive quadrant, i.e. the spatial heterogeneity stabilizes the equilibrium. To cite this article: J.-C. Poggiale, P. Auger, C. R. Biologies 327 (2004).

Foraging by the flower-dwelling spider, Misumenops argenteus (Thomisidae), at high prey density sites

In this study, the foraging sites of the crab spider Misumenops argenteus on Trichogoniopsis adenantha (Asteraceae) were investigated over a 2-year period. The choice of sites was examined in relation to prey density in rainy and dry seasons, in leaves versus stems, reproductive branches versus vegetative branches, and in flowerheads in different phenophases. Misumenops argenteus generally occupied sites where the prey frequency was high, indicating that this species was able to evaluate the quality of the foraging sites, as predicted by optimal foraging theory. One exception to the rule was that adult males occurred at all sites, independently of prey density, as also observed in other spider species in which males search for females and not for prey. In addition, young (third and fourth instar) spiders occupied flowerheads with few prey, but which provided shelter.

Body size, diet and reproductive ecology of Coluber hippocrepis in the Rif (Northern Morocco)

AbstractAlthough it is generally assumed that the Horseshoe Whip Snake (Coluber hippocrepis) originated in northern Africa, its biology and ecology has been studied mainly in southern Europe. In this paper we report on morphology, feeding, and reproductive ecology of Coluber hippocrepis in the Rif region (northern Morocco). Males attained larger sizes than did females, but there was no body-size difference between populations separated by the Strait of Gibraltar. The species feeds exclusively on vertebrates: mammals (45%), reptiles (28%), birds (17%), and amphibians (10%). There was an ontogenetic dietary shift in terms of frequency of prey consumed and in terms of prey size; moreover, an intersexual difference in prey frequency was found. Sexual maturity was attained at 540 mm snout-vent length (SVL) in males, and 720 mm SVL in females. Males showed a vernal spermatogenic cycle. Oviposition occurred at the beginning of summer, and offspring were observed in the field during September.

Sexual dimorphism and trophic constraints: Prey selection in the European polecat (Mustela putorius)

Although widespread among mammals, sexual dimorphism raises several evolutionary and ecological issues. Despite strong sexual dimorphism (reaching the ratio 1.81), a study of diet and prey selection in polecats (Mustela putorius) revealed only minor differences in their feeding habits. There was a greater frequency of large-sized prey (mainly lagomorphs) in the summer diet of females than in that of males. The frequency of anurans (Rana dalmatina and Bufo bufo) in the diet did not differ significantly between the two sexes. Male prey predominated in the diet of both sexes. Although prey availability, as indicated by the trapping of small rodents and anurans, showed a predominance of males in populations, Ivlev's index for selectivity demonstrated selective predation on male prey exceeding availability both by male and female polecats. This selective predation by polecats may affect both population structure and population exchanges. My results suggest that sexual dimorphism of polecats was not linked to a different prey choice but results from independent intrasexual selective pressures, thus refuting the predictions of the trophic niche differentiation hypothesis. The wide size dimorphism reflects selection both for mating access in males and for food in females, illustrating the complementary influence of sexual selection and environmental constraints on sex divergence in growth.

Metazoan parasites and food composition of juvenile Etmopterus spinax (L., 1758) (Dalatiidae, Squaliformes) from the Norwegian Deep.

A total of 37 juvenile Etmopterus spinax from the Norwegian Deep were examined for stomach contents and metazoan ecto- and endoparasites. These squaliform elasmobranchs were caught by benthopelagic net in May 2001 at a depth of 194-214 m. The euphausiid Meganyctiphanes norvegica and the teleost Maurolicus muelleri were the principal prey organisms. With increasing total length of E. spinax, the frequency of Meganyctiphanes norvegica prey decreased and that of M. muelleri increased. Seven different metazoan parasite species were found: adult Monogenea (2), larval and adult Cestoda (3), and larval Nematoda (2). The predominant parasites were an unidentified monocotylid monogenean and the cestode Aporhynchus norvegicus, with respective prevalences of infestation of 83.8% and 81.1%. The sites of infestation were the gills ( Squalonchocotyle spinacis, Monogenea), nasal cavities (Monocotylidae indet.), body cavity ( Lacistorhynchus tenuis, Cestoda), stomach wall and organs of the body cavity ( Anisakis simplex, Nematoda), and stomach and spiral valve ( A. norvegicus and Pseudophyllidea indet., Cestoda; Hysterothylacium aduncum, Nematoda). No other metazoan parasite taxa were found, and the musculature was free of parasites. Five new host and three new locality records were established. M. muelleri seems to be an important intermediate host for the endoparasitic nematodes which were found, with E. spinax serving as a paratenic host. E. spinax also serves as an intermediate host for the trypanorhynch cestode L. tenuis, and as the definitive host for the two monogeneans and the trypanorhynch A. norvegicus. The latter uses Meganyctiphanes norvegica as the second intermediate host in the Norwegian Deep. The relationship between the feeding ecology, habitat, and vagility of E. spinax and the resulting parasite fauna is discussed.

Jaguar (Panthera onca) Food Habits in Atlantic Rain Forest of Southeastern Brazil1

ABSTRACTBetween January and December 1996, the food habits of a relict population of jaguars were studied in 220 km2 Linhares Forest Preserve, which comprises much of the remaining old‐growth Atlantic Forest of Espirito Santo, Brazil. Fecal analysis indicated opportunistic feeding on 24 prey species (N= 101 scats). Mammals represented 87 percent of the total items, followed by reptiles (9.8%) and birds (2.8%). Considering prey weight, 23.4 percent of the items weighed 1–3 kg, 40.5 percent were 3–10 kg, and 27.7 percent weighed more than 10 kg. Analysis of relative prey frequency and biomass indicated that the diet was concentrated in two prey types: long‐nosed armadillo and white‐lipped peccary. Literature data suggest that forest jaguars rely on the same mammal prey over their entire geographic range.RESUMESEntre janeiro e dezembro de 1996, os hábiros alimentares de uma populaçáo da onga pinrada foram estudados na Reserva Florestal de Linhares (220 km2), que cornpreende 25 porcento da floresra Atlintica primlria remanescente do Esrado do Espirito Santo, Brasil. A andise de fezes indicou o consumo de 24 esptcies de presas (N = 101 arnosrras). Mamiferos representaram 87 porcento do total de itens, seguidos por rtpteis (9.8%) e aves (2.8%). Considerando o peso das presas 23.4 porcento dos itens pesavam entre 1 e 3 kg, 40.5 porcenro de 3 a 10 kg, e 27.7 porcento acima de 10 kg. De acordo com a análise de freqütncia relariva de ocorrsncia e a estimariva de biomassa relativa, a dieta concentra‐se em dois itens: o tatu galinha e queixada. A onga pintada parece basear sua dieta nas mesmas esptcies de mamiferos ao longo de sua distribuig8o geogrlfica.

Strong antiapostatic selection against novel rare aposematic prey.

The evolution of aposematism, a phenomenon where prey species conspicuously advertise their unprofitability to predators, is puzzling. How did conspicuousness evolve, if it simultaneously increased the likelihood of an inexperienced predator to detect the prey and presumably kill it? Antiapostatic selection, where rare prey is predated relatively more often, is considered as another major difficulty for aposematism to evolve. However, the risk of being conspicuous in low frequencies has not been experimentally tested. We designed an experiment to test how frequency (4%, 12%, 32%) of conspicuous aposematic prey and its dispersion type (solitary vs. aggregated) affect an initial predation risk of the prey and in avoidance learning of predators. Wild great tits (Parus major) were predators on artificial prey in a "novel world." The relative mortality of aposematic prey was antiapostatic, thus the frequency-dependent predation was most severe at low frequencies. In all frequencies, aggregated aposematic prey survived better than solitary prey. Surprisingly, learning was not determined by a fixed number of unpalatable prey eaten, but at low frequencies fewer aposematic individuals eaten generated predators' avoidance learning. However, per-capita risk for the prey remained highest at low frequencies. Our results underscore the problems of initial evolution of rare conspicuous morphs. Aggregated prey suffered less from predation, indicating selective advantage of aggregation over solitary living for a conspicuous individual.

Frequency-dependent predation by birds at edges and interiors of woodland

Structural variations between edge and interior areas within forest fragments may bring about differences in food availability that may influence the selective behaviour of predators and prey population dynamics. The purpose of this paper was to assess patterns of artificial prey selection by wild birds (House Sparrow Passer domesticus and Rock Dove Columba livid) between edge and interior areas of woodland, taking into account differences in prey frequency (10% of one food type and 90% of the other) and density (30 baits/m-2 and 50 baits/m-2). Experiments were conducted at 24 plots in 3 forest fragments in the city of Madrid, Spain. Selectivity did not vary among parks or between densities. However, selectivity did vary with the frequency and location of baits, showing an anti-apostatic trend (baits were preferred at low rather than at high frequencies) that was more pronounced at interiors than at edges. Two possible factors that may account for stronger anti-apostatic selection at edges are the higher densities of predators and pedestrians found there. However, there are many other possible explanations, and no specific conclusion can be supported with the current data. The results of this study also point out that site heterogeneity should be taken into account in the experimental design of future studies on frequency-dependent food selection by wild birds, particularly in fragmented landscapes.

Prey vulnerability and active predator choice as determinants of prey selection: a carabid beetle and its aphid prey

Petri dish experiments were conducted to study various aspects of prey selection in the predatory carabid Poecilus cupreus. The potential influence of active and passive prey selection, relative prey frequencies and hunger state of the carabid beetle were investigated with respect to the predation of aphids. For prey the focus was on the aphid Rhopalosiphum padi, and the fruit fly Drosophila melanogaster and the house cricket Acheta domestica were used as prey for comparison. Both search time and handling time for live prey items was longest for A. domestica, shorter for D. melanogaster and shortest for R. padi. Absolute maximum consumption in numbers was lowest for A. domestica, whereas the consumed numbers of D. melanogaster and R. padi were not significantly different. In the prey preference experiments with live prey (passive selection), P. cupreus ranked prey types in the order R. padi > D. melanogaster > A. domestica. Due to the predation activity of P. cupreus, prey frequencies changed in the course of the experiments; however, the relative abundance of alternative prey did not affect prey preferences. Although starved P. cupreus consumed slightly more prey individuals, the different saturation level of the carabids had no influence on prey preferences. In the preference experiment with dead prey (active choice), rank order of prey selection was reversed: P. cupreus now selected prey types in the order A. domestica > D. melanogaster > R. padi. The results indicate that for P. cupreus, the cricket A. domestica is the most attractive prey, Drosophila is at an intermediate position, and R. padi is the least attractive one. Nevertheless, in live prey tests P. cupreus preferred the aphid R. padi, probably because this prey type was easier to catch. The results suggest that the outcome of predator–prey encounters in P. cupreus is determined by prey vulnerability rather than by active choice of the carabid predator. Therefore, it is argued that the predation impact of carabid beetles on aphids depends not only on the presence and value of alternative prey, but also strongly on the escape efficiencies of the different prey species. Hence, in studying prey preferences of carabids with the aim of evaluating their effectiveness against aphids, a closer examination is necessary of the behavioural parameters affecting the outcome of specific carabid–prey encounters.

Age-Specific Behavior and Habitat Selection of Adult Male Damselflies, Calopteryx maculata (Odonata: Calopterygidae)

We compared the age, movement, and time–activity budgets of male Calopteryx maculata damselflies occupying off-stream tree-fall gaps with those at stream sites within a 10-ha woodland. All males collected at off-stream sites were younger than males collected at stream sites—as indicated by their significantly higher wing transmittance. Thirty-three percent of teneral males marked at off-stream gaps moved to stream sites within 4 days (mean distance = 140 m), while mature males marked at stream sites never left the stream. In contrast to stream site males, off-stream males spent significantly more time capturing prey and never engaged in aggressive interactions with other males. Behavioral differences were not due to variations in the operative body temperature. However, malaise trapping revealed a greater frequency of suitable prey in forest light gaps. Our findings support the idea that teneral male Calopteryx leave their emergence sites along the stream for off-stream light gaps to forage without interference and build the energy reserves necessary to attain and hold streamside territories.

Does Foraging Activity Change with Ontogeny? An Assessment for Six Sympatric Species of Postmetamorphic Litter Anurans in Central Amazonia

Does Foraging Activity Change with Ontogeny? An Assessment for Six Sympatric Species of Postmetamorphic Litter Anurans in Central Amazonia

Living with failure: the prey capture success of young brook charr in streams

Abstract – We examined the prey capture success of recently emerged brook charr (Salvelinus fontinalis) foraging in shallow, clear, still‐water pools along the edges of streams. Fewer than 42% of attacks ended with ingestion either because of difficulty distinguishing suitable prey from unsuitable items or because of difficulty capturing evasive prey. Probabilities of capture upon attack and ingestion upon capture depended upon where attacks were directed in the water column, the fish's level of activity at the time of attack and its fork length, and the sampling date. In general, success was higher for larger, sedentary fish attacking prey in the lower portion of the water column than for smaller, active fish attacking prey at the water surface. The frequency of items attacked was only a moderate predictor of the frequency of prey ingested. Poor capture success is an important aspect of the early life history of brook charr in particular and probably of young salmonines in general.NOTE

Does frequency-dependent predation really depend on frequency of prey? : A psychological overview

Does frequency-dependent predation really depend on frequency of prey? : A psychological overview

Selective feeding of third- and fourth - instar larvae of Chaoborus flavicans in the field

Zooplankton population dynamics were examined in Lake Klostersee (Bavaria, Southern Germany) from March to September, with special emphasis on third- and fourth-instar larvae of the phantom midge Chaoborus flavicans (Diptera) and their potential zooplankton prey. The samples were taken at night, during the feeding period of the larvae which show a diel vertical migration behaviour. I used an electivity index to compare the crop contents of third- and fourth-instar larvae to the density of their zooplankton prey to see whether the larvae fed selectively on any of them. Regardless of the prey frequencies, Chaoborus always showed negative electivity towards Ceriodaphnia, copepods, and rotifers, but positive electivities towards Bosmina. Electivities shifted from negative to positive during the study period for Daphnia, Diaphanosoma, and copepod nauplii and the reverse for Chydorus. Selective predation by the midge larvae could probably be explained by differential vulnerabilities of the prey due to induced anti-predator defenses.

Does prey dispersion affect frequency-dependent predation by wild birds?

Despite the fact that the vast majority of natural prey items are dispersed in a non-random manner, few studies of frequency-dependent selective predation have explicitly examined the effect of prey dispersion on selectivity. We examined the effect of prey dispersion on the direction and strength of frequency-dependent selection by wild birds feeding on artificial prey (green or brown pastry baits). In a series of four experimental manipulations, we tested for the occurrence of frequency dependence with two different dispersion patterns (random or clumped). Manipulations were carried out at one of two absolute densities (25 prey m-2 or 100 prey m-2), and were repeated at different sites in Southampton, England and Aljarafe, Spain. Our results suggest that prey dispersion has no effect on either frequency-dependent or -independent preferences. One possible explanation for this is that the birds had virtually complete information about prey frequencies at the relatively high densities used and based their preferences on their overall perception of availability. However, we cannot rule out the possibility that dispersion may influence selectivity when prey are cryptic or available at lower absolute densities. Although there was no effect of dispersion, frequency-dependent selection was, overall, significantly anti-apostatic (i.e. rare baits were more preferred than common baits). This anti-apostatic effect was stronger in Southampton than Aljarafe and stronger at 100 prey m-2 than 25 prey m-2. The differences in the strength of selection between the two locations was interpreted in terms of (i) whether the avian predators foraged in flocks or not, and (ii) the number of different species present (and, consequently, the variation in preference among individual birds).

STOMACH CONTENTS OF LONG‐FINNED PILOT WHALES (GLOBICEPHALA MELAS) STRANDED ON THE U.S. MID‐ATLANTIC COAST

AbstractTen prey taxa were recorded from the stomach contents of eight long‐finned pilot whales (Globicepbala melas) independently stranded along the U.S. mid‐Atlantic coast. Relative importance of prey species was determined by methods that incorporate prey frequencies of occurrence, proportions of numerical abundance, and proportions of reconstructed mass. Separate analyses of trace (free, durable body parts representing well‐digested prey items) and non‐trace (relatively intact prey specimens) food material were conducted in order to address biases caused by differential rates of digestion and passage through the gastrointestinal tract. Different measures of prey importance yielded varying results, but the long‐finned squid (Loligo pealei) was the most important prey species regardless of how prey importance was defined. Fishes were relatively unimportant in the diet. Our results indicate that the diets of western North Atlantic long‐finned pilot whales differ substantially from what has been previously reported in the literature and that results from food‐habits studies that utilize different techniques may not be comparable.