Prey Consumption Rates Research Articles

On the mechanistic understanding of predator feeding behavior using the functional response concept

AbstractFunctional response models describe the relationship between prey density and per capita prey consumption rate by a predator. Type II functional responses, in which density‐dependent predation occurs via a decelerating feeding rate, seem to prevail in nature and are commonly described by Holling’s disk equation. In the derivation of the disk equation, Holling did not include digestion time. Although some authors have later extended the interpretation of handling time by also including digestion time, this violates the key assumption of the disk equation that the processes of searching for and handling prey are mutually exclusive. The steady‐state satiation (SSS) equation is a functional response model that discriminates between handling and digestion time. The application of the SSS equation is underutilized so far in the ecological literature, probably due to its complexity. In this study, we first tested the viability of the SSS equation. Second, we investigated the mechanistic basis of the SSS equation, comparing the model’s predictions with directly observed data. For this purpose, we used predator–prey systems of different taxa, that is, the ladybird beetle Hippodamia variegata preying on the aphid Aphis fabae, the lacewing Chrysoperla agilis preying on the aphid Myzus persicae, and the predatory mite Iphiseius degenerans preying on the thrips Frankliniella occidentalis. Our results show that the SSS equation is viable and can realistically describe type II functional response. In all predator–prey systems we tested, the model fitted the data reasonably well and provided realistic estimation of its parameters.

Predator prey interactions between predatory gastropod Reishia clavigera, barnacle Amphibalanusamphitriteamphitrite and mussel Brachidontesvariabilis under ocean acidification

Since the response to ocean acidification is species specific, differences in responses between predator and prey will alter their interactions, hence affect the population dynamics of both species. Changes in predator prey interactions between a predatory muricid gastropod Reishia clavigera and its prey, the barnacle Amphibalanus amphitrite amphitrite and mussel Brachidontes variabilis under three pCO2 levels (380, 950, and 1250 μatm) were investigated. The searching time for barnacles increased and the ability to locate them decreased at higher pCO2 levels. The movement speed and the prey consumption rate, however, were independent of pCO2. There was no preference towards either B. variabilis or A. amphitrite amphitrite regardless of pCO2. Exposure experiments involving multiple generations are suggested to assess transgenerational effects of ocean acidification and the potential compensation responses before any realistic predictions on the long term changes of population dynamics of the interacting species can be made.

Assessing multiple predator, diurnal and search area effects on predatory impacts by ephemeral wetland specialist copepods

Predator–prey interaction strengths can be highly context-dependent. In particular, multiple predator effects (MPEs), variations in predator sex and physical habitat characteristics may affect prey consumption rates and thus the persistence of lower trophic groups. Ephemeral wetlands are transient ecosystems in which predatory copepods can be numerically dominant. We examine the interaction strengths of a specialist copepod Paradiaptomus lamellatus towards mosquito prey in the presence of conspecifics using a functional response approach. Further, we examine sex variability in predation rates of P. lamellatus under circadian and surface area variations. Then, we assess the influence of a co-occurring heterospecific predatory copepod, Lovenula raynerae, on total predation rates. We demonstrate MPEs on consumption, with antagonism between conspecific P. lamellatus predatory units evident, irrespective of prey density. Furthermore, we show differences between sexes in interaction strengths, with female P. lamellatus significantly more voracious than males, irrespective of time of day and experimental arena surface area. Predation rates by P. lamellatus were significantly lower than the heterospecific calanoid copepod L. raynerae, whilst heterospecific copepod groups exhibited the greatest predatory impact. Our results provide insights into the predation dynamics by specialist copepods, wherein species density, diversity and sex affect interaction strengths. In turn, this may influence population-level persistence of lower trophic groups under shifting copepod predator composition.

Prey capture and selection throughout the breeding season in a deep‐diving generalist seabird, the thick‐billed murre

Generalist seabirds forage on a variety of prey items providing the opportunity to monitor diverse aquatic fauna simultaneously. For example, the coupling of prey consumption rates and movement patterns of generalist seabirds might be used to create three‐dimensional prey distribution maps (‘preyscapes’) for multiple prey species in the same region. However, the complex interaction between generalist seabird foraging behaviour and the various prey types clouds the interpretation of such preyscapes, and the mechanisms underlying prey selection need to be understood before such an application can be realized. Central place foraging theory provides a theoretical model for understanding such selectivity by predicting that larger prey items should be 1) selected farther from the colony and 2) for chick‐feeding compared with self‐feeding, but these predictions remain untested on most seabird species. Furthermore, rarely do we know how foraging features such as handling time, capture methods or choice of foraging location varies among prey types. We used three types of animal‐borne biologgers (camera loggers, GPS and depth‐loggers) to examine how a generalist Arctic seabird, the thick‐billed murre Uria lomvia, selects and captures their prey throughout the breeding season. Murres captured small prey at all phases of a dive, including while descending and ascending, but captured large fish mostly while ascending, with considerably longer handling times. Birds captured larger prey and dove deeper during chick‐rearing. As central place foraging theory predicted, birds travelling further also brought bigger prey items for their chick. The location of a dive (distance from colony and distance to shore) best explained which prey type was the most likely to get caught in a dive, and we created a preyscape surrounding our study colony. We discuss how these findings might aid the use of generalist seabirds as bioindicators.

Bistability and Bifurcations in Modified Nicholson-Bailey Model with Age-Structure for Prey

The paper investigates dynamic modes of the predator-prey model with age structure for prey. We use a slight modification of the Nicholson-Bailey model to describe the interaction between predator and prey. We assume the population size is regulated by decreasing juvenile survival rate with growth of age class sizes. Conditions for sustainable coexistence of interacting species are described. It is shown that the coexistence of species becomes possible if there are a transcritical or saddle-node (tangential) bifurcations. Due to the saddle-node bifurcation there is bistability in the system of interacting species: predator either coexists with prey or dies depending on the initial conditions. It is shown that the range of demographic parameters, for which the prey and predator coexist, can significantly increase with growth of survival of adult prey or the proportion of predators born or the prey consumption rate of the predator. We studied the oscillation scenarios of interacting population, influences of reproduction, survival and self-regulation rates of population prey and age-dependent predation as well as variations in the current number on transitions between different dynamic modes. It is shown that an increase in the birth rate of the prey under intraspecific competition can lead to a dynamics destabilization and to oscillations appearance in numbers. Age-dependent predation is shown to be a stabilizing influence. At the same time, with a high birth rate of the prey, the system stability is ensured by the high survival rate of adult prey. It was found that in the model parametric space, both bistability and multistability arises, which are not related to each other. Consequently, even a small variation of the current population size leads to more complex behavior of the interacting species, and can give a significant change in both the observed dynamic mode and the coexistence scenario of the species.

The Impact of Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) on Control of Dysmicoccus neobrevipes Beardsley (Hemiptera: Pseudococcidae).

Cryptolaemus montrouzieri (Coleoptera: Coccinellidae) is an important predator of the mealybug Dysmicoccus neobrevipes (Hemiptera: Pseudococcidae), a major pest of Agave sisalana in China. Limited reports on the efficacy of C. montrouzieri against D. neobrevipes are available. This study reports the predatory efficacy and functional response of C. montrouzieri against D. neobrevipes under laboratory conditions. The prey consumption rate per day of 4th instar larvae of C. montrouzieri feeding on 1st instar D. neobrevipes nymphs (241.3 mealybugs) was the highest among the different larval life stages of the beetle. For C. montrouzieri, the prey consumption per day of adult females (19.8 mealybugs) was significantly higher compared to males (15.2 mealybugs) when feeding on 3rd instar D. neobrevipes nymphs. The functional responses of C. montrouzieri on 1st and 2nd instar D. neobrevipes nymphs were determined as Holling type II. The search rates of C. montrouzieri 4th instar larvae towards the 1st and 2nd instar nymphs of D. neobrevipes were higher than those of the other beetle life stages. In addition, the handling times of 4th instar larvae were shorter than those of the other beetle life stages. The results from this study indicate that C. montrouzieri can be used as a predator of D. neobrevipes and, therefore, it should be evaluated further for use as a biocontrol agent in D. neobrevipes management programs.

The ecological role of cephalopods and their representation in ecosystem models

Cephalopods, especially squids, are believed to have a structuring role in marine ecosystems as a link between different trophic levels, primarily due to their voracious prey consumption and high production rate. Cephalopod ecology, however, is still poorly understood as observational studies often give highly uncertain and variable results due to the peculiarities of cephalopod behaviour and biology, and their responsiveness to external drivers. This review evaluates our representation of cephalopods in ecosystem models and the insights given by these models on the role of cephalopods in our oceans. We examined ecosystem models from 13 regions to analyse the representation of cephalopods and compared their results to local trophic studies. Our analysis indicated that most ecosystem models inadequately include cephalopods in terms of model structure and parametrization; although some models still have the capacity to draw valuable conclusions regarding the impact and role of cephalopods within the system. Oceanic squid species have a major role linking trophic levels and food webs from different habitats. The importance of neritic species varies locally, but generally cephalopods have a substantial impact via their consumer role. To better understand the ecological role of cephalopods, improved representation of these species in ecosystem models is a critical requirement and could be achieved relatively easily to more accurately articulate the mechanisms regulating the ecological role of cephalopods.

Body size mediates the relationship between spider (Arachnida: Araneae) assemblage composition and prey consumption rate: results of a mesocosm experiment in the Yukon, Canada.

Many ecological assemblages are undergoing rapid changes in composition and diversity, and changes at one trophic level can have direct and cascading effects on other trophic levels. Prey consumption typically increases with predator diversity due to niche complementarity and sampling effects. However, the effect of functional traits and interactions between predator species mean that the relationship is far from simple. In July 2016, we performed a series of experiments in the Yukon, Canada, to investigate the relationship between spider assemblage composition and prey consumption, with a focus on the wolf spider Pardosa lapponica (Thorell 1872). We carried out feeding trials, in which P. lapponica and other spider species were offered potential prey, as well as mesocosm experiments, in which we varied spider assemblage composition within small enclosures. We confirmed that P. lapponica is a generalist consumer, individual consumption rate increased with spider body size, and that intraguild predation is present. We found that prey consumption was greatest in the least diverse assemblage but consumption did increase with predator functional trait variation and biomass. The best model of prey consumption included predator assemblage composition, variation in body mass, biomass, and all interactions. The body size of a spider affects its trophic niche, energy requirements, and its interactions with other spiders. As a result, body size mediates the relationship between spider assemblage composition and prey consumption. A deeper understanding of the relationships between traits and functions will allow us to better predict the effect of species loss or gain on ecosystem functions.

Feeding potential of phytoseiid predator, Neoseiulus baraki Athias-Henriot on Coconut eriophyid mite, Aceria guerreronis Keifer

Experimental results showed that the overall daily prey consumption rate of individual larva, protonymph and deutonymphal stage of N. baraki were consumed 6.33 ± 0.50, 11.00 ± 0.75 and 13.45 ± 0.89 prey mites, respectively. Whereas, the consumption rate of adult male and female were 14.07 ± 0.56 and 15.91 ± 0.45 preys, respectively. The total prey consumption rate of larval, protonymph and deutonymphal stage of N. baraki were 12.65 ± 1.00, 22.00 ± 1.50 and 40.35 ± 2.69 preys, respectively. However, total consumption rate for adult male and female were 219.40 ± 5.86 and 477.97 ± 5.51 prey mites, respectively. The prey consumption rate during entire life period of male was 294.40 ± 14.09 preys, while female of 552.97 ± 14.09 prey mites. Thus, the present finding clearly suggest that N.baraki could be a highly efficient biological control agent of A. guerreronis.

Climate effects and bottom‐up controls on growth and size‐at‐age of Pacific halibut (Hippoglossus stenolepis) in Alaska (USA)

AbstractPacific halibut (Hippoglossus stenolepis) are an ecologically, commercially, and culturally important Alaskan groundfish species. Commercial harvest of halibut dates back to the late 19th century and has been managed by the International Pacific Halibut Commission (IPHC) since 1921. IPHC surveys have revealed declining trends in survey biomass in multiple regions and region‐specific declines in mean size‐at‐age (size‐at‐age) over the past two decades (>50% in some areas). Changes in size‐at‐age can arise from a variety of physical, ecological, sampling, and fishery effects, including size‐dependent fishery or predation mortality, alteration in growth from variability in prey quality or quantity, and changes in temperature‐dependent metabolic demands. Here, we develop and apply a bioenergetics model for halibut using survey‐based diet and temperature data for Alaska to evaluate potential environmental drivers of size‐at‐age. In general, juvenile (<40 cm fork length) foraging rates were highest in the Gulf of Alaska concomitant with higher potential growth and elevated basal metabolic demands during warm summer conditions. In contrast, adult (40–120 cm FL) potential growth was highest in the Eastern Bering Sea, potentially reflecting lower metabolic costs and higher rates of prey consumption in that region. We additionally find evidence for interannual variation in potential growth, with a higher frequency of reduced growth potential in the last decade, particularly in the Eastern Bering Sea in 2015 and 2016 for both juvenile and adult halibut. These results suggest the potential for patterns in size‐at‐age to arise from trophic and environmental constraints that collectively limit growth in some regions and years.

A diverse suite of pharmaceuticals contaminates stream and riparian food webs

A multitude of biologically active pharmaceuticals contaminate surface waters globally, yet their presence in aquatic food webs remain largely unknown. Here, we show that over 60 pharmaceutical compounds can be detected in aquatic invertebrates and riparian spiders in six streams near Melbourne, Australia. Similar concentrations in aquatic invertebrate larvae and riparian predators suggest direct trophic transfer via emerging adult insects to riparian predators that consume them. As representative vertebrate predators feeding on aquatic invertebrates, platypus and brown trout could consume some drug classes such as antidepressants at as much as one-half of a recommended therapeutic dose for humans based on their estimated prey consumption rates, yet the consequences for fish and wildlife of this chronic exposure are unknown. Overall, this work highlights the potential exposure of aquatic and riparian biota to a diverse array of pharmaceuticals, resulting in exposures to some drugs that are comparable to human dosages.

Ecological interactions between Gulf of Mexico snappers (Teleostei: Lutjanidae) and invasive red lionfish (Pterois volitans).

Indo-Pacific red lionfish (Pterois volitans) have invaded the western Atlantic, and most recently the northern Gulf of Mexico (nGOM), at a rapid pace. Given their generalist habitat affinities and diet, and strong ecological overlap with members of the commercially valuable snapper-grouper complex, increased density and abundance of lionfish could result in significant competitive interactions with nGOM commercially important species. We experimentally investigated the intensity of behavioral interactions between lionfish and indigenous, abundant and economically important juvenile nGOM red snapper (Lutjanus campechanus), and other increasingly abundant juvenile tropical snapper species (gray snapper—L. griseus and lane snapper—L. synagris) in large outdoor mesocosms to examine snapper vulnerabilities to lionfish competition. When paired with lionfish, red snapper swimming activity (i.e., time swimming and roving around experimental tank or at structure habitat during experiments) was significantly lower than in intraspecific control trials, but gray and lane snapper swimming activities in the presence of lionfish did not significantly differ from their intraspecific controls. Additionally in paired trials, red and lane snapper swimming activities were significantly lower than those of lionfish, while no significant difference in swimming activities was observed between lionfish and gray snapper. We found that red snapper prey consumption rates in the presence of lionfish were significantly lower than in their intraspecific 3-individual control trials, but when paired together no significant differences in prey consumption rates between red snapper and lionfish were observed. When paired with lane or gray snapper, lionfish were observed having comparatively higher prey consumption than snappers, or as observed in lionfish intraspecific 1-individual controls. However, lane and gray snapper consumption rates in the presence of lionfish did not significantly differ from those in intraspecific controls. These findings suggest that competition between juvenile snappers and invasive lionfish may be variable, with lionfish exhibiting differing degrees of competitive dominance and snappers exhibiting partial competitive vulnerability and resistance to lionfish. While the degree of intensity at which these interactions may occur in nGOM reefs may differ from those observed in our findings, this study enables greater understanding of the potential ecological effects of red lionfish on native reef fishes.

Nitrogen Fertilization Increases the Nutritional Quality of Aphis gossypii (Hemiptera: Aphididae) as Prey for Hippodamia variegata (Coleoptera: Coccinellidae) and Alters Predator Foraging Behavior.

Nitrogen (N) fertilization is a common agricultural practice, which, by increasing the quality of plants, also enhances their nutritional suitability for insect herbivores, creating the possibility of a cascade of N across trophic levels, from plant to herbivore to predator. We manipulated the quality of cucumber plants by fertilizing them with three different N rates (110, 160, and 210 ppm), which represented low, medium, and high N levels, respectively. Colonies of Aphis gossypii Glover (Hemiptera: Aphididae) were then reared on these plants and used as prey for adult Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae) in experiments that characterized the predator's foraging behavior and functional response to different aphid densities. The nutritional content of plants and aphids was also measured. As N fertilization increased, so did the nutrient content (total energy) of aphids and this resulted in declining rates of aphid consumption by beetles at higher aphid densities. Females in the 110 N treatment, and males in all treatments, responded to aphids with a type II functional response (decelerating consumption at higher densities), but females in the 160 and 210 ppm N treatments exhibited a type III response (consuming a declining proportion of available aphids at high densities). Beetles fed aphids from the 110 N treatment consumed more prey in both assays than did those fed aphids from the 210 N treatment. Beetle searching time, handling time, and duration of digestive pauses all increased at high levels of N fertilization, especially for females. The results indicate that heavy N fertilization can increase prey nutritional quality to the point where it alters predator foraging and feeding behavior, resulting in slower rates of prey consumption and longer prey handling times.

A Beddington–DeAngelis type one-predator two-prey competitive system with help

In this paper, we present and study a two competing prey and one predator system where during predation both the teams of prey help each other and the rate of predation on both the teams are different. The prey consumption rate per individual of predator is considered as Beddington–DeAngelis type. Beddington–DeAngelis type functional response describes predator feeding rate depending on both the prey and predator density. Ecological significance of considering this type of functional response depends on how frequently a predator encounters another predator while feeding on the same type of prey, resulting in strong intraspecific competition and thereby reducing the predator feeding rate. Firstly we establish persistence and permanence of the system and examine the role of cooperation coefficient. Different conditions for the coexistence of equilibrium solutions are discussed. Then the local asymptotic stability of various equilibrium points and the existence of Hopf bifurcation at the positive equilibrium are carried out to understand the dynamics of the model system. The Kolmogorov analysis of subsystems suggests for the existence of transcritical bifurcation. Sufficient conditions for the nonexistence of periodic orbits of the considered model system have been presented. The analytical results found in this paper are illustrated with the help of numerical examples.

Effects of Ingestion of Soft Plastic Fishing Lures on Largemouth Bass

AbstractSoft plastic lures (SPLs) may comprise a significant amount of fishing gear pollution, yet little is known about their environmental impacts in aquatic systems or their ingestion by fish. We tested whether shape and material composition of ingested SPLs influenced subsequent prey consumption by Largemouth Bass Micropterus salmoides after SPL ingestion. We also quantified the occurrence of SPL ingestion by Largemouth Bass in reservoirs. Biodegradable and nonbiodegradable versions of shad, ribbon‐tail worm, and finesse worm SPLs were fed to Largemouth Bass, and consumption of natural prey was quantified 1 d and 1 week postingestion. Shape and material composition altered prey consumption by Largemouth Bass. Fish that ingested the shad SPL, the largest lure by volume, consumed the fewest number of prey 1 d postingestion. Ingestion of biodegradable SPLs resulted in lower prey consumption rates than ingestion of nonbiodegradable SPLs. Largemouth Bass typically expelled the SPL within 9 d of ingestion; all lures were either regurgitated or egested. Less than 1% of Largemouth Bass sampled in two Illinois reservoirs had SPLs in their stomachs. Our results suggest that discarded SPLs do not pose a significant long‐term threat to the health of individual Largemouth Bass. However, SPLs should still be discarded in a responsible manner.

Warming drives higher rates of prey consumption and increases rates of intraguild predation

Warming due to climate change is expected to alter species interactions. These interactions are shaped by components of individual behavior, particularly foraging behaviors. However, few studies consider species' behavioral responses to warming to predict how species interactions will be affected by warming. We chose two complementary approaches to examine how climate warming may affect the behavior and interactions of aquatic intraguild predators. First, we measured behavioral responses to warming in six larval dragonfly species, expecting that feeding rate and activity would increase with temperature. Secondly, we conducted intraguild predation (IGP) trials with three species to understand how temperature affects IGP, and if species' behavioral responses to warming are indicative of the outcome of IGP interactions. Warming increased feeding rates by 42% on average across species but had no effect on activity rate. The magnitude of change in feeding rate was positively correlated with the maximum temperatures species experience across their ranges. Lastly, warming increased rates of IGP twofold, however, species' behavioral responses alone were not predictive of their susceptibility to become IG prey of other larvae at warmer temperatures. Our results provide evidence that IGP interactions may be greatly affected by future increases in temperature; however, activity responses to warming alone are weak predictors of the outcomes of these interactions. Future studies should consider other species' traits when forecasting the effects of climate change on species interactions.

Effects of Turbidity on Prey Selection and Foraging Rate of Hatchery‐Reared Juvenile Tiger Muskellunge

AbstractTiger muskellunge (Northern Pike Esox lucius × Muskellunge E. masquinongy) are stocked into aquatic systems across North America to control undesirable fish species or to create sportfishing opportunities. Because decreased water clarity can affect the poststocking foraging ability of an ambush predator like the tiger muskellunge, we evaluated the effects of turbidity on the foraging success of tiger muskellunge in a laboratory setting. We tested prey selectivity and total prey consumption by juvenile tiger muskellunge at four turbidity levels (Secchi depths of >84, 53, 26, and 18 cm) using three prey species: Goldfish Carassius auratus (a surrogate for Common Carp Cyprinus carpio), Gizzard Shad Dorosoma cepedianum, and Green Sunfish Lepomis cyanellus. Tiger muskellunge consumed significantly less prey at Secchi depths of 26 and 18 cm than at a Secchi depth of >84 or 53 cm. Selectivity for or against all prey types decreased as turbidity level increased, such that all three prey types had similar neutral selectivity at the highest turbidity level even though Gizzard Shad were positively selected and Goldfish were negatively selected in clearer water. Green Sunfish were neutrally selected at all turbidity levels tested. These results suggest that increasing turbidity levels will negatively impact prey encounters and consumption rates, which likely will reduce growth rates of tiger muskellunge, ultimately reducing fish survival and stocking success.

Bythotrephes longimanus in shallow, nearshore waters: Interactions with Leptodora kindtii, impacts on zooplankton, and implications for secondary dispersal from southern Green Bay, Lake Michigan

Abstract The spiny water flea Bythotrephes longimanus is a predatory cladoceran that invaded Green Bay, Lake Michigan by 1988 and has been shown to negatively affect zooplankton prey. Bythotrephes is thought to occur where a deep-water daytime refuge from fish predation is available. Information from shallow, nearshore environments is relatively sparse, yet risk of secondary dispersal from these areas to inland waters is high. The production of desiccation-tolerant resting eggs, coupled with recreational boating activities, can facilitate spread inland. We determined Bythotrephes population demographics and dynamics at two sites in southern Green Bay during 2015 and 2016 to examine interactions with zooplankton and timing of resting egg production. Estimates of prey consumption rates by Bythotrephes were compared to those for a native predatory zooplankter, Leptodora kindtii, and against productivity estimates for potential crustacean prey. Bythotrephes population dynamics were similar at both sites in each year, with biomass peaks in September 2015 and July 2016. Earliest resting egg production occurred by 8 July 2015 and 17 June 2016; resting eggs occurred until at least October each year, when sampling ceased. Consumption by Bythotrephes generally exceeded that by Leptodora. Zooplankton productivity rates were lower than consumption rates on all dates in 2015 but approximated or exceeded consumption rates in 2016. Bythotrephes has become a major predator in the Green Bay lower food web, changing energy transfer through this major Great Lakes ecosystem. Its success has increased potential dispersal to inland lakes, especially from shallow, nearshore habitats such as occur in southern Green Bay.

Predation by Acanthocyclops americanus (Copepoda: Cyclopoida) in the hypertrophic shallow waterbody, Lake Albufera (Spain): field and laboratory observations

We quantified the predation of Acanthocyclops americanus from the shallow Mediterranean lake Albufera, using gut contents from field collections and laboratory feeding tests. For functional response studies, we used Brachionus plicatilis (at 6 concentrations, 400–4000 ind. 40 ml−1) and Diaphanosoma mongolianum (at 2–20 ind. 40 ml−1). Copepod feeding rates were also estimated using different proportions of rotifer prey and lake seston (0–67.5% of seston + 40 individuals of B. plicatilis). Prey selection studies were conducted using five zooplankton species: Brachionus angularis, Brachionus plicatilis, Keratella tropica, Daphnia magna and Diaphanosoma mongolianum. Gut contents of field-collected adult Acanthocyclops contained filamentous algae and cyanobacteria and 16 zooplankton species (Keratella cochlearis, unspined and spined forms, K. tropica, Brachionus plicatilis, Brachionus calyciflorus, Brachionus angularis, Brachionus variabilis, Asplanchna girodi, Polyarthra vulgaris, Synchaeta pectinata, Lepadella rhomboides, unidentified bdelloids, Alona rectangula, Chydorus sphaericus, Bosmina longirostris, D. magna, Ceriodaphnia dubia and copepod nauplii). When fed B. plicatilis or D. mongolianum, female A. americanus had higher prey consumption rates than males. Increased proportion of lake seston caused reduced consumption of brachionid prey. Our data suggest that A. americanus is omnivorous in nature.

The influence of prey density and fish size on prey consumption in common sole (Solea solea L.)

We examined the influence of prey density and fish size on prey consumption in common sole (Solea solea L.) foraging on buried ragworm Alitta virens (Sars) (formerly known as Nereis virens (Sars)). The tested prey densities of 0.8, 2.2, 4.3 and 6.5 individuals dm−2 were exposed to common soles of either 100 g or 300 g. At each prey density common sole foraged for 48 h. At both common sole classes studied, a positive correlation between prey consumption and prey density was observed (P < 0.001). Relationships however differed between 100 and 300 g common sole. In 300 g common sole the relationship between prey consumption and prey density was linear (P < 0.001), whereas in 100 g common sole the relationship between prey density and prey eaten was polynomial (P = 0.018). Small common sole reached satiety prey consumption rates at nearly every prey density while large common sole did not reach satiation rates even at highest prey densities. The data suggest that in nature, polychaetes such as A. virens may contribute to the diet of small common sole even when they are only moderately abundant. In contrast, polychaetes may not be an ideal prey for larger common sole as indicated by the absence of satiety regardless of prey density.