Prey selection and foraging period of the predaceous rocky intertidal snail,Acanthina punctulata

Summary The diet and foraging period of the neogastropod Acanthina punctulata were investigated in order to test various aspects of recent optimal foraging strategy models. This intertidal snail is an actively searching predator which preys on snails and barnacles by boring a hole in the shell and rasping out the flesh. Unlike many gastropod predators, Acanthina drill its gastropod prey at a very specific location on the columella, the thickest portion of the shell. Acanthina's foraging period can be interpreted as a compromise between maximizing the energy obtained by feeding and minimizing risk of mortality from exposure to wave action. That foraging period minimizing risk of being dislodged by waves appears to be during low tide when the predators can be in shallow pools. However, prey cannot be captured and consumed during one low tide. Thus Acanthina must be exposed during some high tides, and its strategy appears to be to restrict movement while exposed. Thus search is not initiated during high tide, but drilling and prey consumption are continued during that time. A snail not drilling or consuming prey seeks the protection of crevices or large anemones during high tide. A model is presented to indicate the relative amounts of risk and net energy for Acanthina at successive low and high tides. Predictions from the model, e.g., minimizing search time to avoid being exposed for an additional high tide and no movement during high tide are supported by field data. Acanthina commences foraging at the beginning of low tide, searches initially for preferred prey, but if unsuccessful, settles for a less preferred prey and begins drilling this prey before the end of low tide. Drilling and ingestion of prey occur during the following high and sometimes low tides. These handling times take 95% of the total foraging time in the field, while search time takes only 5% (pursuit time is negligible). Drilling alone accounts for 48–70% of the total drilling and eating time. In the laboratory, drilling and eating time for littorine food ranged from 15–60 hrs per item. The time to drill and eat a littorine increases exponentially with prey length. Since handling and processing prey items represents such a large investment of time, Acanthina would be expected to be very selective with respect to choice of prey items. Electivity coefficients from field data suggest that littorines are preferred over barnacles. Acanthina in the laboratory optimizes the amount of biomass ingested per time by choosing larger littorines over smaller ones and by preferring the more readily drilled species.It is suggested that Acanthina obtains information about the range of prey available initially by encountering and evaluating quite a few prey before making a selection, but usually by comparing an item of prey encountered to the prey it recently ingested. This latter method should provide a basis for evaluating prey encountered and has the advantage of reducing search time, the total amount of time spent feeding and thus the high-tide time exposed to wave action.In a similar manner, the decrease in the level of acceptability of prey as search time increases represents a compromise between maximizing energy obtained and minimizing risk from mortality.     

Vulnerability of age-0 pallid sturgeon Scaphirhynchus albus to predation; effects of predator type,turbidity, body size,and prey density

Predation can play an important role in the recruitment dynamics of fishes with intensity regulated by behavioral (i.e., prey selectivity) and/or environmental conditions that may be especially important for rare or endangered fishes. We conducted laboratory experiments to quantify prey selection and capture efficiency by three predators employing distinct foraging strategies: pelagic piscivore (walleye Sander vitreus); benthic piscivore (flathead catfish Pylodictis olivaris) and generalist predator (smallmouth bass Micropterus dolomieu) foraging on two size classes of age-0 pallid sturgeon: large (75–100 mm fork length [FL]) and small (40–50 mm FL). Experiments at high (> 70 nephalometric turbidity units [NTU]) and low (< 5 NTU) turbidity for each predator were conducted with high and low densities of pallid sturgeon and contrasting densities of an alternative prey, fathead minnow Pimephales promelas. Predator behaviors (strikes, captures, and consumed prey) were also quantified for each prey type. Walleye and smallmouth bass negatively selected pallid sturgeon (Chesson’s α?=?0.04–0.1) across all treatments, indicating low relative vulnerability to predation. Relative vulnerability to predation by flathead catfish was moderate for small pallid sturgeon (α?=?0.44, neutral selection), but low for large pallid sturgeon (α?=?0.11, negative selection). Turbidity (up to 100 NTU) did not affect pallid sturgeon vulnerability, even at low density of alternative prey. Age-0 pallid sturgeon were easily captured by all predators, but were rarely consumed, suggesting mechanisms other than predator capture efficiency govern sturgeon predation vulnerability.     

The negative effects of pathogen‐infected prey on predators: a meta‐analysis

Intra‐guild predation (IGP) – where a top predator (IG_Pred) consumes both a basal resource and a competitor for that resource (IG_Prey) – has become a fundamental part of understanding species interactions and community dynamics. IGP communities composed of intraguild predators and prey have been well studied; however, we know less about IGP communities composed of predators, pathogens, and resources. Resource quality plays an important role in community dynamics and may influence IGP dynamics as well. We conducted a meta‐analysis on predator–pathogen–resource communities to determine whether resource quality mediated by the pathogen affected predator life‐history traits and if these effects met the theoretical constraints of IGP communities. To do this, we summarized results from studies that investigated the use of predators and pathogens to control insect pests. In these systems, the predators are the IG_Pred and pathogens are the IG_Prey. We found that consumer longevity, fecundity, and survival decreased by 26%, 31% and 13% respectively, when predators consumed pathogen‐infected prey, making the infected prey a low quality resource. Predators also significantly preferred healthy prey over infected prey. When we divided consumers by enemy type, strict predators (e.g. wolf spiders) had no preference while parasitoids preferred healthy prey. Our results suggest that communities containing parasitoids and pathogens may rarely exhibit intraguild predation; whereas, communities composed of strict predators and pathogens are more likely dominated by IGP dynamics. In these latter communities, the consumption of low and high quality resources suggests that IGP communities composed of strict predators, pathogens and prey should naturally persist, supporting IGP theory. Synthesis We investigated how consuming pathogen‐infected prey influence important life‐history parameters of insect predators. Pathogens are used in a variety of biocontrol programs, especially to control crop pests. We found that true predators (i.e. wolf spiders) have no preference for healthy or infected prey and have reduced fecundity, survival and longevity consuming infected prey. However, parasitoids avoided infected prey when possible. In biocontrol programs with multiple control agents, parasitoids and pathogens would do a better job controlling pests as predators would reduce the amount of pathogen available and have reduced fitness from consuming infected prey. However, theory suggests that true predators, prey and pathogens may coexist long term.     

Insectivorous bats selectively source moths and eat mostly pest insects on dryland and irrigated cotton farms

Insectivorous bats are efficient predators of pest arthropods in agroecosystems. This pest control service has been estimated to be worth billions of dollars to agriculture globally. However, few studies have explicitly investigated the composition and abundance of dietary prey items consumed or assessed the ratio of pest and beneficial arthropods, making it difficult to evaluate the quality of the pest control service provided. In this study, we used metabarcoding to identify the prey items eaten by insectivorous bats over the cotton‐growing season in an intensive cropping region in northern New South Wales, Australia. We found that seven species of insectivorous bat (n = 58) consumed 728 prey species, 13 of which represented around 50% of total prey abundance consumed. Importantly, the identified prey items included major arthropod pests, comprising 65% of prey relative abundance and 13% of prey species recorded. Significant cotton pests such as Helicoverpa punctigera (Australian bollworm) and Achyra affinitalis (cotton webspinner) were detected in at least 76% of bat fecal samples, with Teleogryllus oceanicus (field crickets), Helicoverpa armigera (cotton bollworm), and Crocidosema plebejana (cotton tipworm) detected in 55% of bat fecal samples. Our results indicate that insectivorous bats are selective predators that exploit a narrow selection of preferred pest taxa and potentially play an important role in controlling lepidopteran pests on cotton farms. Our study provides crucial information for farmers to determine the service or disservice provided by insectivorous bats in relation to crops, for on‐farm decision making.     

Encounters between aphids and their predators: the relative frequencies of disturbance and consumption

Ecologists may wish to evaluate the potential for predators to suppress prey populations through the costs of induced defensive behaviors as well as through consumption. In this paper, we measure the ratio of non‐consumptive, defense‐inducing encounters relative to consumptive encounters (henceforth the ‘disturbed : consumed ratio’) for two species of aphids and propose that these disturbed : consumed ratios can help evaluate the potential for behaviorally mediated prey suppression. For the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), the ratio of induced disturbances to consumption events was high, 30 : 1. For the cotton aphid, Aphis gossypii (Glover) (Homoptera: Aphididae), the ratio of induced disturbances to consumption events was low, approximately 1 : 14. These results indicate that the potential for predators to suppress pea aphid populations through induction of defensive behaviors is high, whereas the potential for predators to suppress cotton aphid populations through induced behaviors is low. In measuring the disturbed : consumed ratios of two prey species, this paper makes two novel points: it highlights the variability of the disturbed : consumed ratio, and it offers a simple statistic to help ecologists draw connections between predator–prey behaviors and predator–prey population dynamics.     

Feeding habits and niche partitioning in a predator guild composed of tigers, leopards and dholes in a temperate ecosystem in central Bhutan

We describe the food habits, niche overlap and prey preferences in a predator guild comprised of tigers Panthera tigris , leopards Panthera pardus and dholes Cuon alpinus in a mountainous region of central Bhutan. Scat analyses revealed that these predators consumed 11 different prey species including livestock and rodents, of which leopards consumed 11. The combined relative occurrence of the three species, sambar Cervus unicolor , muntjac Munticus muntjac and wild pig Sus scrofa , constituted 42.7, 33.7 and 71.1% of the tiger, leopard and dhole diets, respectively, while livestock comprised 44.5, 73.4 and 15.9% of the prey consumed, respectively. Regression equations from earlier feeding trials were used to estimate the relative biomass and the numbers of prey consumed. Results showed that sambar featured more frequently than did muntjac and wild pig in the diets of tiger, leopard and dhole and contributed more relative biomass than did muntjac and wild pig. Sambar, muntjac and wild pig together provided 36.9, 28 and 63.1% of the biomass consumed by tigers, leopards and dholes respectively. All else being equal, there was evidence that all three predators ate livestock less than might have been expected on the basis of the abundance and high biomass of this prey category in the area. There was a high dietary niche overlap between the predators (Pianka's overlap index of 0.58–0.92), with a greater overlap between the two felid species than between the felids and the canid. This study provides evidence of a substantial diet overlap among the three sympatric carnivores, and thus highlights the potential for high intra-guild competition among them, especially given the relatively low density of prey.     

Does diet in Celtic Sea fishes reflect prey availability?

Feeding preferences of Celtic Sea fishes were investigated using a database of stomach content records, collected between 1977 and 1994. The diet of cod Gadus morhua , hake Merluccius merluccius , megrim Lepidorhombus whiffiagonis , whiting Merlangius merlangus and saithe Pollachius virens changed markedly as the animals grew larger, and although large predators generally chose larger bodied prey, the variability of prey sizes consumed also increased. Large predators continued to select small, low value, benthic prey ( e.g . Callionymus spp. and Trisopterus spp.) which were easier to catch, rather than larger, more energy lucrative pelagic prey ( e.g . mackerel Scomber scombrus ), even though these pelagic prey‐fishes were nearly always available and were often very abundant. Stock estimates of the International Council for the Exploration of the Sea and U.K. groundfish survey catches were used as indices of prey abundance. Blue‐whiting Micromesistius poutassou and other small pelagic fishes ( Argentina spp. and clupeoids) were identified as being particularly important, and were consumed by some predators more often than would be expected given the abundance of these prey in the environment. There was no evidence for density‐dependent feeding by predators on mackerel and only hake exhibited density‐dependent feeding on horse‐mackerel. Hake, cod and megrim consumed more blue‐whiting when this prey was at higher abundance in the environment. In choosing what prey to consume, predators must balance costs and benefits, considering the quality of prey and the energy expended during search, capture and handling.     

Diet and prey selection of sympatric tropical skinks

Most skinks are opportunistic predators, taking available prey from the environment as it is encountered. Variation in their diet composition is thought to reflect differences in prey abundance in the environment. We studied diet composition and prey selection in a community of three sympatric skink species (genus Carlia) in northern Australia by comparing contents of skink stomachs with arthropod prey available in their habitat. Carlia were entirely carnivorous and fed on a range of arthropod prey. We found high overlap in diet and prey size among the three species and between the wet and dry seasons, but found that skinks generally focused their foraging efforts on prey types and prey sizes that were not abundant in the habitat. Spiders (Aranea), orthopterans, blattarians, isopods and termites (Isoptera) were important prey of skinks, but these arthropods were rarely trapped in the environment. Skinks also frequently consumed large‐bodied prey, despite the higher relative abundance of small prey in the environment. Skinks were more selective in their foraging and diet than previously assumed. Selection of prey by consumers is a fundamental ecological process, important to consumers for maintaining energy requirements to grow and reproduce, but equally important to the community dynamics of the prey consumed.     

Refugees or ravenous predators: detecting predation on new recruits to tropical estuarine nurseries

Many of the most abundant small and juvenile fishes within shallow water estuarine nursery habitats consume other fish to some degree but have rarely been considered as potentially important predators in the functioning of these systems because of the low (<50%) average occurrence of fish in their diets. Predation by abundant minor piscivores on new recruits when they first enter the nursery may make a significant contribution to the predation mortality of this critical life-history stage. To determine the potential importance of minor piscivores as predators on new recruits, temporal patterns in the diets of 15 common species of minor piscivores were examined and related to the abundance of new recruits (≤20 mm FL) in biweekly seine samples over 13 months in shallow (<1.5 m) sandy habitats in the Ross River estuary in north-eastern Queensland, Australia. The high spatial patchiness of new recruits made it difficult to correlate their abundance with their consumption by minor piscivores, and there was no relationship detected between the abundance of new recruits and the occurrence of fish in the diets of minor piscivores. To gain broader insight into spatio-temporal patterns in the consumption of fish prey by minor piscivores, we utilised a collection of fishes sampled during various studies over 6 years from 17 estuaries in the region to examine the diets of >3500 individuals from 20 spp. of minor piscivores. Patterns in the consumption of fish prey by these minor piscivores, especially the highly abundant sparids, sillaginids and ambassids, revealed that the low average occurrence of fish in their diet greatly underestimated the predation pressure imposed by these on fish prey at particular locations and times. For most sampling occasions and locations few minor piscivores consumed fish prey (consumed by 0% of individuals examined), while occasionally a large proportion of individuals within a taxon did so (50–100% of individuals consumed fish prey). Often at such times/locations multiple species of minor piscivores simultaneously preyed heavily on fish. When minor piscivores consumed fish, they preyed mainly on small new recruits. Because many of these minor piscivores are relatively recent recruits, many of the small and juvenile fishes believed to gain refuge in shallow estuarine nurseries may themselves be important predators on fish subsequently recruiting to these habitats, and so potentially play a significant role in structuring estuarine fish faunas and the functioning of shallow water nurseries.     

Behavioural and life history effects of predator diet cues during ontogeny in damselfly larvae

A central issue in predator–prey interactions is how predator associated chemical cues affect the behaviour and life history of prey. In this study, we investigated how growth and behaviour during ontogeny of a damselfly larva (Coenagrion hastulatum) in high and low food environments was affected by the diet of a predator (Aeshna juncea). We reared larvae in three different predator treatments; no predator, predator feeding on conspecifics and predator feeding on heterospecifics. We found that, independent of food availability, larvae displayed the strongest anti-predator behaviours where predators consumed prey conspecifics. Interestingly, the effect of predator diet on prey activity was only present early in ontogeny, whereas late in ontogeny no difference in prey activity between treatments could be found. In contrast, the significant effect of predator diet on prey spatial distribution was unaffected by time. Larval size was affected by both food availability and predator diet. Larvae reared in the high food treatment grew larger than larvae in the low food treatment. Mean larval size was smallest in the treatment where predators consumed prey conspecifics, intermediate where predators consumed heterospecifics and largest in the treatment without predators. The difference in mean larval size between treatments is probably an effect of reduced larval feeding, due to behavioural responses to chemical cues associated with predator diet. Our study suggests that anti-predator responses can be specific for certain stages in ontogeny. This finding shows the importance of considering where in its ontogeny a study organism is before results are interpreted and generalisations are made. Furthermore, this finding accentuates the importance of long-term studies and may have implications for how results generated by short-term studies can be used.     

Intraspecific variation in prey quality: a comparison of nutrient presence in prey and nutrient extraction by predators

Prey quality can have large impacts on the survival, growth and behavior of predators. A number of studies have examined how different species of prey vary in quality. However, far less is known about intraspecific variation in the quality of prey for predators and even less about what nutrients are extracted from prey by predators. We examined how the sex, feeding level and developmental status of prey affected the quantities of nutrients present in prey bodies and the quantities of nutrients that could be extracted from prey by spiders. Female and well‐fed prey were larger and had more nutrients than male and food‐limited prey, respectively. After taking into account differences in prey size, spiders extracted relatively more lipid and less protein from female and well‐fed prey than from male and food‐limited prey, respectively. Mealworms were of higher quality than adult mealworm beetles; spiders were able to extract more lipid, protein and other nutrients from larvae than adults. While lipid present in prey was a good predictor of lipid consumed, protein present in prey was not a reliable predictor of protein consumed. The variation in prey quality that we observed within a single species of prey (i.e. well‐fed vs food‐limited crickets) was as large as variation in quality among the three species of prey used in these experiments. Intraspecific variation in prey quality may be an important factor affecting predatory arthropods, especially in habitats or at times of year when one species of prey is abundant. Further studies are needed to examine the consequences of intraspecific variation in prey quality on the life history and behavior of predators.     

Does diet in Celtic Sea fishes reflect prey availability?

Feeding preferences of Celtic Sea fishes were investigated using a database of stomach content records, collected between 1977 and 1994. The diet of cod Gadus morhua, hake Merluccius merluccius, megrim Lepidorhombus whiffiagonis, whiting Merlangius merlangus and saithe Pollachius virens changed markedly as the animals grew larger, and although large predators generally chose larger bodied prey, the variability of prey sizes consumed also increased. Large predators continued to select small, low value, benthic prey (e.g. Callionymus spp. and Trisopterus spp.) which were easier to catch, rather than larger, more energy lucrative pelagic prey (e.g. mackerel Scomber scombrus), even though these pelagic prey‐fishes were nearly always available and were often very abundant. Stock estimates of the International Council for the Exploration of the Sea and U.K. groundfish survey catches were used as indices of prey abundance. Blue‐whiting Micromesistius poutassou and other small pelagic fishes (Argentina spp. and clupeoids) were identified as being particularly important, and were consumed by some predators more often than would be expected given the abundance of these prey in the environment. There was no evidence for density‐dependent feeding by predators on mackerel and only hake exhibited density‐dependent feeding on horse‐mackerel. Hake, cod and megrim consumed more blue‐whiting when this prey was at higher abundance in the environment. In choosing what prey to consume, predators must balance costs and benefits, considering the quality of prey and the energy expended during search, capture and handling.     

Effects of food deprivation and type of prey on predation by Notiophilus biguttatus F. (Carabidae) on springtails (Collembola)

Summary With diurnally active predators like Notiophilus biquttatus F. food deprivation is involved in predation in two ways: as a consequence of food shortage (i.e., low prey density), and as a consequence of the night period. The pattern of food intake after deprivation at night has been studied with respect to two prey species and differently deprived predators. They prey species represent a locomotory active one (Orchesella cincta) and a locomotory inactive one (Tomocerus minor). It appears that the rate of predation after deprivation shows a distinct pattern, initially high and then slowing to a more or less constant value. This pattern is influenced by food deprivation and type of prey. The beetles preying on O. cincta consumed more prey than those preying on T. minor. The more deprived predators compensated for deprivation by a higher daily predation when O. cincta was the prey, but not when T. minor was. Consequences of these findings are discussed with respect to diet composition and functional response.     

A native dasyurid predator (common planigale,Planigale maculata) rapidly learns to avoid a toxic invader

Abstract Interactions between invasive species and native fauna afford a unique opportunity to examine interspecific encounters as they first occur, without the complications introduced by coevolution. In northern Australia, the continuing invasion of the highly toxic cane toad Bufo marinus poses a threat to many frog‐eating predators. Can predators learn to distinguish the novel toxic prey item from native prey (and thus, avoid being poisoned), or are longer‐term genetically based changes to attack behaviour needed before predators can coexist with toads? To predict the short‐term impact of cane toads on native predators, we need to know the proportion of individuals that will attack toads, the proportion surviving the encounter, and whether surviving predators learn to avoid toads. We quantified these traits in a dasyurid (common planigale, Planigale maculata) that inhabits tropical floodplains across northern Australia. Although 90% of naïve planigales attacked cane toads, 83% of these animals survived because they either rejected the toad unharmed, or killed and consumed the prey snout‐first (thereby avoiding the toxin‐laden parotoid glands). Most planigales showed one‐trial learning and subsequently refused to attack cane toads for long time periods (up to 28 days). Toad‐exposed planigales also avoided native frogs for up to 9 days, thereby providing an immediate benefit to native anurans. However, the predators gradually learnt to use chemical cues to discriminate between frogs and toads. Collectively, our results suggest that generalist predators can learn to distinguish and avoid novel toxic prey very rapidly – and hence, that small dasyurid predators can rapidly adapt to the cane toad invasion. Indeed, it may be feasible to teach especially vulnerable predators to avoid cane toads before the toads invade, by deploying low‐toxicity baits that stimulate taste‐aversion learning.     

Length and weight estimates from diagnostic hard part structures of fish,crustacea and cephalopods forage species in the western Indian Ocean

To estimate the original prey size of well-digested prey (fish, cephalopod and crustacean) of large pelagic fish predators representing 17 species in eight families (Scombridae, Xiphiidae, Istiophoridae, Carangidae, Coryphaenidae, Alepisauridae, Sphyraenidae and Carcharhinidae), we presented regression equations relating the length and weight of the prey to lengths of diagnostic hard part structures recovered from stomach contents. Stomach samples were collected in the western Indian Ocean between 2000 and 2008 from predators caught by three fishing gears: longline, purse seine and troll lines. In addition, fresh specimens were collected from trawls nets carried out during scientific cruises at depths ranging from the surface to 500 m. Parameters of the least-square regression equations were estimated between different diagnostic hard parts and the length and the weight of the prey. These relationships are useful for estimating the reconstructed weight of the diet of top predators and for estimating the predator size-prey size ratios. This work is the first reference on such relationships for the forage fauna of the western Indian Ocean.     

Influence of recruit condition on food competition and predation risk in a coral reef fish

Settlement rate is considered to be a major determinant of the population structure of coral reef fishes. In this study, the effects of larval physiological condition on survival, predation risk and competitive ability are assessed for a small damselfish, Pomacentrus moluccensis. New settlers were collected and fed for 5 days to produce high and low condition (measured as lipid) treatment fish. In a field experiment, pairs (one high and one low condition fish) were transplanted to corals. Persistence over 2 weeks was much higher (100% vs. 25%) in high condition fish. In mixed groups in the laboratory, high condition fish were both aggressively dominant and consumed more of a limiting prey source than low condition fish. In addition, low condition fish were shown to be at much higher risk of predation. All of the low condition fish but only 33% of high condition fish in mixed groups were consumed by fish predators, and in a separate experiment, 73% of feeding strikes by predators were directed at low condition fish. Quality of new settlers can have an important influence on subsequent juvenile survival. The mechanisms for this effect are likely to include a combination of effects of condition on food competition and predation risk.     

Foods of <Emphasis Type="Italic">Velella velella</Emphasis> (Cnidaria: Hydrozoa) in algal rafts and its distribution in Irish seas

The pleustonic hydrozoan, Velella velella, occurs throughout tropical to cold-temperate oceans of the world and sometimes are stranded in masses along hundreds of kilometers of beaches. In June 2009, we encountered algal rafts in the Celtic Sea containing many V. velella that we immediately preserved for gut content analysis. Available prey were enumerated from raft-associated fauna and zooplankton sampled nearby. The identifiable prey (331) in V. velella comprised 78% raft-associated prey (primarily harpacticoid copepods, cumaceans, small fish) and 22% pelagic prey (calanoid copepods, barnacle nauplii, fish eggs). Comparison of ingested with available prey showed selection for fish eggs and small fish, among others; therefore, the null hypothesis, that V. velella consumed all available prey equally, was rejected. Transport by wind and water concentrate Velella spp. in convergences with algal rafts, which suggests that they are important predators of raft—as well as pelagic fauna. A visual survey in September 2004 across the Celtic Sea and beach-stranding data show that V. velella is very abundant in Irish waters at times. Its circumpolar abundance, consumption of pelagic prey and production from symbiotic zooxanthellae, and mass deposition on beaches suggest that V. velella is important in open-ocean carbon cycling and in transport of pelagic production to landmasses.     

Nest predators of woodland open-nesting songbirds in central Europe

I used time-lapse videotaping to identify predators of open songbird nests in fragmented deciduous woodland (nine plots, 2–10 ha each) in the Czech Republic from 2002 to 2006. I documented 22 species of predators at 171 nests of 13 species (mainly Blackcap Sylvia atricapilla , Song Thrush Turdus philomelos , Common Blackbird Turdus merula , Yellowhammer Emberiza citrinella and Chaffinch Fringilla coelebs ). The main predators were Pine Marten Martes martes (37% of 178 predation events), Jay Garrulus glandarius (29%), Buzzard Buteo buteo (7%) and Great Spotted Woodpecker Dendrocopos major (7%); mammals accounted for 48% of total predation. At least 3% of nests were depredated by multiple predators. In spite of their local abundance, Hooded Crows Corvus cornix did not present a serious threat for shrub nesting songbirds (< 1% of total predation). No predation by mice was recorded, suggesting that their importance has been overestimated in artificial nest studies. The proportional species composition of predators depended on which species occupied the monitored nest and location (study plot), but not on the year or the time of season. Corvids and raptors accounted for a relatively larger percentage of total predation of small ('warblers') and large ('thrushes') prey species, respectively, whereas carnivores were important predators of all prey species. Active nests of thrushes were only rarely robbed by Jays (< 4% of 52 events), presumably due to parental nest defence. Predation by woodpeckers was spatially clumped, probably due to individual foraging specialization. Predation by the other major predators was documented on most/all study plots.     

Tadpoles of the bronze frog (Rana temporalis) assess predation risk before evoking antipredator defense behavior

Predation threat-associated behavioral response was studied in Rana temporalis tadpoles to discover the importance of predators’ visual and chemical cues (kairomones and diet-derived metabolites of consumed prey) in evoking antipredator behavior. The caged predators (dragonfly larvae) fed on prey tadpoles or insects (Notonecta spp.) and water conditioned with the predators provided the threat stimuli to the tadpole prey. The predators’ visual cues were ineffective in evoking antipredator behaviors in the tadpole prey. However, exposure to caged tadpole-fed predators or water conditioned with tadpole-fed predators elicited predator avoidance behavior in the tadpoles; they stayed away from the predators, significantly reduced swimming activity (swimming time and distance traveled), and increased burst speed. Interestingly, exposure to water conditioned with starved predators did not elicit any antipredator behavior in the prey. Further, the antipredator responses of predator-experienced tadpoles were significantly greater than those exhibited by predator-na?ve tadpoles. The study shows that R. temporalis tadpoles assess predation threat based exclusively on chemical cues emanating from the predators’ dietary metabolites and that the inclusion of conspecific prey items in the diet of the predators is perceived as a threat. The study also shows that antipredator behavior in these tadpoles is innate and is enhanced during subsequent encounters with the predators.     

The effect of density and mutual interference by a Predator: A laboratory study of predation by the Nudibranch Coryphella rufibranchialis on the hydroid Tubularia larynx

The nudibranch Coryphella rufibranchialis (JOHNSTON) feeds on a variety of hydroids, including Tubularia larynx Ellis & Solander. Experiments in which density of prey and predators were altered showed that more prey were eaten as prey density increased. However, more prey were consumed at low predator densities, presumably because of mutual interference among nudibranchs at the higher predator densities. The number of prey consumed per nudibranch was maximal with low predator densities and a ratio of 25–50 polyps per predator. Coryphella seems to show an opportunistic feeding strategy involving solitary predators rapidly depleting hydroid colonies and moving on to new colonies.