Hunting behaviour of the perlid stonefly nymph Dinocras cephalotes (Plecoptera) under different light conditions

The hunting behaviour of Dinocras cephalotes nymphs was studied during two different light intensities, darkness and twilight (0·1 cd m^?2). Nymphs of the mayfly Baetis rhodani were provided as food. In darkness the predator moved slowly without stopping, encountering the prey with the antennae and the hair fringes on the tibiae. Little time was spent in a shelter. There was little tendency to pursue the prey after a missed first attack and the pursuing distance was short. In twilight the speed of the predator was higher and the movement was interrupted by long periods of rest. The number of successful attacks was higher and more attacks were initiated when the predator was immobile. Time of activity outside the shelter was short. There was a greater tendency to pursue the prey after a missed first attack and the pursuing distance was longer compared with that in darkness. There are two main advantages of changing strategy from ‘searcher’ in darkness to ‘ambusher’ in the light: to avoid being detected by predators hunting by vision and to avoid being detected by potential prey species relying on visual cues for the detection of predators. The optical design of the eye revealed that only those parts of the eye directed upwards and backwards were optimized to the light conditions at which the predator preferred to be active, suggesting that the main function of these areas is to detect predators, though an additional gain in detecting prey could also be seen.     

The Feeding Behaviour of a Sit and Wait Predator Ranatra dispar (Heteroptera: Nepidae): The Effect of Prey Density and Age Structure on the Number of Prey Eaten

Functional response experiments were performed in the laboratory to examine the effect of prey density (as observed in the field) on feeding behaviour, and to measure handling-times and attack-rates for each instar and adult of Ranatra dispar Montandon (Heteroptera: Nepidae) feeding on five size-classes of its common prey, Anisops deanei Brooks (Heteroptera: Notonectidae). The most generally applicable response was the Type 2, although for both the predator fifth instar and adult female and male feeding on the two smallest prey sizes, the asymptote or plateau was not observed even at the highest prey density given. Generally, the handling-time increased as prey-size increased, and decreased as the predator size increased. The attack-rate surface was far more complex. For the first two predator instars (I and II), the maximum attack-rate occurred on the smallest prey sizes (1 and 2). The maximum attack-rate for predator instar III was almost the same for prey sizes 1 and 2, that of predator instar IV was greater for prey size 2, while in the three largest predator sizes (V, female and male), the maximum attack-rate was found for prey size 3. Predator instar V had the largest attack-rate values over all prey sizes, and both the predator adult female and male had lower attack-rates for various prey sizes than instars V, IV and, to some degree, III. The results support the suggestion that small predator instars will usually compete with large instars for prey, unless they are spatially or temporally separated. Observations in the field indicate that a distinct age-specific spatial distribution exists in R. dispar and the prey, A. deanei, with the smallest individuals being found predominantly in the shallow (littoral zone) water, while the larger individuals are found in the deeper water.     

Aposematic coloration, luminance contrast, and the benefits of conspicuousness

Many organisms use warning, or aposematic, coloration to signaltheir unprofitability to potential predators. Aposematicallycolored prey are highly visually conspicuous. There is considerableempirical support that conspicuousness promotes the effectivenessof the aposematic signal. From these experiments, it is welldocumented that conspicuous, unprofitable prey are detectedsooner and aversion learned faster by the predator as comparedwith cryptic, unprofitable prey. Predators also retain memoryof the aversion longer when prey is conspicuous. The presentstudy focused on the elements of conspicuousness that conferthese benefits of aposematic coloration. Drawing on currentunderstanding of animal vision, we distinguish 2 features ofwarning coloration: high chromatic contrast and high brightness,or luminance, contrast. Previous investigations on aposematicsignal efficacy have focused mainly on the role of high chromaticcontrast between prey and background, whereas little researchhas investigated the role of high luminance contrast. Usingthe Chinese mantid as a model predator and gray-painted milkweedbugs as model prey, we found that increased prey luminance contrastincreased detection of prey, facilitated predator aversion learning,and increased predator memory retention of the aversive response.Our results suggest that the luminance contrast component ofaposematic coloration can be an effective warning signal betweenthe prey and predator. Thus, warning coloration can even evolveas an effective signal to color blind predators.     

Distribution of predatory bacteria that attack chromatiaceae in a sulfurous lake

Predatory bacteria that attack Chromatiaceae (purple sulfur bacteria) recovered from Lake Cisó (a mostly anaerobic holomictic lake) have been studied over two annual cycles. During the mixing period the lake was completely anaerobic; both predator and prey populations were found along the water column, and even at the surface. Throughout the stratification period maximum Chromatiaceae occurred between a depth of 1 and 3 m depth. The maximum numbers of predators and prey (Chromatiaceae) also occurred in this range.A collapse took place in the lake during the second annual cycle in 1986. It brought about changes in the physicochemical parameters of the lake, thus altering the population dynamics. Nevertheless, during both cycles the number of predatory bacteria was maximum immediately below the depth at which the maximum number of prey bacteria occurred. Send offprint requests to: N. Gaju.     

Life-history trade-off in two predator species sharing the same prey: a study on cassava-inhabiting mites

In cassava fields, two species of predatory mites, Typhlodromalus aripo and T. manihoti, co-occur at the plant level and feed on Mononychellus tanajoa , a herbivorous mite. The two predator species are spatially segregated within the plant: T. manihoti dwells on the middle leaves, while T. aripo occurs in the apices of the plant during the day and moves to the first leaves below the apex at night.
To monitor the prey densities experienced by the two predator species in their micro-environment, we assessed prey and predator populations in apices and on the leaves of cassava plants in the field. Prey densities peaked from November to January and reached the lowest levels in July. They were higher on leaves than in the apices. To test whether the life histories of the two predator species are tuned to the prey density they experience, we measured age-specific fecundity and survival of the two predators under three prey density regimes (1 prey female/72 h, 1 prey female/24 h and above the predators level of satiation). T. manihoti had a higher growth rate than T. aripo at high prey densities, mainly due to its higher fecundity. T. aripo had a higher growth rate at low prey density regimes, due to its late fecundity and survival. Thus, each of the two species perform better under the prey density that characterizes their micro-habitat within the plant.     

Diving patterns of a Ross seal (Ommatophoca rossii ) near the eastern coast of the Antarctic Peninsula

In January 1987 we documented the diving patterns of a female Ross seal (Ommatophoca rossii) in the marginal pack-ice zone near the eastern coast of the Antarctic Peninsula for 2 days using a microprocessor-based time-depth recorder. The seal hauled out during the day and dived continually when in the water at night. Dives averaged 110 m deep and 6.4 min long; the deepest dive was 212 m and the longest 9.8 min. Dives were deepest near twilight and shallowest at night; this pattern suggests that the seal's prey, presumably mid-water squid and fish, may have been making vertical migrations or changing predator-avoidance behavior in response to diel light patterns. The dives of this Ross seal were substantially deeper, on average, than those of crabeater seals (Lobodon carcinophagus), which forage in the same areas on Antarctic krill (Euphausia superba). Received: 15 August 1996 / Accepted: 22 February 1997     

Preference and performance of a gall-inducing sawfly: plant vigor, sex, gall traits and phenology

Four hypotheses regarding the role of predation in the population dynamics of eruptive small mammal communities were tested using the small mammal assemblage found in mixed forests in New Zealand. Large-scale (750 ha) predator removal was conducted, targeting stoats ( Mustela erminea ). House mouse ( Mus musculus ) and ship rat ( Rattus rattus ) population dynamics during an eruption were compared in areas with and without predator reduction. The success of predator reduction was measured by comparing live-capture rates of predators on treatment and non-treatment areas, and by recruitment rates of the threatened northern brown kiwi ( Apteryx australis mantelli ). Overall, predator reduction was successful, although there was a continual low rate of reinvasion. The predictions and results were that 1) Predators can slow but not prevent a population eruption. Supported: Populations of mice and rats erupted to high densities in areas with and without predator reduction, following synchronous southern beech ( Nothofagus spp.) seeding. 2) Predators cannot truncate peak prey population size. Supported: Peak densities of mice and rats were not significantly different between treatment and non-treatment areas. 3) Predators can hasten the rate of decline in prey populations during the crash phase. Not supported: There was evidence of populations of mice and rats declining slower in areas with predators removed, but none of the trends were significant. 4) Predators can limit low-phase prey populations. Equivocal: Populations of rats in beech forest, and population of mice and rats in coastline habitats were significantly higher in areas with predators removed, but were not significantly different in tawa-podocarp forest. Therefore, the role of food in driving the early stages of the mouse and rat eruption was demonstrated, but the role of predation in the decline and low phases is unclear.     

An avian terrestrial predator of the Arctic relies on the marine ecosystem during winter

Top predators of the arctic tundra are facing a long period of very low prey availability during winter and subsidies from other ecosystems such as the marine environment may help to support their populations. Satellite tracking of snowy owls, a top predator of the tundra, revealed that most adult females breeding in the Canadian Arctic overwinter at high latitudes in the eastern Arctic and spend several weeks (up to 101 d) on the sea‐ice between December and April. Analysis of high‐resolution satellite images of sea‐ice indicated that owls were primarily gathering around open water patches in the ice, which are commonly used by wintering seabirds, a potential prey. Such extensive use of sea‐ice by a tundra predator considered a small mammal specialist was unexpected, and suggests that marine resources subsidize snowy owl populations in winter. As sea‐ice regimes in winter are expected to change over the next decades due to climate warming, this may affect the wintering strategy of this top predator and ultimately the functioning of the tundra ecosystem.     

Do nomadic avian predators synchronize population fluctuations of small mammals? a field experiment

Three-to-five-year population oscillations of northern small rodents are usually synchronous over hundreds of square kilometers. This regional synchrony could be due to similarity in climatic factors, or due to nomadic predators reducing the patches of high prey density close to the average density of a larger area. We estimated avian predator and small rodent densities in 4–5 predator reduction and 4–5 control areas (c. 3 km² each) during 1989–1992 in western Finland. We studied whether nomadic avian predators concentrate at high prey density areas, and whether this decreases spatial variation in prey density. The yearly mean number of avian predator breeding territories was 0.2–1.0 in reduction areas and 3.0–8.2 in control areas. Hunting birds of prey concentrated in high prey density areas after their breeding season (August), but not necessarily during the breeding season (April to June), when they were constrained to hunt in vicinity of the nest. The experimental reduction of breeding avian predators increased variation in prey density among areas but not within areas. The difference in variation between raptor reduction and control areas was largest in the late breeding season of birds of prey, and decreased rapidly after the breeding season. These results appeared to support the hypothesis that the geographic synchrony of population cycles in small mammals may be driven by nomadic predators concentrating in high prey density areas. Predation and climatic factors apparently are complementary, rather than exclusive, factors in contributing to the synchrony.     

The impact of mortality on predator population size and stability in systems with stage-structured prey

The relationships between a predator population's mortality rate and its population size and stability are investigated for several simple predator-prey models with stage-structured prey populations. Several alternative models are considered; these differ in their assumptions about the nature of density dependence in the prey's population growth; the nature of stage-transitions; and the stage-selectivity of the predator. Instability occurs at high, rather than low predator mortality rates in most models with highly stage-selective predation; this is the opposite of the effect of mortality on stability in models with homogeneous prey populations. Stage-selective predation also increases the range of parameters that lead to a stable equilibrium. The results suggest that it may be common for a stable predator population to increase in abundance as its own mortality rate increases in stable systems, provided that the predator has a saturating functional response. Sufficiently strong density dependence in the prey generally reverses this outcome, and results in a decrease in predator population size with increasing predator mortality rate. Stability is decreased when the juvenile stage has a fixed duration, but population increases with increasing mortality are still observed in large areas of stable parameter space. This raises two coupled questions which are as yet unanswered; (1) do such increases in population size with higher mortality actually occur in nature; and (2) if not, what prevents them from occurring? Stage-structured prey and stage-related predation can also reverse the 'paradox of enrichment', leading to stability rather than instability when prey growth is increased.     

Laboratory studies of predation by the Antarctic mite Gamasellus racovitzai (Acarina: Mesostigmata)

Summary Laboratory investigations of predation by Gamasellus racovitzai (Acarina: Mesostigmata) on Cryptopygus antarcticus (Insecta: Collembola) are described. The predator appeared to search at random, but, when contact with prey had been made, a rapid attack involved looping the forelegs over the prey to hold it whilst the chelicerae moved forward horizontally to puncture the side of the prey. The mean predation rate by deutonymphs, approximately one prey per predator per 12 days, was independent of prey density, but with adults this rate increased to about one prey per predator per 3 days. A study of leg geometry predicted a maximum prey size that could be captured: some experimental evidence suggested that mites selected prey near to this predicted size. The contribution of the laboratory results towards understanding the dynamics of field populations is discussed.     

Floater survival affects population persistence. The role of prey availability and environmental stochasticity

We develop two individual-based models using a large and detailed data set (information gathered over more than a century) on a population of a longlived and territorial predator, the Spanish imperial eagle. We investigated the relationship between survival and predator pressure, prey behaviour and patch availability (i.e. settlement areas). Survival of dispersing individuals was highly dependent on the number of available settlement areas, mediated by prey availability. Changes in prey behaviour due to predation pressure (e.g. shifting from diurnal to nocturnal activity) can decrease their availability for predators even if the density significantly exceeds the predator needs. Environmental stochasticity had a strong influence on population viability when it occurred in a synchroneous way between breeding and settlement areas, and an increase in floater mortality negatively influenced stability and dynamics of the breeding segment of populations in reproductive areas. Our simulations demonstrated the link between the dynamics in settlement and breeding areas: factors affecting floater survival also influence whole population dynamics. Moreover, model outputs provided insights into the relationship between environmental stochasticity and population dynamics.     

The forgotten feeding ground: patterns in seasonal and depth-specific food intake of adult cod Gadus morhua in the western Baltic Sea

This study presents the diet composition of western Baltic cod Gadus morhua based on 3150 stomachs sampled year-round between 2016 and 2017 using angling, gillnetting and bottom trawling, which enhanced the spatio-temporal coverage of cod habitats. Cod diet composition in shallow areas (<20 m depth) was dominated by benthic invertebrate species, mainly the common shore crab Carcinus maneas. Compared to historic diet data from the 1960s and 1980s (limited to depth >20 m), the contribution of herring Clupea harengus decreased and round goby Neogobius melanostomus occurred as a new prey species. Statistical modelling revealed significant relationships between diet composition, catch depth, fish length and season. Generalized additive modelling identified a negative relationship between catch depth and stomach content weight, suggesting reduced food intake in winter when cod use deeper areas for spawning and during peak summer when cod tend to avoid high water temperatures. The results of this study highlight the importance of shallow coastal areas as major feeding habitats of adult cod in the western Baltic Sea, which were previously unknown because samples were restricted to deeper trawlable areas. The results strongly suggest that historic stomach analyses overestimated the role of forage fish and underestimated the role of invertebrate prey. Eventually, this study shows the importance of a comprehensive habitat coverage for unbiased stomach sampling programmes to provide a more reliable estimation of top predator diet, a key information for food web analyses and multispecies models.     

Population and behavioural responses of native prey to alien predation

The introduction of invasive alien predators often has catastrophic effects on populations of naïve native prey, but in situations where prey survive the initial impact a predator may act as a strong selective agent for prey that can discriminate and avoid it. Using two common species of Australian small mammals that have persisted in the presence of an alien predator, the European red fox Vulpes vulpes, for over a century, we hypothesised that populations of both would perform better where the activity of the predator was low than where it was high and that prey individuals would avoid signs of the predator’s presence. We found no difference in prey abundance in sites with high and low fox activity, but survival of one species—the bush rat Rattus fuscipes—was almost twofold higher where fox activity was low. Juvenile, but not adult rats, avoided fox odour on traps, as did individuals of the second prey species, the brown antechinus, Antechinus stuartii. Both species also showed reduced activity at foraging trays bearing fox odour in giving-up density (GUD) experiments, although GUDs and avoidance of fox odour declined over time. Young rats avoided fox odour more strongly where fox activity was high than where it was low, but neither adult R. fuscipes nor A. stuartii responded differently to different levels of fox activity. Conservation managers often attempt to eliminate alien predators or to protect predator-naïve prey in protected reserves. Our results suggest that, if predator pressure can be reduced, otherwise susceptible prey may survive the initial impact of an alien predator, and experience selection to discriminate cues to its presence and avoid it over the longer term. Although predator reduction is often feasible, identifying the level of reduction that will conserve prey and allow selection for avoidance remains an important challenge.     

Movement and direction of movement of a simulated prey affect the success rate in barn owl Tyto alba attack

The present study was aimed at testing a novel idea, that rather than maximizing their distance from a predator during close-distance encounters, prey species are better off moving directly or diagonally toward the predator in order to increase the relative speed and confine the attack to a single available clashing point. We used two tamed barn owls Tyto alba to measure the rate of attack success in relation to the direction of prey movement. A dead mouse or chick was used to simulate the prey, pulled to various directions by means of a transparent string during the owl's attack. Both owls showed a high success rate in catching stationary compared with moving food items (90% and 21%, respectively). Success was higher when the prey moved directly away, rather than towards the owls (50% and 18%, respectively). Strikingly, these owls had 0% success in catching food items that were pulled sideways. This failure to catch prey that move sideways may reflect constraints in postural head movements in aerial raptors that cannot move the eyes but rather move the entire head in tracking prey. So far there is no evidence that defensive behavior in terrestrial prey species takes advantage of the above escape directions to lower rates of predator success. However, birds seem to adjust their defensive tactics in the vertical domain by taking-off at a steep angle, thus moving diagonally toward the direction of an approaching aerial predator. These preliminary findings warrant further studies in barn owls and other predators, in both field and laboratory settings, to uncover fine predator head movements during hunting, the corresponding defensive behavior of the prey, and the adaptive significance of these behaviors.     

Deep impact: in situ functional responses reveal context‐dependent interactions between vertically migrating invasive and native mesopredators and shared prey

相似文献   

Piscivore efficiency and refuging prey: the importance of predator search mode

In predator-prey interactions, the efficiency of the predator is dependent on characteristics of both the predator and the prey, as well as the structure of the environment. In a field enclosure experiment, we tested the effects of a prey refuge on predator search mode, predator efficiency and prey behaviour. Replicated enclosures containing young of the year (0+) and 1-year-old (1+) perch were stocked with 3 differentially sized individuals of either of 2 piscivorous species, perch (Perca fluviatilis), pike (Esox lucius) or no piscivorous predators. Each enclosure contained an open predator area with three small vegetation patches, and a vegetated absolute refuge for the prey. We quantified the behaviour of the predators and the prey simultaneously, and at the end of the experiment the growth of the predators and the mortality and habitat use of the prey were estimated. The activity mode of both predator species was stationary. Perch stayed in pairs in the vegetation patches whereas pike remained solitary and occupied the corners of the enclosure. The largest pike individuals stayed closest to the prey refuge whereas the smallest individuals stayed farthest away from the prey refuge, indicating size-dependent interference among pike. Both size classes of prey showed stronger behavioural responses to pike than to perch with respect to refuge use, distance from refuge and distance to the nearest predator. Prey mortality was higher in the presence of pike than in the presence of perch. Predators decreased in body mass in all treatments, and perch showed a relatively stronger decrease in body mass than pike during the experiment. Growth differences of perch and pike, and mortality differences of prey caused by predation, can be explained by predator morphology, predator attack efficiency and social versus interference behaviour of the predators. These considerations suggest that pike are more efficient piscivores around prey refuges such as the littoral zones of lakes, whereas perch have previously been observed to be more efficient in open areas, such as in the pelagic zones of lakes.     

Numerical and dietary responses of a predator community in a temperate zone of Europe

The generalist predation hypothesis predicts that the functional responses of generalist predator species should be quicker than those of specialist predators and have a regulating effect on vole populations. New interpretations of their role in temperate ecosystems have, however, reactivated a debate suggesting generalist predators may have a destabilizing effect under certain conditions (e.g. landscape homogeneity, low prey diversity, temporary dominance of 1 prey species associated with a high degree of dietary specialization). We studied a rich predator community dominated by generalist carnivores ( Martes spp., Vulpes vulpes, Felis catus ) over a 6 yr period in farmland and woodland in France. The most frequent prey were small rodents (mostly Microtus arvalis , a grassland species, and Apodemus spp., a woodland species). Alternative prey were diverse and dominated by lagomorphs ( Oryctolagus cuniculus, Lepus europeus ). We detected a numerical response among specialist carnivores but not among generalist predators. The dietary responses of generalist predators were fairly complex and most often dependent on variation in density of at least 1 prey species. These results support the generalist predation hypothesis. We document a switch to alternative prey, an increase of diet diversity, and a decrease of diet overlap between small and medium-sized generalists during the low density phase of M. arvalis . In this ecosystem, the high density phases of small mammal species are synchronous and cause a temporary specializing of several generalist predator species. This rapid functional response may indicate the predominant role of generalists in low amplitude population cycles of voles observed in some temperate areas.     

The anatomy of predator-prey dynamics in a changing climate

Humans are increasingly influencing global climate and regional predator assemblages, yet a mechanistic understanding of how climate and predation interact to affect fluctuations in prey populations is currently lacking. Here we develop a modelling framework to explore the effects of different predation strategies on the response of age-structured prey populations to a changing climate. We show that predation acts in opposition to temporal correlation in climatic conditions to suppress prey population fluctuations. Ambush predators such as lions are shown to be more effective at suppressing fluctuations in their prey than cursorial predators such as wolves, which chase down prey over long distances, because they are more effective predators on prime-aged adults. We model climate as a Markov process and explore the consequences of future changes in climatic autocorrelation for population dynamics. We show that the presence of healthy predator populations will be particularly important in dampening prey population fluctuations if temporal correlation in climatic conditions increases in the future.     

Diet changes in prey size selectivity in larvae of perch <Emphasis Type="Italic">Perca fluviatilis</Emphasis>

A hypothesis on change in prey size selectivity in relation to illumination level was tested on the basis of data on weight and size composition of the content of the digestive tract of larvae of perch Perca fluviatilis and on zooplankton in the layer 0–6 m (Wallersee Lake, Austria). Larvae foraging in the twilight-night period had almost two times more food in the intestine than those foraging in the daytime. The size composition of perch larvae and concentration and size composition of zooplankton hardly differed in the daytime and twilight-night samples. For the first time, it is shown on field material that more intensive feeding of larvae at twilight is related to selection of significantly larger prey than in daytime feeding. In the day-time, the larvae consumed more prey but their maximum size did not exceed 0.6 of the diameter of mouth opening of the fish; at twilight it was over 0.8. In case of feeding on so large prey, not only the weight of the consumed feed increases but the time used for capture and swallowing also considerably increases. The larvae which in the period of investigation did not yet form schools, which perform the principal defensive function, were especially vulnerable for predators feeding on relatively large prey. The decrease of the part of small-sized prey at twilight is not related to their lesser availability due to a low illumination. It is assumed that feeding on energetically more valuable but less available prey is shifted to the period of low illumination when the larvae are less exposed to predation risk. The obtained results are discussed from positions of the triotroph concept (Manteifel’, 1961).