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1.
Synopsis In northern clear-water systems, bluegill, Lepomis macrochira, select habitats based on relative reward rates and risk of predation. However, because freshwater systems to the south are often turbid, and their resident fish species different, bluegill habitat use patterns may differ from those found in northern clear-water systems. Here I examine the effects of elimination of the inshore macrophyte refuge (an indirect effect of turbidity), and decreased pelagic predation rates on bluegill due to the presence of gizzard shad, Dorosoma cepedianum, in laboratory pools. Bluegill used depths 20 cm more often with largemouth bass, Micropterus salmoides, than without them; the presence of a preferred alternate prey, gizzard shad, did not affect this behavior. Though bluegill did not alter their habitat use in response to bass activity, they did school more as predator activity increased. Even in the presence of a preferred alternate prey without macrophytes, bluegill continue to use shallow littoral areas to avoid predation.This Unit is sponsored jointly by The United States Fish and Wildlife Service, Ohio Department of Natural Resources, The Ohio State University, and the Wildlife Management Institute.  相似文献   

2.
Optimal foraging theory is devoted to understanding how organisms maximize net energy gain. However, both the theory and empirical studies lack critical components, such as effects of environmental variables across habitats. We addressed the hypothesis that energetic returns of juvenile bluegill are affected by environmental variables characteristic of the vegetated habitats. Predicted optimal diet breadths were calculated and compared to prey items eaten by juvenile bluegill to determine if bluegill were foraging to maximize energetic gain. Differences in habitat profitability among vegetated sites were determined by comparing predictions of maximized energetic return rates (cals-1) with prey contents of bluegill stomachs. Sizes of most prey items eaten by juvenile bluegill throughout the vegetated sites were smaller than the predicted optimal diet breadths. However, inclusion of smaller prey items in the diet did not seem to affect rate of energetic gain. Energetic return rates were maximized at the 1.5 and 2mm prey size classes and declined only slightly with inclusion of smaller prey sizes. Predicted energetic return rates and average mass in bluegill stomachs were related negatively. Average mass in bluegill stomachs also was associated negatively with Elodea canadensis stem densities and percent of light transfer, suggesting that foraging efficiency of bluegill decreased as plant density and percent of light increased. Results of our research indicate that maximization of energetic return rates is dependent upon availability of prey sizes that contribute to optimal foraging. Thus, determination of those habitats that provide the highest availability of benthic invertebrate prey with the least interference by stems is critical. Enhanced foraging capabilities can promote recruitment, faster growth, better body condition and survival.  相似文献   

3.
Aquatic macrophytes produce considerable structural variation within the littoral zone and as a result the vegetation provides refuge to prey communities by hindering predator foraging activities. The behavior of planktivorous fish Pseudorasbora parva (Cyprinidae) and their zooplankton prey Daphnia pulex were quantified in a series of laboratory experiments with artificial vegetation at densities of 0, 350, 700, 1400, 2100 and 2800 stemsm–2. Swimming speeds and foraging rates of the fish were recorded at different prey densities for all stem densities. The foraging efficiency of P. parva decreased significantly with increasing habitat complexity. This decline in feeding efficiency was related to two factors: submerged vegetation impeded swimming behavior and obstructed sight while foraging. This study separated the effects of swimming speed variation and of visual impairment, both due to stems, that led to reduced prey–predator encounters and examined how the reduction of the visual field volume may be predicted using a random encounter model.  相似文献   

4.
Summary In situations where foraging sites vary both in food reward and predation risk, conventional optimal foraging models based on the criterion of maximizing net rate of energy intake commonly fail to predict patch choice by foragers. Recently, an alternative model based on the simple rule when foraging, minimize the ratio of mortality rate (u) to foraging rate (f) was successful in predicting patch preference under such conditions (Gilliam and Fraser 1987). In the present study, I compare the predictive ability of these two models under conditions where available patches vary both in predation hazard and foraging returns. Juvenile bluegill sunfish (Lepomis macrochirus) were presented with a choice between two patches of artificial vegetation differing in stem density (i.e. 100, 250, and 500 stems/m2) in which to forage. Each combination (100:250, 250:500, or 100:500) was presented in the absence, presence, and after exposure to a bass predator (Micropterus salmoides). Which patch of vegetation bluegills chose to forage in, and foraging rate within each patch were recorded. Independent measurements of bluegill foraging rate and risk of mortality in the three stem densities provided the data for predicting patch choice by the two models. With no predator, preference between plots was consistent with the maximize energy intake per unit time rule of conventional optimality models. However, with a predator present, patch preference switched to match a minimize u/f criterion. Finally, when tested shortly after exposure to a predator (i.e. 15 min), bluegill preference appeared to be in a transitional phase between these two rules. Results are discussed with respect to factors determining the distribution of organisms within beds of aquatic vegetation.  相似文献   

5.
Summary An approximately constant ratio of number of predator species/number of prey species is observed in several natural communities, although the exact value of the ratio may vary with habitat and the types of organisms in the food web. We test the hypothesis that a constant predator/prey ratio can be generated by what Holt (1977) terms apparent competition and what Jeffries and Lawton (1984) call competition for enemy-free space. We create simple, two trophic-level communities by drawing species of predators and prey at random from a species pool, simulating their interactions using Lotka-Volterra models. The simulated food webs converge over successive periods of invasion and extinction to locally stable systems with approximately constant ratios of number of predator species/number of prey species, despite varying initial conditions. As expected, predator/prey ratios take different values depending upon the biology of the simulated species. We conclude that apparent competition between prey species via shared enemies may be one mechanism whereby approximately constant predator/prey ratios are generated in natural communities.  相似文献   

6.
The direct lethal impacts and the indirect effects predators have on prey characteristics, such as behavior, have fitness consequences for the prey. Whether the level of predation risk that prey face in the presence of multiple predator species can be predicted from a null model that sums the risk from each predator species in isolation is unclear. In field enclosures, we tested whether the predation risk experienced by Stenonema mayfly larvae from a dragonfly larva (Boyeria vinosa) and a hellgrammite (Corydalus cornutus) together matched the predictions of the multiplicative risk model. We then compared whether any deviations from the models predictions were larger in the presence of two predator species than in the presence of an equivalent density of individuals from either predator species alone, to determine if unique effects arise for the prey in the presence of multiple predator species. We also determined if prey moved preferentially into predator-free refuge spaces or decreased their movement in the presence of predators. Stenonemas risk of predation was reduced compared to the models prediction, but no unique multiple predator species effects were present because this risk reduction was comparable in magnitude to the level exhibited in the presence of each predator species alone. The prey did not move into predator-free refuge spaces in the presence of predators in the field enclosures. Thus, these predators appear to interfere interspecifically and intraspecifically, which may facilitate the coexistence of the predators and the prey.  相似文献   

7.
Predator-mediated habitat use: some consequences for species interactions   总被引:6,自引:0,他引:6  
Synopsis Behavioral responses to predators can have a major impact on a fishes' diet and habitat choice. Studies with the bluegill sunfish, Lepomis macrochirus, demonstrate that bluegills undergo pronounced shifts in diet and habitat use as they grow in response to changes in their vulnerability to predators. Other species of fish exhibit similar habitat shifts with body size, presumably also in response to changing predation risks and/or foraging gains. An important but little appreciated consequence of this type of predator-mediated habitat use is that predation risk, by structuring size and/or age-specific resource use, may also indirectly affect species interactions. This paper discusses some of the ways in which behavioral responses to predators may affect intra- and interspecific competition in fish. Observational and experimental studies with sunfish (Centrarchidae) provide most of the examples. These studies suggest that the nonlethal effects of predators may be as important as the actual killing of prey.  相似文献   

8.
Scaling the effects of predation and disturbance in a patchy environment   总被引:3,自引:0,他引:3  
Jill Lancaster 《Oecologia》1996,107(3):321-331
The effects of hydraulic disturbances on the impact of two predatory benthic invertebrates on their prey were examined in a stream at two distinct spatial scales. At the scale of small habitat patches (0.0625 m2), hydraulic patch type was an important determinant of the microdistribution of prey and predators. Prey abundances were similar across all patch types at baseflow, but local densities were higher in patches identified as low-flow refugia after periods of high and fluctuating flow. The microdistribution pattern of predatory larvae of a caddisfly, Plectrocnemia conspersa, was similar to that of its prey, whereas predatory larvae of an alderfly, Sialis fuliginosa, did not shift their microdistribution significantly with discharge and were always most abundant in lowflow refugia. There was little evidence of an aggregative response of predators with prey, even though both predators and prey are mobile. Both predator species showed similar patch-specific patterns of per capita consumption rates: uniform consumption rates across hydraulic patch types at low and moderate flows, but highest in flow refugia during high flows. Species-specific patterns, however, were apparent in the magnitude and direction of differences between consumption rates during disturbance events, and in comparable patches at base flow: At high flow, consumption rates for P. conspersa were exaggerated (3.9 times higher) in flow refugia but at par in other patches; for S. fuliginosa they were at par in flow refugia but reduced in other patches (up to 3.3. times lower). These differences may be related to species-specific foraging behaviours (search vs ambush predators) and the influence of prey movements on feeding success. Using the patch-scale results only, it is difficult to predict the effects of physical disturbance on predation intensity at the larger scales of whole habitats, populations or communities. At the large scale (>200 m2), net predator impacts were estimated over the stream reach, using a spatially explicit model that accounts, in an additive way, for habitat heterogeneity and patch-specific responses of predators and prey. The relationship between predator impact over the whole reach and hydraulic disturbance differed for the two predators. The predator impact of S. fuliginosa decreased with increasing hydraulic disturbance, as predicted by the harsh-benign hypothesis. There was no directional trend for P. conspersa, however, and maximum predator impact may occur at intermediate disturbance levels. For the prey community in this stream, predation pressure from S. fuliginosa appears to fluctuate directly with the discharge hydrograph, whereas predation from P. conspersa may be more persistent. Flow refugia may play a dual role in the sructure of stream communities by preventing catastrophic mortality of animals (predators and prey) from physical forces during disturbances, and by maintaining (or perhaps increasing) predation pressure. Summing the effects of species interactions in small habitat patches to the larger scale of a whole stream reach indicates that the scale of approach influences the observed patterns and their implied underlying process.  相似文献   

9.
Summary Two prey populations that share a common predator can interact indirectly by causing changes in the predator's foraging behaviour. Previous work suggests that adaptive choice of prey by the predator usually has two related consequences: (i) the predation rate on a particular prey species increases with the relative and/or absolute abundance of that prey; and (ii) increases in either prey population produce a short-term increase in the fitness of the other prey (short-term indirect mutualism between prey). This paper investigates how these two consequences are changed if the prey exhibit adaptive anti-predator behaviour. In this case, the predation rate on a particular prey often decreases as the prey's density increases. The predator then usually exhibits negative switching between prey. However, the presence of adaptive antipredator behaviour does not change the short-term mutualism between prey. In this case, as a prey becomes less common, it achieves a larger growth rate by reducing its anti-predator effort. These results imply that observations of the relationship between prey density and predation rate cannot be used to infer the nature of the behavioural indirect effect between prey that share a predator.  相似文献   

10.
Summary The accurate estimation of the amount of energy contained within a food item which is available to a predator is essential in tests of optimal foraging theories. Many studies of optimal foraging measure gross energy content of prey directly by bomb calorimetry. I suggest that a more realistic and accurate estimate of true prey value is available by calculating energy associated with the organic constituents of prey, and then subtracting away energy associated with insoluble and indigestible components. This methodology allows for a much more precise estimate of prey value (useable energy) and therefore a more realistic test of optimal foraging models.  相似文献   

11.
We determined how turbidity affected the reactive distance and foraging success of smallmouth bass, Micropterus dolomieu. Smallmouth bass reactive distance decreased exponentially with increasing turbidity, from 65cm in clear water to 10cm at the highest turbidity. Turbidity significantly decreased the probability of a fish reacting to a prey item, but did not influence foraging success following reaction to the prey. Elevated turbidity may reduce stream fish foraging efficiency and decrease prey consumption.  相似文献   

12.
Summary We compared the patch-choice performances of an ambush predator, the crab spider Misumena vatia (Thomisidae) hunting on common milkweed Asclepias syriaca (Asclepiadaceae) umbles, with two stochastic rule-of-thumb simulation models: one that employed a threshold giving-up time and one that assumed a fixed probability of moving. Adult female Misumena were placed on milkweed plants with three umbels, each with markedly different numbers of flower-seeking prey. Using a variety of visitation regimes derived from observed visitation patterns of insect prey, we found that decreases in among-umbel variance in visitation rates or increases in overall mean visitation rates reduced the clarity of the optimum (the difference in the yield obtained as foraging behavior changes), both locally and globally. Yield profiles from both models were extremely flat or jagged over a wide range of prey visitation regimes; thus, differences between optimal and next-best strategies differed only modestly over large parts of the foraging landscape. Although optimal yields from fixed probability simulations were one-third to one-half those obtained from threshold simulations, spiders appear to depart umbels in accordance with the fixed probability rule.  相似文献   

13.
Summary We evaluated three methods for the analysis of functional response data by asking whether a given method could discriminate among functional responses and whether it could accurately identify regions of positive density-dependent predation. We evaluated comparative curve fitting with foraging models, linear least-squares analysis using the angular transformation, and logit analysis. Using data from nature and simulations, we found that the analyses of predation rates with the angular transformation and logit analysis were best at consistently determining the true functional response, i.e. the model used to generate simulated data. These methods also produced the most accurate estimates of the true regions of density dependence. Of these two methods, functional response data best fulfill the assumptions of logit analysis. Angularly transformed predation rates only approximate the assumptions of linear leastsquares analysis for predation rates between 0.1 and 0.9. Lack-of-fit statistics can reveal inadequate fit of a model to a data set where simple regression statistics might erroneously suggest a good match.  相似文献   

14.
The extent of induced morphological defense in Euplotes daidaleos correlates to this ciliate's predation risk from the defense-inducing predator species. Euplotes daidaleos responded by morphological transformation only to organisms that are able to feed on typically formed Euplotes cells (63 ± 5 m cell width in E. daidaleos). Three of those potential predator species caused defensive changes to various degrees (Student's t-test, P < 0.1 to P < 0.0001): Lembadion bullinum (Ciliata) induced 82 ± 6 m cell width in E. daidaleos; Chaetogaster diastrophus (Oligochaeta) induced 85 = 6 m width; and Stenostomum sphagnetorum (Turbellaria) induced 89 ± 8 m width (at a density of 10 predators per milliliter, respectively). At higher predator densities (50 or 100 organisms per milliliter), Euplotes developed a correspondingly larger width (to a maximum of 103 ± 10 m in the presence of S. sphagnetorum). Euplotes did not respond to organisms (e.g., Blepharisma japonicum, Colpidium campylum, Didinium nasutum, Paramecium caudatum, Spirostomum ambiguum, Stentor coeruleus) that cannot feed on this ciliate species. Daphnia longispina and Bursaria truncatella predators, which can feed on large prey of 125, or 200 m in diameter, respectively, also had no effect on the morphology of Euplotes. The extent of defense in Euplotes that was induced by 10 predators per milliliter during 24 h decreased the predation risk from those predators to 67% in the presence of S. sphagnetorum, to 50% with L. bullinum, and to 15% with C. diastrophus, compared to the typical form of Euplotes. In a natural population, the defensive form of E. daidaleos was found with average cell widths of 88 ± 8 m. The results indicate that predator-induced defense in natural Euplotes populations is beneficial to this prey and that it is adapted to the predation abilities of Euplotes predators, whereby energetical costs related to defensive changes may be saved.  相似文献   

15.
An avoidance learning submodel for a general predation model   总被引:1,自引:0,他引:1  
Lawrence M. Dill 《Oecologia》1973,13(4):291-312
Summary This paper attempts to determine the effect on the number of prey eaten by predators of the addition of the component avoidance learning by prey to a computer model of the predation process developed by Holling. Generality was retained by concentrating upon a basic aspect of the prey's behaviour, its distance of reaction to an approaching predator. The zebra danio (Brachydanio rerio), a small freshwater fish, was used as an analogue of a general vertebrate prey. The predator used was the largemouth bass (Micropterus salmoides).Previous work (Dill, 1973b) showed that prey reactive distance increased with increasing experience with the predator. In the present study, this increased prey reactive distance is shown to increase predator pursuit time and hypothesized to decrease predator pursuit success. These relationships were expressed mathematically and built into Holling's (1965, 1966) model of the predation process, along with an equation describing the way in which reactive distance increases following an unsuccessful attack. Other changes necessitated in the model by the addition of the avoidance learning component included: a) Modifications of the calculation of search time to remove a previously implicit time spent unsuccessfully pursuing prey, and to correct the density of prey to account for those whose reactive distances exceed that of the predator and are therefore not susceptible to discovery; b) Addition of a new subroutine (CHASE) to calculate pursuit time, unsuccessful pursuit time, pursuit success, and strike success; c) Changes in subroutine ADCOM to assign prey to different classes (with different reactive distances) according to the number of times they have been unsuccessfully attacked; and d) Addition of a stochastic element via random numbers to determine the class to which an attacked prey belongs, the time to refuge, and the predator's strike success.Simulation was used to explore the consequences of these additions. The capability of learning substantially increased the prey's probability of surviving subsequent attack. Addition of an avoidance learning component caused declines in the predator's functional responses to both prey and predator density. The new component was also suggested to decrease the predator's numerical response to prey density and to increase the probability of stability in a predator-prey interaction.From a thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, University of British Columbia.  相似文献   

16.
Summary Studies of predation by roach (Rutilus rutilus) on zebra mussel (Dreissena polymorpha) in a large, eutrophic lake showed that there was a clearly marked size threshold ( 160 mm SL) above which roach began to feed on mussels. Roach preying on various sizes of mussels selected them in proportions different from their abundance and accessibility in the habitat. The mean size of mussels ingested by roach of 220 mm and larger, which fed predominantly on Dreissena, closely followed the pattern expected for a constant ratio of mean prey size to mean predator mouth size = 0.59. To explain the size selection we applied an optimal foraging approach, based on the ability of different-sized fish to crush (cost) mussels of different sizes, and hence crushing resistance, and energy contents (benefit). We found that fish smaller than 160 mm, which showed no inclination to eat Dreissena, would only be able to take small mussels with a very high cost/benefit ratio. The real switch to Dreissena would be expected in fish of 230–240 mm that could take most of their prey from highly profitable, numerous, and easily accessible size classes while keeping the mean prey size at the optimal level relative to mean predator mouth size.  相似文献   

17.
In this paper we analyse a stochastic model for invertebrate predation taking account of the predator's satiation. This model approximates Holling's hungry mantid model when handling time is negligible (see Part I). For this model we derive equations from which we can calculate the functional response and the variance of the total catch. Moreover we study a number of approximations which can be used to calculate these quantities in practical cases in a relatively simple manner.List of Notation a rate constant of digestion - b maximum of rate constant of prey encounter in the mantid - c satiation threshold for search - c satiation threshold for pursuit in the mantid - c i (w1/2(N- N)i) - expectation operator - f rate of change of satiation during search - F functional response: mean number of prey eaten per unit of time - g rate constant of prey capture - h probability generating function of N conditional on S = s times p - H probability generating function of N - mi 1 - n, N number of prey caught - p probability density of S - pn simultaneous probability (density) of N and S - q probability of strike success - r dummy variable in generating function - s, S satiation - T s search time - T d digestion time - v asymptotic rate of increase of var v - V asymptotic rate of increase of var N - w weight of edible part of prey - W standard Wiener process - x prey density - z (N{S = s}-N)p - rate constant of prey escape time maximum pursuit time - (v{S = + w 1/2}-v) - present time as a fraction of the time from the start to the end of the experiment - hazard rate of T s - mean time between (downward) passages of S through c - v w–1/2(N-) - edible prey biomass density - probability density of , number pi - parameter of Weibull distribution of T s = (1/2acx(-g(c)))1/2 - w–1/2(S -) - satiation in the guzzler approximation: solution to d/dt = f() + g(), (0)=S(0). - biomass functional response: wF - total biomass catch in the guzzler approximation: solution to d/dt = g(), (0) = 0  相似文献   

18.
Summary We examined predator avoidance behavior of the freshwater snailPhysella (=Physa) virgata in response to the crayfishProcambarus simulans. In both laboratory and field enclosure experiments snails crawled above the waterline for 2 h or longer, then returned to the water.Physella virgata react to chemical signals given off by crayfish actively foraging on conspecific snails; they do not react to inactive crayfish. Low dissolved oxygen, crowding, and disturbance of the sediments did not elicit crawlout behavior. Crawling above the waterline, by reducing the probability of encounter between vulnerable, thin-shelled snails and crayfish, is an adaptive response to predation.  相似文献   

19.
The behavioural response of juvenile bluegill sunfish (Lepomis macrochirus) to predation risk when selecting between patches of artificial vegetation differing in food and stem density was investigated. Bluegill foraging activity was significantly affected by all three factors. Regardless of patch stem density or risk of predation bluegills preferred patches with the highest prey number. During each trial bluegill foraging activity was clearly divided into a between- and within-patch component. In the presence of a predator bluegills reduced their between-patch foraging activity by an equivalent amount regardless of patch stem density or food level, apparently showing a risk-adjusting behavioural response to predation risk. Within patches, however, foraging activity was affected by both food level and patch stem density. When foraging in a patch offering a refuge from predation, the presence of a predator had no effect on bluegill foraging activity within this patch. However, if foraging in a patch with only limited refuge potential, bluegill foraging activity was reduced significantly in the presence of a predator. Further, this reduction was significantly greater if the patch contained a low versus a high food level, indicating a risk-balancing response to predation with respect to within-patch foraging activity. Both these responses differ from the risk-avoidance response to predation demonstrated by juvenile bluegills when selecting among habitats. Therefore, our results demonstrate the flexibility of juvenile bluegill foraging behaviour.  相似文献   

20.
Zusammenfassung Bei der normalen weißen Ratte verhält sich die Zona externa des Infundibulum im Gegensatz zur Zona interna infundibuligomorinegativ.Am 7. Tag nach beidseitiger Adrenalektomie treten in der Zona externa gomoripositive Substanzen auf, deren Menge über den 14. Tag nach der Operation hinaus zunimmt.Im supraoptico-hypophysären System ergibt die quantitative Messung eine Entleerung des neurosekretorischen Materials am 3. Tage nach beidseitiger Adrenalektomie. Im Verlauf von 14 Tagen nach dem operativen Eingriff füllt sich das neurosekretorische System wieder bis zu den beim Normaltier ermittelten Werten auf.Die gomoripositiven Granula in der Zona externa inf. sind möglicherweise das morphologische Äquivalent eines Corticotropin-releasing factors.
On quantitative changes of Gomori-positive substances in the median eminence and neural lobe of the rat hypophysis after bilateral adrenalectomy
Summary In the normal albino rat, the external layer of the median eminence shows a Gomori-negative histochemical reaction as opposed to the internal layer.On the 7th day after bilateral adrenalectomy, Gomori-positive substances appear in the external layer, their amount increasing up to and beyond the 14th day p.o.In the supraoptico-hypophyseal system, quantitative measurements show a depletion of the neurosecretory substance on the 3rd day following bilateral adrenalectomy. This loss of neurosecretory material is restored during the course of 14 days p.o., the amount then corresponding to that found in the normal rat.It is conceivable that the Gomori-positive granules in the outer layer of the median eminence are the morphological equivalent of a CRF.
  相似文献   

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