The effect of prey size and prey density on the functional response,survival, growth and development of a predatory pentatomid bug,Podisus maculiventris say

Two experiments on the nymphal predation of Podisus maculiventris were conducted using Spodoptera litura larvae as prey. First experiment: The predator nymphs divided into three groups were reared individually from second instar to adult in a small vessel. Each nymph in the groups 1, 2 and 3 was allowed to attack the serially growing larvae (these were supplied at the rate of one per day) from 3-, 5- and 7-day old after hatching, respectively. The first prey used for the group 1 was so small that it was not only insufficient to satiate the predator but also was difficult to be searched out. But these disadvantages were soon recuperated due to the rapid growth of the prey and all nymphs could survive to adults. The survival rate of third and fourth instar nymphs in the group 3 was severely affected by vigorous counterattack of older prey larvae. Second experiment: The predator nymphs were individually reared either in a small vessel or in a large one at various rates of food supply (the prey larvae of 7-day old were used). The functional response curves obtained for each instar of the predator took a saturation type within a certain range of the prey density. The saturation level specific to each instar was generally higher for the predator reared in the large vessel than in the small one. The functional response of fourth and fifth instar nymphs was accelerated at a high prey density, viz. 16 larvae per vessel. Even at the low rate of food supply, viz. one larva per day per predator, the predator nymphs could survive to adults, but the size of resultant adults were abnormally small.     

Differential prey utilization by the generalist predator Coleomegilla maculata lengi according to prey size and species

Prey utilization by the generalist predator Coleomegilla maculata lengi Timb. (Coleoptera: Coccinellidae) of three sympatric lepidopterous species was quantified in relation with prey size (age) and prey species. Based on optimal foraging theory, we argued that costs associated with the utilization of small and large prey are higher than those of intermediate prey size. As a result, we expected a higher prey consumption rate on intermediate prey size leading to a convex prey consumption curve. Laboratory experiments showed that, within a given prey instar, Coleomegilla maculata lengi preyed more on Plutella xylostella (L.) compared to Artogeia rapae (L.) and Trichoplusia ni (Hübner). Generally, prey consumption rate by Coleomegilla maculata lengi on the three prey species decreased with increasing immature prey size (age). The predation efficacy of Coleomegilla maculata lengi adults and fourth instar larvae was higher compared to younger coccinellids (L2). Although, Coleomegilla maculata lengi showed a higher level of predation on smaller immature prey, we demonstrated that it is not the optimal size range for this predator. As predicted, prey weight consumption rate by Coleomegilla maculata lengi was higher at intermediate prey size leading to a convex prey utilization curve. The beneficial impact of Coleomegilla maculata lengi predation on the host plant was also estimated by using a Protection Index that considers the differential predation caused by the coccinellids and the relative importance of each pest species in terms of plant injury. Coleomegilla maculata lengi has a more significant beneficial impact when it preys on T. ni immatures.     

The feeding behaviour of Leptodora kindti and its impact on the zooplankton community of Neusiedler See (Austria)

Leptodora kindti is a very efficient invertebrate predator. Its searching mode of preying is tactile. The setae of the first thoracic limb act as mechanoreceptors, the other thoracic limbs, thorax and head together form the shape of an open basket in which after encounter the prey is pushed in by the aid of the first thoracic limbs and the furca. In Neusiedler See, small individuals of Diaphanosoma brachyurum (0.6–0.9 mm) are the preferred prey, rarely copepods are taken. The predation rate is influenced by temperature, prey density and predator size and varies between less than one and 12 prey items per predator per day. At high predator densities, Leptodora will have a substantial effect on the Diaphanosoma population of Neusiedler See.     

Killer whale (Orcinus orca) predation in a multi-prey system

Predation can regulate prey numbers but predator behaviour in multiple-prey systems can complicate understanding of control mechanisms. We investigate killer whale (Orcinus orca) predation in an ocean system where multiple marine mammal prey coexist. Using stochastic models with Monte-Carlo simulations, we test the most likely outcome of predator selection and compare scenarios where killer whales: (1) focus predation on larger prey which presumably offer more energy per effort, (2) generalize by feeding on prey as encountered during searches, or (3) follow a mixed foraging strategy based on a combination of encounter rate and prey size selection. We test alternative relationships within the Hudson Bay geographic region, where evidence suggests killer whales seasonally concentrate feeding activities on the large-bodied bowhead whale (Balaena mysticetus). However, model results indicate that killer whales do not show strong prey specialization and instead alternatively feed on narwhal (Monodon monoceros) and beluga (Delphinapterus leucas) whales early and late in the ice-free season. Evidence does support the conjecture that during the peak of the open water season, killer whale predation can differ regionally and feeding techniques can focus on bowhead whale prey. The mixed foraging strategy used by killer whales includes seasonal predator specialization and has management and conservation significance since killer whale predation may not be constrained by a regulatory functional response.     

Virtual plankton: A novel approach to the investigation of aquatic predator‐prey interactions

Small‐scale zooplankton swimming behaviors can affect aquatic predator‐prey interactions. Difficulties in controlling prey swimming behavior however, have restricted the ability to test hypotheses relating differences in small‐scale swimming behavior to frequency of predation by fish. We report here a Virtual Plankton (VP) system that circumvents this problem by allowing the observation of fish “preying"on computer‐generated prey images whose size, shape, color and swimming behavior can be precisely controlled. Two experiments were performed in which bluegill sunfish (Lepomis macrochirus) were given a choice of either two VP images, one of which moved twice as fast as the other, or six VP, one of which moved either faster (1.25 x, 1.5 x or 2 x ) or slower (0.5 x) than the other five. Current predator‐prey models based on encounter probabilities and prey visibility predict that moving faster increases predation risk and conversely, moving slower decreases predation risk. In agreement with existing predator‐prey models, in both experiments, fish chose faster moving VP significantly more often than their slower moving neighbors. Contrary to the predictions of existing models, in the second experiment with six VP, the rate at which fish chose a prey image moving half as fast as the five surrounding images did not differ significantly from the rate predicted by chance(l/6). These results suggest that current fish‐zooplankton predation models would benefit by the incorporation of small‐scale swimming behavior and assessments of its influence on overall prey visibility.     

Predator size and phenology shape prey survival in temporary ponds

Theoretical efforts suggest that the relative sizes of predators and their prey can shape community dynamics, the structure of food webs, and the evolution of life histories. However, much of this work has assumed static predator and prey body sizes. The timing of recruitment and the growth patterns of both predator and prey have the potential to modify the strength of predator–prey interactions. In this study, I examined how predator size dynamics in 40 temporary ponds over a 3-year period affected the survival of spotted salamander (Ambystoma maculatum) larvae. Across communities, gape-limited predator richness, but not size, was correlated with habitat duration (pond permanence). Within communities, mean gape-limited predator size diminished as the growing season progressed. This size reduction occurred because prey individuals grew into a body size refuge and because the largest of the predators left ponds by mid-season. Elevated gape-limited predation risk across time and space was predicted by the occurrence of two large predatory salamanders: marbled salamander larvae (Ambystoma opacum) and red-spotted newt adults (Notophthalmus viridescens). The presence of the largest gape-limited predator, A. opacum, predicted A. maculatum larval survival in the field. The distribution of large predatory salamanders among ponds and across time is expected to lead to differing community dynamics and to generate divergent natural selection on early growth and body size in A. maculatum. In general, a dynamic perspective on predator size often will be necessary to understand the ecology and evolution of species interactions. This will be especially true in frequently disturbed or seasonal habitats where phenology and ontogeny interact to determine body size asymmetries. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Studies on the basic components of the predation ofPhytoseiulus persimilis Athias-Henriot (Acarina: Phytoseiidae)

The basic components of the predation of Phytoseiulus persimilisAthias-Henriot feeding upon eggs of Tetranychus urticaeKoch were studied in an open system where the predator could disperse freely. The type of the functional response of the predator to the density of its prey was the same as that studied so far in a closed system, i.e.,Holling's Type 2. The search rate of the predator, however, was much lower in comparison with the result from a closed system. The oviposition of the predator per day was only weakly related to prey densities higher than 10 per leaf disc. But the emigration rate was inversely dependent upon the initial prey density up to 60 per leaf disc. The searching behaviour of the predator was influenced by both the web density spun by T. urticae and the density of the prey: the predator searched for its prey intensively only after it had contact with web. Mutual interference was observed in prey consumption, but not in the emigration rate. The emigration rate was largely dependent upon the prey density available per predator.     

Density-dependent effects of multiple predators sharing a common prey in an endophytic habitat

Multiple predator species feeding on a common prey can lead to higher or lower predation than would be expected by simply combining their individual effects. Such emergent multiple predator effects may be especially prevalent if predators share feeding habitat. Despite the prevalence of endophagous insects, no studies have examined how multiple predators sharing an endophytic habitat affect prey or predator reproduction. We investigated density-dependent predation of Thanasimus dubius (Coleoptera: Cleridae) and Platysoma cylindrica (Coleoptera: Histeridae) on a bark beetle prey, Ips pini (Coleoptera: Scolytidae), in a laboratory assay. I. pini utilize aggregation pheromones to group-colonize and reproduce within the stems of conifers. T. dubius and P. cylindrica exploit these aggregation pheromones to arrive simultaneously with the herbivore. Adult T. dubius prey exophytically, while P. cylindrica adults enter and prey within the bark beetle galleries. Larvae of both predators prey endophytically. We used a multiple regression analysis, which avoids confounding predator composition with density, to examine the effects of varying predator densities alone and in combination on herbivore establishment, herbivore reproduction, and predator reproduction. Predators reduced colonization success by both sexes, and decreased I. pini reproduction on a per male and per female basis. The combined effects of these predators did not enhance or reduce prey establishment or reproduction in unexpected manners, and these predators were entirely substitutable. The herbivores net replacement rate was never reduced significantly below one at prey and predator densities emulating field conditions. Similar numbers of each predator species emerged from the logs, but predator reproduction suffered from high intraspecific interference. The net replacement rate of P. cylindrica was not affected by conspecifics or T. dubius. In contrast, the net replacement rate of T. dubius decreased with the presence of conspecifics or P. cylindrica. Combinations of both predators led to an emergent effect, a slightly increased net replacement rate of T. dubius. This may have been due to predation by larval T. dubius on pupal P. cylindrica, as P. cylindrica develops more rapidly than T. dubius within this shared habitat.     

Scaling up from individual behaviour of <Emphasis Type="Italic">Orius sauteri</Emphasis> foraging on <Emphasis Type="Italic">Thrips palmi</Emphasis> to its daily functional response

Functional responses of predators are generally measured under laboratory conditions at rather high prey densities. This is also true for the predation capability of the anthocorid predatory bug Orius sauteri (Poppius). To quantify the daily impact of one female Orius predator on its prey Thrips palmi Karny on greenhouse eggplants where the prey is present below the economic threshold density, we use its patch-leaving and feeding behaviour on eggplant leaves with different prey numbers and scale up to the larger spatio-temporal scale of the greenhouse and one foraging day by means of a simulation model. For this, we also use literature data on the distribution of T. palmi over eggplant leaves. The simulation results in a typical type II functional response for O. sauteri as a function of average T. palmi density: O. sauteri can find and eat approximately 10 prey items per day if T. palmi is present around its economic injury level. The daily mean number of prey eaten per O. sauteri predator, i.e., its predation capability, is highly sensitive to the actual baseline leaving tendency, the effect size of the presence of prey on the baseline leaving tendency and the effect size of the encounter rate with prey thereon.     

How predation by Podisus nigrispinus is influenced by developmental stage and density of its prey Alabama argillacea

The functional response of a predator to the density of its prey is affected by several factors, including the prey's developmental stage. This study evaluated the functional response of Podisus nigrispinus (Dallas) (Hemiptera: Heteroptera: Pentatomidae) females to fourth instars and pupae of Alabama argillacea (Hübner) (Lepidoptera: Noctuidae), an important pest of cotton (Gossypium hirsutum L., Malvaceae) in Brazil. The prey were exposed to the predator for 12 and 24 h, and in densities of 1, 6, 12, 18, 24, and 30 items per predator female. The predation data were subjected to polynomial regression logistic analysis to determine the type of functional response. Holling and Rogers' equations were used to estimate parameters such as attack rate and handling time. Podisus nigrispinus females showed functional response types II and III by preying on larvae and pupae, respectively. The attack rate and handling time did not differ between the 12 and 24 h exposure times. Predation rate was higher at higher larval and pupal densities; predation was highest at a density of 30 prey items per female, and it was similar at 18 and 24 prey per predator. Understanding the interaction of predators and their food resources helps to optimize biological control strategies. It also helps the decision‐making and the improvement of release techniques of P. nigrispinus in the field.     

Body size distribution in <Emphasis Type="Italic">Daphnia</Emphasis> populations as an effect of prey selectivity by planktivorous fish

We test the hypothesis that size distribution of a Daphnia population reflects the vulnerability of each size category (instar) to predation by planktivorous fish. We hypothesize that due to the different reaction distances from which separate prey categories can be seen by a foraging fish, each category is preyed upon until its density is reduced and its size-specific apparent density level (number of prey within a hemisphere of radius equal to the reaction distance) or encounter rate (number of prey encountered per time within a tube with a cross section of radius equal to the reaction distance) become equal to those of other size categories. An experiment was performed with populations of Daphnia hyalina and D. pulicaria grown at two Scenedesmus + Chlamydomonas food levels (0.2 and 0.05 mg C per liter) in outdoor mesocosms (1000 l tanks) with predation by invertebrates (phantom midge) prevented by mosquito netting. Once the populations had become established, roach were added to the tanks at dusk each day and allowed to feed for 3 h, while control tanks were kept fish-free. After 20–60 days, while D. pulicaria was at low density level, the densities of D. hyalina in fish tanks were high enough to see that the age structure and size distribution matched those from simulations with the age-structured population model based on size-specific encounter rate. This match, however, remained only up to the point of first reproduction when—in contrast to the size/age distribution predicted by the model—the percentage share of adult instars in the total population decreased rapidly with age. This deviation from the predicted densities of adult instars suggests that neither encounter rates nor apparent densities derived from instar-specific reaction distances are sufficient to explain the instar-specific impact of a visual predator on planktonic prey. This implies that a foraging fish may temporarily change its feeding mode from the typical low-speed harvesting of small but abundant prey from within its visual field volume, to high-speed hunting for more scarce but larger ovigerous females when their abundance allows higher net energy gain. Shifting from one feeding mode to the other may be responsible for damping population density oscillations in Daphnia.     

Studies on predation of the mosquito Culex fatigans by Rana tigrina tadpoles

Satiated predation, predation rate and prey preference of different weight groups of Rana tigrina (Daud) tadpoles on different larval and pupal stages of Culex fatigans were studied. Irrespective of the prey and predator size, the satiation time remained more or less equal. There exists a mass-dependent predation: Calculated predation rates or predatory constants (Kpr) showed that I instar prey was preyed upon at about equal rate, while other instars and pupa showed an increasing trend with increasing body weight of the predator. The prey preference assessed using the Kpr, revealed that prey size is an important parameter in predation. The R. tigrina tadpole is a more efficient pupal predator than other mosquito predators.     

Invasion success in communities with reciprocal intraguild predation depends on the stage structure of the resident population

The probability of individuals being targeted as prey often decreases as they grow in size. Such size‐dependent predation risk is very common in systems with intraguild predation (IGP), i.e. when predatory species interact through predation and competition. Theory on IGP predicts that community composition depends on productivity. When recently testing this prediction using a terrestrial experimental system consisting of two phytoseiid mite species, Iphiseius degenerans as the IG‐predator and Neoseiulus cucumeris as the IG‐prey, and pollen (Typha latifolia) as the shared resource, we could not find the predicted community shift. Instead, we observed that IG‐prey excluded IG‐predators when the initial IG‐prey/IG‐predator ratio was high, whereas the opposite held when the initial ratio was low, which is also not predicted by theory. We therefore hypothesized that the existence of vulnerable and invulnerable stages in the two populations could be an important driver of the community composition. To test this, we first demonstrate that IG‐prey adults indeed attacked IG‐predator juveniles in the presence of the shared resource. Second, we show that the invasion capacity of IG‐predators at high productivity levels indeed depended on the structure of resident IG‐prey populations. Third, we further confirmed our hypothesis by mimicking successive invasion events of IG‐predators into an established population of IG‐prey at high productivity levels, which consistently failed. Our results show that the interplay between stage structure of populations and reciprocal intraguild predation is decisive at determining the species composition of communities with intraguild predation.     

The effect of size and temperature on the predation of cockles Cerastoderma edule (L.) by the shore crab Carcinus maenas (L.)

Laboratory studies demonstrated that shore crabs Carcinus maenas (L.) can consume <40 cockles Cerastoderma (= Cardium) edule (L.) per individual · day⁻¹. Various predation techniques used by the crabs are reported. The time required to open and consume individual cockles increased exponentially with prey size. Small (<l5-mm shell height), easily broken cockles appeared to be the most profitable in terms of energy acquisition per unit of handling time, the optimal size of prey increasing with predator size. With unlimited prey available, however, crabs selected prey of mean size smaller than these predicted optima, and much below the maximum size they were capable of opening. Feeding rates, both in terms of cockles ingested or energy intake per day, rose steeply with increasing temperature, but the size range of prey consumed remained unchanged. These data strongly suggest that Carcinus maenas is a potentially important predator of small cockles, particularly during the wanner summer months.     

Environmental variation and the predator-specific responses of tropical stream insects: effects of temperature and predation on survival and development of Australian Chironomidae (Diptera)

The threat posed by predation varies among predator species and with environmental context, and prey species often adjust their responses accordingly. We investigated such effects within an insect assemblage from a tropical Australian stream. These systems are frequently subjected to catastrophic floods, often suggested to reduce the importance of predation in streams, and invertebrate faunas are characterised by relatively broad environmental tolerances. Impacts of the hunting predator Australopelopia prionoptera (Diptera: Chironomidae) and an undescribed ambush predator from the Polycentropodidae (Trichoptera) on survival and development of two species of tubicolous Chironomidae, Echinocladius martini (Orthocladiinae) and Polypedilum australotropicus (Chironominae), were assessed in laboratory microcosms. A further experiment investigated how impacts of Australopelopia varied over a broad range of temperatures, exceeding that experienced annually by the studied populations. Neither predator impacted survivorship for E. martini, but the presence of the polycentropodid caused E. martini to spend longer as larvae and reduced adult longevity, and adult females were smaller-sized and had smaller oocytes. In contrast, both predators reduced survivorship of P. australotropicus, but only Australopelopia affected its development, causing reductions in pupal duration and oocyte size. The observed non-lethal impacts of predation reflect the threat each predator is known to pose to each prey species in situ. Impacts of predation varied little with temperature, reflecting the broad thermal tolerances of all study species. The predator-specific responses of the prey species imply that predation is a significant selective force in tropical Australian streams, although fluctuation in intensity of predation associated with flooding may limit its importance for community structure and prey diversity at larger scales. Our results indicate a more limited scope for environmental modification of predator–prey relationships in faunas characterised by broad physiological tolerances.     

Foraging time and spatial patterns of predation in experimental populations

Summary Responses of the predaceous mites Phytoseiulus persimilis, Typhlodromus (=Metaseiulus) occidentalis, and Amblyseius andersoni to spatial variation in egg density of the phytophagous mite, Tetranychus urticae, were studied in the laboratory.The oligophagous predator P. persimilis showed initially a direct density dependent foraging time allocation and variation in foraging time increased with prey density. With changes in prey density due to predation, predator foraging rates (per hour) decreased with time and density dependent foraging gradually became density independence, because P. persimilis continued to respond to initial prey density, instead of the changing prey density and distribution. The consequent spatial pattern of predation by P. persimilis was density independent, although slopes of predation rate-prey density regressions increased with time.Compared with P. persimilis, the narrowly polyphagous predator T. occidentalis responded relatively slowly to the the presence or absence of prey eggs but not to prey density: the mean and variation of foraging time spent in patches with prey did not differ with prey density, but was significantly greater in patches with prey eggs than in patches without eggs. Prey density and distribution changed only slightly due to predation and overall foraging rates remained more or less constant. The consequent spatial pattern of predation by T. occidentalis was inversely density dependent. As with P. persimilis, slopes of predation rate-prey density regressions increased with time (i.e. the inverse density dependence in T. occidentalis became weaker through time).The broadly polyphagous predator A. andersoni showed density independent foraging time allocation with variation independent of prey density. With changes in prey density over time due to prey depletion, overall foraging rates decreased. The consequent spatial pattern of predation by A. andersoni also changed through time; it initially was inversely density dependent, but soon became density independent.Overall, P. persimilis and T. occidentalis spent more time in prey patches than A. andersoni, suggesting that A. andersoni tended to spend more time moving outside patches. The overall predation rates and searching efficiency were higher in P. persimilis than in A. andersoni and T. occidentalis. Predator reproduction was highest in P. persimilis, lower in T. occidentalis and the lowest A. andersoni.The differences in response to prey distribution among the three predaceous species probably reflect the evolution of these species in environments with different patterns of prey distribution. The degree of polyphagy is a major determinant of the aggregative response, but other attributes such as handling time are also important in other aspects of phytoseiid foraging behavior (e.g. searching efficiency or predation rate).     

Prey: predator ratio dependence in the functional response of a freshwater amphipod

1. First known for their shredding activity, freshwater amphipods also behave as active predators with consequences for prey population regulation and amphipod coexistence in the context of biological invasions. 2. A way to quantify predation is to determine the average consumption rate per predator, also known as its functional response (FR). 3. Although amphipods are gregarious and can display social interactions that can alter per capita consumption rates, previous studies using the FR approach to investigate amphipod predation ignored such potential mutual interference because they did not consider variations in predator density. 4. We investigated the FR of Echinogammarus berilloni feeding on dipteran larvae with joint variations in prey and predator densities. This bivariate experimental design allowed us to estimate interference and to compare the fits of the three main classes of theoretical FR models, in which the predation rate is a function of prey density alone (prey‐dependent models), of both prey and predator densities (predator‐dependent models) or of the prey‐to‐predator ratio (ratio‐dependent models). 5. The Arditi–Ginzburg ratio‐dependent FR model provided the best representation of the FR of E. berilloni, whose predation rate showed a decelerating rise to a horizontal asymptote as prey abundance increased. 6. Ratio dependence means that mutual interference between amphipods leads to prey sharing. Mutual interference is likely to vary between amphipod species, depending on their level of aggressiveness.     

Differences in predation among morphotypes of the rotifer Asplanchna silvestrii

1. Interactions were observed between three morphotypes of the predatory rotifer Asplanchna silvestrii and six different prey (Brachionus plicatilis, B. rotundiformis, B. pterodinoides, B. satanicus, Hexarthra jenkinae and copepod nauplii) to understand the differences in feeding abilities among morphotypes that may have led to the evolution of this predator polymorphism. The outcome of predation events was affected significantly, both by predator morphotype and prey type. Predator morphotypes also interacted differently with different prey types. 2. The two smaller morphotypes, the saccate and the cruciform, responded similarly to prey overall, except that the smallest morphotype (saccate) was unable to ingest the most mobile prey (nauplii) and less able to ingest relatively large prey (B. plicatilis). The largest morphotype, the campanulate, had the highest encounter rate with prey, but the lowest probability of attack after encounter, so that it consumed far fewer prey per feeding bout than did the smaller morphotypes. This may have been because campanulates prefer larger prey than used in this study. 3. Highly mobile prey (H. jenkinae and copepod nauplii) were much less susceptible to predation than the less mobile Brachionus species. While evasiveness reduced attacks by saccates and cruciforms, campanulates did not have a significantly lower attack rate on H. jenkinae and copepod nauplii than on less evasive prey. Large body size moderately defended B. plicatilis against ingestion by saccates only. The short-spined B. satanicus was the only prey that was rejected after capture, resulting in lower ingestion probabilities for B. satanicus than other brachionid prey.     

Application of a model of scale dependence to quantify scale domains in open predation experiments

We use a model of open predation experiments to define scale domains that differ in terms of the controlling processes and scale dependence of predator impacts. For experimental arenas that are small compared to the movements of the prey (small scale domain) the model predicts that predator impacts are scale independent and controlled by prey movements. For arenas of intermediate scale we predict that predator impacts are scale dependent and controlled by both prey movements and direct predation, and for the largest scale domain we predict weak scale dependence and predation control.
We propose that the scale‐domain concept is useful when designing and interpreting field experiments. As an illustration we apply the concept to experiments examining predator effects on the stream benthos. First, we test two key assumptions of the underlying model: that area‐specific prey migration rates decrease with increasing size of experimental arenas and that predation rates are independent of arena size. For this purpose we used published estimates of prey emigration and predator consumption rates for nine studies examining the effects of stream predators on benthic prey. We found that prey per capita emigration rates but not predation rates decreased with increasing arena length.
Second, we demonstrate a method for identifying the scale domain of real experiments. The model of predation experiments was parameterized using experimental data and the expected spatial and temporal scale dependence of predator impacts on prey in these experiments was simulated. The simulations suggest that the studies conducted in the largest arenas (length 15–35 m) should be classified as large‐scale, consumption‐controlled experiments, whereas the experiments conducted in smaller arenas (length 1.5–6 m) should be classified as small or intermediate‐scale. We also attempted to determine the scale domain of the experiments in a large data set, including results from most published stream predation experiments. The majority of arenas used in these experiments (73%) were smaller than 1 m in length. Our data on the scale dependence of predation and prey migration rate suggest that experiments in this scale range (<1 m) should be classified as small‐scale, movement‐controlled experiments for most prey taxa.     

The Effects of Prey Patchiness, Predator Aggregation, and Mutual Interference on the Functional Response of Phytoseiulus persimilis Feeding on Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae)

The spatial distributions of two-spotted spider mites Tetranychus urticae and their natural enemy, the phytoseiid predator Phytoseiulus persimilis, were studied on six full-grown cucumber plants. Both mite species were very patchily distributed and P. persimilis tended to aggregate on leaves with abundant prey. The effects of non-homogenous distributions and degree of spatial overlap between prey and predators on the per capita predation rate were studied by means of a stage-specific predation model that averages the predation rates over all the local populations inhabiting the individual leaves. The empirical predation rates were compared with predictions assuming random predator search and/or an even distribution of prey. The analysis clearly shows that the ability of the predators to search non-randomly increases their predation rate. On the other hand, the prey may gain if it adopts a more even distribution when its density is low and a more patchy distribution when density increases. Mutual interference between searching predators reduces the predation rate, but the effect is negligible. The stage-specific functional response model was compared with two simpler models without explicit stage structure. Both unstructured models yielded predictions that were quite similar to those of the stage-structured model.