Intra- and interspecific predation on four life stage groups by the adult females of Metaseiulus occidentalis, Typhlodromus pyri, Neoseiulus fallacis and Amblyseius andersoni

Do adult females of oligophagous species such as Neoseiulus fallacis (Garman) and Metaseiulus occidentalis (Nesbitt) show less intra- and interspecific predation on phytoseiids when other foods are scarce than polyphagous species such as Amblyseius andersoni Chant and Typhlodromus pyri Scheuten? We caged single adult females of each species without food with ten of their own eggs or larvae, with ten eggs or larvae of the other species or with ten nymphs or adult females of M. occidentalis (T. pyri for M. occidentalis). We assessed the ambulatory activity, survival time, egg levels and prey loss in each test. Polyphages (in particular T. pyri) lived longer than oligophages (in particular N. fallacis) without food. The small T. pyri detected its own stages and benefited most by feeding on small active stages of other species. Amblyseius andersoni, the largest mite, fed and gained the most of any species when held with nymphs and female adults. Metaseiulus occidentalis fed on eggs of all four species to enhance survival. The large hyperactive N. fallacis gained the least from these behaviours. Each mite seemed uniquely adapted to survive conditions of scarce prey and these behaviours may explain their roles in phytoseiid mite complexes. Overall, oligophagous adult females fed less and gained less by feeding on phytoseiids than did polyphagous adult females.     

Role of intraguild predation in aphidophagous guilds

The concept of intraguild predation (IGP) appeared in 1987–1989 to describe trophic interactions within a guild of arthropods inhabiting a sand dune desert: consumers B prey on consumers A and both of them prey on a common resource. Theory predicts that the two types of consumers should only coexist if consumer A is more efficient in the conversion of the common resource than B. As a consequence, this resource is more abundant in the presence than in the absence of intraguild predators. Such a theoretical prediction probably explains the vivid interest shown by ecologists involved in biological control for IGP. It is therefore not surprising that many papers report on IGP among natural enemies of aphids. A close examination of these reported cases indicates that they rarely fulfil the theoretical requirements for IGP. That is, guilds of aphidophagous insects are rarely the theatre of IGP but frequently of interspecific predation. This is confirmed by experimental assessment of the cost of attacking and eating intraguild prey instead of extraguild in ladybird beetles.     

Does predation contribute to tree diversity?

Seed and seedling predation may differentially affect competitively superior tree species to increase the relative recruitment success of poor competitors and contribute to the coexistence of tree species. We examined the effect of seed and seedling predation on the seedling recruitment of three tree species, Acer rubrum (red maple), Liriodendron tulipifera (yellow poplar), and Quercus rubra (northern red oak), over three years by manipulating seed and seedling exposure to predators under contrasting microsite conditions of shrub cover, leaf litter, and overstory canopy. Species rankings of seedling emergence were constant across microsites, regardless of exposure to seed predators, but varied across years. A. rubrum had the highest emergence probabilities across microsites in 1997, but Q. rubra had the highest emergence probabilities in 1999. Predators decreased seedling survival uniformly across species, but did not affect relative growth rates (RGRs). Q. rubra had the highest seedling survivorship across microsites, while L. tulipifera had the highest RGRs. Our results suggest that annual variability in recruitment success contributes more to seedling diversity than differential predation across microsites. We synthesized our results from separate seedling emergence and survival experiments to project seedling bank composition. With equal fecundity assumed across species, Q. rubra dominated the seedling bank, capturing 90% of the regeneration sites on average, followed by A. rubrum (8% of sites) and L. tulipifera (2% of sites). When seed abundance was weighted by species-specific fecundity, seedling bank composition was more diverse; L. tulipifera captured 62% of the regeneration sites, followed by A. rubrum (21% of sites) and Q. rubra (17% of sites). Tradeoffs between seedling performance and fecundity may promote the diversity of seedling regeneration by increasing the probability of inferior competitors capturing regeneration sites.     

Diel patterns of predation and fledging at nests of four species of grassland songbirds

Although it is common for nestlings to exhibit a strong bias for fledging in the morning, the mechanisms underlying this behavior are not well understood. Avoiding predation risk has been proposed as a likely mechanism by a number of researchers. We used video surveillance records from studies of grassland birds nesting in North Dakota, Minnesota, and Wisconsin to determine the diel pattern of nest predation and fledging patterns of four ground‐nesting obligate grassland passerines (Grasshopper Sparrow (Ammodramus savannarum), Savannah Sparrow (Passerculus sandwichensis), Bobolink (Dolichonyx oryzivorus), and Eastern Meadowlark (Sturnella magna)). We used the nest predation pattern as a surrogate for predation activity to test whether nestlings minimized predation risk by avoiding fledging when predation activity was high and preferentially fledging when predation risk was low. Predation activity was significantly lower starting 3 hr before sunrise and ending 3 hr after sunrise, followed by a transition to a period of significantly higher activity lasting for 4 hr, before declining to an average activity level for the rest of the diel period. There was little evidence that the four grassland bird species avoided fledging during the high‐risk period and Savannah Sparrow fledged at higher rates during that period. All four species had hours during the low‐risk period where they fledged at higher rates, but only Grasshopper Sparrow fledged preferentially during that period. Bobolink and Eastern Meadowlark had multiple hours with high fledging rates throughout the daytime period, resulting in no relationship between probability of fledging and predation risk. Given the species variability in fledging pattern seen in our study, it is unlikely that there is a universal response to any driver that affects time of fledging. Further study is needed to understand the complex interplay between species ecology and drivers such as physiology, energetics, and predation in affecting grassland bird fledging behavior.     

Predatory interactions between a cyclopoid copepod and three sibling rotifer species

SUMMARY 1. Cyclopoid copepod predation on rotifers affects the dynamics and structure of zooplankton communities. We address the differential vulnerability of three sympatric rotifer sibling species belonging to the Brachionus plicatilis species complex. These co-occur with their cyclopoid predator, Diacyclops bicuspidatus odessanus .
2. Using video recording and tracking, we analysed the steps in predation including attack distance, attack angle, and rotifer species swimming in the presence and absence of the predator. Our results show the greater vulnerability of B. rotundiformis (the smallest species) to D. b. odessanus predation, which is associated with a high percentage of attacks after contact. Brachionus plicatilis (the biggest species) is the less vulnerable prey, with low percentage of attacks after contact and captures after attacks. Branchionus ibericus , the intermediate sized species, had also intermediate vulnerability.
3. The differential vulnerability provides insight into the coexistence and seasonal succession of these competing rotifer species. Our results show that the competitive superiority of B. rotundiformis may be balanced by its greater vulnerability to copepod predation.     

WHEN SHOULD A TROPHICALLY TRANSMITTED PARASITE MANIPULATE ITS HOST?

We investigate evolution of two categories of adaptive host manipulation by trophically transmitted helminths: (1) predation suppression decreases the host's mortality before the helminth is capable of establishing in its next host; (2) predation enhancement increases the existing host's mortality after it can establish in its next host. If all parasite mortality is purely random (time-independent), enhancement must increase predation by the next host sufficiently more (depending on manipulative costs) than it increases the average for all forms of host mortality; thus if host and parasite die only through random predation, manipulation must increase the "right" predation more than the "wrong" predation. But if almost all parasites die in their intermediate host through reaching the end of a fixed life span, enhancement can evolve if it increases the right predation, regardless of how much it attracts wrong predators. Although enhancement is always most favorable when it targets the right host, suppression aids survival to the time when establishment in the next host is possible: it is most favorable if it reduces all aspects of host (and hence parasite) mortality. If constrained to have selective effects, suppression should reduce the commonest form of mortality.     

Factors regulating predation by first-instar spined assassin bugs [Sinea diadema (Fabricius)] (Hemiptera: Reduviidae)

Selected nutritional and developmental factors regulating the predatory behavior of first-instar spined assassin bugsSinea diadema (Fabricius) (Hemiptera: Reduviidae) were investigated. The longevity of unfed nymphs provided with free water, bean pod sections, or glucose solutions was not significantly greater than that of unfed nymphs which were not provided with a source of water. First-instarS. diadema that were provided with larvae ofEphestia kuehniella Zeller (Lepidoptera: Pyralidae) as prey began feeding 1.9 (±0.9) days after hatching. In contrast, first-instarS. diadema that were provided with conspecifics of the same age did not begin feeding until they were 3.9 (±0.9) days old. These results suggest that the potential nutritional benefits to be gained from feeding equal or outweigh the risk of attacking prey capable of effective self-defense only when nymphs have not fed for 4 days after hatching. Providing the nymphs with water or glucose solutions significantly delayed the onset of conspecific predation. Additional data are presented which demonstrate that first-instarS. diadema are not restrained from preying on siblings by kin recognition.     

Mothers vigilantly guard nests after partial brood loss: a cue of nest predation risk in a paper wasp

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The effect of samara wing presence on predation of Acer pseudoplatanus (Sapindaceae) seeds on the ground

The key selective pressure shaping the morphology of samaras is seen as enhancing primary wind-borne dispersal from the parent plant to the ground. However, the consequences of the samara wing of primarily wind-dispersed tree species for post-dispersal processes has not been well studied. We explored whether the presence of this wing in Acer pseudoplatanus either deters or promotes predation after dispersal, either by increasing the time and energy required to predate the seed or by increasing the seed's visibility to predators. We found that wing-removed fruits were preferred, suggesting that the presence of samaras makes seed handling more expensive for granivores. Further, we found that fewer seeds were consumed from treatments that contained the most winged seeds, thus there was no evidence of the samaras making seed finding easier for granivores. We conclude that the presence of the wing may offer an anti-predatory benefit as well as aiding primary dispersal.     

Bats as prey of diurnal birds: a global perspective

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Flight initiation distances in relation to sexual dichromatism and body size in birds from three continents

Predators exert strong selection pressures on their prey. Prey would therefore benefit by adjusting their behaviour to the risk of predation, while predators conversely would benefit from adjusting their behaviour to that of their prey. Extravagant ornamentation has evolved to attract mates and/or successfully compete with conspecifics of the same sex to secure high mating success, even if that occurs at a cost of increased risk of predation. Thus, sexually dichromatic species may be more susceptible to predation than sexually monochromatic species, and the presence of compensation is indicative of such species being more vulnerable. If extravagant ornamentation is costly in terms of predation risk, then we should expect sexually dichromatic species to have longer flight initiation distances (FID) than sexually monochromatic species. If ornamentation is acquired as a handicap with only individuals in prime condition being able to display with the smallest viability cost, we should expect sexually dichromatic individuals to have shorter FID than sexually monochromatic individuals. Such differences among individuals should, on an evolutionary time scale, translate into differences in FID being related to differences in sexual dichromatism among species. We investigated the relationship between FID and sexual dichromatism in phylogenetic analyses, while accounting for effects of continent (Australia, North America, and Europe), body mass, the interaction between sexual dichromatism and body mass and the interaction between sexual dichromatism and continent. In an analysis of 447 species we found shorter FID in sexually dichromatic than in sexually monochromatic species (consistent with the handicap hypothesis because sexually dichromatic species took greater risks), especially so at large body size. FID differed among continents and the relative difference in FID between sexually monochromatic and sexually dichromatic species was larger in Europe than in Australia and North America. These differences among continents may be attributed to latitudinal effects of predation. These findings are important for current ideas about the evolution of secondary sexual characters because they imply covarying continental differences in predation, especially for large bodied sexually dichromatic species.     

The potential of carabid beetles to control slugs in grass/clover swards

Experiments conducted in sward boxes under controlled conditions showed that the carabid beetlesAbax parallelepipedus (Piller &; Mitterpacher) andPterostichus madidus F. controlled slugs in a grass/clover sward. Control was shown to be as good as that by the molluscicide, methiocarb.A. parallelepipedus proved to be more successful thanP. madidus at controlling the slugs, damage to the clover being kept to a minimum.P. madidus controlled the slugs only after some damage to the clover was sustained.     

Habitat effects on second-order predation of the seed predator Harpalus rufipes and implications for weed seedbank management

Seed predators provide a valuable ecosystem service to farmers by reducing densities of weed seeds, and, in turn, densities of weed seedlings they must manage. The predominant invertebrate weed seed predator in Maine, USA, agroecosystems is the carabid beetle Harpalus rufipes DeGeer. Pitfall trapping has shown that H. rufipes prefers sites with vegetative cover to fallow sites, preference speculated to be driven by predator avoidance behavior. To test this hypothesis, ‘second-order predation assays’ were developed, in which live H. rufipes prey were presented to second-order predators. Field experiments were conducted to determine foremost if H. rufipes was subject to second-order predation, and secondly, whether (a) vegetative cover affords H. rufipes protection from second-order predators, and (b) high rates of second-order predation correspond with decreased invertebrate seed predation rates. Two 72-h experiments were conducted (mid August and September 2012) at crop and non-crop sites across a 28 ha diversified farm in Stillwater, ME, USA.Second-order predation was 2.8% per day. Based on images from motion-sensing cameras, H. rufipes’ predators included birds and small mammals. Neither a relationship between second-order predation and vegetative treatment, nor an empirical relationship between second-order predation and invertebrate seed predation were detected. However, a simulation model predicted that 2.8% per day second-order predation could increase the number of seeds entering the seedbank by more than 17% annually. Additionally, complex habitats supported higher rates of second-order predation than did simple habitats.     

Predation on primates: Ecological patterns and evolutionary consequences

It has long been thought that predation has had important ecological and evolutionary effects on primates as prey. Predation has been theorized to have been a major selective force in the evolution of hominids.¹ In modern primates, behaviors such as active defense, concealment, vigilance, flight, and alarm calls have been attributed to the selective pressures of predation, as has group living itself. It is clear that primates, like other animals, have evolved ways to minimize their risk of predation. However, the extent to which they have been able to do so, given other constraints of living such as their own need to acquire food, has not yet been resolved. Perhaps most hotly debated is whether predation has been the primary selective force favoring the evolution of group living in primates. Part of the difficulty in resolving the debate lies in a paucity of direct evidence of predation. This is regrettable yet understandable since primatologists, by definition, focus on the study of primates, not predators of primates (unless these are also primates). Systematic direct evidence of the effects of predation can best be obtained by studying predators that are as habituated to observers as are their primate prey. Until this is done, we must continue to rely on opportunistic accounts of predation and predation attempts, and on systematically obtained indirect evidence. Such data reveal several interesting patterns: (1) although smaller primates may have greater predation rates than larger primates, even the largest primates are not invulnerable to predation; (2) the use by primates of unfamiliar areas can result in higher predation rates, which might be one pressure favoring philopatry, or site fidelity; (3) arboreal primates are at greater risk of predation when they are more exposed (at forest edges and tops of canopies) than in more concealed locations; (4) predation by mammalian carnivores may often be episodic; and (5) terrestrial primates may not experience greater predation than arboreal primates.     

Predation Preference of Typhlodromus Pyri and Kampimodromus Aberrans (Acari: Phytoseiidae) When Offered Con- and Heterospecific Immature Life Stages

The predation preference of singly caged adult females and nymphs of Typhlodromus pyri and Kampimodromus aberrans for con- or heterospecific immature stages as prey was tested in the laboratory. Both polyphagous predatory mite species have been previously shown to interact directly through predation on each other. The present study demonstrated that the adult females of T. pyri and K. aberrans are able to discriminate between con- and heterospecific larvae and protonymphs and that they prefer to prey upon heterospecifics when given the choice. Hunger did not reduce the propensity of the females to prefer heterospecifics over conspecifics. For proto-and deutonymphs the trends followed the results obtained with the adult females, but the preference for heterospecifics was not distinct enough to be significant. In competitive situations reciprocal predation may be a crucial mechanism in the interaction of polyphagous phytoseiid species and may contribute significantly to population persistence. The results are discussed with regard to possible associations between the ability to discriminate con- and heterospecifics and the type of feeding specialization (generalists versus specialists).     

Pupal warning color development in above-ground pupating species but cryptic color in ground-surface pupating species of the nine-spotted diurnal moths (Erebidae: Arctiinae: Syntomini)

Insects usually have cryptic colors to avoid detection by visually hunting predators. However, if the insects acquire toxic or repellent substances against predators, some of them develop conspicuous coloration to exhibit their unpalatability. Such warning colors allow insects to survive. In the nine-spotted diurnal moths (Erebidae: Arctiinae: Syntomini), we found the above-ground pupating species to have conspicuous colored pupae, but the ground-surface pupating species to have cryptic colored pupae. In this study, the relationships between unpalatability and coloration of these pupae are examined among three species of Amata and one species of Syntomoides. Pupae of the two species (A. germana and A. flava) are conspicuous in their color pattern with seven black dotted lines longitudinally on their pale-yellow bodies. These pupae are exposed to the aerial predators in a coarse silk mesh hanging from leaves and/or branches. The other two species (A. fortunei and S. imaon) pupate in spaces under stones, fallen twigs and leaves on the ground surface, and the pupae in a coarse silk cocoon is cryptic dark brown. Their pupation site selections are reproduced in the rearing glass vessels. Palatability assessment using lizards as a potential predator suggests that pupae of A. germana, A. flava and A. fortunei are unpalatable and the lizard's feeding response decreases with experience. However, pupae of S. imaon are all eaten (palatable). Finally, the possible evolutionary scenario of pupal colors of these four species is discussed in relation to pupation site selection and palatability.     

Consequences of size structure in the prey for predator-prey dynamics: the composite functional response

1. Current formulations of functional responses assume that the prey is homogeneous and independent of intraspecific processes. Most prey populations consist of different coexisting size classes that often engage in asymmetrical intraspecific interactions, including cannibalism, which can lead to nonlinear interaction effects. This may be important as the size structure with the prey could alter the overall density-dependent predation rates. 2. In a field experiment with damselfly and dragonfly larvae, 16 treatments manipulated the density of a small prey stage, the presence of large conspecific prey and the presence of heterospecific predators. 3. Size structure in the prey (i.e. when both prey stages were present) decreased the impact of the predator on overall prey mortality by 25-48% at mid and high prey densities, possibly due to density-dependent size-structured cannibalism in the prey. The predation rates on small prey stages were determined by the interaction of large prey and predators. Predation rates increased with prey density in the absence of large prey, but predation rates were constant across densities when large conspecifics were present. 4. The functional response for unstructured prey followed a Holling type III model, but the predation rate for size-structured prey was completely different and followed a complex pattern that could not be explained with any standard functional response. 5. Using additional laboratory experiments, a mortality model was developed and parameterized. It showed that the overall prey mortality of size-structured prey can be adequately predicted with a composite functional response model that modelled the individual functional responses of each prey stage separately and accounted for their cannibalistic interaction. 6. Thus, treating a prey population as a homogeneous entity will lead to erroneous predictions in most real-world food webs. However, if we account for the effects of size structure and the intraspecific interactions on functional responses by treating size classes as different functional groups, it is possible to reliably predict the dynamics of size-structured predator-prey systems.     

Alternative forms of competition and predation dramatically affect habitat selection under foraging--predation-risk trade-offs

Habitat selection under foraging—predation-risk trade-offshas been a frequent topic of interest to theoretical behavioraland evolutionary ecologists. However, most habitat selectionmodels assume that individuals compete exploitatively for resourcesand that predation is either density independent or dilutedcompletely by competitor number, despite empirical evidencethat other forms of competition and predation also occur innature. I developed an individual-based model for studyingthe effects of alternative forms of competition and predationon the process of habitat selection under foraging—predation-risktrade-offs. To make the model more relevant to natural populations,I assumed that individuals vary continuously in traits relatedto competitive ability and vulnerability to predation and allowed resources and predators to be distributed across more than twohabitats. The results of my investigation demonstrate thatthe predicted pattern of habitat selection can be affecteddramatically by the form predation is assumed to take. Whenpredation is density dependent or frequency dependent, individuals will tend to be distributed across habitats according to theirabsolute vulnerability to predation. In contrast, when predationis density dependent or vulnerability dependent, individualswill tend to segregate by competitive ability. Whether oneassumes that individuals compete for resources via exploitationor interference also influences the predicted pattern of habitat selection. In general, interference competition results in amore even distribution of competitors across habitats.