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PubMed2004

Mortality due to fox predation in free-range poultry flocks in Britain.

Information derived from questionnaires sent to producers of free-range eggs, chickens, turkeys and geese was used to assess the extent of fox predation in terms of the density of the fox population and farm management factors. The mean reported bird mortality was less than 2 per cent for all the producers, but there were marked differences between them. Egg producers reported losing many more birds to foxes than other types of producer (up to 1000 birds in a laying cycle). On average, egg and goose producers lost the highest proportions of their total flocks (0.5 per cent). The extent of predation was not associated either with large-scale estimations of the density of the fox population or with variations in the farms' habitat. Chicken predation was not linked to differences in types of housing or fencing. However, there was a positive association between losses due to other causes and chicken predation. The results suggest that changes in farm management would be the most cost-effective means of reducing fox predation, rather than greater fox control.

Animals↗
PubMed2002

Can generalist predators be effective biocontrol agents?

Theoretical developments are helping us to comprehend the basic parameters governing the dynamics of the interactions between generalist predators and their many pest and nonpest prey. In practice, however, inter- and intraspecific interactions between generalist predators, and between the predators and their prey, within multispecies systems under the influence of rapidly changing biotic and abiotic variables are difficult to predict. We discuss trade-offs between the relative merits of specialists and generalists that allow both to be effective, and often complementary, under different circumstances. A review of manipulative field studies showed that in approximately 75% of cases, generalist predators, whether single species or species assemblages, reduced pest numbers significantly. Techniques for manipulating predator numbers to enhance pest control at different scales are discussed. We now need to find ways of disentangling the factors influencing positive and negative interactions within natural enemy communities in order to optimize beneficial synergies leading to pest control.

Animals↗
PubMedDate not supplied

Predation experiments on infant spectral tarsiers (Tarsius spectrum).

In this paper, I investigate how mother and infant spectral tarsiers, Tarsius spectrum, respond to the presence of potential predators. I conducted this study at Tangkoko Nature Reserve in Sulawesi, Indonesia, from June to November 1999. I exposed 2 infants to 3 types of potential predators (large models of birds of prey, large rubber snakes and the vocalizations of large birds of prey) for a total of 18 nights. Infants moved a greater distance from their parked location when exposed to rubber snakes (1.8 m) compared to nights when they were not exposed to potential predators (0.23 m). On the other hand, when large bird of prey models were placed near the parked infant, the infant did not move from its parked locale (0.05 m). Parked infants repeatedly gave alarm calls in response to the presentation of all potential predator types. When an infant produced an alarm call following the presentation of a potential predator, the mother responded with her own alarm call approximately 88% of the time. However, when an infant produced an inappropriate alarm call, the mother responded with her own alarm call only 19% of the time. These results suggest that spectral tarsier infants use alarm calls to ask questions about the things they encounter in their environment. Infants and mothers both produced a twittering alarm call in response to the bird of prey models, whereas they both produced a harsh loud call 3 times in rapid succession in response to the presence of the rubber snakes.

Analysis of Variance↗
PubMed1997

Evolutionary stagnation due to pattern-pattern interactions in a coevolutionary predator-prey model.

We consider a spatially structured model of a coevolutionary predator-prey system with interactions in a one-dimensional phenotype space. We show that in phenotype space predators and prey organize themselves into distinct clusters of phenotypes called quasi-species. The prey quasi-species also cluster in patches in real space. As the prey quasi-species evolve away from the predator quasi-species (in phenotype space) the prey patch size reduces and the single predator quasi-species is inhibited from evolving toward either of the two prey species. We show that it is the interaction between the phenotype space patterns (quasi-species) and the real space patterns (patches) that inhibit the predators from evolving.

Biological Evolution↗
PubMed1997

Emergence of collective strategies in a prey-predator game model.

The emergence of collective strategies in a prey-predator system is studied. We use the term "collective" in the sense of the collective motion of defense or attack often found in behaviors of animal groups. In our prey-predator system, both prey and predators move around on a two-dimensional plane, interacting by playing a game; predators can score by touching the backside of a prey. Thresholds are assumed for the scores of both prey and predators. The species with the higher scores can reproduce more, and that with the lower scores will be diminished. As a result, strategies as collective motions are observed; these consist of rotating cluster motions, line formations, disordered but one-way marching, and random swarming. In particular, the strategy of random swarming encourages symbiosis in the sense that it is associated with a low extinction probability for the whole system.

Animals↗
PubMed2003

Stress integration after acute and chronic predator stress: differential activation of central stress circuitry and sensitization of the hypothalamo-pituitary-adrenocortical axis.

Predator exposure is a naturalistic stressor of high ethological relevance. In the current study, our group examined central and peripheral integration of stress responses in rats after acute or repeated exposure to a natural predator (cat). Acute cat exposure rapidly induced hypothalamo-pituitary-adrenocortical (HPA) axis activation and paraventricular nucleus (PVN) CRH mRNA production. Repeated daily cat exposure (7 and 14 d) also up-regulated PVN mRNA CRH expression, but did not result in frank adrenocortical hyperactivity. Unlike other chronic homotypic stress regimens, repeated cat exposure facilitated corticosterone secretion after the 6th or 13th day of exposure. Notably, ACTH secretion and central amygdaloid nucleus CRH mRNA expression were enhanced in animals that were preexposed to the holding chamber relative to chamber-naive rats, suggesting that contextual cues can sensitize subsequent responses to a fearful stimulus. Analysis of c-fos activation was then used to identify brain circuits activated by acute predator stress. Cat exposure elicited a pattern of central c-fos activation that differed substantially from that after either restraint or hypoxia. Predator-specific c-fos mRNA induction was observed in several brain regions comprising the hypothetical brain defense circuit (bed nucleus of the stria terminalis, medial region of the ventromedial nucleus, and dorsal premammillary nucleus). Surprisingly, acute cat exposure did not induce c-fos expression in the PVN. In summary, the data indicate that 1) predation stress invokes a unique stress circuitry that promotes homotypic sensitization of the HPA axis, and 2) familiarization of animals to testing environments can prime central stress pathways to respond robustly to novel threats.

Amygdala↗
PubMed2004

Predation by cosmopolitan spiders upon the medically significant pest species Loxosceles reclusa (Araneae: Sicariidae): limited possibilities for biological control.

Interspecific predation of three cosmopolitan house spiders, Achearanea tepidariorum (Kock 1841) (Theridiidae), Steotoda triangulosa (Walckenaer 1802) (Theridiidae), and Pholcus phalangioides (Doleschall 1859) (Pholcidae), and the medically significant brown recluse spider, Loxosceles reclusa (Sicariidae) were examined to evaluate transitive predatory relationships and to explore the potential use of cosmopolitan spiders as effective biological control agents on L. reclusa. Fifty houses from northeastern Kansas were visually inspected from May to December 2002 for cosmopolitan spiders and L. reclusa. In 25 houses, insect monitoring traps were used to sample spider diversity and abundance. The remaining 25 houses were monitored to examine intraguild predation and spider behavior. If cosmopolitan spiders have the ability to regulate or decrease L. reclusa populations, houses with large cosmopolitan spider populations are expected to have significantly fewer L. reclusa than houses without cosmopolitan spiders. Predation and/or evidence of predation by all three cosmopolitan spiders on L. reclusa was detected in 68% of houses. Spearman's rank correlation analysis showed overall positive relationships between population densities of cosmopolitan spiders and L. reclusa. When evaluated independently, the presence of both A. tepidariorum and S. triangulosa showed negative, yet nonsignificant, relationships with L. reclusa densities, whereas P. phalangioides showed a positive nonsignificant relationship. Although statistical tests showed a decrease in L. reclusa population densities with increased population densities of two cosmopolitan species, alluding to a potential beneficial interaction for biological control, observations of spider behavior, web positioning (niche partitioning), and predation showed little possibility of biological control capabilities.

Animals↗
PubMed2006

Effect of corn hybrids expressing the coleopteran-specific cry3Bb1 protein for corn rootworm control on aboveground insect predators.

Field and laboratory studies were conducted to determine the effect of transgenic Bacillus thuringiensis (Bt) corn, Zea mays L. (YieldGard Rootworm), expressing the Cry3Bb1 protein on aboveground nontarget insect predators (minute pirate bug, ladybird beetles, and carabids). Visual counts of adult and immature Orius insidiosus (Say), Coleomegilla maculata (DeGeer), Hippodamia convergens Gurin-Meneville, and Scymnus spp. occurring in Bt corn and its non-Bt isoline were made at Manhattan, KS, in 2002 and at Manhattan and Scandia, KS, in 2003. No significant differences were found between the Bt corn and non-Bt isoline plots in the abundance (number per plant) of O. insidiosus, C. maculata, H. convergens, and Scymnus spp. Field predation on Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) egg masses was also observed during the silking stage of corn at Manhattan and Scandia in 2003. No significant differences were observed among treatments in predation rate for predators with chewing versus sucking mouthparts. Two laboratory studies determined the effect of Cry3Bb1 protein expressed in Bt corn pollen on C. maculata and carabids. The larvae of C. maculata were reared on Bt pollen, non-Bt pollen, or greenbugs, Schizaphis graminum (Rondani). The duration of larval and pupal stages, developmental time from egg hatch to adult emergence, percentage of survival, and elytra length were compared among treatments. There were no significant differences in developmental time of larvae fed pollen or greenbugs during their first two instars. However, significantly prolonged development of the third (1 d) and fourth instars (2 d) was observed for larvae fed greenbugs only. Total time for larval development was significantly longer for larvae that fed on greenbugs versus larvae fed on pollen. No significant differences were observed among treatments in the percentage of larvae that pupated or pupal stage duration. Larvae that fed on greenbugs had higher pupal and adult weights compared with pollen-fed larvae. However, pupal and adult weights did not vary between the Bt and non-Bt pollen treatments. No significant differences occurred in longevity and elytra length of beetles among all treatments. Two carabid species, Harpalus caliginosus F. and Harpalus pensylvanicus DeGeer, were reared on moistened dog food sprinkled with Bt or non-Bt corn pollen. No significant differences in mortality of H. caliginosus and H. pensylvanicus were detected among any of the treatments. There was no significant effect of Bt pollen on fecundity and egg viability of H. caliginosus. Our studies showed that YieldGard Rootworm had no effect on the selected coleopteran predators; therefore, this Bt corn hybrid could be used in an integrated pest management system.

Animals↗
PubMed2004

Foraging behavior and prey interactions by a guild of predators on various lifestages of Bemisia tabaci.

The sweetpotato whitefly, Bemisia tabaci (Gennadius) is fed on by a wide variety of generalist predators, but there is little information on these predator-prey interactions. A laboratory investigation was conducted to quantify the foraging behavior of the adults of five common whitefly predators presented with a surfeit of whitefly eggs, nymphs, and adults. The beetles, Hippodamia convergens Guerin-Meneville and Collops vittatus (Say) fed mostly on whitefly eggs, but readily and rapidly preyed on all of the whitefly lifestages. The true bugs, Geocoris punctipes (Say) and Orius tristicolor (Say) preyed almost exclusively on adult whiteflies, while Lygus hesperus Knight preyed almost exclusively on nymphs. The true bugs had much longer prey handling times than the beetles and spent much more of their time feeding (35-42%) than the beetles (6-7%). These results indicate that generalist predators vary significantly in their interaction with this host, and that foraging behavior should be considered during development of a predator-based biological control program for B. tabaci.

Animals↗
PubMed2006

Asymmetry in community regulation: effects of predators and productivity.

Eutrophication and predator additions and extinctions are occurring in ecosystems worldwide. Although theory predicts that both will strongly alter the distribution of biomass in whole communities, empirical evidence has not been consolidated to quantitatively determine whether these theoretical predictions are generally borne out in real ecosystems. Here we analyze data from two types of trophic cascade studies, predator removals in factorial combination with fertilization and observed productivity gradients, to assess the role of top-down and bottom-up forces in structuring multi-trophic communities and compare results from these analyses to those from an extensive database of trophic cascade studies. We find that herbivore biomass declines and plant biomass increases in the presence of predators, regardless of system productivity. In contrast, while plants are increased by fertilization, this effect does not significantly increase herbivores in either the presence or absence of predators. These patterns are consistent among marine, freshwater, and terrestrial ecosystems and are largely independent of study size and duration. Thus, top-down effects of predation are transferred through more trophic levels than are bottom-up effects of eutrophication, showing strong asymmetry in the direction of control of biomass distribution in communities.

Analysis of Variance↗
PubMed2006

Lethal and nonlethal predator effects on an herbivore guild mediated by system productivity.

Indirect effects propagated through intervening species in a food web have important effects on community properties. Traditionally, these indirect effects have been conceptualized as mediated through density changes of the intervening species, but it is becoming increasingly apparent that those mediated through trait (phenotypic) responses also can be very important. Because density- and trait-mediated indirect effects have different properties, it is critical that we understand the mechanisms of transmission in order to predict how they will interact, and when or where they will be important. In this study, we examined the mechanisms and consequences of the lethal (density-mediated) and nonlethal (trait-mediated) effects of a larval odonate predator on a guild of four herbivore species (a larval anuran and three species of snails) and their resources. We also manipulated system productivity in order to explore the effects of environmental context on the transmission of these two types of indirect effects. We show that trait-mediated effects arising from the predator can be very strong relative to density-mediated effects on both the competing herbivores and the species composition and production of their resources. A number of these indirect effects are shown to be contingent on productivity of the system. We further present evidence that trait- and density-mediated indirect effects originating from a predator may be transmitted independently through different routes in a food web, particularly when spatial responses of the transmitting prey are involved. Finally, effects on prey growth due to trait responses to the predator varied from negative to positive in predictable ways as a function of time and indirect effects on the larger food web. These results indicate the important role that trait-mediated indirect effects can play in trophic cascades and keystone predator interactions, and we discuss how the mechanisms involved can be incorporated in theory.

Animals↗
PubMed2006

Additive effects of vertebrate predators on insects in a Puerto Rican coffee plantation.

A variety of studies have established the value of shaded coffee plantations as habitat for birds. While the value of birds as biological controls in coffee has received some attention, the interactions between birds and other predators of insects have not been tested. We used exclosures to examine the effects of vertebrate predators on the arthropods associated with coffee, in particular the coffee leafminer (Leucoptera coffeella) and the flatid planthopper Petrusa epilepsis, in a shaded coffee plantation in Puerto Rico. We used a 2 x 2 factorial design with four treatments: exclusion of birds, lizards, birds and lizards, and control (no exclusion). Abundance of insects > 5 mm increased when birds or both birds and lizards were removed. Birds and lizards had an additive effect for insects < 5 mm and for all insects combined. Coffee leafminers showed a weak response to removal of predators while planthopper abundance increased significantly in the absence of avian predators. Arthropod predators and parasitoids did not differ significantly between treatments. Our findings suggest that vertebrate insectivores have an additive effect on insects in coffee and may help control abundances of some coffee pests. Equally important, we present evidence suggesting that they do not interfere with other known natural enemies of coffee pests.

Animals↗
PubMed2006

Orientation and navigation relative to water flow, prey, conspecifics, and predators by the nudibranch mollusc Tritonia diomedea.

Progress in understanding sensory and locomotory systems in Tritonia diomedea has created the potential for the neuroethological study of animal navigation in this species. Our goal is to describe the navigational behaviors to guide further work on how the nervous system integrates information from multiple senses to produce oriented locomotion. Observation of T. diomedea in its habitat has suggested that it uses water flow to navigate relative to prey, predators, and conspecifics. We test these hypotheses in the field by comparing slug orientation in time-lapse videos to flow direction in circumstances with and without prey, predators, or conspecifics upstream. T. diomedea oriented upstream both while crawling and after turning. This trend was strongest before feeding or mating; after feeding or mating, the slugs did not orient significantly to flow. Slugs turned downstream away from an upstream predator but did not react in control situations without an upstream predator. These data support the hypothesis that T. diomedea uses a combination of odors (or some other cue transported downstream) and water flow to navigate relative to prey, predators, and conspecifics. Understanding the context-dependent choice between upstream and downstream crawling in T. diomedea provides an opportunity for further work on the sensory integration underlying navigation behavior.

Animals↗
PubMed2005

Effects of larval density and predation by Toxorhynchites amboinensis on Aedes polynesiensis (Diptera: Culicidae) developing in coconuts.

Organisms manipulated as biological control agents of disease vectors should tolerate ranges of developmental conditions exploited by their target species. Furthermore, they should reduce numbers of host-seeking vector adults without providing fitness benefits to larval survivors developing among fewer competitors. We studied electrochemistry in rat-chewed coconuts, an important developmental habitat used by Aedes polynesiensis, a vector of lymphatic filariasis. We also studied the effects of larval density and predation by the mosquito Toxorhynchites amboinensis as predators of Ae. polynesiensis. The predators significantly reduced survival rates of Ae. polynesiensis and numbers of males and females developing in coconut husks. Adults from cohorts of Ae. polynesiensis exposed to predators emerged at the same time and were equal in size to adults emerging from predator-free cohorts. No differences were detected in the numbers or sizes of Ae. polynesiensis reaching adulthood among the densities tested. At least for this common natural habitat, Tx. amboinensis gave a good level of biological control of the vector Ae. polynesiensis.

Aedes↗
PubMed2001

Altered predation susceptibility of mosquitofish infected with Eustrongylides ignotus.

Eustrongylides ignotus is a parasitic nematode whose definitive hosts are often piscivorous wading birds (Ciconiiformes). Several species of small fishes are intermediate hosts, while larger predatory fish may be paratenic (transport) hosts. We examined predation susceptibility of infected mosquitofish (Gambusia holbrooki) to three species of predatory fishes, including juvenile largemouth bass (Micropterus salminoides), warmouth (Lepomis gulosus), and bluegill (Lepomis macrochirus). A 250 L aquarium with removable plexiglass divider and remote observation windows was constructed. Aquatic macrophytes were placed in the tank to provide refuge for the fishes. Predatory fish were allowed to acclimate to one half of the tank, while one infected and one uninfected mosquitofish were placed in the other. The divider was removed and an observer recorded the number of capture attempts and time required for capture. Predators were observed for behavioral alterations for 4 days after ingestion of infected mosquitofish, then examined at necropsy. Infected prey were selected preferentially in 31 of 38 (82%) trials. The number of capture attempts was 2.7+/-0.2 (x +/- SE) for infected fish and 3.9+/-0.4 for uninfected fish. Mean time of capture was 12.4+/-1.6 min for infected fish and 21.7+/-2.9 for uninfected fish. Because of these differences, infected mosquitofish were more susceptible to predation (P < 0.01) than uninfected fish. Aberrant behavior including lethargy, convulsions, and buoyancy abnormalities was observed in eight (67%) predatory fish. At necropsy, larvae of E. ignotus were found in the coelomic cavity, viscera, and swim bladders of predators. Parasite-induced behavior modification of intermediate hosts may predispose them to predation by wading birds and thereby facilitate the transmission of this nematode in natural populations.

Animals↗
PubMed2000

Influence of host plant on growth and reproduction of Aphis nerii and feeding and prey utilization of its predator Menochilus sexmaculatus.

Influence of different physiological stages (young, mature and senescent) of Calotropis gigantea leaves on growth and reproductive ability of A. nerii and feeding, prey utilization, fecundity and lipid content of its predator M. sexmaculatus were investigated. Increased reproductive period, total life span and reproduction of nymphs per female of A. nerii were observed when reared on mature leaves. This relative preference of A. nerii and maximum utilization of mature leaves as compared to other physiological aged leaves are mainly due to changes in the chemical composition such as protein, carbohydrate, lipid, amino acid, nitrogen and phenolic of C. gigantea. Further, aphids reared on mature leaves influenced its predator's (M. sexmaculatus) growth, prey utilization and reproductive performances. Fecundity and longevity were high, while developmental time of predator was shorter on mature leaves fed aphid. Maximum prey utilization and increased efficiency of ingested and digested food of predator was observed on mature leaves reared aphid. The results are interpreted and discussed in relation to plant aphid and predator interaction (tritrophic).

Animals↗
PubMed2003

Container surface area and water depth influence the population dynamics of the mosquito Culex pervigilans (Diptera: Culicidae) and its associated predators in New Zealand.

The density of larval mosquitoes in containers is related to adult mosquito ovipositional preferences and to other factors such as the abundance of predators. We examined the effects of anthropogenic container size and water depth on the population dynamics of mosquitoes and their macroinvertebrate predators in Wellington, New Zealand. Culex pervigilans was the only mosquito species observed in these containers. With the exception of one sampling date, throughout the year Cx. pevigilans larvae, egg rafts, and pupal exuviae were observed. The highest densities of Cx. pervigilans were observed in the containers with the smallest surface area. A multiple regression analysis was used to analyze the effects of container surface area and depth on the mean density of mosquito larvae in each container. This analysis showed larval densities significantly decreased with increasing container surface area, for two-thirds of the year. Although fewer Cx. pervigilans were generally observed in similarly sized containers with greater depths, this effect was not statistically significant. The significant effect of container surface area appeared to be related to adult ovipositional preferences, as few observations of predators were made in any of the container treatments. Of the predators that were observed, damselfly larvae and diving beetles tended to be more common in the larger containers. Our results suggest that mosquitoes may have strong preferences based on container size alone that influence larval population dynamics, irrespective of the abundance of aquatic predators.

Animals↗
PubMed2004

Aphid specific predators in potato in Belgium.

In summer 2003, aphid specific predators populations were sampled in four potato fields located in Wallonia. Ladybirds, hoverflies and lacewings were the most abundant predators collected. A total of 6 ladybird, 8 syrphid and 2 lacewing species was found. Predator species composition and abundance greatly differed from field to field, while aphids populations were more or less similar with a peak of 3 to 5 aphid/potato leaf in mid-July. All chrysopidae sampled belong to the Chrysoperla kolthoffi (NAVAS) species except 2 specimens of Chrysopa perla L. Episyrphus balteatus DEGEER was the dominant syrphid species. Sphaerophoria scripta L. and Syrphus vitripiennis MEIGEN were subdominant species and 1 or 2 specimens of Melanostoma scalare F., Melanostoma mellinum (L.), Melliscaeva cinctella (ZETTERSTED), Metasyrphus corollae (F.) and Platycheirus albimanus F. were also collected. Coccinella septempunctata (L.) and Propylea quatuordecimpunctata (L.) were the dominant ladybird species. P. 14-punctata was proportionally more abundant in beating samples than with visual inspection samples, indicating that this ladybird is probably more discrete than C. septempunctata and that their populations can be underestimated with only visual inspection. Adalia bipunctata (L.) was also present in nearly all samples, but with lower levels of populations. Coccinella quinquepunctata (L.) and Adalia tenpunctata (L.) were found in small numbers at one occasion. Larvae and adults of Harmonia axyridis PALLAS, the multicoloured Asian beetle introduced in glasshouse for aphid control, were found in 3 fields out of 4, with 1.5 to 6% of ladybirds sampled. This is the first record of H. axyridis in open field in Belgium. As this beetle has been found in numbers at different locations and with different growth stages including larvae and pupae, it is supposed that H. axyridis is adapted to ware potato aphid and able to complete a full life cycle in this crop. As this species is very competitive for exploitation of food resources and aggressive for other predators, they are several questions about the evolution in the future of aphid specific predator biodiversity in ware potato.

Animals↗