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1.
A computational model of a stealth strategy inspired by the apparent mating tactics of male hoverflies is presented. The stealth strategy (motion camouflage) paradoxically allows a predator to approach a moving prey in such a way that it appears to be a stationary object. In the model, the predators are controlled by neural sensorimotor systems that base their decisions on realistic levels of input information. They are shown to be able to employ motion camouflage to approach prey that move along both real hoverfly flight paths and artificially generated flight paths. The camouflaged approaches made demonstrate that the control systems have an ability to predict future prey movements. This is illustrated using two- and three-dimensional simulations.  相似文献   

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Critical to our many daily choices between larger delayed rewards, and smaller more immediate rewards, are the shape and the steepness of the function that discounts rewards with time. Although research in artificial intelligence favors exponential discounting in uncertain environments, studies with humans and animals have consistently shown hyperbolic discounting. We investigated how humans perform in a reward decision task with temporal constraints, in which each choice affects the time remaining for later trials, and in which the delays vary at each trial. We demonstrated that most of our subjects adopted exponential discounting in this experiment. Further, we confirmed analytically that exponential discounting, with a decay rate comparable to that used by our subjects, maximized the total reward gain in our task. Our results suggest that the particular shape and steepness of temporal discounting is determined by the task that the subject is facing, and question the notion of hyperbolic reward discounting as a universal principle.  相似文献   

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Synovigenic insects resorb oocytes when food is scarce and mature oocytes when food is plentiful. These two antagonistic processes allow an optimal allocation of resources to reproduction and somatic functions. Unlike hymenopteran parasitoids, ladybirds cannot resorb mature oocytes present in the oviducts. Is the energy contained in these oocytes lost or is there a mechanism for recovering it when needed? Females of two species of ladybird beetles Adalia bipunctata (L.) and Adalia decempunctata (L.) that are starved for >24 h lay single infertile eggs, which they immediately eat, and these eggs comprise the mature oocytes in the oviducts at the onset of starvation. This behaviour has some similarities to egg dumping reported in herbivorous insects and is part, in ladybird beetles, of a process to retrieve energy invested in reproduction. Such behaviour may exist in other predatory synovigenic insects species that do not invest in maternal care.  相似文献   

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As we move through the world, our eyes acquire a sequence of images. The information from this sequence is sufficient to determine the structure of a three-dimensional scene, up to a scale factor determined by the distance that the eyes have moved. Previous evidence shows that the human visual system accounts for the distance the observer has walked and the separation of the eyes when judging the scale, shape, and distance of objects. However, in an immersive virtual-reality environment, observers failed to notice when a scene expanded or contracted, despite having consistent information about scale from both distance walked and binocular vision. This failure led to large errors in judging the size of objects. The pattern of errors cannot be explained by assuming a visual reconstruction of the scene with an incorrect estimate of interocular separation or distance walked. Instead, it is consistent with a Bayesian model of cue integration in which the efficacy of motion and disparity cues is greater at near viewing distances. Our results imply that observers are more willing to adjust their estimate of interocular separation or distance walked than to accept that the scene has changed in size.  相似文献   

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Zoophytophagous predators of the family Miridae (Heteroptera), which feed both on plant and prey, often maintain a close relationship with certain host plants. In this study, we aimed to select a suitable mirid predatory bug for aphid control in sweet pepper. Four species were compared: Macrolophus pygmaeus (Rambur), Dicyphus errans (Wolff), Dicyphus tamaninii Wagner and Deraeocoris pallens (Reuter). They were assessed on their establishment on sweet pepper plants with and without supplemental food (eggs of the flour moth Ephestia kuehniella Zeller and decapsulated cysts of the brine shrimp Artemia franciscana Kellogg) and on their effects on aphids with releases before and after aphid infestations. None of the predator species was able to control an established population of aphids on sweet pepper plants; however, the predators M. pygmaeus and D. tamaninii could successfully reduce aphid populations when released prior to an artificially introduced aphid infestation. The best results were achieved with M. pygmaeus in combination with a weekly application of supplemental food. Hence, our results demonstrate that the order and level of plant colonization by mirid predators and aphids determines how successful biological control is. Further studies are needed to evaluate the performance of mirid predatory bugs in sweet pepper crops in commercial greenhouses with multiple pests and natural enemies, in particular to understand how increased variation in food sources affects their feeding behaviour and preferences.  相似文献   

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Several of today's most prominent diseases arise as a result of aberrant secretory or enzymatic function, or loss of the corresponding tissue. While an obvious approach to treating these diseases is to simply replace the malfunctioning, damaged, or lost tissue, the need to immunosuppress recipients places them at increased risk of pathogenic infection and development of cancer. Limited availability of donor tissue is also problematic, and while xenogenic tissue could be used in some instances, immunosuppression alone is insufficient to prevent rejection. As an alternative, a physical barrier could be employed to mask the implanted tissue from immune surveillance at a local level, without the need for systemic immunosuppression. This approach is embodied through tissue microencapsulation. We review the underlying rationale of alginate based tissue microencapsulation technologies, current challenges, and possible solutions to these challenges in the form of a simple emulsion coating system incorporating functionalized alginate for local immunomodulation.  相似文献   

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Plant feeding by arthropod predators may strongly affect the dynamics of bi- and tri-trophic interactions. We tested whether a predatory mite, Typhlodromalus aripo, feeds upon its host plant, cassava. This predator species is an effective biological control agent of Monoychellus tanajoa (the cassava green mite or CGM) a herbivorous mite specific to cassava. We developed a technique to detect plant feeding, based on the use of a systemic insecticide. We found that T. aripo feeds upon plant-borne material, while other predatory mite species, Neoseiulus idaeus and Phytoseiulus persimilis, do not. Subsequently, we measured survival of juveniles and adult females of T. aripo and N. idaeus, both cassava-inhabiting predator species, on cassava leaf discs. Survival of T. aripo was higher than that of N. idaeus. Thus, T. aripo was able to withstand longer periods of prey scarcity. Because CGM populations fluctuate yearly and are heterogeneously distributed within plants, plant feeding may facilitate the persistence of populations of T. aripo in cassava fields and its control of CGM outbreaks. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

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To test the hypothesis that fecal magnesium excretion is related to fecal volume, fecal specimens were collected from healthy persons who drank 32 single doses of poorly absorbed carbohydrate (mannitol, lactulose or raffinose): the concentration of Mg++ (Y) in fecal water (X) was linearly and inversely related to fecal volume—that is, Y = 42−0.03 X. In contrast, after drinking magnesium sulfate, the concentration of Mg++ in fecal water rose and, except after the lowest ingested dose of 10 mmol, the points relating Mg++ concentration and fecal volume were outside the upper 95% confidence limit of the linear regression line. These findings could be useful when physicians are analyzing stool specimens for supportive evidence of magnesium misuse in baffling cases of diarrhea.  相似文献   

10.
Motivated by cycles of intergroup revenge in real-world conflicts, we experimentally test the hypothesis that humans practice group-based reciprocity: if someone harms or helps them, they harm or help other members of that person's group. Subjects played a trust game, then allocated money between other people. Senders whose partners returned more in the trust game gave more to that partner's group members. The effect was about half as large as the effect of direct reciprocity. Receivers' allocations to group members were not affected by their partners' play in the trust game, suggesting that group reciprocity was only triggered by strong norm violations. We discuss the role of group reciprocity in conflict among early humans.  相似文献   

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Promotion of harmful algal blooms by zooplankton predatory activity   总被引:1,自引:0,他引:1  
Mitra A  Flynn KJ 《Biology letters》2006,2(2):194-197
The relationship between algae and their zooplanktonic predators typically involves consumption of nutrients by algae, grazing of the algae by zooplankton which in turn enhances predator biomass, controls algal growth and regenerates nutrients. Eutrophication raises nutrient levels, but does not simply increase normal predator-prey activity; rather, harmful algal bloom (HAB) events develop often with serious ecological and aesthetic implications. Generally, HAB species are outwardly poor competitors for nutrients, while their development of grazing deterrents during nutrient stress ostensibly occurs too late, after the nutrients have largely been consumed already by fast-growing non-HAB species. A new mechanism is presented to explain HAB dynamics under these circumstances. Using a multi-nutrient predator-prey model, it is demonstrated that these blooms can develop through the self-propagating failure of normal predator-prey activity, resulting in the transfer of nutrients into HAB growth at the expense of competing algal species. Rate limitation of this transfer provides a continual level of nutrient stress that results in HAB species exhibiting grazing deterrents protecting them from top-down control. This process is self-stabilizing as long as nutrient demand exceeds supply, maintaining the unpalatable status of HABs; such events are most likely under eutrophic conditions with skewed nutrient ratios.  相似文献   

13.
Rañó I 《Biological cybernetics》2012,106(4-5):261-270
Motion camouflage is a stealth behaviour observed both in hover-flies and in dragonflies. Existing controllers for mimicking motion camouflage generate this behaviour on an empirical basis or without considering the kinematic motion restrictions present in animal trajectories. This study summarises our formal contributions to solve the generation of motion camouflage as a non-linear optimal control problem. The dynamics of the system capture the kinematic restrictions to motion of the agents, while the performance index ensures camouflage trajectories. An extensive set of simulations support the technique, and a novel analysis of the obtained trajectories contributes to our understanding of possible mechanisms to obtain sensor based motion camouflage, for instance, in mobile robots.  相似文献   

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Colonization and Infection by Helicobacter pylori in Humans   总被引:2,自引:0,他引:2  
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17.
New record of predatory behavior by the mandrill in Cameroon   总被引:4,自引:0,他引:4  
The predatory behavior of the mandrill (Mandrillus sphinx,Linnaeus 1758), a forestliving baboon, on the bay duiker (Cephalophus dorsalis,Gray 1864) was observed under natural conditions. In the predatory episode, at least two mandrills (one adult female and one adult male) attacked a bay duiker, but no overt aggressive interactions between the attackers occurred during consumption. The estimated predation pattern based on scars—intensive attacking of the head and pulling of the hind legs to eat the thigh muscles first—resembled the predation patterns of captive mandrills observed experimentally. The findings suggest that the predatory behavior is established in mandrills as a feeding behavior pattern as in savanna-living baboons. New data are thus presented which are relevant to the discussion of the origins of hunting behavior in early hominids.  相似文献   

18.
Ocean acidification affects prey detection by a predatory reef fish   总被引:1,自引:0,他引:1  
Changes in olfactory-mediated behaviour caused by elevated CO(2) levels in the ocean could affect recruitment to reef fish populations because larval fish become more vulnerable to predation. However, it is currently unclear how elevated CO(2) will impact the other key part of the predator-prey interaction--the predators. We investigated the effects of elevated CO(2) and reduced pH on olfactory preferences, activity levels and feeding behaviour of a common coral reef meso-predator, the brown dottyback (Pseudochromis fuscus). Predators were exposed to either current-day CO(2) levels or one of two elevated CO(2) levels (~600 μatm or ~950 μatm) that may occur by 2100 according to climate change predictions. Exposure to elevated CO(2) and reduced pH caused a shift from preference to avoidance of the smell of injured prey, with CO(2) treated predators spending approximately 20% less time in a water stream containing prey odour compared with controls. Furthermore, activity levels of fish was higher in the high CO(2) treatment and feeding activity was lower for fish in the mid CO(2) treatment; indicating that future conditions may potentially reduce the ability of the fish to respond rapidly to fluctuations in food availability. Elevated activity levels of predators in the high CO(2) treatment, however, may compensate for reduced olfactory ability, as greater movement facilitated visual detection of food. Our findings show that, at least for the species tested to date, both parties in the predator-prey relationship may be affected by ocean acidification. Although impairment of olfactory-mediated behaviour of predators might reduce the risk of predation for larval fishes, the magnitude of the observed effects of elevated CO(2) acidification appear to be more dramatic for prey compared to predators. Thus, it is unlikely that the altered behaviour of predators is sufficient to fully compensate for the effects of ocean acidification on prey mortality.  相似文献   

19.
1. Aphid‐tending ants that feed on honeydew have evolved strategies against aphidophagous insects and tune their aggressive behaviour according to the level of danger for their trophobionts. Here we investigate how Lasius niger Linnaeus (Hymenoptera: Formicidae) ants react to different instars of Episyrphus balteatus De Geer (Diptera: Syrphidae) hoverflies which vary in their voracity and defensive abilities. 2. During pairwise encounters, early syrphid instars (eggs, L1, and L2 larvae) elicited lower aggression scores compared to third larval instars (L3), which was intensively bitten by ants. L3 tried to escape from ants by releasing a sticky and toxic secretion over biting ants that died or underwent severe morbidity. 3. In a standardised system including the host plant, aphid, tending ant, and hoverfly, the ability of ants to protect an Aphis fabae Scopoli (Hemiptera: Aphididae) colony was evaluated. Early E. balteatus instars placed onto the plant elicited no mobilisation of ants, which often removed the hoverfly successfully. Eggs and early instars appeared as the weak links for integrated pest management by hoverfly auxiliaries. 4. In contrast, L3 induced the number of ant patrollers to increase at a local scale without any further recruitment from inside the ant nest. L3 syrphids were quite efficient at gluing ants with defensive secretions and at resisting to removal attempts by ants. 5. While supporting the assumption that ants tune their defensive response to the aphidophagous predator, the present results also showed a lack of efficient protection of their trophobionts from the most voracious late syrphid instar.  相似文献   

20.
兰鑫  罗辑  成新跃 《昆虫知识》2011,48(6):1625-1630
食蚜蝇是蚜虫的主要天敌之一。通过对东北大豆生态区捕食性食蚜蝇的种类和种群数量调查,共发现9属15种捕食性食蚜蝇,其中,黑带食蚜蝇Episyrphus balteatus(De Geer)、大灰食蚜蝇Eupeodes corollae(Fabricius)、印度细腹食蚜蝇Sphaerophoria indiana(Bigot)和宽尾细腹食蚜蝇Sphaerophoria rueppelli(Wiedemann)为田间常见种;黑带食蚜蝇是大豆整个生长过程中的主要优势种,大灰食蚜蝇是大豆生长前期的优势种,细腹食蚜蝇是大豆生长中后期的优势种群;食蚜蝇幼虫发生高峰期与大豆蚜发生高峰期基本吻合。通过捕食量测定,发现黑带食蚜蝇平均每头幼虫对大豆蚜的理论最大捕食量为984头;在田间益害比为1∶150时,控害效果达到最大,近60%;而在1:250时单头控制蚜量最多,为102头,且控害效果可达到40%以上。以上研究结果表明,食蚜蝇对大豆蚜具有较强的捕食能力,具有很大的生防应用潜能。本文还提出了关于食蚜蝇田间保护的可行性措施。  相似文献   

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