Nutrient-specific foraging in invertebrate predators

Many herbivores and omnivores adjust their food selection behavior to regulate the intake of multiple nutrients. Carnivores, however, are generally assumed to optimize the rate of prey capture rather than select prey according to nutrient composition. We showed experimentally that invertebrate predators can forage selectively for protein and lipids to redress specific nutritional imbalances. This selection can take place at different stages of prey handling: The predator may select among foods of different nutritional composition, eat more of a prey if it is rich in nutrients that the predator is deficient in, or extract specific nutrients from a single prey item.     

Late triassic naticid drillholes: carnivorous gastropods gain a major adaptation but fail to radiate

Infaunal and reclining bivalves of the Late Triassic Cassian Formation of northern Italy contain drillholes that closely resemble those produced by modern naticid gastropods. The oldest drillholes previously reported are from the late Early Cretaceous; this suggests that the drilling adaptation was lost soon after its appearance in the Late Triassic and originated independently in another naticid clade 120 million years later. The perceived selective value of such an adaptation may thus not always be a good predictor of its long-term survival, which is ultimately governed by factors that affect the speciation and extinction rates of the clade that carries it.     

Capture Enhancement in a Carnivorous Aquatic Plant: Function of Antennae and Bristles in Utricularia vulgaris

Traps of the carnivorous hydrophyte Utricularia vulgaris Linnaeus (Lentibulariaceae) have structures termed antennae and bristles around their trapdoors that increase their rate of entrapment of the substrate-dwelling prey Chydorus sphaericus (Chydoridae, Crustacea). The kind and number of these structures are important in determining capture rate. Experimental data and corresponding behavioral observations support Darwin's hypothesis that antennae and bristles function as a "funnel" leading potential prey toward the trapdoor and their capture by offering the prey a favorable substrate that exploits their natural locomotor and feeding behavior.     

The Ecological Significance of Sexual Dimorphism in Size in the Lizard Anolis conspersus

Adult males of Anolis conspersus capture prey of significantly larger size and occupy perches of significantly greater diameter and height than do adult females; similarly, these three dimensions of the niche are significantly larger for adult females than for juveniles. Adult males on the average eat a smaller number of prey, and the range in size of prey is larger. The relationship between the average length of the prey and that of the predator is linear when the predator size is above 36 millimeters, but becomes asymptotic when it is below that value. Subadult males as long as adult females eat significantly larger food than do the latter, but only in the larger lizards is this correlated with a relatively larger head. Anolis conspersus selects prey from a wide range of taxa and shows no obvious intraspecific specialization not connected to differences in microhabitat and prey size. The efficiency of this system for solitary species is pointed out.     

Rational choice, context dependence, and the value of information in European starlings (Sturnus vulgaris)

Both human and nonhuman decision-makers can deviate from optimal choice by making context-dependent choices. Because ignoring context information can be beneficial, this is called a "less-is-more effect." The fact that organisms are so sensitive to the context is thus paradoxical and calls for the inclusion of an ecological perspective. In an experiment with starlings, adding cues that identified the context impaired performance in simultaneous prey choices but improved it in sequential prey encounters, in which subjects could reject opportunities in order to search instead in the background. Because sequential prey encounters are likely to be more frequent in nature, storing and using contextual information appears to be ecologically rational on balance by conditioning acceptance of each opportunity to the relative richness of the background, even if this causes context-dependent suboptimal preferences in (less-frequent) simultaneous choices. In ecologically relevant scenarios, more information seems to be more.     

Effects of prey density on the growth and survival of hybrid snakehead larvae

The effects of prey density (0.1, 0.3, 1, 3 and 10 prey·mL⁻¹) on the growth and survival of hybrid snakehead (Channa argus × C. maculate) larvae were investigated. The larvae were divided into three groups with different body lengths of 0.68 cm, 1.50 cm and 3.20 cm, respectively. The growth of the hybrid snakehead larvae in all three groups increased with prey density increasing from 0.1 to 1 prey·mL⁻¹. The specific growth rate (SGR) was the highest when the prey density was 1 prey·mL⁻¹. When prey density was higher than 1 prey·mL⁻¹, SGR of larvae in Group I (the larvae of early development stage) decreased, while no significant change was observed in those of Group II and Group III. The survival rates of hybrid snakehead larvae in all three groups were high (91.11%–100%) and not significantly affected by the prey densities except in Group I with the highest prey density (10.0 prey·mL⁻¹) which was significantly lower than the others. Body size was not sensitive to prey density. The optimum prey density was confirmed at 1 prey·mL⁻¹ in all the treatments. __________ Translated from Journal of Huazhong Agricultural University, 2007, 26(3): 367–370 [译自: 华中农业大学学报]     

Cnidocyte mechanoreceptors are tuned to the movements of swimming prey by chemoreceptors

Cnidocytes, the stinging cells of cnidarians, discharge nematocysts in response to physical contact accompanied by the stimulation of specific chemoreceptors. Cnidocytes in fishing tentacles of a sea anemone are now found to discharge nematocysts preferentially into targets vibrating at 30, 55, and 65 to 75 hertz. Moreover, in the presence of submicromolar concentrations of known chemosensitizers, such as N-acetylated sugars and mucin, these optima shift to 5, 15, 30, and 40 hertz, frequencies that correspond to the movements of swimming prey. Hence, chemoreceptors for these substances tune cnidocyte mechanoreceptors to frequencies that match the movements of the prey.     

Predatory fish select for coordinated collective motion in virtual prey

Movement in animal groups is highly varied and ranges from seemingly disordered motion in swarms to coordinated aligned motion in flocks and schools. These social interactions are often thought to reduce risk from predators, despite a lack of direct evidence. We investigated risk-related selection for collective motion by allowing real predators (bluegill sunfish) to hunt mobile virtual prey. By fusing simulated and real animal behavior, we isolated predator effects while controlling for confounding factors. Prey with a tendency to be attracted toward, and to align direction of travel with, near neighbors tended to form mobile coordinated groups and were rarely attacked. These results demonstrate that collective motion could evolve as a response to predation, without prey being able to detect and respond to predators.     

Erratic display as a device against predators

Prey animals in many different taxonomic groups behave erratically when attacked by predators. This reaction is not accidental, but acts as a specific antipredator device. Observational data and theoretical considerations indicate that such protean displays function to confuse and disorient the predator and to increase its reaction time. Thus the survival of the prey is assisted, and the selective advntage whereby such erratic patterns of the prey animals may have evolved is created.     

Search Image Formation in the Blue Jay (Cyanocitta cristata)

Blue jays trained to detect Catocala moths in slides were exposed to two types of slide series containing these moths: series of one species and series of two species intermixed. In one-species series, detection ability increased with successive encounters with one prey type. No similar effect occurred in two-species series. These results are a direct demonstration of a specific search image.     

Cascading effects of the loss of apex predatory sharks from a coastal ocean

Impacts of chronic overfishing are evident in population depletions worldwide, yet indirect ecosystem effects induced by predator removal from oceanic food webs remain unpredictable. As abundances of all 11 great sharks that consume other elasmobranchs (rays, skates, and small sharks) fell over the past 35 years, 12 of 14 of these prey species increased in coastal northwest Atlantic ecosystems. Effects of this community restructuring have cascaded downward from the cownose ray, whose enhanced predation on its bay scallop prey was sufficient to terminate a century-long scallop fishery. Analogous top-down effects may be a predictable consequence of eliminating entire functional groups of predators.     

Faking giants: the evolution of high prey clearance rates in jellyfishes

Jellyfishes have functionally replaced several overexploited commercial stocks of planktivorous fishes. This is paradoxical, because they use a primitive prey capture mechanism requiring direct contact with the prey, whereas fishes use more efficient visual detection. We have compiled published data to show that, in spite of their primitive life-style, jellyfishes exhibit similar instantaneous prey clearance and respiration rates as their fish competitors and similar potential for growth and reproduction. To achieve this production, they have evolved large, water-laden bodies that increase prey contact rates. Although larger bodies are less efficient for swimming, optimization analysis reveals that large collectors are advantageous if they move through the water sufficiently slowly.     

Culling prey promotes predator recovery--alternative states in a whole-lake experiment

Many top-predator fish stocks in both freshwater and marine systems have collapsed as a result of overharvesting. Consequently, some of these communities have shifted into seemingly irreversible new states. We showed, for predators feeding on prey that exhibit food-dependent growth, that culling of fish prey may promote predator recovery. We removed old stunted individuals of a prey-fish species in a large, low-productive lake, which caused an increase in the availability of small-sized prey and allowed the predator to recover. The shift in community state has been sustained for more than 15 years after the cull ended and represents an experimental demonstration of an alternative stable state in a large-scale field system. Because most animals exhibit food-dependent growth, shifts into alternative stable states resulting from overcompensating prey growth may be common in nature and may require counterintuitive management strategies.     

Predators accelerate nutrient cycling in a bromeliad ecosystem

Conventional ecological theory predicts that predators affect nutrient cycling by decreasing the abundance or activity of prey. By using a predator-detritivore-detritus food chain in bromeliads, we show that predators can increase nutrient cycling by a previously undescribed, but broadly applicable, mechanism: reducing nutrient export by prey emigration. Contrary to expectations, predation on detritivores increases detrital nitrogen uptake by bromeliads. Predation reduces detritivore emergence and hence export of nitrogen from the system. Detritivores therefore benefit their host plant, but only when predators are present. More generally, our results show that predator loss or extinction can dramatically and unexpectedly affect ecosystem functioning.     

Coyote predation control by aversive conditioning

Conditioned aversions were induced in coyotes by producing lithium chloride illness in them following a meal, and the effects upon eating and attack behavior were observed. One trial with a given meat and lithium is sufficient to establish a strong aversion which inhibits eating the flesh of that prey. One or two trials with a given flesh (lamb or rabbit) specifically suppresses the attack upon the averted prey but leaves the coyote free to attack the alternative prey. A method of saving both prey and predator is discussed.     

黑肩绿盲蝽对不均匀分布猎物的捕食行为

在人工气候室内黑肩绿盲蝽Cyrtorhinous lividipennis(Reuter)褐对飞虱Nilaparvata lugens Stal高密度小区表现出明显的聚集反应。在褐飞虱密度高的小区出现的时间大于在低密度小区内的时间。其聚集的机制很可能是该捕食者对高猎物密度小区的捕食频繁,停留的时间也更长。尽管黑肩绿盲蝽表现出很明显的聚集行为,但是它们对褐飞虱的捕食率却与褐飞虱的密度无关或成逆密度相关。形成这种现象的据本原因是捕食者的最大食量和该捕食者在各害虫密度小区内的搜索时间限制。     

Chemical mimicry: bolas spiders emit components of moth prey species sex pheromones

Field studies have indicated that bolas spiders attract male moth prey, apparently by mimicking the odor of female moth sex pheromones. Three moth sex pheromone compounds, (Z)-9-tetradecenyl acetate, (Z)-9-tetradecenal, and (Z)-11-hexadecenal, were identified in volatile substances emitted by hunting adult female Mastophora cornigera spiders. These compounds are components of pheromone blends that attract some of this spider's moth prey species.     

饵料鱼大小对乌鳢捕食的影响

测量了乌鳢口裂形态,以泥鳅(Misgurnus anguillicaudatus)作为饵料鱼,估算了不同规格乌鳢的摄食率,研究了饵料鱼大小对乌鳢捕食的影响.乌鳢口宽(M_w,cm)、口高(M_H,cm)和口面积(M_A,cm~2)与其全长(T_L,cm)的回归方程分别为:M_W=1.65~(e0.0242TL);MH=1.64 ~(e0.022TL);MA=2.12e~(0.0465TL).当水温保持在22～23℃时,4个规格组的乌鳢对泥鳅的摄食率无显著的差别(ANOVA,P>0.05),均值为1.68%.乌鳢对泥鳅的捕食具有明显的大小选择性,乌鳢最喜欢捕食猎物/捕食者大小比为0.25的泥鳅,很少捕食或不捕食猎物/捕食者大小比小于0.06或大于0.45的泥鳅.     

染病食饵种群中疾病的持久性和灭绝性

研究在食饵种群中疾病传播的传染病模型,得到了捕食者是如何控制在食饵种群中的疾病的流行,给出了疾病持久和灭绝的条件,并且分析了捕食者对食饵优先选择的影响.     

食螨瓢虫(Stethorus sp.)对啤酒花害螨的控制作用

本文利用回归最优设计方法探讨了食螨瓢虫(Stethorus sp.)对啤酒花害螨—土耳其斯坦叶螨 Tetranychus turkeslani 的控制作用。回归最优设计适合捕食者—猎物系统相互关系的研究,能够揭示猎物密度、捕食者密度对捕食作用的影响。食螨瓢虫成虫每日可捕食成螨28～30头或捕食幼若螨40～50头。一头食螨瓢虫成虫一生累计可捕食成螨1700多头或幼若螨2750头。田间自然控制效果表明,食螨瓢虫可有效地控制啤酒花害螨种群的增长,控制效果可达87%以上。由于食螨瓢虫的自然控制作用,使得用药时间推迟30d 左右,农药成本减少71.4%,提高了啤酒花的产量和品质,利用食螨瓢虫控制叶螨,可以获得良好的经济、生态、社会效益。