Effects of predator hunting mode on grassland ecosystem function

The way predators control their prey populations is determined by the interplay between predator hunting mode and prey antipredator behavior. It is uncertain, however, how the effects of such interplay control ecosystem function. A 3-year experiment in grassland mesocosms revealed that actively hunting spiders reduced plant species diversity and enhanced aboveground net primary production and nitrogen mineralization rate, whereas sit-and-wait ambush spiders had opposite effects. These effects arise from the different responses to the two different predators by their grasshopper prey-the dominant herbivore species that controls plant species composition and accordingly ecosystem functioning. Predator hunting mode is thus a key functional trait that can help to explain variation in the nature of top-down control of ecosystems.     

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.     

Effect of lizards on spider populations: manipulative reconstruction of a natural experiment

Which species affect one another, how intensely, and the mechanisms of those effects are crucial data for understanding how ecological communities work. Tropical islands without lizards, the major top predators, have about ten times as dense web spider populations as those with lizards; processes responsible for this effect were experimentally simulated by removing lizards from randomly selected mainland plots. Spider densities in removal plots averaged 2.5 times as high as controls. Spider survival, prey abundance, and prey consumption were all negatively affected by lizards. Contrary to most studies, predator removal caused an increase in the number of spider species.     

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.     

Predator-induced trophic shift of a free-living ciliate: parasitism of mosquito larvae by their prey

Larvae of the treehole mosquito, Aedes sierrensis, release a waterborne factor that induces morphogenesis of one of their prey, the tetrahymenid ciliate Lambornella clarki. Induced free-living trophonts of L. clarki undergo a synchronous response in which cells divide and transform into parasitic cells (theronts) that encyst on larval predators. Parasitic ciliates penetrate the cuticle, enter the hemocoel, and ultimately kill their predator-host. In nature, this trophic shift can lead to predator extinction and dramatic changes in microbial populations. Facultative parasitism by this polymorphic ciliate may have evolved as an antipredator strategy. The experimentally inducible parasitic response of L. clarki provides a novel model for studying cellular morphogenesis of ciliated protozoa.     

Symbiotic bacterium modifies aphid body color

Color variation within populations of the pea aphid influences relative susceptibility to predators and parasites. We have discovered that infection with a facultative endosymbiont of the genus Rickettsiella changes the insects' body color from red to green in natural populations. Approximately 8% of pea aphids collected in Western Europe carried the Rickettsiella infection. The infection increased amounts of blue-green polycyclic quinones, whereas it had less of an effect on yellow-red carotenoid pigments. The effect of the endosymbiont on body color is expected to influence prey-predator interactions, as well as interactions with other endosymbionts.     

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.     

剑毛帕厉螨与黔下盾螨种间相残的研究

【目的】研究食用菌害虫2种天敌剑毛帕厉螨(Stratiolaelaps scimitus)和黔下盾螨(Hyposipis chianensis)的种间相残特性,为开展两者的协调应用提供理论依据。【方法】在有或无自然猎物(腐食酪螨Tyrophagus putrescentiae)条件下,观察2种捕食螨不同螨态间的相残程度及相残后若螨的发育和雌成螨的产卵量。【结果】有自然猎物腐食酪螨时,2种螨较少发生相残。无自然猎物时,2种螨发生相残,相残程度与捕食者螨态和猎物螨态密切相关,但黔下盾螨若螨不捕食剑毛帕厉螨幼螨。捕食黔下盾螨卵或幼螨的剑毛帕厉螨若螨80%和100%发育到成螨,若螨期分别为7.88d和7.30d;捕食剑毛帕厉螨卵的黔下盾螨若螨仅有30%发育至成螨;缺乏自然猎物时,2种捕食螨相残后雌成螨的产卵量均显著低于存在腐食酪螨时的产卵量,一种捕食螨仅通过捕食另一种捕食螨,无法维持种群正常增长速度。【结论】剑毛帕厉螨与黔下盾螨不适合作为相互的猎物,存在其它更为适合的猎物时,不优先选择相残,在害虫密度较大的条件下可以同时应用。     

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.     

Reduced competition and altered feeding behavior among marine snails after a mass extinction

Extinction may alter competitive interactions among surviving species, affecting their subsequent recovery and evolution, but these processes remain poorly understood. Analysis of predation traces produced by shell-drilling muricid snails on bivalve prey reveals that species interactions were substantially different before and after a Plio-Pleistocene mass extinction in the western Atlantic. Muricids edge- and wall-drilled their prey in the Pliocene, but Pleistocene and Recent snails attacked prey only through the shell wall. Experiments with living animals suggest that intense competition induces muricid snails to attack shell edges. Pliocene predators, therefore, probably competed for resources more intensely than their post-extinction counterparts.     

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.     

Introduced predators transform subarctic islands from grassland to tundra

Top predators often have powerful direct effects on prey populations, but whether these direct effects propagate to the base of terrestrial food webs is debated. There are few examples of trophic cascades strong enough to alter the abundance and composition of entire plant communities. We show that the introduction of arctic foxes (Alopex lagopus) to the Aleutian archipelago induced strong shifts in plant productivity and community structure via a previously unknown pathway. By preying on seabirds, foxes reduced nutrient transport from ocean to land, affecting soil fertility and transforming grasslands to dwarf shrub/forb-dominated ecosystems.     

Recolonizing carnivores and naïve prey: conservation lessons from Pleistocene extinctions

The current extinction of many of Earth's large terrestrial carnivores has left some extant prey species lacking knowledge about contemporary predators, a situation roughly parallel to that 10,000 to 50,000 years ago, when naive animals first encountered colonizing human hunters. Along present-day carnivore recolonization fronts, brown (also called grizzly) bears killed predator-naive adult moose at disproportionately high rates in Scandinavia, and moose mothers who lost juveniles to recolonizing wolves in North America's Yellowstone region developed hypersensitivity to wolf howls. Although prey that had been unfamiliar with dangerous predators for as few as 50 to 130 years were highly vulnerable to initial encounters, behavioral adjustments to reduce predation transpired within a single generation. The fact that at least one prey species quickly learns to be wary of restored carnivores should negate fears about localized prey extinction.     

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.     

天敌胁迫下食饵种群动态模型的突变分析

在Logistic模型的基础上增加天敌的胁迫项,构造了天敌胁迫下食饵种群的动态模型。在食饵种群的增长量和天敌的捕食量达到动态平衡的情况下,推导出食饵种群动态的尖角突变模型。运用突变分析的方法,解释了食饵种群在天敌胁迫下也有可能爆发的生态现象。尖角突变模型中的复合控制变量无需坐标转化即可判断系统所处的状态。从理论上解决了以往研究复合控制变量时参数转化的问题。参数简化后可得到折叠突变模型。     

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.     

牧草害虫捕食性天敌毛婪步甲的研究

[目的]研究牧草害虫捕食性天敌毛婪步甲的生物学特性。[方法]2008年4月初至10月底采集毛婪步甲进行生物学饲养试验,然后进行捕食行为的观察,并测试农药对毛婪步甲的毒杀作用。[结果]毛婪步甲在贵州1年发生1代,以成虫在土壤内过冬。主要以成虫捕食猎物为主,1头成虫24h最大捕食黏虫量6.36头。农药对毛婪步甲前10d毒杀效果明显,后期主要是驱避作用。[结论]该研究可为保护毛婪步甲、防治牧草害虫提供理论依据。     

A Sheep in Wolf's Clothing: Tephritid Flies Mimic Spider Predators

Mimicry where prey resemble predators to avoid predation is unusual. Snowberry flies, Rhagoletis zephyria Snow, possess striped wing patterns that resemble the legs of jumping spiders. Observations and comparisons of responses of the jumping spider Salticus scenicus (Clerck) to conspecifics, snowberry flies, and other prey flies showed that snowberry flies can avoid predation by jumping spiders through spider mimicry. The mimicry effect was decreased by obliterating snowberry fly wing stripes.     

七星瓢虫对刺槐蚜和绣线菊蚜的功能反应

试验研究了七星瓢虫对刺槐蚜和绣线菊蚜的捕食功能反应．捕食者与猎物的功能反应均属于ＨｏｌｉｎｇⅡ型,经Ｘ２测验,其理论值与观察值很接近,说明模拟后的各方程可用来描述瓢虫的功能反应．七星瓢虫对刺槐蚜和绣线菊蚜的理论最大捕食量,三、四龄幼虫明显大于一、二龄幼虫．而且七星瓢虫对不同蚜虫的捕食量有一定的差异     

Testing predator-driven evolution with Paleozoic crinoid arm regeneration

Regenerating arms of crinoids represent direct evidence of nonlethal attacks by predators and provide an opportunity for exploring the importance of predation through geologic time. Analysis of 11 Paleozoic crinoid Lagerst?tten revealed a significant increase in arm regeneration during the Siluro-Devonian. During this interval, referred to as the Middle Paleozoic Marine Revolution, the diversity of shell-crushing predators increased, and antipredatory morphologies among invertebrate prey, such as crinoids, became more common. Crinoid arm regeneration data suggest an increase in nonlethal attacks at this time and represent a causal link between those patterns, which implies an important role for predator-driven evolution.