Raptorial jaws in the throat help moray eels swallow large prey

Most bony fishes rely on suction mechanisms to capture and transport prey. Once captured, prey are carried by water movement inside the oral cavity to a second set of jaws in the throat, the pharyngeal jaws, which manipulate the prey and assist in swallowing. Moray eels display much less effective suction-feeding abilities. Given this reduction in a feeding mechanism that is widespread and highly conserved in aquatic vertebrates, it is not known how moray eels swallow large fish and cephalopods. Here we show that the moray eel (Muraena retifera) overcomes reduced suction capacity by launching raptorial pharyngeal jaws out of its throat and into its oral cavity, where the jaws grasp the struggling prey animal and transport it back to the throat and into the oesophagus. This is the first described case of a vertebrate using a second set of jaws to both restrain and transport prey, and is the only alternative to the hydraulic prey transport reported in teleost fishes. The extreme mobility of the moray pharyngeal jaws is made possible by elongation of the muscles that control the jaws, coupled with reduction of adjacent gill-arch structures. The discovery that pharyngeal jaws can reach up from behind the skull to grasp prey in the oral jaws reveals a major innovation that may have contributed to the success of moray eels as apex predators hunting within the complex matrix of coral reefs. This alternative prey transport mode is mechanically similar to the ratcheting mechanisms used in snakes--a group of terrestrial vertebrates that share striking morphological, behavioural and ecological convergence with moray eels.     

Biomechanics: deadly strike mechanism of a mantis shrimp

Stomatopods (mantis shrimp) are well known for the feeding appendages they use to smash shells and impale fish. Here we show that the peacock mantis shrimp (Odontodactylus scyllarus) generates an extremely fast strike that requires major energy storage and release, which we explain in terms of a saddle-shaped exoskeletal spring mechanism. High-speed images reveal the formation and collapse of vapour bubbles next to the prey due to swift movement of the appendage towards it, indicating that O. scyllarus may use destructive cavitation forces to damage its prey.     

二种植绥螨对朱砂叶螨利他素定位反应的比较

利用嗅觉仪测定智利小植绥螨和拟长钝绥螨对其猎物朱砂叶螨所释放的利他素的定向行为并作了比较研究，阐明了与这二种植绥螨的定位反应有关的刺激源是除雄螨以外不同发育阶段的叶螨及其分泌物和排泄物，而与叶螨的寄主植物无关，不同植绥螨对同一种叶螨不同发育阶段产生的利他素源反应有着一定的种间特异性。     

Asymptotic prey profitability drives star-nosed moles to the foraging speed limit

Foraging theory provides models for predicting predator diet choices assuming natural selection has favoured predators that maximize their rate of energy intake during foraging. Prey profitability (energy gained divided by prey handling time) is an essential variable for estimating the optimal diet. Time constraints of capturing and consuming prey generally result in handling times ranging from minutes to seconds, yet profitability increases dramatically as handling time approaches zero, providing the potential for strong directional selection for increasing predator speed at high encounter rates (tiny increments in speed increase profitability markedly, allowing expanded diets of smaller prey). We provide evidence that the unusual anatomical and behavioural specializations characterizing star-nosed moles resulted from progressively stronger selection for speed, allowing the progressive addition of small prey to their diet. Here we report handling times as short as 120 ms (mean 227 ms) for moles identifying and eating prey. 'Double takes' during prey identification suggest that star-nosed moles have reached the speed limit for processing tactile information. The exceptional speed of star-nosed moles, coupled with unusual specializations for finding and eating tiny prey, provide new support for optimal foraging theory.     

The effects of competition and predation on diversification in a model adaptive radiation

Much of life's diversity is thought to have arisen through successive rounds of adaptive radiation-the rapid diversification of a lineage into a range of ecologically and phenotypically distinct species. Both resource competition and predation have been suggested as mechanisms driving this process, although the former is better studied than the latter. Here we show experimentally how predation by a protist, Tetrahymena thermophila, affects diversification in a model adaptive radiation of the bacterial prey, Pseudomonas fluorescens. We estimate the frequency-dependent fitness functions of competing niche-specialist prey in the presence and absence of predation, and use these to test hypotheses about the extent (measured as the number of new genotypes) and rate of diversification. Competition and predation independently generated diversifying selection that we show is capable of driving prey diversification to similar extents but at different rates, diversification being markedly delayed in the presence of predators. The cause of this delay stems from weaker diversifying selection due to the reduction in prey density caused by predation. Our results suggest that predation may play an under-appreciated role in driving adaptive radiations.     

POPs在湖泊水生动物中的积累及其危害

对近期开展的有关持久性有机污染物（POPs）在水生动物中的分布、积累及其危害方面的研究工作进行了详细的评述。研究表明，POPs广泛存在于湖泊动植物系，不断地由被捕食者向捕食者转移，并随着年龄、体长的增长和食物链的延伸在水生动物的高脂肪部位逐渐积累。时至今日，POP污染在湖泊的存在仍然对不生动物的生长发育构成一定程度的影响，并有可能通过食物链转移给人类并对人类的健康构成威胁，采取相应保护措施仍有一定必要性。     

Scaling laws of marine predator search behaviour

Many free-ranging predators have to make foraging decisions with little, if any, knowledge of present resource distribution and availability. The optimal search strategy they should use to maximize encounter rates with prey in heterogeneous natural environments remains a largely unresolved issue in ecology. Lévy walks are specialized random walks giving rise to fractal movement trajectories that may represent an optimal solution for searching complex landscapes. However, the adaptive significance of this putative strategy in response to natural prey distributions remains untested. Here we analyse over a million movement displacements recorded from animal-attached electronic tags to show that diverse marine predators-sharks, bony fishes, sea turtles and penguins-exhibit Lévy-walk-like behaviour close to a theoretical optimum. Prey density distributions also display Lévy-like fractal patterns, suggesting response movements by predators to prey distributions. Simulations show that predators have higher encounter rates when adopting Lévy-type foraging in natural-like prey fields compared with purely random landscapes. This is consistent with the hypothesis that observed search patterns are adapted to observed statistical patterns of the landscape. This may explain why Lévy-like behaviour seems to be widespread among diverse organisms, from microbes to humans, as a 'rule' that evolved in response to patchy resource distributions.     

The evolution of müllerian mimicry in multispecies communities

Prey species that are unprofitable to attack often share conspicuous colours and patterns with other coexisting defended species. This phenomenon, termed müllerian mimicry, has long been explained as a consequence of selection on defended prey to adopt a common way of advertising their unprofitability. However, studies using two unpalatable prey types have not always supported this theory. Here we show, using a system of humans hunting for computer-generated prey, that predators do not always generate strong selection for mimicry when there are two unprofitable prey types. By contrast, we demonstrate that when predators are faced with a range of different prey species, selection on unprofitable prey to resemble one another can be intense. Here the primary selective force is not one in which predators evaluate the profitabilities of distinct prey types independently, but one in which predators learn better to avoid unprofitable phenotypes that share traits distinguishing them from profitable prey. This need to simplify decision making readily facilitates the spread of imperfect mimetic forms from rarity, and suggests that müllerian mimicry is more likely to arise in multispecies communities.     

依赖比率的捕食被捕食系统的全局分析:捕食与被捕食者均有密度制约的情况

近年来依赖比率的捕食与被捕食模型已引起了生态学者和生物数学研究者的密切注意，这是因为它们比传统的模型更加接近实际情形．本文研究了依赖比率的捕食与被捕食系统的全局定性性态，这里捕食与被捕食者均为密度制约的．     

对一类被开发的功能反应的食饵捕食系统的定性分析

考虑捕食者无密度制约、无捕捞,而食饵具有非线性密度制约和常投放率的一类功能性反应的食饵捕食系统,对其进行了定性分析,证明了在不稳定的正平衡点附近存在唯一的极限环。     

Biomechanics (Communication arising): prey attack by a large theropod dinosaur

Prey-capture strategies in carnivorous dinosaurs have been inferred from the biomechanical features of their tooth structure, the estimated bite force produced, and their diet. Rayfield et al. have used finite-element analysis (FEA) to investigate such structure-function relationships in Allosaurus fragilis, and have found that the skull was designed to bear more stress than could be generated by simple biting. They conclude that this large theropod dinosaur delivered a chop-and-slash 'hatchet' blow to its prey, which it approached with its mouth wide open before driving its upper tooth row downwards. We argue that this mode of predation is unlikely, and that the FEA results, which relate to an 'overengineered' skull, are better explained by the biomechanical demands of prey capture. Understanding the mechanics of predation is important to our knowledge of the feeding habits of carnivorous dinosaurs and for accurate reconstruction their lifestyles.     

Patterns of predation in a diverse predator-prey system

There are many cases where animal populations are affected by predators and resources in terrestrial ecosystems, but the factors that determine when one or the other predominates remain poorly understood. Here we show, using 40 years of data from the highly diverse mammal community of the Serengeti ecosystem, East Africa, that the primary cause of mortality for adults of a particular species is determined by two factors--the species diversity of both the predators and prey and the body size of that prey species relative to other prey and predators. Small ungulates in Serengeti are exposed to more predators, owing to opportunistic predation, than are larger ungulates; they also suffer greater predation rates, and experience strong predation pressure. A threshold occurs at prey body sizes of approximately 150 kg, above which ungulate species have few natural predators and exhibit food limitation. Thus, biodiversity allows both predation (top-down) and resource limitation (bottom-up) to act simultaneously to affect herbivore populations. This result may apply generally in systems where there is a diversity of predators and prey.     

Rapid evolution drives ecological dynamics in a predator-prey system

Ecological and evolutionary dynamics can occur on similar timescales. However, theoretical predictions of how rapid evolution can affect ecological dynamics are inconclusive and often depend on untested model assumptions. Here we report that rapid prey evolution in response to oscillating predator density affects predator-prey (rotifer-algal) cycles in laboratory microcosms. Our experiments tested explicit predictions from a model for our system that allows prey evolution. We verified the predicted existence of an evolutionary tradeoff between algal competitive ability and defence against consumption, and examined its effects on cycle dynamics by manipulating the evolutionary potential of the prey population. Single-clone algal cultures (lacking genetic variability) produced short cycle periods and typical quarter-period phase lags between prey and predator densities, whereas multi-clonal (genetically variable) algal cultures produced long cycles with prey and predator densities nearly out of phase, exactly as predicted. These results confirm that prey evolution can substantially alter predator-prey dynamics, and therefore that attempts to understand population oscillations in nature cannot neglect potential effects from ongoing rapid evolution.     

Geobacter metallireducens accesses insoluble Fe(III) oxide by chemotaxis

Microorganisms that use insoluble Fe(III) oxide as an electron acceptor can have an important function in the carbon and nutrient cycles of aquatic sediments and in the bioremediation of organic and metal contaminants in groundwater. Although Fe(III) oxides are often abundant, Fe(III)-reducing microbes are faced with the problem of how to access effectively an electron acceptor that can not diffuse to the cell. Fe(III)-reducing microorganisms in the genus Shewanella have resolved this problem by releasing soluble quinones that can carry electrons from the cell surface to Fe(III) oxide that is at a distance from the cell. Here we report that another Fe(III)-reducer, Geobacter metallireducens, has an alternative strategy for accessing Fe(III) oxides. Geobacter metallireducens specifically expresses flagella and pili only when grown on insoluble Fe(III) or Mn(IV) oxide, and is chemotactic towards Fe(II) and Mn(II) under these conditions. These results suggest that G. metallireducens senses when soluble electron acceptors are depleted and then synthesizes the appropriate appendages to permit it to search for, and establish contact with, insoluble Fe(III) or Mn(IV) oxide. This approach to the use of an insoluble electron acceptor may explain why Geobacter species predominate over other Fe(III) oxide-reducing microorganisms in a wide variety of sedimentary environments.     

Diet and prey consumption of breeding Common Kestrel （Falco tinnunculus） in Northeast China

The diet of Common Kestrels Falco tinnunculus was studied during the breeding seasons from 2004 to 2008 in Northeast China. Diet was determined by direct observation of the prey brought to nests, and analysis of prey remains collected from nests. Fifteen vertebrate species from three classes, and two groups of insects were identified as prey items. Rodents were the main prey items, comprising 93.9% of the total prey items (TPI) and 97.0% of total prey biomass (TPB). Birds, frogs and insects were also eaten. The kestrels preferred to prey on small rodents (mean weight 20-40 g) and displayed density-dependent prey selection. Daily prey consumption of an adult and a nestling was 2.6 individual rodents or 87.6 g, and 1.7 individual vertebrates or 48.2 g, respectively. The estimated prey consumption of a breeding pair (adults and nestlings) during the breeding season was 520.1 individual vertebrates or 19.7 kg.     

具有避难所的离散捕食者-食饵系统的动力学行为分析建生猪产品质量安全长效监管机制的探讨

本文研究食饵具有恐惧效应和避难所的修正Leslie-Gower离散捕食者-食饵系统。首先，本文分析了该模型平衡点的存在性和局部稳定性，通过严格的推导得到了系统的食饵灭绝边界平衡点和正平衡点局部稳定的充分性条件。其次，分析了在平衡点处存在的分支现象，讨论了食饵灭绝边界平衡点处的跨临界分支和翻转分支，以及捕食者灭绝边界平衡点处的翻转分支，所得结果补充和完善了Ma Rui, Yuzhen Bai等学者的相应结果。最后，本文通过数值模拟验证了主要结果的可行性，探讨了避难所对系统的影响。结果表明，避难所会促进捕食者种群与食饵种群的稳定共存，同步增长。     

Mass march of termites into the deadly trap.

Carnivorous pitcher plants of the genus Nepenthes are not usually very selective about their prey, catching anything that is careless enough to walk on their slippery peristome, but Nepenthes albomarginata is an exception. We show here that this plant uses a fringe of edible white hairs to lure and then trap its prey, which consists exclusively of termites in enormous numbers. This singular feature accounts for the specialization of N. albomarginata for one prey taxon, unique so far among carnivorous plants.     

颍州西湖湿地风景区水生植物资源调查与分析

在对颍州西湖湿地风景区水生植物资源调查的基础上,结合相关资料,总结了水生植物的种类组成、观赏特性和生活型。结果表明,目前该区域主要水生植物约29科,45属,52种,其中以禾本科和莎草科水生植物种类居多。同时,对该地区水生植物应用现状进行初步分析,找出存在的问题,提出今后水生植物应用的对策,以期为水生植物在颍州西湖湿地风...     

具有线性收获率的捕食——食饵扩散系统的捕获问题

研究具有线性收获率的捕食－禽饵扩散系统的捕获问题,讨论了收获和扩散对系统平衡点的影响，证明了若系统存在平衡点，则它必然是[全局渐近稳定的。     

Membrane currents that govern smooth muscle contraction in a ctenophore

Ctenophores are transparent marine organisms that swim by means of beating cilia; they are the simplest animals with individual muscle fibres. Predatory species, such as Beroe ovata, have particularly well-developed muscles and are capable of an elaborate feeding response. When Beroe contacts its prey, the mouth opens, the body shortens, the pharynx expands, the prey is engulfed and the lips then close tightly. How this sequence, which lasts 1 s, is accomplished is unclear. The muscles concerned are structurally uniform and are innervated at each end by a neuronal nerve net with no centre for coordination. Isolated muscle cells studied under voltage-clamp provide a solution to this puzzle. We find that different groups of muscle cells have different time-dependent membrane currents. Because muscle contraction depends upon calcium entry during each action potential, these different currents produce different patterns of contraction. We conclude that in a simple animal such as a ctenophore, a sophisticated set of membrane conductances can compensate for the absence of an elaborate system of effectors.