Predator mimicry,not conspicuousness,explains the efficacy of butterfly eyespots

Large conspicuous eyespots on butterfly wings have been shown to deter predators. This has been traditionally explained by mimicry of vertebrate eyes, but recently the classic eye-mimicry hypothesis has been challenged. It is proposed that the conspicuousness of the eyespot, not mimicry, is what causes aversion due to sensory biases, neophobia or sensory overloads. We conducted an experiment to directly test whether the eye-mimicry or the conspicuousness hypothesis better explain eyespot efficacy. We used great tits (Parus major) as model predator, and tested their reaction towards animated images on a computer display. Birds were tested against images of butterflies without eyespots, with natural-looking eyespots, and manipulated spots with the same contrast but reduced resemblance to an eye, as well as images of predators (owls) with and without eyes. We found that mimetic eyespots were as effective as true eyes of owls and more efficient in eliciting an aversive response than modified, less mimetic but equally contrasting eyespots. We conclude that the eye-mimicry hypothesis explains our results better than the conspicuousness hypothesis and is thus likely to be an important mechanism behind the evolution of butterfly eyespots.     

Do Exotic Vertebrates Structure the Biota of Australia? An Experimental Test in New South Wales

From 1993 to 2001, we conducted a series of experiments in a mixed grassland–woodland system in central New South Wales (NSW) to quantify the interactions between red foxes and their prey and competitors. Foxes were removed from two areas around the perimeter of Lake Burrendong, and data were collected from these areas and a nearby untreated area before, during, and after the period of fox control. The arrival of rabbit hemorrhagic disease (RHD) in 1996 provided an opportunity to examine the interactive effects of controlling foxes and rabbits. In this landscape, typical of central NSW, (a) the fox population was not affected by a large reduction in the abundance of rabbits, or vice versa; (b) the cat population declined in areas where foxes were removed after the large RHD-induced reduction in rabbit numbers, but there was no consistent response to the removal of foxes; (c) the abundance of some macropod species increased in response only to the combined removal of rabbits and foxes; (d) there were no consistent changes in the abundances of bird species in response to the removal of either foxes or rabbits, but there were clear habitat differences in bird species richness; and (e) there was likely to be an increase in woody plant species after the large reduction in rabbit populations by RHD. We conclude that (a) long-term field experiments (more than 3 years) are required to quantify the indirect consequences of controlling foxes and rabbits, and (b) single manipulations, such as fox control or rabbit control, are not necessarily sufficient for the conservation of remnant woodland communities in southeastern Australia.     

Patterns, mechanisms and spatial scale of aggregation in generalist and specialist predatory mites (Acari: Phytoseiidae)

Prey species often distribute themselves patchily in their habitats. In response to this spatial variation in prey density, some predator species aggregate in patches of higher prey density. This paper reviews a series of laboratory experiments to demonstrate the patterns of responses by phytoseiid predators (Phytoseiulus persimilis, Typhlodromus occidentalis and Amblyseius andersoni) to spatial variation in the density of their spider mite prey (Tetranychus urticae) and reveal the behavioural mechanisms underlying the observed patterns. In addition, patterns of aggregation were examined at a variety of spatial scales on plants in greenhouses. The patterns, mechanisms and spatial scale of aggregation in three predatory species are discussed in relation to their varying degrees of polyphagy. The results show that a specialist predator species (1) aggregates more strongly than generalist predators, (2) does so not because it finds prey patches of high density more easily but because it remains in these patches longer than generalist predators and (3) tends to aggregate more often at lower levels of spatial scale than generalist predators. It is suggested that these conclusions, based mainly on laboratory studies of a small sample of species, should be tested in the future on a wider selection of specialist and generalist species at different scales in the field. This revised version was published online in November 2006 with corrections to the Cover Date.     

An overview of the relationships between mimicry and crypsis

There have been many different and conflicting definitions of mimicry. Some of the definitions of mimicry include crypsis and others do not. Each definition includes different groups of phenomena and uses different criteria to distinguish mimetic from non-mimetic phenomena. The confusion is eliminated by a consideration of the criteria of all definitions. This shows that there are in fact three major criteria dividing six phenomona, rather than a single dichotomy between mimicry and crypsis (Table 2). The criteria are defined by the results of a mistake in discrimination between the model and mimìc: (a) the mistake does or does not depend upon relationship between mimic and background; (b) the mistake has or has no effect on the population dynamics or evolution of the model and (c) the mistake affects dynamics or evolution of one or of many models. The main reason for the contusion about mimicry and crypsis is that each author's definition includes differing and partially overlapping subsets of the six classes: crypsis; masquerade; Batesism; Müllerism; polymorphism and convergence.     

An overview of the relationships between mimicry and crypsis

There have been many different and conflicting definitions of mimicry. Some of the definitions of mimicry include crypsis and others do not. Each definition includes different groups of phenomena and uses different criteria to distinguish mimetic from non-mimetic phenomena. The confusion is eliminated by a consideration of the criteria of all definitions. This shows that there are in fact three major criteria dividing six phenomona, rather than a single dichotomy between mimicry and crypsis (Table 2). The criteria are defined by the results of a mistake in discrimination between the model and mimìc: (a) the mistake does or does not depend upon relationship between mimic and background; (b) the mistake has or has no effect on the population dynamics or evolution of the model and (c) the mistake affects dynamics or evolution of one or of many models. The main reason for the contusion about mimicry and crypsis is that each author's definition includes differing and partially overlapping subsets of the six classes: crypsis; masquerade; Batesism; Müllerism; polymorphism and convergence.     

The Effects of Spatial Scale on Trophic Interactions

Food chain models have dominated empirical studies of trophic interactions in the past decades, and have lead to important insights into the factors that control ecological communities. Despite the importance of food chain models in instigating ecological investigations, many empirical studies still show a strong deviation from the dynamics that food chain models predict. We present a theoretical framework that explains some of the discrepancies by showing that trophic interactions are likely to be strongly influenced by the spatial configuration of consumers and their resources. Differences in the spatial scale at which consumers and their resources function lead to uncoupling of the population dynamics of the interacting species, and may explain overexploitation and depletion of resource populations. We discuss how changed land use, likely the most prominent future stress on natural systems, may affect food web dynamics by interfering with the scale of interaction between consumers and their resource.     

Investigations of pod characters in the Vivieae

A study of the fruits of modern members of the Vicieae (vetch tribe) has been undertaken to seek morphological, micromorphological and anatomical criteria which may assist in the identification of the archaeological remains of pods and in particular ones that may be useful for the diagnosis of their wild or domesticated status. The study included wild and domesticated Pisum (peas), Lens (lentils) and Vicia (common vetch) and some of their wild relatives found in the Old World. The results show that the micromorphological features of the pod surface tend to be highly variable, and do not distinguish the taxa. Most importantly, the pods of less-developed domesticated taxa show no reduction in the number of fibrous layers in the pod wall compared with those of their closest wild relatives, and no morphological or anatomical evidence has been found to indicate the dehiscent or indehiscent status of a pod. This appears to challenge some of our accepted wisdom on the mechanics of legume dehiscence. Received August 8, 2001 / Accepted January 15, 2002     

昆虫拟态的历史发展

昆虫的拟态理论是由英国自然学家Bates于1862年提出的,Fisher称其为达尔文后自然选择最重要的依据之一.大量的科学研究表明,昆虫的拟态行为最晚出现在石炭纪,自那时起昆虫与捕食者、昆虫与植物之间开始出现了共同的演变和进化.拟态的模仿方式一般包括颜色、花纹以及形态,但是也可以单指行为方面,且拟态大部分情况下可能模仿的是一个动物群体或者只是另外一种动物身上的一部分.拟态包括多种定义,不同的定义之间用小同的标准来区分拟态现象和非拟态现象,如贝茨氏拟态、缪勒氏拟态、侵略性拟态和瓦曼氏拟态等.本文从其中广义拟态的角度,对当前不同类群昆虫化石中拟态现象的研究进展进行了简要总结.     

Metapopulation dynamics of a persisting predator–prey system in the laboratory: time series analysis

The scarcity of experimental evidence for the persistence of predator–prey systems at the metapopulation level inspired us to develop a simple predator–prey experiment that could be used for testing several theoretical predictions concerning persistence and its causes. The experimental system used consisted of one or several islands with small bean plants, the phytophagous mite Tetranychus urticae and the predatory mite Phytoseiulus persimilis. In the first experiment, one large system was used consisting of 90 small bean plants, prey and predators. The system persisted for only 120 days. Second, a system was used consisting of eight islands with ten plants each where the islands were connected by bridges. Two replicate experiments showed persistence for at least 393 days. The difference between the first and the second experiments suggests that the longer persistence is caused by a limited migration between the eight islands. Despite efforts to start both replicates of the second experiment with similar initial conditions, the dynamics of both replicates varied substantially. In one replicate the prey and predator numbers showed a trend through time, whereas the numbers fluctuated around a fixed value in the other replicate. A time series analysis of the data of the prey and predators showed the presence of periodicity with a lag of 8.5 weeks in one replicate, whereas such cyclic behaviour was not found in the other replicate. The differences between the two replicates suggest that it is difficult to perform experiments where one replicate is perturbed and the other serves as an undisturbed control. We suggest using a longer time series, where a system is disturbed only during the second half of the experiment. The data from the first and second halves can subsequently be used to estimate the effect of the perturbation. The advantages and disadvantages of this method are discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Predation as a shaping force for the phenotypic and genotypic composition of planktonic bacteria

Predation is a major mortality factor of planktonic bacteria and an important shaping force for the phenotypic and taxonomic structure of bacterial communities. In this paper we: (1) summarise current knowledge on bacterial phenotypic properties which affect their vulnerability towards grazers, and (2) review experimental evidence demonstrating that this phenotypic heterogeneity results in shifts of bacterial community composition during enhanced protist grazing pressure. Size-structured interactions are especially important in planktonic systems and bacterial cell size influences the mortality rate and the type of grazer to which bacteria are most susceptible. When protists are the major bacterivores, both very small and large bacterial cells gain some size refuge. Recent studies have revealed that also various non-morphological traits such as motility, physicochemical surface characters and toxicity affect bacterial vulnerability and protist feeding success. These properties are effective at different stages during the feeding process of interception feeding flagellates (encounter, capture, ingestion, digestion). Grazing-resistant bacteria in natural communities can account for a substantial portion of the total bacterial biomass at least in more productive aquatic systems. In field and laboratory experiments it has been demonstrated that increased protozoan grazing results in shifts in the phenotypic and genotypic composition of the bacterial assemblage. The importance of this shaping force for the bacterial community structure depends, however, on the overall food web structure, especially on the composition of the metazooplankton. Whereas the structuring impact of bacterial grazers is well documented, relatively little is known about how grazing-mediated changes in bacterial communities influence microbially mediated processes and biogeochemically important transformations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Bayesian Inference for Functional Response in a Stochastic Predator–Prey System

We present a Bayesian method for functional response parameter estimation starting from time series of field data on predator–prey dynamics. Population dynamics is described by a system of stochastic differential equations in which behavioral stochasticities are represented by noise terms affecting each population as well as their interaction. We focus on the estimation of a behavioral parameter appearing in the functional response of predator to prey abundance when a small number of observations is available. To deal with small sample sizes, latent data are introduced between each pair of field observations and are considered as missing data. The method is applied to both simulated and observational data. The results obtained using different numbers of latent data are compared with those achieved following a frequentist approach. As a case study, we consider an acarine predator–prey system relevant to biological control problems.     

昆虫拟态的多样性

综述了昆虫拟态的常见类型及其研究动态 ,特别对光学拟态、声学拟态、化学拟态和拟态的多型现象及复杂性作了较详细的介绍     

Aggressive use of Batesian mimicry by an ant-like jumping spider

Batesian and aggressive mimicry are united by deceit: Batesian mimics deceive predators and aggressive mimics deceive prey. This distinction is blurred by Myrmarachne melanotarsa, an ant-like jumping spider (Salticidae). Besides often preying on salticids, ants are well defended against most salticids that might target them as potential prey. Earlier studies have shown that salticids identify ants by their distinctive appearance and avoid them. They also avoid ant-like salticids from the genus Myrmarachne. Myrmarachne melanotarsa is an unusual species from this genus because it typically preys on the eggs and juveniles of ant-averse salticid species. The hypothesis considered here is that, for M. melanotarsa, the distinction between Batesian and aggressive mimicry is blurred. We tested this by placing female Menemerus sp. and their associated hatchling within visual range of M. melanotarsa, its model, and various non-ant-like arthropods. Menemerus is an ant-averse salticid species. When seeing ants or ant mimics, Menemerus females abandoned their broods more frequently than when seeing non-ant-like arthropods or in control tests (no arthropods visible), as predicted by our hypothesis that resembling ants functions as a predatory ploy.     

Unexpected Effects of Predators Upon Their Prey: The Case of the American Alligator

Indirect trophic effects play important roles in ecosystem dynamics and can at times oppose and dominate the action of direct feeding linkages. Each predator directly exerts a negative effect upon its prey, but predators may also provide indirect benefits to their prey. In ecosystems, such benefits are effected via indirect trophic pathways that can provide a more than compensating positive influence. The ecosystem of the Big Cypress National Preserve (southwest Florida) appears to contain an unusually high number of such predators—most notably, the American alligator, Alligator mississippiensis. The trophic exchanges of carbon among the 68 principal taxa comprising the cypress wetland ecosystem have been quantified during both wet and dry seasons. The network analysis program IMPACTS identified predators that potentially have a positive influence on some of their prey. A total of 64 of these instances were recorded for the wet season and 44 for the dry. Taxa that, on balance, have positive effects upon their prey include fishes, turtles, snakes, birds, and, most significantly, alligators. The feeding habits of alligators benefit a conspicuous number (11) of their prey (invertebrates, frogs, mice, and rats). Further trophic analysis reveals that the predation by alligators on snakes and turtles accounts for most of the trophic benefits bestowed. The actions of alligators in modifying their physical environment has been cited elsewhere as contributing to the maintenance of biotic diversity. It appears that the trophic influence of this species adds further evidence to the important role it plays in the functional ecology of the cypress wetland. Received 4 March 1998; accepted 21 October 1998     

Predation of Northern Pike (Esox lucius L.) Eggs: A Possible Cause of Regionally Poor Recruitment in the Baltic Sea

Northern pike (Esox lucius) spawning habitat and egg mortality were studied in three spawning areas in 2001 along the Swedish coast of the Baltic proper: the Blekinge Archipelago, Kalmar Sound and coastal freshwater streams. Spawning peaked during the last week of April in streams, at temperatures ranging from 7.7 to 8.9 °C and during the first week of May in brackish waters, at temperatures ranging from 8.9 to 13.8 °C. Spawning occurred in shallow waters, at depths between 0.2–1.5 m, but generally most of the spawn was found in the shallowest areas. In streams, eggs were mainly attached to emersed vegetation, while in brackish sites pike eggs were well scattered among flooded emersed plants, submersed plants and filamentous algae. Mean egg density varied between 469–1829 m^–2 with the lowest density observed in Kalmar Sound. The calculated egg loss occurring from approximately one day after spawning to one day before hatching ranged from 41±7% in coastal streams to 67±6% in the Blekinge Archipelago and 100% in Kalmar Sound. The significant removal of eggs from spawning sites in Kalmar Sound and Blekinge was most likely due to predation from several fish species. In situ observations and stomach analyses suggested that many pike eggs in Kalmar Sound were lost to the three-spined stickleback (Gasterosteus aculeatus), a species that presently dominate the littoral small fish community. This study therefore suggests that egg predation by sticklebacks and other fishes may be a possible cause of the reported poor recruitment of coastal pike populations in the Kalmar Sound region.     

The evolution of imperfect mimicry

Examples of imperfect resemblance between Batesian mimics andtheir models appear widespread in the natural world, but sofar few quantitative models have been proposed to explain thephenomenon. I used a simple signal detection model to showthat the relationship between model—mimic similarity and mimic effectiveness is typically nonlinear. In particular, Ifound that there will be little or no further selection toimprove model—mimic resemblance beyond a certain levelif the model species is costly to attack, if the mimic speciesis not particularly profitable (e.g., hard to catch), or ifthe mimic is relatively rare. When there are two different sympatricmodel species, then mimics should usually evolve a phenotypicsimilarity to one or the other model species, but not to both.In contrast, when several model species occur in differentareas (or emerge at different times) and individual mimicsuse each of these areas, then the optimal phenotype should bea "jack-of-all-trades" intermediate phenotype that does notclosely resemble any particular model species. Somewhat surprisingly,the theory predicts that if mimics spend an equal amount oftime with each model species, then the optimal intermediatephenotype should more closely resemble the least numerous andleast noxious model. This phenomenon arises because a vague similarity to an extremely noxious species is usually sufficientto guarantee significant protection, whereas a much closerresemblance to a mildly noxious model species is necessaryto afford a similar level of benefit.     

Travelling of proteins through membranes: translocation into chloroplasts

 Most proteins involved in plastid biogenesis are encoded by the nuclear genome. They are synthesised in the cytosol and have to be transported toward and subsequently translocated into the organelle. This targeting and import process is initiated by a specific chloroplast-targeting signal. The targeting signal of the preprotein is recognised and modified by cytosolic proteins which function in transport toward the chloroplast and in maintaining the import-competent state of the preprotein. The precursor is transferred onto a multi-component complex in the outer envelope of the chloroplasts, which is formed by receptor proteins and the translocation channel. Some proteins, not containing transit sequences, are directly sorted into the outer membrane whereas the majority, containing transit sequences, will be translocated into the stroma. This involves the joint action of a protein complex in the outer envelope, one complex in the inner envelope, and soluble proteins in the intermembrane space and the stroma. The origin of this translocation complex following the endosymbiotic events is an unsolved question. Recent identification of homologous proteins to some members of this machinery in the cyanobacterium Synechocystis PCC6803 gives an initial insight into the origin of the translocation complex. Received: 27 December 1999 / Accepted: 29 March 2000     

The evolution of multicomponent mimicry

The relative sizes of phenotypic mutations contributing to evolutionary change has long been the subject of debate. We describe how mimicry research can shed light on this debate, and frame mimicry studies within the general context of macromutationism and micromutationism, and punctuated versus gradual evolution. Balogh and Leimar [Müllerian mimicry: an examination of Fisher's theory of gradual evolutionary change. Proc. Roy. Soc. Lond. B Biol. Sci. 272, 2269-2275] have recently used a model to readdress the question of whether or not mimicry evolves gradually along a single dimension. We extend their approach, and present the first model to consider the effect of predator generalization along multiple components on the evolution of mimicry. We find that the gradual evolution of mimicry becomes increasingly less likely as the number of signal components increases, unless predators generalize widely over all components. However, we show that the contemporary two-step hypothesis (punctuated evolution followed by gradual refinement) can explain the evolution of Müllerian mimicry under all tested conditions. Thus, although the gradual evolution of mimicry is possible, the two-step hypothesis appears more generally applicable.