The protective value of conspicuous signals is not impaired by shape, size, or position asymmetry

Various conspicuous signals in nature promote initial and learnedavoidance by predators. It is widely thought that such signalsare most effective when highly symmetrical in features suchas size and shape, supported by recent laboratory experimentswith domestic chicks and artificial prey. However, no studyhas investigated the effect of asymmetry on conspicuous signalsin a natural setting, where viewing distances, angles, predatorspecies, and light conditions vary and where predators encounterprey sequentially rather than simultaneously. We undertook 2field experiments with artificial gray-scale prey, marked witha pair of white markings presented to wild avian predators,to test the effect of asymmetry on the survival value of conspicuoussignals in the field. Experiment 1 had treatments with symmetricalspots or with spots asymmetrical in area between 5 and 50%.All marked treatments survived better than unmarked controls,but there was no benefit of being symmetrical. Experiment 2tested the effect of possessing markings asymmetrical for shapeor position and any additive effect of these 2 features. Again,symmetry conferred no benefit and targets with markings asymmetricalfor position and/or shape survived equally well as those withsymmetrical arrangements. These findings indicate that asymmetryin warning signals may not be costly to prey in nature or beof less importance compared with other features of the signal,such as color and overall size.     

Predator perception and the interrelation between different forms of protective coloration

Animals possess a range of defensive markings to reduce the risk of predation, including warning colours, camouflage, eyespots and mimicry. These different strategies are frequently considered independently, and with little regard towards predator vision, even though they may be linked in various ways and can be fully understood only in terms of predator perception. For example, camouflage and warning coloration need not be mutually exclusive, and may frequently exploit similar features of visual perception. This paper outlines how different forms of protective markings can be understood from predator perception and illustrates how this is fundamental in determining the mechanisms underlying, and the interrelation between, different strategies. Suggestions are made for future work, and potential mechanisms discussed in relation to various forms of defensive coloration, including disruptive coloration, eyespots, dazzle markings, motion camouflage, aposematism and mimicry.     

The role of eyespots as anti-predator mechanisms, principally demonstrated in the Lepidoptera

Eyespots are found in a variety of animals, in particular lepidopterans. The role of eyespots as antipredator mechanisms has been discussed since the 19th Century, with two main hypotheses invoked to explain their occurrence. The first is that large, centrally located eyespots intimidate predators by resembling the eyes of the predators' own enemies; the second, though not necessarily conflicting, hypothesis is that small, peripherally located eyespots function as markers to deflect the attacks of predators to non-vital regions of the body. A third possibility is also proposed; that eyespots intimidate predators merely because they are novel or rarely encountered salient features. These hypotheses are reviewed, with special reference given to avian predators, since these are likely to be the principal visually hunting predators of the lepidopterans considered. Also highlighted is the necessity to consider the potential influence of sexual selection on lepidopteran wing patterns, and the genetics and development of eyespot formation.     

Different colour morphs of the poison frog Andinobates bombetes (Dendrobatidae) are similarly effective visual predator deterrents

Aposematism is the use of warning signals to advertise unpleasant or dangerous defences to potential predators. As the effectiveness of this strategy depends on predator learning, little variation is expected in aposematic warning signals, as similar signals facilitate predator learning. However, warning signals are frequently variable in aposematic species. Such variability could arise as a result of geographic variation in the interpretation that local predators give warning signals. We tested this divergent learning hypothesis in the polytypic poison frog Andinobates bombetes (Anura: Dendrobatidae), focusing on visual predators. Our study was conducted in two populations of this species located in the Western Andes of Colombia, where individuals at some localities exhibit red dorsolateral stripes, while those in others exhibit yellow dorsolateral stripes. We deployed paraffin models imitating both forms of A. bombetes in size and colouration, as well as dull‐coloured controls, at sites inhabited by either red‐striped or yellow‐striped frogs. Red and yellow models were attacked at similar rates at both sites, and brown models were attacked more frequently at one of the sites. These results suggest that red and yellow colourations function as similarly effective aposematic signals for primarily visual predators, regardless of the form previously experienced by these predators. Therefore, our results do not support the hypothesis of divergent predator learning as a driver of the polytypism present in this species. Finally, we discuss other mechanisms that may be involved in the evolution and maintenance of this polytypism.     

A case of Batesian mimicry between a myrmecophilous staphylinid beetle, Pella comes, and its host ant, Lasius (Dendrolasius) spathepus: an experiment using the Japanese treefrog, Hyla japonica as a real predator

Some myrmecophilous animals show myrmecomorphy, however, its adaptive significance is still controversial. We investigated a possible benefit of Batesianmimicry between a myrmecophilous staphylinid beetle, Pella comes, and its host ant, Lasius (Dendrolasius) spathepus, by using a common ant predator, the Japanese treefrog, Hyla japonica. In the field, H. japonica were found to feed on numerous ants and other insects, but in laboratory experiments they refused feeding on L. spathepus. L. spathepus was highly repellent to these frogs, while P. comes was potentially palatable. After repeated contacts with L. spathepus which led to its avoidance the treefrogs started to reject P. comes as well . This suggests that myrmecomorphy is beneficial to P. comes, reducing the risk of predation, and that it , may represent a case of Batesian mimicry. may represent a case of Batesian mimicry. Received 15 February 2005; revised 12 April 2005; accepted 18 April 2005.     

Evolutionary implications of the form of predator generalization for aposematic signals and mimicry in prey

Generalization is at the heart of many aspects of behavioral ecology; for foragers it can be seen as an essential feature of learning about potential prey, because natural populations of prey are unlikely to be perfectly homogenous. Aposematic signals are considered to aid predators in learning to avoid a class of defended prey. Predators do this by generalizing between the appearance of prey they have previously sampled and the appearance of prey they subsequently encounter. Mimicry arises when such generalization occurs between individuals of different species. Our aim here is to explore whether the specific shape of the generalization curve can be expected to be important for theoretical predictions relating to the evolution of aposematism and mimicry. We do this by a reanalysis and development of the models provided in two recent papers. We argue that the shape of the generalization curve, in combination with the nature of genetic and phenotypic variation in prey traits, can have evolutionary significance under certain delineated circumstances. We also demonstrate that the process of gradual evolution of Müllerian mimicry proposed by Fisher is particularly efficient in populations with a rich supply of standing genetic variation in mimetic traits.     

Bird attacks on a butterfly with marginal eyespots and the role of prey concealment against the background

Small eyespots on butterflies have long been thought to deflect attacks, and birds are the presumptive drivers selecting for these patterns; however, evidence of this function is still ambiguous. Marginal eyespots typically consist of a UV‐reflective white pupil, surrounded by one black and one yellowish ring. We have recently shown that Cyanistes caeruleus (blue tits) attack such eyespots, but only under low light intensities with accentuated UV levels: the increased salience of the eyespots relative to the rest of the butterfly probably explains this result. Possibly the background against which the butterfly is concealed may deceive birds to make similar errors. We therefore presented speckled wood butterflies decorated with eyespots (or controls without eyespots) to C. caeruleus against two backgrounds: oak and birch bark. Our results show that: (1) eyespots, independent of background, were effective in deflecting attacks; (2) the time elapsed between a bird landing and the attack was interactively dependent on the background and whether the butterfly bore an eyespot; and (3) the speed at which a butterfly was attacked predicted the outcome, with faster birds being more prone to errors than slower birds. This underscores a speed–accuracy trade‐off in the predators, and that background plays a role in the defensive qualities of marginal eyespots. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 290–297.     

Status of the Nemertea as prey in marine ecosystems

Nemerteans are predators of a wide variety of animals, but little is known of their role as prey for other animals. The presence of toxins in the tissues and secretions of these worms has led to the assumption usually suggested that they are ingested only rarely. However, analysis of a Food Habits Data Base from the United States National Marine Fisheries Service, compiled for fishes collected in the Atlantic Ocean from the Canadian border to Cape Hatteras, North Carolina (1973–1990), showed that nemerteans were recovered from the stomachs of 27 species of fishes in 14 families. They were found in 223 of 26 642 (0.84%) fish stomachs examined in the laboratory, but only in 0.09% of 58 812 fish examined in the field. Among species in the former category, for which 1000 were examined, the winter flounder, Pseudopleuronectes americanus(Walbaum), and the yellowtail flounder, Limanda ferruginea (Storer), had the greatest frequency of nemerteans, 71 of 1545 (4.6%) and 33 of 1045 (3.2%), respectively. These nemerteans were identified as Nemertea, Cerebratulus sp. or Micrura sp., but it is likely that they were all of a Cerebratulus-like type. Nemerteans have also been recorded from the guts of eight additional species (including four additional families) of fishes collected from the western Atlantic Ocean, Gulf of Mexico, eastern Pacific Ocean (Washington, Alaska), North Sea and Indian Ocean off South Africa. The black-bellied plover, Pluvialis squatarola(L.), semipalmated plover, Charadrius semipalmatus Bonapart and the herring gull, Larus argentatus Pontoppidan are the only three species known to feed on nemerteans (Cerebratulus lacteus (Leidy) and Paranemertes peregrina Coe by the black-bellied plover and C. lacteus by the other species). Several species of nemerteans are known to ingest other nemerteans, and several arthropods, a squid, and a few other invertebrates also feed on these worms. On the other hand, careful laboratory studies have shown that some members of the Palaeonemertea, Heteronemertea and Hoplonemertea, when fed to various species of fishes, crustaceans (Astacidea, Anomura, Brachyura and Amphipoda) and a polychaete, were rejected, usually violently. There is a history of using large nemerteans, e.g. Cerebratulus lacteus and Polybrachiorhynchus dayi, as bait by sport fishermen in the United States and South Africa. The incongruity of successfuly using these toxic animals to catch fish is discussed in relation to conclusions on the importance of nemerteans as prey in the marine environment.     

Nonconsumptive predator effects modify crayfish‐induced bioturbation as mediated by limb loss: Field and mesocosm experiments

1. We addressed the implications of limb loss and regeneration for multispecies interactions and their impacts on ecosystem engineering in freshwater stream environments.
2. We included regenerative and nonregenerative crayfish as well as fish predators in a 2 × 2 factorial design to assess the effects on water turbidity of interactions between crayfish ecosystem engineers differing in regenerative status and their fish predators.
3. We demonstrated that crayfish limb loss and predation risks lead to more turbidity in field and mesocosm conditions. Moreover, ongoing regeneration of crayfish increased turbidity, while fish presence seemed to hinder crayfish turbidity‐inducing behaviors (such as tail‐flipping and burrowing) in the mesocosm experiment.
4. We confirmed that greater numbers of crayfish produce a greater amount of turbidity in situ in streams.
5. Although mechanical burrowing crayfish capacities may depend on crayfish burrowing classification (primary, secondary, or tertiary), our work emphasizes the implication for turbidity levels of crayfish autotomy in freshwater streams.

     

Exposing the grey seal as a major predator of harbour porpoises

Harbour porpoises (Phocoena phocoena) stranding in large numbers around the southern North Sea with fatal, sharp-edged mutilations have spurred controversy among scientists, the fishing industry and conservationists, whose views about the likely cause differ. The recent detection of grey seal (Halichoerus grypus) DNA in bite marks on three mutilated harbour porpoises, as well as direct observations of grey seal attacks on porpoises, have identified this seal species as a probable cause. Bite mark characteristics were assessed in a retrospective analysis of photographs of dead harbour porpoises that stranded between 2003 and 2013 (n = 1081) on the Dutch coastline. There were 271 animals that were sufficiently fresh to allow macroscopic assessment of grey seal-associated wounds with certainty. In 25% of these, bite and claw marks were identified that were consistent with the marks found on animals that had tested positive for grey seal DNA. Affected animals were mostly healthy juveniles that had a thick blubber layer and had recently fed. We conclude that the majority of the mutilated harbour porpoises were victims of grey seal attacks and that predation by this species is one of the main causes of death in harbour porpoises in The Netherlands. We provide a decision tree that will help in the identification of future cases of grey seal predation on porpoises.     

Absence of effects of predator control on nesting success of Northern Lapwings Vanellus vanellus: implications for conservation

The control of generalist predator populations is increasingly adopted as a management tool to combat declines in ground‐nesting bird populations. However, compensatory predation by uncontrolled species frequently occurs, so determining the relative impacts of different predatory species, and hence the relative benefits of their control, can be difficult. Islands, with their reduced faunas, provide natural experimental units for investigating specific predator–prey interactions in detail. We studied Northern Lapwing Vanellus vanellus breeding success on an island where feral Ferrets Mustela furo and Hooded Crows Corvus cornix were subjected to trial control regimes over 2 years. In both years, Lapwing hatching success was >80%, with neither Ferret nor Crow control selected as important predictors. Fledging rates in both years were 0.7 young per pair, despite highly effective predator removal, although Crow control potentially resulted in compensatory predation by Common Ravens C. corax. Neither mustelid nor corvid control produced significant immediate benefits for Lapwings. This suggests that mesopredator release of mustelids in mainland situations is unlikely to be a consistent threat to Lapwing, and provides further evidence that declines in this species are unlikely to be tackled successfully through predator management alone.     

Selective bird predation on the peppered moth: the last experiment of Michael Majerus

Colour variation in the peppered moth Biston betularia was long accepted to be under strong natural selection. Melanics were believed to be fitter than pale morphs because of lower predation at daytime resting sites on dark, sooty bark. Melanics became common during the industrial revolution, but since 1970 there has been a rapid reversal, assumed to have been caused by predators selecting against melanics resting on today's less sooty bark. Recently, these classical explanations of melanism were attacked, and there has been general scepticism about birds as selective agents. Experiments and observations were accordingly carried out by Michael Majerus to address perceived weaknesses of earlier work. Unfortunately, he did not live to publish the results, which are analysed and presented here by the authors. Majerus released 4864 moths in his six-year experiment, the largest ever attempted for any similar study. There was strong differential bird predation against melanic peppered moths. Daily selection against melanics (s ≈ 0.1) was sufficient in magnitude and direction to explain the recent rapid decline of melanism in post-industrial Britain. These data provide the most direct evidence yet to implicate camouflage and bird predation as the overriding explanation for the rise and fall of melanism in moths.     

Effect of spatial heterogeneity on the role of Coccinella septempunctata as an intra-guild predator of the aphid pathogen Pandora neoaphidis

The foraging behavior of starved and non-starved adult and larval Coccinella septempunctata on groups of plants in the presence of Pandora neoaphidis-infected Acyrthosiphon pisum, uninfected aphids or a mixture of these two prey types was compared. In general results of these studies confirmed the results of previous work comparing foraging behavior on a smaller spatial scale in Petri dishes. However, behaviors were modified in response to spatial complexity, prey quality, and the host plant. Starved C. septempunctata adults and larvae fed for longer and consumed more aphids than non-starved coccinellids. Both larvae and adults fed on infected aphids and in some cases entirely consumed them. This was thought to be due to the ease of capture of infected (dead) aphids and the feeding stimuli provided by the presence of the host plant and, where there was a choice of prey, uninfected aphids in the environment. Both larvae and adults spent the majority of the time foraging in the upper regions of plants and visited more plants when they were not starved or when they were in the presence of less suitable, infected aphid prey.     

Effects of predation,parasites, and phylogeny on the evolution of bright coloration in north american male passerines

Summary Numerous mechanisms have been proposed to account for the evolution of cryptic and bright coloration in passerine birds. The Hamilton-Zuk revealing handicap model holds that cyclic interactions between hosts and parasites maintain additive genetic variance in secondary sexual traits and adaptive mate choice of resistant genotypes ensues (Hamilton and Zuk, 1982). Here I report no support for this model using various within-taxa techniques to test the functional relationship between the prevalence of hematozoan parasites and male brightness in many species of North American passerines. I establish that phylogeny and predation risk are most strongly associated with variation in male coloration. Ground-nesting passerines are considerably more cryptic than off-ground nesters, and there is evidence that ground-nesting passerines are under greater predation risk. Predation risk may limit the role of sexual selection in the development of bright coloration.