Predatory Strategies Research Articles

Behavioural strategies of cormorants (Phalacrocoracidae) foraging under challenging light conditions

Diving is indicative of foraging in cormorants (Phalacrocoracidae). We have investigated a range of parameters associated with diving in Great Cormorants Phalacrocorax carbo to provide insight into the bases of cormorant predatory strategies. We hypothesize that if vision is important in cormorant foraging behaviour, and if they are not constrained by the position of their prey in the water column, then diving behaviour will be modulated primarily in response to the diel variation in ambient light levels. Specifically, we propose that cormorants forage at shallower depths when light levels are low, and more deeply when light levels are high. We provide evidence that this is the case. We recorded the occurrence of cormorant diving behaviour using implanted data loggers and recorded ambient light levels and water temperature using leg‐mounted loggers in a sample of free‐living Great Cormorants in Greenland. Our results show that dives are shallower at the beginning and end of each day when light levels are lower. We suggest that these data support the hypothesis that cormorant foraging is visually‐guided even though recent evidence has shown that their underwater visual acuity is poor.

Leucopis annulipes larvae (Diptera: Chamaemyiidae) use a furtive predation strategy within aphid colonies

A laboratory experiment was conducted to determine whether the predation strategy of larvae of the aphidophagous silver fly Leucopis annulipes Zetterstedt (Diptera: Chamaemyiidae) is furtive, as are larvae of the aphidophagous midge Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae), or active like aphidophagous ladybird beetle larvae (Coleoptera: Coccinellidae). The impact of L. annulipes larvae on pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae), colony disturbance was evaluated and compared with that of the furtive predator A. aphidimyza and the active-searching ladybird beetle Harmonia axyridis Pallas. Results indicate that aphids showed significantly fewer defensive acts (dropping, walking away, wriggling) in the presence of L. annulipes larvae than of ladybird beetle larvae. Furthermore, the impact of L. annulipes larvae on aphid colony disturbance was similar to that of A. aphidimyza and to a control treatment without predators. These results clearly indicate that L. annulipes larvae use a furtive predation strategy.

An examination of saltatory predation strategies employed by fish larvae foraging in a variety of different turbulent regimes

Saltatory or pause-travel predation strategies are exhibited by a wide variety of different species of fish larvae (e.g. Atlantic cod Gadus morhua and herring Clupea harengus, white crappie Pomoxis annularis and red drum Sciaenops ocellatus), usually classified as visual predators. Given the frequency that saltatory predation behaviour is observed, one would expect that this type of foraging provides an optimal balance between the energy expended whilst swimming, as against the potential energy to be gained upon successfully capturing some suitable prey. However, visual predators must live and forage in the upper 10s of metres of the ocean mixed layer, where light levels are relatively high, which means that their ability to find and capture prey is strongly influenced by small-scale turbulence. The strength of the turbulence regime characterising the water motion of the mixed layer is subject to considerable variation, but given the commonalty of saltatory predation, one would suspect that it remains a robust strategy under a variety of different conditions. This paper seeks to address this issue by studying the impact of saltatory predation over a wide cross section of turbulent environments. By means of a combination of kinematic simulations and theoretical predictions, the paper demonstrates that saltatory predation is indeed a robust and optimal strategy in the sense described, provided the larva’s travel speed is not too high. However, when subject to very high levels of turbulence a larva’s net energy gain peaks and then falls, leading to a prediction that it would either cease foraging altogether, or seek an escape from such an environment.

Mandible strike: The lethal weapon of Odontomachus opaciventris against small prey

In order to study both the hunting efficiency and the flexibility of their predatory behavior, solitary hunters of the trap-jaw ant Odontomachus opaciventris were offered small prey (termites, fruit flies and tenebrionid larvae), presenting different morphological or defensive characteristics. The monomorphic hunters showed a moderately flexible predatory behavior characterized by short capture sequences and a noteworthy efficiency of their mandible strike (76.7-100% of prey retrievals), even when presented with Nasutitermes soldiers. Contrary to most poneromorph ants, antennal palpation of the prey before the attack was always missing, no particular targeted region of the prey's body was preferred, and no 'prudent' posture was ever exhibited. Moreover, stinging was regularly performed on bulky, fast moving fruit flies, very scarcely with sclerotized tenebrionid larvae, but never occurred with Nasutitermes workers or soldiers despite their noxious chemical defense. These results suggest that, whatever the risk linked to potentially dangerous prey, O. opaciventris predatory strategy optimizes venom use giving top priority to the swiftness and strength of the lethal trap-jaw system used by hunters as first strike weapon to subdue rapidly a variety of small prey, ranging from 0.3 to 2 times their own body size and from 0.1 to 2 times their weight. Such risk-prone predatory behavior is likely to be related to the large size of O. opaciventris colonies where the death of a forager might be of lesser vital outcome than in small colony-size species.

Discount Policies in US and EU Antitrust Enforcement Models: Protecting Competition, Competitors or Consumer Welfare?

Discount Policies in US and EU Antitrust Enforcement Models: Protecting Competition, Competitors or Consumer Welfare?

Patronage Politics and the Behavior of Armed Groups

The structures of pre-conflict patronage politics in West Africa play a major role in shaping the organization and behavior of armed groups that have appeared in that region since the 1990s. Patronage networks provide the social context in which armed group leaders arise and influences how they obtain and use resources. It weighs heavily in influencing who they recruit and how fighters and leaders define their goals. Two general principles emerge out of this investigation. First, political leaders who enjoyed close ties to prewar capital-based patronage networks tend to organize predatory armed groups. Leaders who come from communities that were marginal to these networks organize armed groups that are more likely to benefit local communities and take community norms more seriously. Overall, the latter maintain more stable internal organizations and are less prone to commit extreme human rights violations, at least in comparison to their better connected rivals. Evidence indicates that leaders of these groups often are tempted to pursue more predatory strategies. They discover, however, that this social context in which they gather resources and recruit fighters inhibits the pursuit of such strategies.

Strong coupling of predation intensity and diversity in the Phanerozoic fossil record

The importance of ecological interactions in driving the evolution of animals has been the focus of intense debate among paleontologists, evolutionary biologists, and macroecologists. To test whether the intensity of such interactions covaries with the secular evolutionary trend in global biodiversity, we compiled a species-level database of predation intensity, as measured by the frequency of common predation traces (drillings and repair scars ranging in age from Ediacaran to Holocene). The results indicate that the frequency of predation traces increased notably by the Ordovician, and not in the mid-Paleozoic as suggested by multiple previous studies. Importantly, these estimates of predation intensity and global diversity of marine metazoans correlate throughout the Phanerozoic fossil record regardless of corrections and methods applied. This concordance may represent (i) an ecological signal: long-term coupling of diversity and predation; (ii) a diversity-driven diffusion of predatory behaviors: an increased probability of more complex predatory strategies to appear at higher diversity levels; or (iii) a spurious concordance in signal capture: an artifact where rare species and less-frequent (e.g., trace-producing) predatory behaviors are both more detectable at times when sampling improves. The coupling of predation and diversity records suggests that macroevolutionary and macroecological patterns share common causative mechanisms that may reflect either historical processes or sampling artifacts.

Comparison of predation signatures left by Atlantic oyster drills ( Urosalpinx cinerea Say, Muricidae) and veined rapa whelks ( Rapana venosa Valenciennes, Muricidae) in bivalve prey

Predation signatures left by Atlantic oyster drills ( Urosalpinx cinerea, 8.8 to 29.8 mm shell length, SL) and veined rapa whelks ( Rapana venosa, 3.0 to 79.9 mm SL) in oyster and mussel prey were quantitatively described and compared for a similar size range of predators (8–33 mm SL). Rapa whelks and Atlantic oyster drills leave boreholes in the valves of mussels and oysters when predator shell lengths are less than 34 mm. Rapa whelks with shell lengths greater than 34 mm consumed their oyster and mussel prey without drilling or edge boring. The absence of a predation signature of any kind on prey was first observed at rapa whelk shell lengths greater than 10 mm. In rapa whelks, the shell length range of 10 to 34 mm appears to parallel a transition in predation strategy between evident signatures (drilling) and no signatures (non-drilling). The zones over adductor muscle scars were the most frequent site for drilling by both predators. Borehole dimensions scale with size of the predator for Urosalpinx and Rapana. Rapa whelk outer borehole diameters were significantly larger than outer borehole diameters made by similarly sized Atlantic oyster drills. Rapa whelks leave a borehole that has a more steep-sided vertical profile than Atlantic oyster drills. Observed differences in borehole morphology between species may provide a valuable tool to identify predators in field collected valves of prey species. The ability to identify the presence of rapa whelks < 34 mm shell length in a habitat would offer an earlier warning for the presence of this invader than is currently offered by collections of rapa whelks as bycatch in commercial fishing gear at shell lengths greater than 70 mm. Differences in predation strategies between native and introduced gastropods may result in functional trophic differences that have broad scale ecological consequences.

Crossover and Evolutionary Stability in the Prisoner's Dilemma

We examine the role played by crossover in a series of genetic algorithm-based evolutionary simulations of the iterated prisoner's dilemma. The simulations are characterized by extended periods of stability, during which evolutionarily meta-stable strategies remain more or less fixed in the population, interrupted by transient, unstable episodes triggered by the appearance of adaptively targeted predators. This leads to a global evolutionary pattern whereby the population shifts from one of a few evolutionarily metastable strategies to another to evade emerging predator strategies. While crossover is not particularly helpful in producing better average scores, it markedly enhances overall evolutionary stability. We show that crossover achieves this by (1) impeding the appearance and spread of targeted predator strategies during stable phases, and (2) greatly reducing the duration of unstable epochs, presumably by efficient recombination of building blocks to rediscover prior metastable strategies. We also speculate that during stable phases, crossover's operation on the persistently heterogeneous gene pool enhances the survival of useful building blocks, thus sustaining long-range temporal correlations in the evolving population. Empirical support for this conjecture is found in the extended tails of probability distribution functions for stable phase lifetimes.

The anatomy of predator–prey dynamics in a changing climate

Humans are increasingly influencing global climate and regional predator assemblages, yet a mechanistic understanding of how climate and predation interact to affect fluctuations in prey populations is currently lacking. Here we develop a modelling framework to explore the effects of different predation strategies on the response of age-structured prey populations to a changing climate. We show that predation acts in opposition to temporal correlation in climatic conditions to suppress prey population fluctuations. Ambush predators such as lions are shown to be more effective at suppressing fluctuations in their prey than cursorial predators such as wolves, which chase down prey over long distances, because they are more effective predators on prime-aged adults. We model climate as a Markov process and explore the consequences of future changes in climatic autocorrelation for population dynamics. We show that the presence of healthy predator populations will be particularly important in dampening prey population fluctuations if temporal correlation in climatic conditions increases in the future.

Convergent evolution of eye ultrastructure and divergent evolution of vision‐mediated predatory behaviour in jumping spiders

All jumping spiders have unique, complex eyes with exceptional spatial acuity and some of the most elaborate vision-guided predatory strategies ever documented for any animal of their size. However, it is only recently that phylogenetic techniques have been used to reconstruct the relationships and key evolutionary events within the Salticidae. Here, we used data for 35 species and six genes (4.8 kb) for reconstructing the phylogenetic relationships between Spartaeinae, Lyssomaninae and Salticoida. We document a remarkable case of morphological convergence of eye ultrastructure in two clades with divergent predatory behaviour. We, furthermore, find evidence for a stepwise, gradual evolution of a complex predatory strategy. Divergent predatory behaviour ranges from cursorial hunting to building prey-catching webs and araneophagy with web invasion and aggressive mimicry. Web invasion and aggressive mimicry evolved once from an ancestral spartaeine that was already araneophagic and had no difficulty entering webs due to glue immunity. Web invasion and aggressive mimicry was lost once, in Paracyrba, which has replaced one highly specialized predation strategy with another (hunting mosquitoes). In contrast to the evolution of divergent behaviour, eyes with similarly high spatial acuity and ultrastructural design evolved convergently in the Salticoida and in Portia.

Early Cambrian Yangtze Plate Maotianshan Shale macrofauna biodiversity and the evolution of predation

The large number of soft-part preserved fossils from the Lower Cambrian Maotianshan Shale (Chengjiang) Lagerstätten suggests particularly favourable conditions for a rich life on the shelf-zone sea bottom of the Yangtze Plate, China. This high degree of biodiversity opens an excellent window into the early radiation phase of Metazoa and represents a significant data source for the study of adaptive strategies among early animals. Feeding and locomotion are the main life strategies of organisms we investigated with regard to two major benthic macrofaunal components of the Maotianshan Shale biota, the nemathelminths and the arthropods. Our attempt was to test whether food, feeding and locomotory strategies of the benthic Lower Cambrian shallow-water communities were as diversified as it appears from the morphological diversity of the organisms present. Two major types of feeders can be discerned: suspension/micro-particle feeders – mostly epibenthic sedentary taxa – and larger-particle feeders, living in benthic to bentho-pelagic realms. Scant evidence exists for exclusive vegetarians, fungi eaters, biomat utilizers and for in-faunal vertical burrowers or grazers (bioturbators). Predation, in a wider sense, seems to be a, if not the, major feeding mode among metazoans. Nemathelminths and arthropods are amongst the best examples. In the benthic shallow-water regime, as exposed by the Maotianshan Shale biota, animals and their ontogenetic stages were the most suitable and readily available food source. At least for arthropods, we propose that improvement of predatory strategies was paralleled by the enhancement of locomotory and food manipulation structures. Accumulating evidence of late Precambrian to Early Cambrian metazoans exposing diverse morphologies and life styles indicates that, on the large scale, phylogenesis progressed gradually in the Late Precambrian. This renders an “explosive” radiation of Metazoa unlikely.

Evolutionary branching and long-term coexistence of cycling predators: Critical function analysis

It is well known that two predators with different functional responses can coexist on one prey when the system exhibits nonequilibrium dynamics. In this paper, we investigate under which conditions such coexistence is evolutionarily stable, and whether the two predators may evolve from a single ancestor via evolutionary branching. We assume that predator strategies differ in handling time, and hence in the shape of their Holling type II functional response. Longer handling times are costly in terms of lost foraging time, but allow the predator to extract more nutrients from the prey and therefore to produce more offspring per consumed prey. In the analysis, we apply a new method to accommodate arbitrary trade-off functions between handling time and offspring production. Contrary to previous results obtained assuming a particular trade-off [Kisdi, E. and Liu, S., 2006. J. Evol. Biol. 19, 49–58], we find that evolutionary branching of handling time is possible, although it does not appear to be very likely and can be excluded for a class of trade-offs. Evolutionarily stable coexistence of two predators occurs under less restrictive conditions, which are always satisfied when the trade-off function has two strongly concave parts connected by a convex piece.

Exploitation of Other Social Amoebae by Dictyostelium caveatum

Dictyostelium amoebae faced with starvation trigger a developmental program during which many cells aggregate and form fruiting bodies that consist of a ball of spores held aloft by a thin stalk. This developmental strategy is open to several forms of exploitation, including the remarkable case of Dictyostelium caveatum, which, even when it constitutes 1/103 of the cells in an aggregate, can inhibit the development of the host and eventually devour it. We show that it accomplishes this feat by inhibiting a region of cells, called the tip, which organizes the development of the aggregate into a fruiting body. We use live-cell microscopy to define the D. caveatum developmental cycle and to show that D. caveatum amoebae have the capacity to ingest amoebae of other Dictyostelid species, but do not attack each other. The block in development induced by D. caveatum does not affect the expression of specific markers of prespore cell or prestalk cell differentiation, but does stop the coordinated cell movement leading to tip formation. The inhibition mechanism involves the constitutive secretion of a small molecule by D. caveatum and is reversible. Four Dictyostelid species were inhibited in their development, while D. caveatum is not inhibited by its own compound(s). D. caveatum has evolved a predation strategy to exploit other members of its genus, including mechanisms of developmental inhibition and specific phagocytosis.

Exit and Upgrading in Response to Entry: The Case of Gasoline Retailing

Spatial competition models have established the importance of localized competition in determining competitive outcomes. However, few empirical studies attempt to determine to what extent actual local market conditions affect strategic decisions. This paper uses data provided by the acquisition of the Vancouver area Super‐Save chain of retail gasoline stations by ARCO to study the role of geographic space in competition, and the spatial response of the major competitors in the market to entry. The possibility of both accommodating and aggressive capacity responses by the major incumbent firms to entry are considered. While the empirical results show that proximity to ARCO increased the probability that a station shuts down, proximity to ARCO can explain only a limited amount of shutdown after ARCO’s entry. There is no evidence that incumbent firms used station locations and capacity changes to respond aggressively to ARCO’s entry with a spatial predation strategy.

SEXUAL DIMORPHISM IN THE METABOLIC RATE OF TWO SPECIES OF WOLF SPIDER (ARANEAE, LYCOSIDAE)

Abstract Spiders have long been noted as classic examples of extreme sexual dimorphism and adaptations to the lifestyle of a sit-and-wait predator. We examined sex-based differences in the metabolic rate of two species of wolf spider that differ in their degree of sexual dimorphism and predatory strategy. Pardosa milvina (Hentz 1877) is a small active wolf spider that does not exhibit a large degree of sexual dimorphism in body size. Hogna helluo (Walckenaer 1837) is a large, strongly sexually dimorphic wolf spider with large, sedentary females and smaller, active males. We found that P. milvina had a higher mass-specific metabolic rate than H. helluo. Also, P. milvina males had a higher metabolic rate than P. milvina females but there was no difference in mass-specific metabolic rate between H. helluo males and females. Our data demonstrate that an actively foraging species, P. milvina, exhibits a higher metabolic rate than species with a sit-and-wait strategy, H. helluo. This suggests that activity leve...

Plankton predation rates in turbulence: A study of the limitations imposed on a predator with a non-spherical field of sensory perception

This paper presents an extension to previously published work which studied encounter rates of planktonic predators with restricted perception fields, to examine the related problems of prey capture and predation rates. Small-scale turbulence influences planktonic predation in two ways: the extra energy of the flow enhances the number of encounter events between individual predator and prey meso/micro-zooplankton, but it lowers the capture probability (because the time spent by the predator and prey in close proximity is reduced). Typically, an ‘encounter’ has usually been defined as an event when a potential prey swims (or is advected) to within a distance R of the predator in any direction. However, there is a considerable body of experimental evidence showing that predators perception fields are far from spherical; often they are wedge shaped (e.g. fish larvae), or strongly aligned with the directions of sensory antennae (e.g. copepods); and this is certain to influence optimal predation strategies. This paper presents a theoretical model which for the first time examines the combined problems of both encounter and capture for a predator with a restricted perception field swimming in a turbulent flow. If such a predator adopts a cruising strategy (continuous swimming, possibly with direction changes) the model predictions suggest that predation rates actually vary little with swimming speed, in contrast to predictions made for spherical perception fields. Consequently, cruising predators are predicted to swim at relatively low speeds whilst foraging. However, application of the model to examine the net energy gain of a typical pause-travel predator (the Atlantic cod larva), does predict the existence of an optimal ratio of the length of pauses to time spent swimming (specifically one pause phase to every two travel phases), in line with experimental observations. Kinematic simulations are presented which support these findings.

Evolution of handling time can destroy the coexistence of cycling predators

Several consumers (predators) with Holling type II functional response may robustly coexist even if they utilize the same resource (prey), provided that the population exhibits nonequilibrium dynamics and the handling time of predators is sufficiently different. We investigate the evolution of handling time and, in particular, its effect on coexistence. Longer handling time is costly in terms of lost foraging time, but allows more nutrients to be extracted from a captured prey individual. Assuming a hyperbolically saturating relationship between handling time and the number of new predators produced per prey consumed, we obtain three results: (i) There is a globally evolutionarily stable handling time; (ii) At most two predator strategies can coexist in this model; (iii) When two predators coexist, a mutant with intermediate handling time can always invade. This implies that there is no evolutionarily stable coexistence, and the evolution of handling time eventually leads to a single evolutionarily stable predator. These results are proven analytically and are valid for arbitrary (not only small) mutations; they however depend on the relationship between handling time and offspring production and on the assumption that predators differ only in their prey handling strategy.

Interactions between fangblennies (Plagiotremus rhinorhynchus) and their potential victims: fooling the model rather than the client?

Lepidophagous (scale-eating) blue-striped fangblennies (Plagiotremus rhinorhynchus Bleeker 1852) are often found sympatrically with the bluestreak cleaner wrasse (Labroides dimidiatus Valenciennes 1839). They have some resemblance to the juvenile L. dimidiatus and have previously been reported as aggressive cleaner wrasse mimics. We observed 14 P. rhinorhynchus on a small area in the barrier reef near Hoga Island, Indonesia to assess the effects of client size on the behaviour and attack success of fangblennies: our results suggest that fangblennies are selective with regard to victim size; fish avoided by the fangblennies are significantly larger than those not avoided and attack success is significantly higher at intermediate victim size classes. The behaviour of the victims also has a significant direct effect on the foraging success of the fangblennies; where the potential victim posed, 63.6% were ignored by the fangblenny and only 7.4% of attacks were successful on posing fish as opposed to a surprise attack success rate of 71.6%. Overall, victims which exhibited the pose behaviour were significantly smaller in size. It appears likely that the predatory strategy of these fangblennies varies with victim size and that mimicry plays a minor role in attracting potential victims. We suggest that in common with other mimetic fish the resemblance of fangblennies to juvenile bluestreak cleaner wrasse allows them to actively hunt in areas where adult cleaners are common thus, indirectly improving their feeding opportunities.

HOW JAPAN FIRST BEGAN TO EXPORT MACHINE-MADE MANUFACTURES TO EAST ASIA*

Drawing on late Meiji period data, the efforts of Japan’s cotton spinning mills to overcome overseas competition and establish themselves in the Chinese, Korean and Hong Kong markets are examined. Estimating a probit model of the decision to export, it is found that despite readily available export finance and commercial networks that should have greatly lowered the costs of participating in East Asian markets, sunk entry costs still appear to have been quite large. Many otherwise capable mills apparently saw little prospect of entering tariff-less East Asian markets, notwithstanding the possibility of generous subsidies and trade association devised predatory strategies.