Predatory Strategies Research Articles

Refuge use in sticklebacks as a function of body length and group size

A change in anti–predator strategy from hiding to grouping outside a refuge was observed in large three–spined sticklebacks. No such change in strategy was seen in small fish. The body–length dependence of this strategy change is discussed in the context of metabolic constraints.

Refuge use in sticklebacks as a function of body length and group size

A change in anti–predator strategy from hiding to grouping outside a refuge was observed in large three–spined sticklebacks. No such change in strategy was seen in small fish. The body–length dependence of this strategy change is discussed in the context of metabolic constraints.

Early effects of rodent post‐dispersal seed predation on the outcome of the plant–seed disperser interaction

We analysed two potential effects of post‐dispersal seed predation on recruitment of the wild olive tree (Olea europaea var. sylvestris), a Mediterranean bird‐dispersed tree: (a) the limitation of abundance and distribution of seedlings after dispersal, and (b) the selection of certain seed characteristics of the recruited plants. An observational approach was used to compare seed rain among microhabitats, and how it was affected by seed predation. The relation of microhabitat, scrub density, and seed size with predation risk was explored by a field experiment. Seed density ranged from 0 seeds/m2 in open places to 93.2 seeds/m2 under O. europaea. The overall predation rate was low, as shown in the observational approach (35%). The mean percentage of predation in the experimental approach was 51%, ranging across microhabitats between 28% and 88%. It was higher in dense scrub patches (67%) than in sparse ones (33%), and lower for large seeds (42%) than for medium and small ones (57% and 55%, respectively). Finally, seed density near seed depots did not increase their probability of being detected by rodents or the predation rate. Although predation rates were low, wild olive seeds could be frequently found by rodents due to their spatial ubiquity and local abundance. Together with the efficient foraging strategy of predators (92% of experimental seed depots were found), this allowed a widespread post‐dispersal predation, but it did not modify the relative distribution of seeds among microhabitats. Thus, in our study, the seed dispersal pattern of the wild olive tree was not reshaped by post‐dispersal predation, because (1) rodents did not alter significantly its initial spatial distribution and (2) mice did not seem to limit the number of recruits. Finally, our results indicate that, as a consequence of seed size preferences of rodents, large seeds have a higher probability to survive post‐dispersal predation. Thus, seed size may be a key trait to determine the identity of the future recruits in the wild olive tree, at least affecting the characteristics of the seeds that reach the soil seed bank.

BREEDING SUPPRESSION AND PREDATOR–PREY DYNAMICS

In a biotic environment, current reproduction will affect future population sizes, but these future changes may also affect the optimality of current reproductive decisions. We investigate the dynamics of predator–prey cycles if both predators and prey respond to each other’s (and their own) population density by adjusting their breeding effort. We find that adaptive breeding strategies of predators can produce equally profound changes to the dynamics as those produced by analogous strategies of their prey. Contrary to earlier, more limited models, we find that breeding suppression can be either destabilizing (i.e., generating cycles or chaotic behavior) or stabilizing, in cases where predators, prey, or both can adopt adjustable strategies. The direction of change depends on the shape of the density dependence in the growth rates, as well as how it is affected by the breeding decisions. We discuss these findings in light of the Fennoscandian vole cycle, where antipredatory behavior of voles has been evoked to explain some properties of the cycle, and where many predators show pronounced variability in their breeding effort according to the phase of the cycle.

Hunting strategy of a generalist ant species proposed as a biological control agent against termites

AbstractWe studied the hunting behaviour of Myrmicaria opaciventris (Hymenoptera: Formicidae) in order to evaluate if it can be used as a biological control agent against the termites that damage sugarcane plantations. Hunting workers foraged in groups and recruited nestmates at short‐range when they encountered large termite soldiers or groups of small termite workers. Differences in prey capture concerned the: (1) means of detection (from a distance or by contact); (2) termite body part seized (small termites seized by the body; large termites by an appendage); (3) percentages of prey abandoned; and (4) use of venom. The sting of the workers is spatulated implying a topical application of the venom on the prey. Large termites were stretched by several workers whose adherence to the substrate is facilitated by well‐developed arolia and claws on the legs while others spread venom on the body and carved it up. An adaptation to termite capture was noted with a distribution of tasks between the workers which subdued prey, and those which transported it. In the former case, the workers easily eliminated termite soldiers, successively attacked several termite workers and even captured new individuals while holding the first ones captured between their mandibles before retrieving them all at once. The remaining individuals were retrieved by the transporting workers. Given this particularly effective predatory strategy, we concluded that, under certain conditions, M. opaciventris can be used as a biological control agent against termites.

Nonequilibrium Population Dynamics of "Ideal and Free" Prey and Predators.

Aggregated spatial distributions of prey and predators promote stability of the otherwise unstable Nicholson-Bailey model. Nevertheless, when both predators and prey choose patches in an ideal free way, sufficiently aggregated distributions will only arise if patch quality (e.g., reflected in prey fecundity) is very heterogeneous. This requirement profoundly limits the possibilities for simultaneous population dynamical and evolutionary stability. However, stability is not necessary for coexistence. Under cyclic or chaotic dynamics, the rate at which species change their distributions becomes important. Here we consider two endpoints of a continuum of rates. The first is "rigid" selection of patch types based on the expected long-term distribution of conditions. The second is "flexible" selection based on current conditions. We carried out systematic surveys of the population-level consequences of coevolutionarily stable patch-selection strategies for different combinations of rigid and flexible strategies of predator and prey. First, if both prey and predators have rigid strategies, the evolutionary end result is either a stable population dynamical equilibrium or diverging cycles eventually leading to extinction. Second, for the case with rigid prey and flexible predators, the persistence boundary in parameter space is shifted from the boundaries obtained for rigid predators. The mechanism underlying persistence is different in that the flexible strategies of the predators destabilize the equilibrium, while the evolutionary response of the rigid prey leads to reduced cycles. Third, if both prey and predators are flexible, simulations lead either to chaotic fluctuations or to extinction (but not to stable equilibria, nor to limit cycles), and the conditions for coexistence are much wider than those under rigid patch selection. These simulations suggest that information constraints on adaptive patch choice have a major impact on predator-prey persistence under nonequilibrium conditions. We discuss how these predictions can be tested by field observations on expansions and contractions in dietary range (or habitat range) in relation to population fluctuations.

Parental and predatory behaviour of Scytodes sp., an araneophagic spitting spider (Araneae: Scytodidae) from the Philippines

AbstractParental care, especially as it relates to our understanding of sociality, is a topic that has received considerable recent attention in research on spiders (Aviles, 1997). Predatory strategies, including foraging decisions, prey preferences and predatory versatility, have also been emphasized in the recent literature. The present paper is concerned with both of these areas, parental care and predatory strategies. Scytodes sp. indet. is a versatile predator that captures prey either in its web or away from webs, and prey capture may be either by ambush or by active pursuit regardless of whether in the presence and absence of webs. The web is a sparsely woven sheet across a concave upper leaf surface, with a three‐dimensional tubular nest linked to the sheet via a small opening. Leaves may be green and living or brown and dead. In the field, a wide range of insects and spiders is taken, but jumping spiders (Salticidae) are the dominant prey. Predatory attacks are by spitting, with large prey being spat at repeatedly before being subdued. After spitting, the scytodid wraps prey in silk before feeding. Eggs are enclosed in a silk egg sac. The female uses her chelicerae to hold her eggs until hatching. After hatching, there is an extended mother–offspring association, with juveniles tending to remain in their mother's web until after the third moult. Females take prey to their juveniles and either feed alongside the juveniles or leave the juveniles to feed alone.

Ambush Predation by the Ponerine Ant Ectatomma ruidum Roger (Formicidae) on a Sweat Bee Lasioglossum umbripenne (Halictidae), in Panama

An individual ambush predation is used by huntresses of the ponerine ant Ectatomma ruidum to capture halictid bees (Lasioglossum umbripenne) in the Panamanian mountains. Workers, which use this strategy and originated from a colony (A) situated within a nest aggregation of halictid bees, capture almost four times more prey than colony (B) with a foraging area which does not include this type of bee's nest. Forty-eight percent of the prey of colony (A) are halictid bees, demonstrating the local importance of this predatory strategy in E. ruidum. A close examination of the behavioral sequence of predation shows that ambush is successful in only 4.8% of cases, a very low success rate in comparison to other predatory strategies described in this species. Nevertheless, due to the high repetition (16.1 ± 5.9 times on average) of very short waiting phases (6.3 ± 1.9 s), the true success rate (i.e., according to the number of individual trips) can reach up to 80%. A review of ambush predation among ant species allows us to distinguish approaches between jumping, long stealth approaches, and true ambushes. Implications of learning and expectation processes are also discussed.

Nonequilibrium Population Dynamics of "Ideal and Free" Prey and Predators

Aggregated spatial distributions of prey and predators promote stability of the otherwise unstable Nicholson‐Bailey model. Nevertheless, when both predators and prey choose patches in an ideal free way, sufficiently aggregated distributions will only arise if patch quality (e.g., reflected in prey fecundity) is very heterogeneous. This requirement profoundly limits the possibilities for simultaneous population dynamical and evolutionary stability. However, stability is not necessary for coexistence. Under cyclic or chaotic dynamics, the rate at which species change their distributions becomes important. Here we consider two endpoints of a continuum of rates. The first is “rigid” selection of patch types based on the expected long‐term distribution of conditions. The second is “flexible” selection based on current conditions. We carried out systematic surveys of the population‐level consequences of coevolutionarily stable patch‐selection strategies for different combinations of rigid and flexible strategies of predator and prey. First, if both prey and predators have rigid strategies, the evolutionary end result is either a stable population dynamical equilibrium or diverging cycles eventually leading to extinction. Second, for the case with rigid prey and flexible predators, the persistence boundary in parameter space is shifted from the boundaries obtained for rigid predators. The mechanism underlying persistence is different in that the flexible strategies of the predators destabilize the equilibrium, while the evolutionary response of the rigid prey leads to reduced cycles. Third, if both prey and predators are flexible, simulations lead either to chaotic fluctuations or to extinction (but not to stable equilibria, nor to limit cycles), and the conditions for coexistence are much wider than those under rigid patch selection. These simulations suggest that information constraints on adaptive patch choice have a major impact on predator‐prey persistence under nonequilibrium conditions. We discuss how these predictions can be tested by field observations on expansions and contractions in dietary range (or habitat range) in relation to population fluctuations.

Black widow spider α-latrotoxin: a presynaptic neurotoxin that shares structural homology with the glucagon-like peptide-1 family of insulin secretagogic hormones

α-Latrotoxin is a presynaptic neurotoxin isolated from the venom of the black widow spider Latrodectus tredecimguttatus. It exerts toxic effects in the vertebrate central nervous system by depolarizing neurons, by increasing [Ca 2+] i and by stimulating uncontrolled exocytosis of neurotransmitters from nerve terminals. The actions of α-latrotoxin are mediated, in part, by a GTP-binding protein-coupled receptor referred to as CIRL or latrophilin. Exendin-4 is also a venom toxin, and it is derived from the salivary gland of the Gila monster Heloderma suspectum. It acts as an agonist at the receptor for glucagon-like peptide-1(7–36)-amide (GLP-1), thereby stimulating secretion of insulin from pancreatic β-cells of the islets of Langerhans. Here is reported a surprising structural homology between α-latrotoxin and exendin-4 that is also apparent amongst all members of the GLP-1-like family of secretagogic hormones (GLP-1, glucagon, vasoactive intestinal polypeptide, secretin, pituitary adenylyl cyclase activating polypeptide). On the basis of this homology, we report the synthesis and initial characterization of a chimeric peptide (Black Widow GLP-1) that stimulates Ca 2+ signaling and insulin secretion in human β-cells and MIN6 insulinoma cells. It is also reported here that the GTP-binding protein-coupled receptors for α-latrotoxin and exendin-4 share highly significant structural similarity in their extracellularly-oriented amino-termini. We propose that molecular mimicry has generated conserved structural motifs in secretagogic toxins and their receptors, thereby explaining the evolution of defense or predatory strategies that are shared in common amongst distantly related species including spiders, lizards, and snakes. Evidently, the toxic effects of α-latrotoxin and exendin-4 are explained by their ability to interact with GTP-binding protein-coupled receptors that normally mediate the actions of endogenous hormones or neuropeptides.

Exclusive Dealing and the Whiskey Trust, 1890–1895

This article uses the history of the Whiskey Trust to explore the competitive effects of vertical restraints such as exclusive dealing. The Whiskey Trust distilled alcoholic spirits and bribed distributors not to carry competing brands of spirits. For the Whiskey Trust, exclusive dealing was an ineffective predatory strategy. Despite the trust's market dominance and manifold predatory strategies, it failed to preempt entry. The trust failed, in part, because its rivals could vertically integrate at low cost. Competition disciplined the trust more effectively than did numerous antitrust suits.

No association between sexual size dimorphism and life histories in spiders

In spiders, females are commonly larger than males. The majority of hypotheses that attempt to explain sexual size dimorphism in spiders concentrate on reduction in male size, although there is evidence to suggest that the independent evolution of marked sexual size dimorphism and reversion to a less extreme dimorphic state has occurred several times. Recent debate has centred on two conflicting hypotheses involving male dwarfism and increased female size through fecundity selection, and has focused on the golden orb-weaving spider, Nephila clavipes (Tetragnathidae), and its relatives. In Nephila, males are tiny in comparison to females, however, other orb-web spiders do not show such extremes in dimorphism. Here, we incorporate phylogeny into a comparative investigation of the patterns of sexual dimorphism predicted by the hypothesis of male dwarfism via sex-linked differential mortality during mate searching and note an absence of supporting evidence. There was no evidence of the predicted association between male and female size and sexual size dimorphism with life histories, exemplified by variation in predatory strategies, in spiders.

PREDATORY ACTIVITY AND SPATIAL STRATEGIES OF EPIXANTHUS DENTATUS (DECAPODA: OZIIDAE), AN AMBUSH PREDATOR AMONG THE MANGROVES

ABSTRACT The predatory patterns and spatial strategies of Epixanthus dentatus were studied in a mangrove creek on the Kenyan coast, together with laboratory analysis aimed at assessing the natural diet. This xanthoid fed on almost all the slowly moving invertebrates common in the forest and actively preyed at night, using an ambush technique. Epixanthus dentatus is faithful to individual dens among the roots and to well-defined feeding areas within a 3-m radius, which they shared with an average of 2 other individuals. The high density of E. dentatus seemed to affect the behavior of major prey species; various grapsid crab species reduced their climbing activity during the peak activity periods of E. dentatus. The density of E. dentatus among the mangrove roots was determined both by the number of suitable dens, and, more directly, by the density of prey species.

Graded recruitment and hunting strategies linked to prey weight and size in the ponerine ant Ectatomma ruidum

According to the weight and size of their prey, Ectatomma ruidum workers can employ different recruitment systems (solitary hunting, cooperative hunting and group hunting with recruitment) when mastering and retrieving prey items from short distances from the nest. Prey size determined the backwards entry typically adopted by this species, while prey weight determined the predatory strategy selected. After a common initial sequence (search for prey, detection, localization), predatory sequences varied in terms of the type of approach, the site of seizure, the reaction after stinging and the type of transport. Nevertheless, irrespective of prey weight and size, seizure was preferentially oriented towards the head and prey were always stung. Short-range recruitment and mass recruitment without trail laying were elicited by a large range of heavy prey (> 2.5 times the weight of an individual worker). According to the mortality risk associated with each prey, hunters exhibited a “prudent” stinging posture associated with an increase in the duration of the subsequent phase of waiting for prey immobilization. The overall time of capture was positively correlated with the weight of the prey. When collective hunting strategies were involved, E. ruidum colonies matched the number of recruited hunters to the size and weight of the prey. Compared to solitary hunting strategies, for short food–nest distances, this graded recruitment appeared to enhance the energetic benefits derived by this species from the use of recruitment systems: the higher the number of workers involved in the recruitment process, the greater the energetic benefits obtained. The exhibition or absence of trail laying behavior in the recruitment responses displayed by E. ruidum workers is discussed in relation to their involvement in scavenging or predatory behavior.

Observations on the Feeding Ecology of Estuarine Nematodes

Observations on living estuarine nematodes show that previous feeding type classifications do not accurately represent the trophic structure of an intertidal mudflat in the Westerschelde Estuary (Netherlands). A new scheme with six major nematode feeding guilds is proposed: (1) microvores; (2) ciliate feeders; and (3) deposit feeders sensu stricto are all nematodes without a distinct buccal armature. In the first two groups bacteria and protozoa, respectively are the major particulate food sources, while other items are included in the diet of the third. The three other categories are recognized among the nematodes with a buccal armature: (4) epigrowth feeders; (5) facultative predators; and (6) predators. Diatoms and other microalgae are an important particulate food for many epigrowth feeders. The importance of bacteria as a food source for these nematodes remains poorly documented. A strictly or mainly predatory behaviour has been described for only few species from the study area. Several nematodes, however, are facultative predators. The predatory strategy of Calyptronema maxweberi, as described in this paper, suggests the use of a paralysing or lethal secretion in prey capture, which, to our knowledge, is the first report for aquatic nematodes. Furthermore, the importance of sources other than particulate food in free-living aquatic nematodes is stressed. Our observations show that many aquatic nematodes are in fact opportunistic feeders, which may change feeding strategies in response to available food.

Deficit Reduction Through Diversity: How Affirmative Action at the FCC Increased Auction Competition

INTRODUCTION 2 I. THEORY 4 A. Set-Asides Can Enhance Intragroup Competition Among Strong Bidders 6 B. Bidding Credits Can Create Effective Set-Asides 7 C. Bidding Credits Can Create Intergroup Competition 7 D. Affirmative Action Can Increase Expected Revenue When the Government Is Imperfectly Informed About Bidder Valuations 7 E. Affirmative Action Can Destabilize Tacit Collusion 9 II. EMPIRICISM 9 A. Describing the Licenses and the Auction Rules 10 B. The Impact of Affirmative Action 14 1. Comparing the nationwide and regional results 14 2. The impact of designated crossover bidding 17 3. The impact of the set-aside licenses. 22 C. Alternative Hypotheses 23 1. Hiding in the grass 24 2. The designated bidders would have bid anyway 25 3. Affirmative action might have chilled non-designated bidder participation 26 D. Strategic Perversities: Bidding Above Atomistic Reservation Prices 26 1. Risk of partial aggregation. 26 2. Raising rivals’ costs and predatory strategies. 27 3. Reduced retail competition. 28 III. APPLICATIONS TO GOVERNMENT PROCUREMENT AND PRIVATE EMPLOYMENT 29 A. Government Procurement 29 B. Private Employment 31 IV. LEGAL IMPLICATIONS 32 A. Public Affirmative Action 32 1. Revenue enhancement is constitutionally insufficient. 32 2. Did the FCC’s rules enhance minority or female control of the airwaves ? 33 3. Affirmative action costs the government less than is commonly assumed. 34 B. Private Affirmative Action May Deserve Higher Scrutiny 35 CONCLUSION 36 APPENDIX 37

Predatory behavior of jumping spiders.

Salticids, the largest family of spiders, have unique eyes, acute vision, and elaborate vision-mediated predatory behavior, which is more pronounced than in any other spider group. Diverse predatory strategies have evolved, including araneophagy, aggressive mimicry, myrmicophagy, and prey-specific prey-catching behavior. Salticids are also distinctive for development of behavioral flexibility, including conditional predatory strategies, the use of trial-and-error to solve predatory problems, and the undertaking of detours to reach prey. Predatory behavior of araneophagic salticids has undergone local adaptation to local prey, and there is evidence of predator-prey coevolution. Trade-offs between mating and predatory strategies appear to be important in ant-mimicking and araneophagic species.

Genetic variation for the rate of recruitment of novel insect prey into the diet of a bird

Two lines of quail (Cotumix coturnix japonicus) were selected over three generations for the speed of their response to the red colour form of the two-spot ladybird beede (Adalia bipunctata), an aposematic, semi-palatable prey insect. One line was bred for fast recruitment of die new prey into the diet and die odier for slow recruitment. Differences between the lines suggested additive genetic variation. The birds' response to insect prey with different colour patterns and toxicities (brown beetles, green butterfly pupae, melanic two-spot ladybirds and toxic seven-spot ladybirds) demonstrated that die selection involved a specific response to novel prey. The results are discussed in relation to predator strategy and the evolution of aposematism.

The chemistry of eavesdropping, alarm, and deceit.

Arthropods that prey on or parasitize other arthropods frequently employ those chemical cues that reliably indicate the presence of their prey or hosts. Eavesdropping on the sex pheromone signals emitted to attract mates allows many predators and parasitoids to find and attack adult insects. The sex pheromones are also useful signals for egg parasitoids since eggs are frequently deposited on nearby plants soon after mating. When the larval stages of insects or other arthropods are the targets, a different foraging strategy is employed. The larvae are often chemically inconspicuous, but when they feed on plants the injured plants respond by producing and releasing defensive chemicals. These plant chemicals may also serve as "alarm signals" that are exploited by predators and parasitoids to locate their victims. There is considerable evidence that the volatile "alarm signals" are induced by interactions of substances from the herbivore with the damaged plant tissue. A very different strategy is employed by several groups of spiders that remain stationary and send out chemical signals that attract prey. Some of these spiders prey exclusively on male moths. They attract the males by emitting chemicals identical to the sex pheromones emitted by female moths. These few examples indicate the diversity of foraging strategies of arthropod predators and parasitoids. It is likely that many other interesting chemically mediated interactions between arthropod hunters and their victims remain to be discovered. Increased understanding of these systems will enable us to capitalize on natural interactions to develop more ecologically sound, environmentally safe methods for biological control of insect pests of agriculture.

Fish feeding behaviour and fish capture: the case for variation in Lapita fishing strategies

Relationships between fish feeding behavior and human predation strategies are examined in order to identify Lapita fishing strategies. Inherent properties of herbivores/omnivores versus carnivores suggest the kinds of fishing strategies best able to catch fishes representing these feeding groups. Comparison of fish faunal assemblages from nine Lapita sites distributed from the Mussau Islands, Papua New Guinea to Western Polynesia reveals some striking contrasts in fish representation. Most western Melanesian assemblages are comprised of similar frequencies of carnivores and herbivores/omnivores while eastern Lapita site assemblages are dominated by herbivores/omnivores. Differences in analytic and archaeological recovery practices do not account for these differences; rather, variation in fishing strategies better explains the faunal variation. Apparently, angling and netting were commonly practiced at some sites, while netting techniques were more widely used at others. Contrasts in habitat structure, labour organization, or technological costs presumably account for such variation in procurement strategies.