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Journal ArticleDOI

Costs of aggregation: shadow competition in a sit-and-wait predator

01 Oct 2001-Oikos (Munksgaard International Publishers)-Vol. 95, Iss: 1, pp 59-68
TL;DR: Modeling confirmed that shadow competition adequately explains the patterns of foraging, growth and survival of sedentary foragers such as these spiders, and is likely to have wider implications for other sit-and-wait predators.
Abstract: Shadow competition, when sedentary foragers closer to a source of food reduce its availability to those further away, is predicted to increase with the size and density of a group. We tested the occurrence of shadow competition and examined its consequences for a burrowing spider Seothyra henscheli (Eresidae) in the Namib Desert. Differences between individual spiders occurring inside or on the periphery of clusters compared to solitary spiders were examined in a natural population, by experimental manipulation of densities and by computer simulation of the experimental manipulation. Spiders in the population grew more slowly in clusters than did solitary spiders and this was confirmed by the experiment. The experiment showed that spiders grew more rapidly on the periphery of a cluster than inside it, but that survival showed the opposite trend. The largest effect was in the highest density, where all spiders maintained active webs throughout the experiment, indicating a state of hunger. Modeling indicated that such effects may be explained by the way ants, the principal prey of the spiders, reach spider webs at different locations within the patches of different densities. Modeling confirmed that shadow competition adequately explains the patterns of foraging, growth and survival of sedentary foragers such as these spiders, and is likely to have wider implications for other sit-and-wait predators.
Citations
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BookDOI
01 Jan 2016
TL;DR: In Animal Social Behaviour as discussed by the authors, the authors integrate the most up-to-date empirical and theoretical research to provide a new synthesis of the field, which is aimed at fellow researchers and postgraduate students on the topic.
Abstract: The last decade has seen a surge of interest among biologists in a range of social animal phenomena, including collective behaviour and social networks. In Animal Social Behaviour , authors Ashley Ward and Michael Webster integrate the most up-to-date empirical and theoretical research to provide a new synthesis of the field, which is aimed at fellow researchers and postgraduate students on the topic

291 citations

Journal ArticleDOI
TL;DR: This synthesis shows that prey abundance may have relatively little effect on pit relocation and that physical properties of the habitat or competition often override its effect, and proposes new research directions, such as studying whether pit relocation is an adaptive response, when controlling for possible phylogenetic effects.
Abstract: There is a large body of evidence indicating that predator behavior may strongly influence patterns and processes at the population and community level. Site selection is a major component of fitness in sit-and-wait predators, especially when relocation is rare. Although several review articles dealt with these issues in web-building spiders, this is the first attempt to summarize the effects of biotic and abiotic factors on site selection and relocation in another group of sit-and-wait predators, the pit-building antlions (Neuroptera: Myrmeleontidae). Our synthesis shows that prey abundance may have relatively little effect on pit relocation and that physical properties of the habitat or competition often override its effect. We suggest that owing to a variety of constraints such as physiological constraints or difficulties in assessing site quality, site selection and relocation are not necessarily optimal and thus food intake rate is not maximized. We call for a multi-factorial study on a single species in order to pinpoint the dominant factors and to assess to what extent they influence site selection and relocation. We conclude by proposing new research directions, such as studying whether pit relocation is an adaptive response, when controlling for possible phylogenetic effects.

148 citations


Cites background from "Costs of aggregation: shadow compet..."

  • ...However, some studies suggest that grouping actually contributes to the individual foraging success by the ‘ricochet effect’ (Uetz, 1989; Lubin et al., 2001): the capture of prey items after they were slowed and weakened by several webs in succession....

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  • ..., 1991), and this has also been documented in spiders (Lubin et al., 2001)....

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  • ...Shadow competition occurs when one sit-and-wait predator can catch the moving prey before it encounters other predators (Linton et al., 1991), and this has also been documented in spiders (Lubin et al., 2001)....

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Journal ArticleDOI
TL;DR: Evidence is provided that the behaviour of trap‐building predators is not stereotypic or fixed as was once commonly accepted, rather it can vary greatly, depending on the individual's internal state and its interactions with external environmental factors.
Abstract: Foraging theory was first developed to predict the behaviour of widely-foraging animals that actively search for prey. Although the behaviour of sit-and-wait predators often follows predictions derived from foraging theory, the similarity between these two distinct groups of predators is not always obvious. In this review, we compare foraging activities of trap-building predators (mainly pit-building antlions and web-building spiders), a specific group of sit-and-wait predators that construct traps as a foraging device, with those of widely-foraging predators. We refer to modifications of the trap characteristics as analogous to changes in foraging intensity. Our review illustrates that the responses of trap-building and widely-foraging predators to different internal and external factors, such as hunger level, conspecific density and predation threat are quite similar, calling for additional studies of foraging theory using trap-building predators. In each chapter of this review, we summarize the response of trap-building predators to a different factor, while contrasting it with the equivalent response characterizing widely-foraging predators. We provide here evidence that the behaviour of trap-building predators is not stereotypic or fixed as was once commonly accepted, rather it can vary greatly, depending on the individual's internal state and its interactions with external environmental factors.

143 citations


Cites background from "Costs of aggregation: shadow compet..."

  • ...Exploitation also increases with density in its special form of ‘‘shadow competition’’ (one TB predator catches the moving prey before it encounters other predators; e.g. Wilson, 1974; Lubin et al., 2001; Rao, 2009)....

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Journal ArticleDOI
TL;DR: This work uses simulation models to demonstrate how predation risk and food gains differ for different positions within a group, and develops a novel model of the trade-off between the costs and the benefits of occupying different positions and predicts the optimal location for an animal in a group.
Abstract: Animal groups are highly variable in their spatial structure, and individual fitness is strongly associated with the spatial position of an animal within a group. Predation risk and food gains are often higher at the group peripheries; thus, animals must trade-off predation costs and foraging benefits when choosing a position. Assuming this is the case, we first use simulation models to demonstrate how predation risk and food gains differ for different positions within a group. Second, we use the patterns from the simulation to develop a novel model of the trade-off between the costs and the benefits of occupying different positions and predict the optimal location for an animal in a group. A variety of testable patterns emerge. As expected, increasing levels of satiation and vulnerability to predators and increasing predation risk result in increased preferences for central positions, likely to lead to increased competition or more tightly packed groups. As food availability increases, individuals should first prefer center positions, then edge, and returning to central positions under highest food levels. Increasing group size and/or density lead to more uniform preferences across individuals. Finally, we predict some situations where individuals differing in satiation and vulnerability prefer a range of different locations and other situations where there is an abrupt dichotomy between central and edge positions, dependent on the levels of monopolization of food by peripheral individuals. We discuss the implications of our findings for the structure of groups and the levels of competition within them and make suggestions for empirical tests.

75 citations


Cites background from "Costs of aggregation: shadow compet..."

  • ...In high density groups, only peripheral individuals 11 can forage successfully, but in low density groups, some prey items reach the group 12 centre (Lubin et al. 2001)....

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  • ...Simulation of predation risk and foraging gains 17 Previous authors have modeled how predation risk and foraging gains change as a 18 function of the distance from the centre of a group (Linton et al. 1991; Bumann et al. 19 1997; Lubin et al. 2001)....

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  • ...Burrowing spiders 1 (Seothyra henscheli) show increased growth rates when they are positioned at the 2 edge of a group (Lubin et al. 2001)....

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Journal ArticleDOI
TL;DR: This study is the first to demonstrate shadow competition in a vertebrate species, but has also shown that territorial defence may modify the consequences of shadow competition when densities are high and there is strong competition for the acquisition of a territory.
Abstract: Shadow competition occurs in a group of sit-and-wait predators when those closer to a source of mobile prey reduce the feeding success of those further from the prey source. It was examined in territorial juvenile sea trout Salmo trutta in a small stream. The fry formed groups of two to six fish with adjacent territories and a social hierarchy within each group. It was hypothesized that: (i) as group size increased, the mean number of prey eaten per fish within a group decreased and the variability in prey consumption between fish increased; (ii) prey consumption by individual fish decreased with increasing distance from the food source; (iii) group size increased as the mean water velocity immediately upstream from a group, and hence potential drifting food, increased. Five groups of fry were fed on small shrimps released upstream from each group at a rate of one every 15 s over a 10 min period, this procedure being repeated over 5 days to provide five replicates per group. Experiments were performed three times in 1967, 1969 and 1974 to provide information on 45 groups of fry. The first and third hypotheses were supported, but the second was only partially supported. In 1967 and 1969, territory size and shrimp consumption by individual fry decreased with increasing distance from the food source. This also occurred in 1974, except during a critical period for survival when fry density was exceptionally high with large numbers of sea trout lacking territories. This resulted in sea trout fry with the largest territories eating fewer shrimps than those with medium-sized territories because they spent more time defending their territories against sea trout lacking territories. This study is the first to demonstrate shadow competition in a vertebrate species, but has also shown that territorial defence may modify the consequences of shadow competition when densities are high and there is strong competition for the acquisition of a territory.

66 citations

References
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Journal ArticleDOI
TL;DR: A comparison of prey capture efficiency of colonial M. incrassata with that of solitary M. atascadero shows that the ricochet effect provides an increase in efficiency across all size classes of prey.
Abstract: Increased prey capture efficiency in colonial spiders is a consequence of the “ricochet effect”, as prey are captured after they bounce off several webs in succession In this study, the prey capture of three species of colonial spiders in the genus Metepeira from Mexico are compared These species, from different habitats, show varying levels of social organization (group size and withingroup spacing) that affect prey capture from ricochets Metepeira sp a (a presumed new species tentatively named atascadero) from desert grassland habitats, occur solitarily or in small groups, and gain little from prey ricochets: prey capture rates are low and variance in prey captured/spider is high M spinipes, from mesic agricultural sites, occur in groups of 10–150, and show a ricochet effect resulting in more and larger prey, and reduced variance in capture rate M incrassata, from tropical rainforest/agricultural sites, occur in large colonies of hundreds to thousands of individuals, and show a similar ricochet effect The ricochet effect does not influence taxonomic composition of prey in either M atascadero or M spinipes, but does in tropical M incrassata This result, however, is primarily due to the capacity of certain taxa (eg, Lepidoptera), more common in the tropics, to escape more easily from spider webs A comparison of prey capture efficiency of colonial M incrassata with that of solitary M atascadero shows that the ricochet effect provides an increase in efficiency across all size classes of prey

99 citations

Journal ArticleDOI
TL;DR: It is shown that group-living spiderlings capture less food than do solitary spiderlings, and the main benefit of group living is likely to be the reduction of the cost of web building when spiderlings take advantage of webs built by larger conspecifics.

87 citations

Journal ArticleDOI
01 Oct 1975-Ecology
TL;DR: Cost-benefit analysis for different positions within the colony suggests no single optimal position on the basis of prey capture and the construction, maintenance, and defense of orbs, which suggests relatively permanent aggregations.
Abstract: A bstract. Orb-weaving spiders Metabus gravidus (Cambridge) (Araneae: Araneidae) spin, maintain, and defend individual webs. Colonies of 5-70 spiders form multilayered meshes of orbs connected by common support lines over mountain streams at the study site, Monteverde, Costa Rica. Habitat selection, preference for spinning within a group, and maintenance of year-round population levels result in relatively permanent aggregations. Grouped spiders can build orbs in areas of high prey density more efficiently than single spiders, but they do not cooperate in web construction or food capture. Activity patterns relate closely to prey abundance and also depend upon individual energy demands. Cost-benefit analysis for different positions within the colony suggests no single optimal position on the basis of prey capture and the construction, maintenance, and defense of orbs. Colonies are maintained by the composite movements of unspecialized individuals, which benefit in the exploitation of resources not available to solitary spiders.

87 citations

Journal ArticleDOI
TL;DR: The parameters of prey capture and competition are remarkably simple to measure in the larval ant lion (Neuroptera: Myrmeliontidae) and it is shown that the searching capacity, prey size range, and success of capturing prey within this range can all be measured by taking the diameter of the pit.
Abstract: The parameters of prey capture and competition are remarkably simple to measure in the larval ant lion (Neuroptera: Myrmeliontidae). There exists a thirteen- to fifty-fold difference in food availability (mg. prey available/mg. predator) between the largest and smallest individuals. The larva grows to the optimal size as a food getter, but no larger before metamorphosing. A special distribution of ant lions minimizing competition is hypothesized and observed. The ant lion does not conform to the concepts of limiting similarity or niche variation. THE ANT LION has long been a naturalist's delight in its exotic method of prey captLre. The larva digs a conical pit in loose sand and lies buried at the vertex. When an insect falls in, the ant lion attempts to grab it with its long ice-tong-shaped mandibles. If it fails and the prey starts to scramble up the side of the pit, the ant lion tosses sand with violent flips of its head, creating land slides that carry the prey back into its jaws. After extracting the fluids, it throws the carcass out of the pit, along the rim. Interest in the ant lion died together with interest in simple natural history, for the last nontaxonomic paper was Wheeler's (1930) monograph. What has not been appreciated is the ant lion's elegance for ecological study. Here I show that the searching capacity, prey size range, and success of capturing prey within this range can all be measured by taking the diameter of the pit; the nutritional history, prey size distribution and abundance by collecting the carcasses around the rim of the pit; and the competitive effect of neighbors, in percent prey intercepted, by the spatial configuration of the pits. Also, while not studied here, it is worth noting that when the animal disperses it does so half submerged in the sand, leaving an easily visable trough as a record of its movements.

83 citations


"Costs of aggregation: shadow compet..." refers background in this paper

  • ...One form of exploitative competition among group members, 'shadow' competition (Wilson 1974), occurs when sedentary foragers closer to the source of mobile prey reduce the foraging success of those further from the prey source....

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