Predation Costs Research Articles

The Cost Of Transportation In Pre-Industrial Europe

In pre-industrial Europe, rising productivity both in agriculture and in industry depended on the expansion of trade, and the expansion of trade depended in turn on the reduction of trading costs. An important component of trading costs—for some goods the most important—was the cost of transportation. This had two elements: the cost of predation and the cost of carriage. This paper examines these two elements and how they changed over time. It also discusses the relative importance in lowering the cost of transportation of organizational change and technological progress.

Variation in predation costs with Chiastocheta egg number on Trollius europaeus: how many seeds to pay for pollination?

Summary1. In obligate plant/seed parasite–pollinator mutualisms, the plant is exclusively pollinated by an insect whose larvae are specific seed predators. Hence, outcomes of the interaction for the plant can vary with the number of eggs laid and the number of seeds eaten per larva.2. In the work reported here, predation by Chiastocheta larvae on seeds of Trollius europaeus was analysed as a function of the number of eggs laid on the flower. Flowers with an increasing number of eggs were bagged in three populations and seeds were counted after the end of larval predation, in order to assess whether there was competition among larvae.3. Seed predation on single‐egg flowers was high and variable (mean per population ranging from 15 to 40% of the developed seeds). Seed predation increased weakly with increasing egg load and was lower than gross seed production (always < 85%) whatever the number of eggs laid. This corresponds to a strong decrease in seed consumption per larva with increasing egg load, i.e. severe larval competition for resources.4. The results suggest that both interference among Chiastocheta larvae and carpel dehiscence may protect T. europaeus seeds from total predation. Estimates of seed predation based on egg load observed in 20 natural populations in the French Alps typically ranged from 30 to 60%. The interaction was always beneficial for the plant and there was no risk of total seed destruction by Chiastocheta larvae, favouring stability of the mutualism.

THE EVOLUTION OF BODY ARMOR IN MAMMALS: PLANTIGRADE CONSTRAINTS OF LARGE BODY SIZE

Predictions associated with opposing selection generating minimum variance in basal metabolic rate (BMR) in mammals at a constrained body mass (CBM; 358 g) were tested. The CBM is presumed to be associated with energetic constraints linked to predation and variable resources at intermediate sizes on a logarithmic mass scale. Opposing selection is thought to occur in response to energetic constraints associated with predation and unpredictable resources. As body size approaches and exceeds the CBM, mammals face increasing risks of predation and daily energy requirements. Fast running speeds may require high BMRs, but unpredictable and low resources may select for low BMRs, which also reduce foraging time and distances and thus predation risks. If these two selection forces oppose each other persistently, minimum BMR variance may result. However, extreme BMR outliers at and close to the CBM should be indicative of unbalanced selection and predator avoidance alternatives (escapers vs. defenders), and may therefore provide indirect support for opposing selection. It was confirmed that body armor in defenders evolves at and above the CBM, and armored mammals had significantly lower BMRs than their nonarmored counterparts. However, analyses comparing the BMR of escapers—the fastest nonarmored runners (Lagomorpha)—with similar-sized counterparts were inconclusive and were confounded by limb morphology associated with speed optimization. These analyses suggest that the risks and costs of predation and the speed limitations of the plantigrade foot may constrain the evolution of large body sizes in plantigrade mammals.Corresponding Editor: T. Garland Jr.

BOOM-OR-BUST DEVELOPMENT OF A PREDATORY MOSQUITO IN TEMPORARY AQUATIC HABITATS OF FLORIDA, USA

Hypotheses concerning the developmental plasticity of species that occupy temporary versus permanent aquatic habitats were tested on Psorophora howardii, a mosquito whose predatory larvae occur in ditches flooded for brief periods to irrigate citrus trees in Florida. Responses of P. howardii to experimental variations in temperature and prey availability were compared to those of Toxorhynchites rutilus, a mosquito species whose predatory larvae occupy the relatively permanent waters of treeholes. As predicted, the permanent-water species was more variable in developmental time, and some results suggested that the temporary-habitat predator was more plastic in weight at pupation. Survival of P. howardii was reduced when prey were scarce, and in the complete absence of prey this species died 7–12 times faster than T. rutilus, probably as a result of the higher energy costs of active versus ambush predation. Adults of P. howardii mated precociously after emergence in cages and lived, on average, only 6–11 da...

ABIOTIC VS. BIOTIC INFLUENCES ON HABITAT SELECTION OF COEXISTING SPECIES: CLIMATE CHANGE IMPACTS?

Species are commonly segregated along gradients of microclimate and veg- etation. I explore the question of whether segregation is the result of microhabitat parti- tioning (biotic effects) or choice of differing microclimates (abiotic effects). I explored this question for four ground-nesting bird species that are segregated along a microclimate and vegetation gradient in Arizona. Birds shifted position of their nests on the microhabitat and microclimate gradient in response to changing precipitation over nine years. Similarly, annual bird abundance varied with precipitation across 12 yr. Those shifts in abundance and nesting microhabitat with changing precipitation demonstrate the importance of abiotic influences on bird distributions and habitat choice. However, nest-site shifts and micro- habitat use also appear to be influenced by interactions among coexisting species. Moreover, shifts in habitat use by all species caused nest predation (i.e., biotic) costs that increased with increasing distance along the microclimate gradient. These results indicate that abiotic and biotic costs can strongly interact to influence microhabitat choice and abundances of coexisting species. Global climate change impacts have been considered largely in terms of simple distributional shifts, but these results indicate that shifts can also increase biotic costs when species move into habitat types for which they are poorly adapted or that create new biotic interactions.

On the Use of the Time Axis for Ecological Separation: Diel Rhythms as an Evolutionary Constraint

On the Use of the Time Axis for Ecological Separation: Diel Rhythms as an Evolutionary Constraint

SCREAMING AS A STRATEGY TO REDUCE THE PREDATION RISK INCURRED BY BEGGING?

AbstractFollowing the theory of parent-offspring conflict parents request from their offspring an honest signal of food requirement to optimally adjust feeding rate. For this purpose, offspring display a highly informative signalling system, begging vocalisation, for which the conspicuousness to predators maintains honesty, since only hungry offspring are willing to take this risk. The risk of predation incurred by begging activities challenges our understanding of how begging vocalisation could evolve towards a high degree of noisiness. A solution to this apparent paradox resides in the possibility that alongside the evolution of begging, birds also evolved strategies that reduce the risk of being depredated. Following the ornithological literature nestlings scream in the presence of a predator to frighten it, induce parents to rescue them and siblings to flee from the nest and hide in the vegetation. I therefore propose the hypothesis that nestling screaming behaviour evolved as a means of reducing the risk of predation incurred by conspicuous begging. Comparative analyses supported the prediction postulating that species in which nestlings scream in the presence of a predator produce begging calls that are more conspicuous to predators than calls of non-screaming species. This suggests that the predation cost of begging lies not only in terms of predation per se but also in the requirement of anti-predator strategies.

Nutritive cost of intraguild predation on eggs of Coccinella septempunctata and Adalia bipunctata (Coleoptera: Coccinellidae)

Coccinella septempunctata was approximately 20% more reluctant to eat the eggs of Adalia bipunctata than the reverse. In addition, fourth instar larvae of C. septempunctata failed to complete their development on a diet of A. bipunctata eggs and only 30% of those of A. bipunctata completed their development on a diet of C. septempunctata eggs, and the survivors took nearly 2 times as long as those fed aphids. This is an indication that the costs of intraguild predation might outweigh the benefits.

On the move: how and why animals travel in groups

Getting from here to there may be simple for one individual. But as any parent, scout leader, or CEO knows, herding a whole troop in one direction is a lot more complicated. Who leads the group? Who decides where the group will travel, and using what information? How do they accomplish these tasks? On the Move addresses these questions, examining the social, cognitive and ecological processes that underlie patterns and strategies of group travel. Chapters discuss how factors such as group size, resource distribution and availability, the costs of travel, predation, social cohesion and cognitive skills affect how individuals as well as social groups exploit their environment. Most chapters focus on field studies of a wide range of human and nonhuman primate groups, from squirrel monkeys to Turkana pastoralists, but chapters covering group travel in hyenas, birds, dolphins and bees provide a broad taxonomic perspective and offer new insights into comparative questions, such as whether primates are unique in their ability to coordinate group-level activities.

The economic costs of wildlife predation on livestock in Gokwe communal land, Zimbabwe

In areas bordering wildlife reserves in Zimbabwe, agro‐pastoralists suffer livestock depredation by wild carnivores. However, the economic value of these losses, and therefore the levels of compensation required has never been calculated. Between January 1993 and June 1996 in a 33‐km2 area of Gokwe communal land bordering the Sengwa Wildlife Research Area, 241 livestock were killed by wild carnivores. Baboons (Papio ursinus Kerr), lions (Panthera leo Linnaeus) and leopards (P. pardus Linnaeus) were the most serious predators, contributing 52%, 34% and 12% of kills, respectively. Baboons only killed young goats (Capra hircus Linnaeus) and sheep (Ovis aries Linnaeus) by day, while lions and leopards jumped into fortified kraals at night and killed cattle (Bos indicus Linnaeus), donkeys (Equus asinus Linnaeus) and smallstock. In 1995, predators killed 5% of livestock holdings, double that recorded by other African studies. The annual total value of losses depended upon the degree of lion predation on the most valuable species, cattle and donkeys. The average annual loss per livestock‐owning household was US$13, or 12% of each household's net annual income. Losses could be reduced by improving kraal defences against lion and leopard predation in the dry season, when attacks were most common.

Foraging under Multiple Costs: The Importance of Predation, Energetic, and Assessment Error Costs to a Desert Forager

We investigated spatial and temporal variation in the use of resource patches by Chaetodipus penicillatus by documenting changes in foraging activity over several seasons, under two moon phases, and in two resource patch types. In particular, we examined the influence of nocturnal illumination (a surrogate for predation risk) and ambient temperature on: (1) foraging effort (which is inversely proportional to the giving-up density, GUD), and (2) GUD equality, i.e. the ability of foragers to accurately assess patch quality by equalizing heterogeneous resource patches to the same GUD. There were significant positive relationships between foraging effort and relative GUD equality, ambient temperature and foraging effort, and ambient temperature and GUD equality. In contrast, despite having a strong effect at the beginning of our study, moonlight did not have a consistent or significant impact on foraging effort and GUD equality when analyzed over several seasons. Our results indicate that as energetic or predation costs decline, foraging effort rises, which in turn, leads to an increase in GUD equality and a reduction in assessment error costs. This increased harvesting equality is due to both enhanced functional harvest rates and increased accuracy of patch assessment by foragers as more time is spent within a patch. In addition, predation risk and energetic costs appeared to switch in relative importance in C. penicillatus over the course of several seasons. These results emphasize the importance of considering multiple foraging costs and their additive effects in studies of foraging and patch use.

The relationship between signal quality and physical condition: is sexual signalling honest in the three-spined stickleback?

Honest sexual signalling requires that the level of advertisement reveals mate quality. In the three-spined stickleback, Gasterosteus aculeatus, females base their mate choice mainly on the intensity of the males' red breeding coloration. Different results have, however, been obtained on the relationship between red breeding coloration and physical condition. In this study, the relationship was curvilinear in a natural population, with males in good and poor condition (measured as lipid content) having larger red areas than males of intermediate condition. By manipulating food intake and thus male condition prior to breeding, I further show that poor condition can induce an increase in signalling effort. This effect was further strengthened when the predation cost of signalling was increased by exposing the males to predators. This suggests that the reason for the high signalling effort of males in poor condition is their low probability of future reproduction and thus lower cost of signalling in terms of loss of future reproductive opportunities. Males in poor condition signal as a terminal effort and take larger risks and invest more in current reproduction than males in good condition. Finally, I discuss whether an effect of decreasing residual reproductive value on signalling effort could result in the breakdown of the honesty of the signal.

Predation costs associated with parental care in the golden egg bug Phyllomorpha laciniata (Heteroptera: Coreidae)

Parental care will evolve when the benefits in terms of offspring survival are greater than the costs to the parents. Costs have been classified as reproductive and survival costs. Greater predation rates among adults caring for young are included among survival costs, but few studies have been able to demonstrate such a link. Among golden egg bugs (Phyllomorpha laciniata) females can lay eggs on plants, males, or other females; adults carry the eggs until they hatch. Using an experimental approach, we show that adults carrying eggs are more likely to be preyed upon by birds than adults without eggs. These greater predation rates may be the consequence of adults being more easily detected by predators when carrying eggs, and/or to their reduced ability to escape, as most eggs are carried over the wings, making it impossible for individuals carrying eggs to fly. Despite these survival costs to carrying adults, caring for eggs is favored by natural selection because it greatly increases the survival of offspring.

Energetic Cost of Predation: Aerobic Metabolism during Prey Ingestion by Juvenile Rattlesnakes, Crotalus durissus

Departamento de Zoologia Institute de Biociencias Universidade Estadual Paulista, C. P. 199, CEP 33506-900, Rio Claro, SP

The effect of predation on begging-call evolution in nestling wood warblers

I combined a comparative study of begging in ground- and tree-nesting wood warblers (Parulidae) with experimental measures of the predation costs of warbler begging calls. Throughout their development, ground-nesting warbler nestlings had significantly higher-frequency begging calls than did tree-nesting warblers. There was also a trend for ground-nesting birds to have less rapidly modulated calls. There were no consistent associations between nesting site and the amplitude of the calls. Using miniature walkie-talkies hidden inside artificial nests, I reciprocally transplanted the begging calls of 5- and 8-day-old black-throated blue warblers,Dendroica caerulescens(tree-nesting) and ovenbirds,Seiurus aurocapillus(ground-nesting) and measured the corresponding changes in rates of nest predation. For the begging calls of 8-day-old nestlings, but not those of 5-day-olds, the calls of the tree-nesting species coming from ground nests incurred greater costs than did the calls of ground nesters. The reciprocal transplant had little effect on the rate of predation. Tooth imprints on clay eggs placed in artificial nests indicated that eastern chipmunks,Tamias striatus, were responsible for the increased cost of begging for black-throated blue calls coming from the ground. These data suggest that nest predation may be responsible for maintaining some of the interspecific differences in the acoustic structure of begging calls.

Food availability and the nocturnal vs. diurnal foraging trade‐off in juvenile salmon

1.Much attention has been devoted to explaining the spatial distribution of foraging animals, but rather little to their temporal distribution (i.e. whether they are diurnal, nocturnal or crepuscular). Many animals face predictable diel cycles of food availability or predation risk, and so the approach of measuring the relative ratio of mortality risk to food gained (the ‘minimize μ/f’ rule) can be applied equally as well to different time periods of the day as to alternative food patches or habitats.2.This method is used here to investigate the diel activity patterns of juvenile Atlantic salmon, which have previously been shown to become increasingly biased towards nocturnal activity in winter, hiding for much of the day in streambed refuges. Calculations based on published data show that nocturnal foraging in winter is far safer per unit of food obtained than is diurnal, despite greatly reduced food capture efficiency at night‐time light levels.3.Using an automated activity monitoring system based on passive integrated transponder (PIT) tags, this study shows that winter diel activity patterns in salmon are dependent on food availability. A change in food density led to a parallel change in time spent in the refuge, but (as predicted by the μ/frule) the effect was greatest at the time of day with the least favourable ratio of predation cost to feeding benefit. Thus an experimental increase in food availability led to a 16% reduction in time spent in nocturnal foraging but a 98% reduction in time spent foraging by day, with fish spending only 0·6% of the daylight hours out of the refuge at the highest food density.4.However, brief daytime foraging bouts had a major impact on growth rates (presumably because feeding efficiency was much greater in daylight), especially when food was scarce. Daytime feeding was thus profitable in terms of rapid food acquisition but normally suboptimal in terms of risk of predation.5.Daily activity patterns are therefore suggested to be the result of a complex trade‐off between growth and survival, which takes account of diel fluctuations in food availability, food capture efficiency and predation risk; individual variation in the extent of diurnal feeding in salmon may result from state‐dependent differences in the benefits of rapid feeding and growth.

Producers and Predators

This paper explores a series of general‐equilibrium models in which people can choose to be either producers or predators, and in which producers can allocate their resources either to production or to guarding their production against predators. The analysis shows how the ratio of predators to producers and the social cost of predation depend on the technology of predation, on the interpersonal distribution of productive resources, and in a fundamental way on whether the decision to allocate resources to guarding against predators is made individually or collectively.

The functional response of oystercatchers (Haematopus ostralegus) searching for cockles (Cerastoderma edule) by touch

1. We describe the functional response of oystercatchers (Haematopus ostralegus L.) searching for cockles (Cerastoderma edule L.) by touch, using a multiple‐prey version of the disc equation developed by Charnov (1976). 2. The model includes probabilistic time costs associated with the successful and unsuccessful handling of prey, seasonal changes in the flesh content of prey, and factors that affect prey availability. The encounter rate with cockles is estimated using a simple random search model. This model calculates the likelihood that a bird would locate a cockle buried in the sand per unit of time spent searching, as a function of the touch area of buried cockles (the largest cross‐sectional area of the shell enlarged by the surface area of the bill‐tip) and the bird’s probing rate. 3. Prey profitability increased with cockle size, and the model predicted birds should preferentially take cockles > 15 mm in length to maximize their rate of energy intake. The birds showed a systematic seasonal departure from the model’s predictions. During late winter, the observed and predicted maximum intake rates for individual birds were comparable. However, the mean size of cockles observed being taken by the birds was consistent with the predicted mean size taken by a bird, including all size classes in its diet, rather than the predicted size for a bird taking only size classes > 15 mm (for a bird maximizing its intake rate). During early winter, observed intake rates were lower than predicted values for a bird feeding unselectively, suggesting birds either reduced their searching effort, preferentially ignored the larger, more profitable size classes, or experienced longer time costs. The lower than expected intake rates observed during early winter resulted from prey choice: birds preferentially ignored the larger, more profitable size classes. 4. Data presented in this paper suggest that birds attempting to maximize their intake rate incur significant costs, in addition to those associated with searching for and handling prey, which are included in the model. Such costs could include a risk of bill damage when attacking large cockles, an increased risk of parasitism associated with large cockles, or a mass‐dependent metabolic or predation cost incurred by birds storing any excess ingested food in the form of fat. 5. A simple graphical model is presented to show how such costs, together with the need to achieve a given intake rate to avoid starvation, might interact to determine optimal intake rates. Within this framework, the maximum intake rate predicted by Charnov’s model should be viewed as a means of describing the constraints on intake rates, rather than as an explicit optimality model. Depending on energy demands and the costs of maintaining a given intake rate, birds could experience a range of optimal intake rates, but only under certain conditions would the optimal intake rate be the maximum. This has implications for models of the dispersion of predators across a gradient of resource densities, and behaviour‐based models of population dynamics, both of which implicitly assume that a predator would maximize its fitness by maximizing its rate of energy intake.

Nestling cuckoos, Cuculus canorus, exploit hosts with begging calls that mimic a brood

Nestling cuckoos, Cuculus canorus , eject host eggs or young from the nest and are then raised alone by the hosts. Using reed warblers, Acrocephalus scirpaceus , as hosts, we investigated how the single cuckoo chick can command the same provisioning rate as a whole brood of host young. Large size alone is not sufficient to stimulate adequate provisioning because single blackbird, Turdus merula , or song thrush, T. philomelos , chicks of the same mass as a cuckoo were fed at a lower rate. Our experiments show that the key stimulus is the cuckoo chick9s rapid begging call (‘si, si, si, si ...’), which sounds remarkably like a whole brood of host chicks, and which it matched in calling rate. When single blackbird or song thrush chicks were accompanied by loudspeakers that broadcast either cuckoo begging calls or calls of a brood of reed warblers, the hosts increased their provisioning rate to that for a cuckoo chick. We suggest that the cuckoo needs vocal trickery to stimulate adequate care to compensate for the fact that it presents a visual stimulus of just one gape.

Receptor noise as a determinant of colour thresholds.

Inferences about mechanisms at one particular stage of a visual pathway may be made from psychophysical thresholds only if the noise at the stage in question dominates that in the others. Spectral sensitivities, measured under bright conditions, for di-, tri-, and tetrachromatic eyes from a range of animals can be modelled by assuming that thresholds are set by colour opponency mechanisms whose performance is limited by photoreceptor noise, the achromatic signal being disregarded. Noise in the opponency channels themselves is therefore not statistically independent, and it is not possible to infer anything more about the channels from psychophysical thresholds. As well as giving insight into mechanisms of vision, the model predicts the performance of colour vision in animals where physiological and anatomical data on the eye are available, but there are no direct measurements of perceptual thresholds. The model, therefore, is widely applicable to comparative studies of eye design and visual ecology.