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At least 487 records · Page 27Linked to original sources
PubMed2004

Should "handled" prey be considered? Some consequences for functional response, predator-prey dynamics and optimal foraging theory.

Predator-prey models consider those prey that are free. They assume that once a prey is captured by a predator it leaves the system. A question arises whether in predator-prey population models the variable describing prey population shall consider only those prey which are free, or both free and handled prey together. In the latter case prey leave the system after they have been handled. The classical Holling type II functional response was derived with respect to free prey. In this article we derive a functional response with respect to prey density which considers also handled prey. This functional response depends on predator density, i.e., it accounts naturally for interference. We study consequences of this functional response for stability of a simple predator-prey model and for optimal foraging theory. We show that, qualitatively, the population dynamics are similar regardless of whether we consider only free or free and handled prey. However, the latter case may change predictions in some other cases. We document this for optimal foraging theory where the functional response which considers both free and handled prey leads to partial preferences which are not observed when only free prey are considered.

Animals↗
PubMed2004

What determines probability of surviving predator attacks in bird migration?: the relative importance of vigilance and fuel load.

Migrating birds must accumulate fuel during their journeys and this fuel load should incur an increased risk of predation. Migratory fuelling should increase individual mass-dependent predation risk for two reasons. First, acquisition costs are connected to the increased time a bird must spend foraging to accumulate the fuel loads and the reduced predator detection that accompanies foraging. Second, birds with large fuel loads have been shown to suffer from impaired predator evasion which makes them more vulnerable when actually attacked. Here, I investigate the relative importance of these two aspects of mass-dependent predation risk and I have used published data and a hypothetical situation for a foraging bird to investigate how much migratory fuelling in terms of escape performance and natural variation in predator detection contribute to individual risk during foraging. Results suggest that for birds foraging close to protective cover the negative impact of fuel load on flight performance is very small, whereas variation in time to predator detection is of great importance for a bird's survival. However, the importance of flight performance for predation risk increases as the distance to cover increases. Hence, variation in predator detection (and vigilance) probably influences individual survival much more than migratory fuel load and consequently, to understand risk management during migration studies that focus on vigilance and predator detection during fuelling are much needed.

Animal Migration↗
PubMed2005

Searching on patch networks using correlated random walks: space usage and optimal foraging predictions using Markov chain models.

We describe a novel representation of a discrete correlated random walk as the transition matrix of a Markov chain with the displacements as the states. Such a representation makes it possible to utilize results from the theory of absorbing Markov chains, to make biologically interesting predictions without having to resort to Monte Carlo simulations. Our motivation for constructing such a representation is to explore the relationship between the movement strategy of an animal searching for resources upon a network of patches, and its consequent utilization of space and foraging success. As an illustrative case study, we have determined the optimal movement strategy and the consequent usage of space for a central place forager utilizing a continuous movement space which is discretized as a hexagonal lattice. The optimal movement strategy determines the size of the optimal home range. In this example, the animal uses mnemokinesis, which is a sinuosity regulating mechanism, to return it to the central place. The movement strategy thus refers to the choice of the intrinsic path sinuosity and the strength of the mnemokinetic mechanism. Although the movement space has been discretized as a regular lattice in this example, the method can be readily applied to naturally compartmentalized movement spaces, such as forest canopy networks. This paper is thus an attempt at incorporating results from the theory of random walk-based animal movements into Foraging Theory.

Animals↗
PubMed1985

On the optimality of coarse behavior rules.

Animal behavior can be characterized by the degree of responsiveness it has to variations in the environment. Some behavior rules lead to fine-tuned responses that carefully adjust to environmental cues, while other rules fail to discriminate as carefully, and lead to more inflexible responses. In this paper we seek to explain such inflexible behavior. We show that coarse behavior, behavior which appears to be rule-bound and inflexible, and which fails to adapt to predictable changes in the environment, is an optimal response to a particular type of uncertainty we call extended uncertainty. We show that the very variability and unpredictability that arises from extended uncertainty will lead to more rigid and possibly more predictable behavior. We relate coarse behavior to the failures to meet optimality conditions in animal behavior, most notably in foraging behavior, and also address the implications of extended uncertainty and coarse behavior rules for some results in experimental versus naturalistic approaches to ethology.

Adaptation, Physiological↗
PubMed1998

Singular homoclinic bifurcations in tritrophic food chains.

The Rosenzweig-MacArthur food chain model is proved to have homoclinic orbits. The proof is in two steps. First, we use a geometric approach based on singular perturbation and detect singular homoclinic orbits as well as parameter combinations for which these orbits exist. Second, we show, numerically, that for slightly different parameter values there exist also nonsingular homoclinic orbits that tend toward the singular ones when the time responses of the three trophic levels are extremely diversified. The analysis is performed without exploiting too deeply the mathematical structure of the Rosenzweig-MacArthur model. This is done intentionally, to assist readers interested more in the methodology than in the application to food chains.

Animals↗
PubMed2000

Effect of aging on manipulative behavior in the cuttlefish, sepia.

The cuttlefish is an active predator that is able to catch crabs of a size that is large relative to its own. The capture is followed by a complex manipulative behavior leading to paralysis of the prey by injection of a cephalotoxin. This manipulative behavior is relatively stereotyped, and earlier research has shown that the cuttlefish concentrates its bite on the articular basi-ischiocoxopodite membrane of the crab's fifth pair of pereiopods. By placing mechanical constraints on the base of the fifth pereiopods, we were able to demonstrate that this manipulative behavior presents a marked degree of stereotypy but is not rigidly fixed. Substantial behavioral differences, however, were observed between subadult and senescent cuttlefish. The existence of a reduction in behavioral flexibility in the older animals in reaction to the constraints is discussed.

Aging↗
PubMed1998

Role of claws and pads in taking and holding food in cats.

In order to investigate the role of claws and pads in taking food the planter surface of the distal forelimb paw was recorded with a conventional video camera. The claws were involved in the great majority of trials. The morsel of food may be taken by piercing with one claw (rarely two) either alone or by pressure against a digital pad; support by pressure from another claw was also common, while pressure between two claws was used more rarely. Another technique was pressure between claws (without piercing) and digital pads. The morsel was also taken without participation of claws by pressure between digital pads and the central pad and more rarely between two digital pads.

Animals↗
PubMed2003

Heart rate and respiration in reptiles: contrasts between a sit-and-wait predator and an intensive forager.

The current study investigated respiration and heart rate in two species of reptiles with distinct behavioral strategies: (1) the Sudan plated lizard (Gerrhosaurus major), a sit-and-wait predator; and (2) the Savanna monitor (Varanus exanthematicus), an intensive forager. It was hypothesized that (a) the plated lizard would not express respiratory sinus arrhythmia, and (b) the monitor, a reptile with behavioral and physiological characteristics similar to mammals, might express respiratory sinus arrhythmia, a pattern previously observed only in mammals. The data demonstrated that although there were strong vagal influences on the heart, respiratory activity was not manifested in the heart rate pattern of the plated lizards. In contrast, the monitor exhibited a reliable ventilatory influence on the heart rate pattern, although the pattern differed from the respiratory sinus arrhythmia observed in mammals. Consistent with the Polyvagal Theory (), the vagal control of the reptilian heart in both species appears to be mediated through the phylogenetically older unmyelinated system, a system that evolved to support metabolic conservation and not social behavior.

Animals↗
PubMed2000

Flexible search behavior in domestic cats (Felis catus): a case study of predator-prey interaction.

Domestic cats (Felis catus) were administered an object permanence task in a novel and a familiar situation to investigate flexibility (i.e., pause behavior and searching by following a path opposite of that taken by the object when it disappeared) in search behavior. Pause and opposite search were assumed to be independent, equiprobable, and randomly exhibited (i.e., random model). The random model predicted that cats would exhibit flexible behavior on 75% of the trials. The results revealed that flexible behavior occurred on 69% of the trials in the novel situation, but only on 52% of the trials in the familiar setting in which pauses were less frequent and shorter than in the novel situation. Thus, the random model provided a good fit of the data in the novel but not in the familiar situation. It is argued that pause and opposite search reflect decision processes when cats are dealing with the behavior of prey that has disappeared while being pursued.

Analysis of Variance↗
PubMed2004

Iberian rock lizards (Lacerta monticola) assess short-term changes in predation risk level when deciding refuge use.

Prey might assess that risk level estimated in the first encounter with a predator was fixed in subsequent responses, whereas prey using flexible behavior would track short-term changes in risk. The authors examined, in the field, refuge use of Iberian rock lizards (Lacerta monticola) after simulated predator attacks and tested (a) how risk was assessed when multiple sources of risk were present simultaneously, (b) how short-term changes in risk level of successive attacks affected refuge use, and (c) whether the interval between attacks was important, insofar as attacks were considered to be coming from the same or different predators. Results suggest that lizards have a flexible estimate of risk that is based on multiple sources and flexibly dependent on previous estimates.

Animals↗
PubMed2001

Multiple benefits of gregariousness cover detectability costs in aposematic aggregations.

Understanding the early evolution of aposematic (warning) coloration has been a challenge for scientists, as a new conspicuous morph in a population of cryptic insects would have a high predation risk and would probably die out before local predators learnt to avoid it. Fisher presented the idea of aggregation benefit through the survival of related individuals; however, his theory has been strongly debated as the mechanisms that favour grouping have never been explored experimentally with the incorporation of detectability costs. Here we create a comprehensive 'novel world' experiment with the great tit (Parus major) as a predator to explore simultaneously the predation-related benefits and costs for aposematic aggregated prey, manipulating both group size and signal strength. Our results show that grouping would have been highly beneficial for the first aposematic prey individuals surrounded by naive predators, because (1) detectability risk increased only asymptotically with group size; (2) additional detectability costs due to conspicuous signals were marginal in groups; (3) even naive predators deserted the group after detecting unpalatability (dilution effect); and (4) avoidance learning of signal was faster in groups. None of these mechanisms require kin selection.

Animals↗
PubMed2003

Rapid evolution drives ecological dynamics in a predator-prey system.

Ecological and evolutionary dynamics can occur on similar timescales. However, theoretical predictions of how rapid evolution can affect ecological dynamics are inconclusive and often depend on untested model assumptions. Here we report that rapid prey evolution in response to oscillating predator density affects predator-prey (rotifer-algal) cycles in laboratory microcosms. Our experiments tested explicit predictions from a model for our system that allows prey evolution. We verified the predicted existence of an evolutionary tradeoff between algal competitive ability and defence against consumption, and examined its effects on cycle dynamics by manipulating the evolutionary potential of the prey population. Single-clone algal cultures (lacking genetic variability) produced short cycle periods and typical quarter-period phase lags between prey and predator densities, whereas multi-clonal (genetically variable) algal cultures produced long cycles with prey and predator densities nearly out of phase, exactly as predicted. These results confirm that prey evolution can substantially alter predator-prey dynamics, and therefore that attempts to understand population oscillations in nature cannot neglect potential effects from ongoing rapid evolution.

Animals↗
PubMed2004

Competition among fishermen and fish causes the collapse of Barents Sea capelin.

The vast majority of the world's fisheries are typically managed within a single-species perspective, ignoring the dynamic feedback mechanisms generated by the ecological web of which they are a part. Here we show that the dynamics of the Barents Sea capelin (Mallotus villosus), the world's largest stock of this species, is strongly influenced by both within-system ecological feedback mechanisms and the impact of harvesting. Both overexploitation and predation by herring (Clupea harengus) can cause the population to collapse, whereas predation by cod (Gadus morhua) is demonstrated a delay in the stock's recovery after a collapse. Such collapses, which have occurred twice in 20 years, affect the entire Barents Sea ecosystem, a region that for ages has provided food for all of Europe.

Animals↗
PubMed2005

A spider that feeds indirectly on vertebrate blood by choosing female mosquitoes as prey.

Spiders do not feed directly on vertebrate blood, but a small East African jumping spider (Salticidae), Evarcha culicivora, feeds indirectly on vertebrate blood by choosing as preferred prey female mosquitoes that have had recent blood meals. Experiments show that this spider can identify its preferred prey by sight alone and by odor alone. When presented with two types of size-matched motionless lures, E. culicivora consistently chose blood-fed female mosquitoes in preference to nonmosquito prey, male mosquitoes, and sugar-fed female mosquitoes (i.e., females that had not been feeding on blood). When the choice was between mosquitoes of different sizes (both blood- or both sugar-fed), small juveniles chose the smaller prey, whereas adults and larger juveniles chose the larger prey. However, preference for blood took precedence over preference for size (i.e., to get a blood meal, small individuals took prey that were larger than the preferred size, and larger individuals took prey that were smaller than the preferred size). When presented with odor from two prey types, E. culicivora approached the odor from blood-fed female mosquitoes significantly more often the odor of the prey that were not carrying blood.

Animals↗