Search

The article discusses a study about the optimal annual routines for the new tools in conservation biology. This paper focuses on applied methodologies in ecology and conservation where prediction and population models are important tools based on matrix models. Limitations on the existing models are studied for behavioral rules imposed on individual level to establish emergent consequences. Strengths and weaknesses in these strategies are discussed based on modeling optimal annual routines. Results of the study is presented in brief.

Tropical birds lay smaller clutches than birds breeding in temperate regions and care for their young for longer. We develop a model in which birds choose when and how often to breed and their clutch size, depending on their foraging ability and the food availability. The food supply is density dependent. Seasonal environments necessarily have a high food peak in summer; in winter, food levels drop below those characteristic of constant environments. A bird that cannot balance its energy needs during a week dies of starvation. If adult predation is negligible, birds in low seasonal environments are constrained by low food during breeding seasons, whereas birds in high seasonal environments die during the winter. Low food seasonality selects for small clutch sizes, long parental care times, greater age at first breeding, and high juvenile survival. The inclusion of adult predation has no major effect on any life-history variables. However, increased nest predation reduces clutch size. The same trends with seasonality are also found in a version of the model that includes a condition variable. Our results show that seasonal changes in food supply are sufficient to explain the observed trends in clutch size, care times, and age at first breeding. [ABSTRACT FROM AUTHOR]

Ideal free distributions characterise how a group of animals should be distributed between sources of food. In a simple case, the ratio of the number of animals matches the ratio of input rates, a result known as input matching. The matching law characterises how an animal should allocate responses to sources of food. If matching holds then the ratio of behaviour allocated to the sources matches the ratio of rewards obtained. Several authors have drawn attention to the analogy between input matching and the matching law. I present a critical review of this topic, and go on to investigate the claim that the distribution of animals should be analyzed in the same way that the generalized matching law is analyzed. This involves assuming that the relationship between the ratio of animals and the ratio of resources obeys a power law with two parameters, one corresponding to bias and the other to sensitivity. On this view, a plot of the log of the ratio of animals against the log of the ratio of input rates will be a straight line and its intercept and slope will provide estimates of bias and sensitivity. I show that this approach can give a good fit even when the underlying model does not result in a power law. A consequence is that the parameters estimated cannot be interpreted as bias and sensitivity. I conclude that there are no compelling reasons for analyzing the distribution of animals using log-log plots, and the method has the disadvantage of encouraging the mistaken view that deviations from input matching follow a power law. [ABSTRACT FROM AUTHOR]

The classical viewpoint in sperm competition theory, which holds that males evolve sperm allocation strategies in response to a given degree of sperm competition, has recently been challenged by an alternative viewpoint, which holds that the degree of sperm competition is itself a consequence of these same strategies. Here, we present a game theory model that unites these alternative views as the endpoints of a continuum. Based on the recognition that female control over mating may limit the extent to which male strategies affect the degree of sperm competition, we investigate sperm allocation strategies in a setting where females can resist excessive matings more or less successfully. We discuss how conflicting predictions made by previous theory relate to implicit assumptions about female resistance behavior. Moreover, we show that female resistance, while being highly relevant to the predicted relationship between ejaculate size and the degree of sperm competition, has little effect on the predicted positive correlation between relative testis size and the degree of sperm competition. This result strengthens one of the central predictions of sperm competition theory and is in accordance with empirical findings from a wide range of taxa. [ABSTRACT FROM AUTHOR]

Simple scaling arguments suggest that, among air-breathing divers, dive duration should scale approximately with mass to the one-third power. Recent phylogenetic analyses appear to confirm this. The same analyses showed that duration of time spent at the surface between dives has scaling very similar to that of dive duration, with the result that the ratio of dive duration to surface pause duration is approximately mass invariant. This finding runs counter to other arguments found in the diving literature that suggest that surface pause duration should scale more positively with mass, leading to a negative scaling of the dive-pause ratio. We use a published model of optimal time allocation in the dive cycle to show that optimal decisions can predict approximate mass invariance in the dive-pause ratio, especially if metabolism scales approximately with mass to the two-thirds power (as indicated by some recent analyses) and oxygen uptake is assumed to have evolved to supply the body tissues at the required rate. However, emergent scaling rules are sensitive to input parameters, especially to the relationship between the scaling of metabolism and oxygen uptake rate at the surface. Our results illustrate the utility of an optimality approach for developing predictions and identifying key areas for empirical research on the allometry of diving behavior. [ABSTRACT FROM AUTHOR]

Explaining the rise and maintenance of cooperation is central to our understanding of biological systems and human societies. When an individual’s cooperativeness is used by other individuals as a choice criterion, there can be competition to be more generous than others, a situation called competitive altruism. The evolution of cooperation between non-relatives can then be driven by a positive feedback between increasing levels of cooperativeness and choosiness. Here we use evolutionary simulations to show that, in a situation where individuals have the opportunity to engage in repeated pairwise interactions, the equilibrium degree of cooperativeness depends critically on the amount of behavioural variation that is being maintained in the population by processes such as mutation. Because our model does not invoke complex mechanisms such as negotiation behaviour, it can be applied to a wide range of species. The results suggest an important role of lifespan in the evolution of cooperation. [ABSTRACT FROM AUTHOR]

I review previous models of the speed at which parent birds should fly when delivering food to their young. Norberg gives a graphical method of finding a parent's best flight speed. This speed maximizes the overall rate at which energy is delivered to the young. An alternative assumption is that a parent maximizes the net rate of delivery of energy. I suggest that in general we cannot distinguish between net rate and overall rate on the basis of whether the parent feeds itself. The best way to distinguish between these currencies may be to use qualitative predictions. I present new results on the effect of a constraint on energy expenditure on the parent's optimal speed. I show that the optimal speed when foraging should be less than the optimal speed when traveling. I also analyse the advantage to a parent of flying faster than the maximum range speed and evaluate previous empirical studies of the speed at which parent birds fly. Only one study claims that parent birds fly at the speed identified by Norberg, but I raise doubts about this claim. [ABSTRACT FROM AUTHOR]

In a periodically changing environment it is important for animals to properly time the major events of their life in order to maximise their lifetime fitness. For a non-migratory bird the timing of breeding and moult are thought to be the most crucial. We develop a state-dependent optimal annual routine model that incorporates explicit density dependence in the food supply. In the model the birds’ decisions depend on the time of year, their energy reserves, breeding status, experience, and the quality of two types of feathers (outer and inner primaries). Our model predicts that, under a seasonal environment, feathers with large effects on flight ability, higher abrasion rate and lower energetic cost of moult should be moulted closer to the winter (i.e. later) than those with the opposite attributes. Therefore, we argue that the sequence of moult may be an adaptive response to the problem of optimal timing of moult of differing feathers within the same feather tract. The model also predicts that environmental seasonality greatly affects optimal annual routines. Under high seasonality birds breed first then immediately moult, whereas under low seasonality an alternation occurs between breeding and moulting some of the feathers in one year and having a complete moult but no breeding in the other year. Increasing food abundance has a similar effect. [ABSTRACT FROM AUTHOR]

The Prisoner's Dilemma game is widely used to investigate how cooperation between unrelated individuals can evolve by natural selection. In this game, each player can either ‘cooperate’ (invest in a common good) or ‘defect’ (exploit the other's investment). If the opponent cooperates, you get R if you cooperate and T if you defect. If the opponent defects, you get S if you cooperate and P if you defect. Here T > R > 0 and P > S, so that ‘defect’ is the best response to any action by the opponent. Thus in a single play of the game, each player should defect. In our game, a fixed maximum number of rounds of the Prisoner's Dilemma game is played against the same opponent. A standard argument based on working backwards from the last round shows that defection on all rounds is the only stable outcome. In contrast, we show that if extrinsic factors maintain variation in behaviour, high levels of co-operation are stable. Our results highlight the importance of extrinsic variability in determining the outcome of evolutionary games. [ABSTRACT FROM AUTHOR]

Previous models have predicted the body mass of small birds in winter on the basis of a trade-off between starvation and predation. Many of these models have assumed that energy expenditure while active increases with body mass. The implications of the fact that the metabolic cost of activity can substitute for internal heat production and help keep the bird warm have not been investigated. In this paper we show that if thermoregulatory substitution occurs then there is a critical level of energy reserves above which an active bird is thermoneutral. This critical level increases as temperature decreases. Below this level, substitution of energy results in higher optimal levels of reserves than would be predicted in the absence of substitution. Our model thus predicts that at low temperatures body mass will be higher when thermoregulatory substitution occurs. [ABSTRACT FROM AUTHOR]

Parental care often increases the survival of offspring, but it is costly to parents. Because of this trade-off, a sexual conflict over care arises. The solution to this conflict depends on the inter-actions between the male and female parents, the behavior of other animals in the population, and the individual differences within a sex. We take an integrated approach and develop a state-dependent dynamic game model of parental care. The model investigates a single breeding season in which the animals can breed several times. Each parent's decision about whether to care for the brood or desert depends on its own energy reserves, its mate's reserves, and the time in the season. We develop a fully consistent solution in which the behavior of an animal is the best given the behavior of its mate and of all other animals in the population. The model predicts that females may strategically reduce their own reserves so as to "force" their mate to provide care. We investigate how the energy costs of caring and searching for a mate, values of care (how the probability of offspring survival depends on the pattern of care), and population sex ratio influence the pattern of care over the breeding season. [ABSTRACT FROM AUTHOR]

We use a dynamic optimization model to assess the consequences of habitat loss at migratory stopover sites. We emphasize costs birds face during stopover (e.g. costs of gaining energy), the timing of site use and the behavioural rules birds might use to implement migratory strategies. Behavioural rules may be flexible enough that birds can still produce optimal behaviour in the changed environment, or the rules may result in suboptimal behaviour. In birds behave optimally in the altered environment, habitat loss on the wintering ground has the highest impact, because this site, unlike the intermediate stopover sites, cannot be skipped if the quality drops below a threshold. If birds continue to use the old behavioural rules that now result in suboptimal behavior, we can distinguish two cases. Birds can continue to use a constant foraging behaviour that was optimal in the unaltered environment under many circumstances. Then the effects of habitat loss are proportional to the length of stay before habitat loss and the departure fuel load from a site. however, the effects of habitat loss do not depend on the location of the site within the network. In some circumstances birds are expected to forage with intensities that are below maximum. If birds use the foraging behaviour that is appropriate for a given fuel load, time and site but inappropriate for the altered fuel gain, then changes at sites close to the breeding ground have a greater impact than more distant sites. Finally we discuss the importance of sites that are not used before habitat loss. If birds behave optimally these sites may be used in an altered environment and can buffer against habitat loss at other sites. [ABSTRACT FROM AUTHOR]

Discusses evolutionary game theory relative to the process of natural selection. Standard assumption that two players choose a single action; Approach of the authors which suggests a series of interactions with the final outcome negotiated; Variations in quality; Analysis of negotiation given in the context of a pair of animals feeding their young; Authors' contention that there should be a fundamental remodelling in evolutionary game theory. INSET: Evolutionary stability.

Time-minimizing migrants should leave a stopover site if the instantaneous speed of migration drops to the average speed of migration in the environment. This argument has been used in two different ways: either there is local variation in the fuel deposition rate and a fixed expected speed or there is global variation in the fuel deposition rate, i.e. locally experienced variation represents global variation along the route. The first case leads to a far steeper relationship between departure load and fuel deposition rate than the second case. So far, data on departure loads have mainly been analysed within the concept of local variation of the fuel deposition rate and the result that the observed slopes are much lower than predicted has been explained by changes in the expected speed along the route or by individual differences in the expected speed. We show here that the observed relationships generally fall close to the predictions for global variation. We propose that migrants use a behavioural rule which projects the current experience into the future and therefore interprets local variation as global variation. [ABSTRACT FROM AUTHOR]

Evaluates the models of foraging and fuel loads in the context of avian migrations. Consideration of time, speed and predation risk factors that birds minimize on a migratory journey; Belief of a suitable understanding of models based on time and energy; Discrepancies between the models; Need to extend the analysis to models that take into account changes of internal state.

Investigates the amount of energy obtained and the amount of energy delivered to another animal, by a foraging animal. Effects of the amount of energy the animal can acquire; Methodology used to conduct the investigation; Results of the investigation.

In this article the authors discuss the analysis of M.V. Abrahams and L.M. Dill on titration process and energetic equivalence of risk predation. They said that a common currency with reproductive success is needed to identify the relationship of energetic gain and risk of predation. They cited that the analysis uses the ideal free distribution (IFD) for the separation of a group of animals into two patches. They added that energetic equivalence as an important factor in rating the patches.

The study of optimal life histories involves the maximization of lifetime fitness but usually ignores the details of behavioral sequences. In contrast, the study of optimal behavioral sequences usually looks at the details of a sequence in isolation and not as part of the whole life history of the animal. The currency that is maximized is assumed to be related to lifetime fitness, but this relationship is rarely explored. In this paper we develop a common currency for behavioral decisions that is directly related to lifetime fitness. The common currency makes it possible to compare the benefits of qualitatively different behaviors. We show that many different costs can be used to explain a given behavioral sequence. Most of these costs have no biological interpretation. From these we single out a particular cost, the canonical cost, which measures the reduction in fitness that results from choosing a suboptimal action. Our general framework is illustrated by the example of a small bird in winter. We quantify the value of energy in terms of fitness and show how this value depends on energy reserves and time of day. As a result of this dependence, optimal foraging decisions depend on energy reserves and time of day, as does the optimal trade-off between foraging and looking around for predators. [ABSTRACT FROM AUTHOR]

Cites the application of a general technique for finding optimal cyclic routines to annual routines of migration. Presentation of a schematic model of two locations different in terms of food availability; Use of the model for investigating the factors that determine the timing of migration; Relationship between reproductive value and energy reserves of birds; Comparison between an autumn and spring migration.

Honeybees often abandon non-depleting food sources with a partially filled crop. This behaviour does not maximise the net rate of energy extraction from the food sources, and thus contradicts predictions of some common models for central place foragers. We show that including the metabolic costs of transport of nectar leads to models that predict partial crop-loading. Furthermore, the observed crop loads of honeybees are less consistent with those predicted by maximization of delivery rate to the hive (net energetic gain/ unit time), than with those predicted by maximization of energetic efficiency (net energetic gain/unit energy expenditure). We argue that maximization of energetic efficiency may be an adaptation to a limited flight-cost budget. This constraint is to be expected because a worker's condition seems to deteriorate as a function of the amount of flight performed. [ABSTRACT FROM AUTHOR]

Janetos and Cole (1981) make several errors in their analysis. We point out these errors and supply the correct analysis. In doing so we illustrate techniques and ideas which can be usefully applied to many problems in this area. [ABSTRACT FROM AUTHOR]

We describe an experiment designed to investigate the trade-off between foraging and territorial vigilance in the Great Tit. Captive territorial male Great Tits were observed while foraging in a large indoor aviary. They obtained food from two operant 'patches' in which the supply of food was gradually depleted during a visit. We predicted that during control sessions the birds would switch between patches in such a way as to maximise their overall feeding rate. In experimental sessions, we introduced briefly a rival male as an 'intruder' at the start of the test. The foraging male could see the rival only when travelling between patches and not while feeding within patches. We predicted that during experimental sessions birds would switch between patches more often than in control tests, sacrificing food intake for territorial vigilance. Three of the four males tested behaved in approximately the predicted manner. We discuss the use of an inverse optimality argument to provide a calibration of feeding against the benefit resulting from territorial vigilance. [ABSTRACT FROM AUTHOR]

1. We tested the predictions of an optimal diet model which incorporated time taken to discriminate between prey types. Five captive great tits were presented with a choice of two prey types. The prey were large (profitable) and small (unprofitable) pieces of mealworm inside pieces of plastic drinking straw. 2. When the worms were inside clear plastic straws, the birds selected only large worms, as predicted by the optimal diet model. When the straws were opaque, so that the birds had to spend time discriminating between large and small worms, four out of five individuals became, as predicted, unselective. The fifth individual had a short enough discrimination time for selection to be the optima policy. 3. An attempt to alter the encounter rate with profitable opaque straws so that birds would resort to selective foraging was not successful because discrimination time for most individuals was too long for the model to predict selection. [ABSTRACT FROM AUTHOR]

Interactions in social groups can promote behavioural specialization. One way this can happen is when individuals engage in activities with two behavioural options and learn which option to choose. We analyse interactions in groups where individuals learn from playing games with two actions and negatively frequency-dependent payoffs, such as producer–scrounger, caller–satellite, or hawk–dove games. Group members are placed in social networks, characterized by the group size and the number of neighbours to interact with, ranging from just a few neighbours to interactions between all group members. The networks we analyse include ring lattices and the much-studied small-world networks. By implementing two basic reinforcement-learning approaches, action–value learning and actor–critic learning, in different games, we find that individuals often show behavioural specialization. Specialization develops more rapidly when there are few neighbours in a network and when learning rates are high. There can be learned specialization also with many neighbours, but we show that, for action–value learning, behavioural consistency over time is higher with a smaller number of neighbours. We conclude that frequency-dependent competition for resources is a main driver of specialization. We discuss our theoretical results in relation to experimental and field observations of behavioural specialization in social situations. [ABSTRACT FROM AUTHOR]