1,848 research outputs found
A framework for modelling and analysing conspecific brood parasitism
Recently several papers that model parasitic egg-laying by birds in the nests of others of their own species have been published. Whilst these papers are concerned with answering different questions, they approach the problem in a similar way and have a lot of common features. In this paper a framework is developed which unifies these models, in the sense that they all become special cases of a more general model. This is useful for two main reasons; firstly in order to aid clarity, in that the assumptions and conclusions of each of the models are easier to compare. Secondly it provides a base for further similar models to start from. The basic assumptions for this framework are outlined and a method for finding the ESSs of such models is introduced. Some mathematical results for the general, and more specific, models are considered and their implications discussed. In addition we explore the biological consequences of the results that we have obtained and suggest possible questions which could be investigated using models within or very closely related to our framework
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Chris Cannings: A Life in Games
Chris Cannings was one of the pioneers of evolutionary game theory. His early work was inspired by the formulations of John Maynard Smith, Geoff Parker and Geoff Price; Chris recognized the need for a strong mathematical foundation both to validate stated results and to give a basis for extensions of the models. He was responsible for fundamental results on matrix games, as well as much of the theory of the important war of attrition game, patterns of evolutionarily stable strategies, multiplayer games and games on networks. In this paper we describe his work, key insights and their influence on research by others in this increasingly important field. Chris made substantial contributions to other areas such as population genetics and segregation analysis, but it was to games that he always returned. This review is written by three of his students from different stages of his career
An evolutionarily stable joining policy for group foragers
For foragers that exploit patchily distributed resources that are challenging to locate, detecting discoveries made by others with a view to joining them and sharing the patch may often be an attractive tactic, and such behavior has been observed across many taxa. If, as will commonly be true, the time taken to join another individual on a patch increases with the distance to that patch, then we would expect foragers to be selective in accepting joining opportunities: preferentially joining nearby discoveries. If competition occurs on patches, then the profitability of joining (and of not joining) will be influenced by the strategies adopted by others. Here we present a series of models designed to illuminate the evolutionarily stable joining strategy. We confirm rigorously the previous suggestion that there should be a critical joining distance, with all joining opportunities within that distance being accepted and all others being declined. Further, we predict that this distance should be unaffected by the total availability of food in the environment, but should increase with decreasing density of other foragers, increasing speed of movement towards joining opportunities, increased difficulty in finding undiscovered food patches, and decreasing speed with which discovered patches can be harvested. We are further able to make predictions as to how fully discovered patches should be exploited before being abandoned as unprofitable, with discovered patches being more heavily exploited when patches are hard to find: patches can be searched for remaining food more quickly, forager density is low, and foragers are relatively slow in traveling to discovered patches
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Kleptoparasitic melees--modelling food stealing featuring contests with multiple individuals
Kleptoparasitism is the stealing of food by one animal from another. This has been modelled in various ways before, but all previous models have only allowed contests between two individuals. We investigate a model of kleptoparasitism where individuals are allowed to fight in groups of more than two, as often occurs in real populations. We find the equilibrium distribution of the population amongst various behavioural states, conditional upon the strategies played and environmental parameters, and then find evolutionarily stable challenging strategies. We find that there is always at least one ESS, but sometimes there are two or more, and discuss the circumstances when particular ESSs occur, and when there are likely to be multiple ESSs
A game-theoretic model of kleptoparasitic behavior in polymorphic populations
Kleptoparasitism, the stealing of food by one animal from another, is a widespread biological phenomenon. In this paper we build upon earlier models to investigate a population of conspecifics involved in foraging and, potentially, kleptoparasitism. We assume that the population is composed of four types of individuals, according to their strategic choices when faced with an opportunity to steal and to resist an attack. The fitness of each type of individual depends upon various natural parameters, for example food density, the handling time of a food item and the probability of mounting a successful attack against resistance, as well as the choices that they make. We find the evolutionarily stable strategies (ESSs) for all parameter combinations and show that there are six possible ESSs, four pure and two mixtures of two strategies, that can occur. We show that there is always at least one ESS, and sometimes two or three. We further investigate the influence of the different parameters on when each type of solution occurs
Tiered Market Structures: an Empirical Examination of NASDAQ
This dissertation consists of two essays examining tiered market structures. We focus on the June 2006 restructuring of the NASDAQ Stock Exchange where the listing environment changed from two to three tiers, creating a top tier with the highest listing standards for any exchange in the world. The first essay examines market quality. Theoretical motivation indicates that different listing and disclosure requirements could result in different levels of information production across tiers, and thus different market quality characteristics. While we do find cross-sectional evidence of market quality differences, we do not find evidence of market quality changes when firms change tiers. Within the NASDAQ trading environment, this result is consistent with a visibility effect, where better (lesser) known stocks are more (less) liquid due to higher levels of investor participation. With the exception of increased effective spreads as firms drop to a lower tier, no other short-term changes in market quality appear to result from firms adhering to new listing standards, when controlling for disclosure standards. The second essay examines any reputation effect resulting from NASDAQ’s tiered structure. Theoretical motivation indicates that exchanges choose listing and disclosure standards to maximize the combination of its reputation value and the value of cash flows from listing and trading fees. We find that NASDAQ’s 2006 restructuring did not appear to enhance its reputation, either directly or indirectly. The restructuring did not result in any positive announcement effect for NASDAQ firms. Further, we find little evidence to support any announcement effects as firms cross into new tiers. Lastly, we find that the restructuring does not appear to have helped NASDAQ become more competitive in the marketplace for attracting new initial public offerings
The effects of land transport on animal welfare
Animal welfare during and as a result of transport can be assessed by using a range of behavioural, physiological, pathological and carcass-quality indicators that are described in this paper. Measures of the extent of any disease, injury or mortality resulting from, or exacerbated by, transport are important because health is an important part of welfare. Many of the indicators are measures of stress as they involve long-term adverse effects on the individual. Factors affecting the welfare of animals before, during and after transport which are discussed are: definition of the responsibilities and competence, attitudes to animals and need for training of staff; planning of journeys and methods of payment of staff; laws and retailers’ codes; genetics, especially selection for high productivity; rearing conditions and experience; the mixing of animals from different social groups; handling and loading procedures; driving methods; space allowance; increased susceptibility to disease and efforts to minimise the spread of disease
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Evolutionarily stable sexual allocation by both stressed and unstressed potentially simultaneous hermaphrodites within the same population.
Factors influencing allocation of resources to male and female offspring continue to be of great interest to evolutionary biologists. A simultaneous hermaphrodite is capable of functioning in both male and female mode at the same time, and such a life-history strategy is adopted by most flowering plants and by many sessile aquatic animals. In this paper, we focus on hermaphrodites that nourish post-zygotic stages, e.g. flowering plants and internally fertilising invertebrates, and consider how their sex allocation should respond to an environmental stress that reduces prospects of survival but does not affect all individuals equally, rather acting only on a subset of the population. Whereas dissemination of pollen and sperm can begin at sexual maturation, release of seeds and larvae is delayed by embryonic development. We find that the evolutionarily stable strategy for allocation between male and female functions will be critically dependent on the effect of stress on the trade-off between the costs of male and female reproduction, (i.e. of sperm and embryos). Thus, we identify evaluation of this factor as an important challenge to empiricists interested in the effects of stress on sex allocation. When only a small fraction of the population is stressed, we predict that stressed individuals will allocate their resources entirely to male function and unstressed individuals will increase their allocation to female function. Conversely, when the fraction of stress-affected individuals is high, stressed individuals should respond to this stressor by increasing investment in sperm and unstressed individuals should invest solely in embryos. A further prediction of the model is that we would not expect to find populations in the natural world where both stressed and unstressed individuals are both hermaphrodite
A theory for investment across defences triggered at different stages of a predator-prey encounter
We introduce a general theoretical description of a combination of defences acting sequentially at different stages in the predatory sequence in order to make predictions about how animal prey should best allocate investment across different defensive stages. We predict that defensive investment will often be concentrated at stages early in the interaction between a predator individual and the prey (especially if investment is concentrated in only one defence, then it will be in the first defence). Key to making this prediction is the assumption that there is a cost to a prey when it has a defence tested by an enemy, for example because this incurs costs of deployment or tested costs as a defence is exposed to the enemies; and the assumption that the investment functions are the same among defences. But if investment functions are different across defences (e.g. the investment efficiency in making resources into defences is higher in later defences than in earlier defences), then the contrary could happen. The framework we propose can be applied to other victim-exploiter systems, such as insect herbivores feeding on plant tissues. This leads us to propose a novel explanation for the observation that herbivory damage is often not well explained by variation in concentrations of toxic plant secondary metabolites. We compare our general theoretical structure with related examples in the literature, and conclude that coevolutionary approaches will be profitable in future work
NOVEL CHARACTERISATION OF ARTICULAR CARTILAGE IN THE EQUINE ATHLETIC JOINT
We present a novel method of characterising articular cartilage using its free-swelling behaviour. We have attempted to quantify the site-specific matrix swelling properties of the third (C3) and radius carpal (Cr) cartilage from middle carpal joints obtained from 18 month-old Thoroughbred horses. The highly stressed dorsal region produced 63.7% more swelling than the lesser loaded palmar region (22.6% vs. 13.9%). For any given site there was a strong depth-dependence of swelling with the mid-zone being the highest (p = 0.0002). The technique was sufficiently sensitive to detect an increased swelling of +4.23% in sites with a mild lesion relative to those sites that were lesion free (p = 0.04)
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