Biomedical subjects

Mark Broom

Publications and source records attributed to Mark Broom.

9 recordsLinked to original sources

PubMed2006

Evolution of anti-predator traits in response to a flexible targeting strategy by predators.

Anti-predator benefits increase with vigilance rate and group size in many species of animal, while simultaneously resource intake rates usually decrease. This implies that there is an optimal group size and vigilance rate that will maximize individual fitness. While this basic theory of vigilance has been modelled and tested extensively, it has often been assumed that the predator represents a 'fixed-risk' such that groups of prey are essentially independent entities that exert little or no effect on one another either directly or indirectly. We argue that this is an over-simplification, and propose that the behaviour of one group of prey will likely affect the fitness of another local group of prey if the predator preferentially attacks the most vulnerable group-rather than attack both with constant rates. Using a numerical simulation model, we make the first examination of this game and allow the prey to dynamically evolve both optimal group size distributions between two habitats and vigilance rates in response to a predator with a preference for whichever group is the more vulnerable. We show that the density of prey in the population and the sensitivity of a predator to differences in prey vulnerability are likely to drive the dynamics of such a game. This novel approach to vigilance theory opens the door to several challenging lines of future research, both experimental and theoretical.

Animals↗

PubMed2005

Antipredator vigilance in birds: modelling the 'edge' effect.

Many animals spend a large proportion of their time either foraging for food or watching out for predators (antipredator vigilance). There have been many theoretical and empirical studies investigating the trade-off between these two activities, especially in birds. Previous models of antipredator vigilance assume that all birds within the group spend the same amount of time feeding. However, many empirical studies have shown that individuals on the edge of flocks are more vigilant. Here we describe a vigilance model which investigates the effect of position on the birds' strategies by dividing the feeding area into an inner and outer region. The model examines how various parameters such as food availability and predation risk affect the strategies of individual birds according to whether they are in the inner or outer region. Our model predicts that birds in the outer group are always more vigilant than those in the inner region. Birds in the centre receive a higher payoff in each of the wide range of scenarios that we have considered, and so our model also indicates why dominant birds would choose to feed in the centre of the group; a prediction in accord with several empirical studies.

Algorithms↗

PubMed2005

A stochastic model of the distribution of unequal competitors between resource patches.

We present a stochastic model of individuals' movements between two patches of resources. The population is made up of two types of individual with differing competitive abilities, and two types of movements occur, with individuals moving either to increase their intake rate or at random. Several previous models have used simulations to evaluate the likely distribution of individuals. We instead derive equations for the equilibrium distribution of the population, which can be solved numerically. This avoids the need to choose an initial distribution for the population, and enables us to obtain the probability with which rare events occur. This may not be possible when simulations are used, since a rare event may not occur at all. We find that when random movements are rare, an increase in the rate of random movements out of a patch can increase the number of individuals on that patch. We consider an approximation to the model with rare random movements, which provides an explanation for this phenomenon.

Competitive Behavior↗

PubMed2005

Evolutionary games with variable payoffs.

Matrix games, defined by a set of strategies and a corresponding matrix of payoffs, are commonly used to model animal populations because they are both simple and generate meaningful results. It is generally assumed that payoffs are independent of time. However, the timing of contests in real populations may have a marked effect on the value of rewards. We consider matrix games where the payoffs are functions of time. Rules are found which hold in this more general situation, and the complexity of possible behaviour is underlined by demonstrating other conditions which do not hold and an illustrative game.

Biological Evolution↗

PubMed2004

Infanticide and infant defence by males--modelling the conditions in primate multi-male groups.

Infanticide by primate males was considered rare if groups contain more than one adult male because, owing to lower paternity certainty, a male should be less likely to benefit from infanticide. Guided by recent evidence for strong variation of infanticide in primate multi-male groups, we modelled the conditions for when infanticide should occur for a group with a resident and an immigrant male. Setting the parameters (e.g. infant mortality, reduction of interbirth interval, life-time reproductive success, genetic representation) to fit the conditions most commonly found in nature, we develop a game-theoretic model to explore the influence of age and dominance on the occurrence of infanticide and infant defence. Male age strongly impacts the likelihood of an attack which is modified by the father's defence. If the new male is dominant he is likely to attack under most circumstances whereas a subordinate male will only attack if the father does not defend. These model scenarios fit the conditions under which infanticide is known to occur in primate multi-male groups and offer an explanation why infanticide is common in some multi-male groups and rare in others. Overall, the benefits for infanticidal males are strongly governed by a reduced interbirth interval while advantages via improved genetic representation in the gene pool contribute but a minor fraction.

Animals↗

PubMed2004

Resistance is useless?--Extensions to the game theory of kleptoparasitism.

We extend the game theoretic model of kleptoparasitism introduced by Broom and Ruxton (1998, Behav. Ecol. 9, 397-403) in two ways: we allow for asymmetric contests, where the probability alpha of the challenger winning can take any value from 0 to 1; and we allow the handler to choose not to resist the challenge, but to immediately concede and relinquish its food to the challenger. We find, in general, three possible evolutionarily stable strategies--challenge-and-resist (Hawk), challenge-but-do-not-resist (Marauder) and do-not-challenge-but-resist (Retaliator). When alpha = 1/2, we find that Hawk and Marauder are the only ESS's, in contrast to the result of the original model; we also find an overlap region, in parameter space, where two different ESS's are possible, depending on initial conditions. For general alpha, we see that all three ESS are possible, depending on different values of the environmental parameters; however, as the average time of a contest over food becomes long, then the Marauder strategy becomes more and more prevalent. The model makes a potentially significant prediction about animal behaviour in the area of kleptoparasitism, that a searcher, when it meets a handler, will only decline to attack that handler when alpha < 1/2 i.e. when the defender is more likely to win. One possible converse of this statement, that a handler whose probability of success is greater than 1/2 should always resist a challenge, is not true.

Animals↗

PubMed2003

A communication-based spatial model of antipredator vigilance.

Many animals spend their lives performing two often mutually exclusive tasks: feeding and watching out for predators (anti-predator vigilance). There have been many theoretical and empirical studies investigating this trade-off, especially for birds. An important characteristic of a flock of real birds is the area occupied by the flock. Individuals feeding close together experience increased competition so that the feeding rate decreases. Widely spaced individuals may suffer a loss in vigilance efficiency, since communication between individuals is more difficult, such that the predation risk increases. A vigilance model is developed which allows birds to control their spacing (and so the area of the flock) as well as their vigilance rate. The best strategy for the birds is found under a variety of environmental conditions, under the assumption that each individual acts selfishly to maximize its own fitness.

Animal Communication↗

PubMed2002

Association patterns and shoal fidelity in the three-spined stickleback.

We investigated pairwise association patterns and shoal fidelity in free-ranging, individual three-spine sticklebacks (Gasterosteus aculeatus) by capturing entire shoals of sticklebacks and tagging each shoal member with a unique individual mark before releasing the shoal at the point of capture. We recaptured tagged fishes in the study area on five subsequent days, noting their identity, their location and the individuals with which they were associated. Stable partner associations between fishes were observed which might provide the basis for shoal fidelity via social networks. These results suggest the potential for the kinds of inter-individual association patterns assumed by models of predator inspection and 'tit-for-tat' behaviours in free-ranging fishes.

Animals↗

PubMed2002

Intraspecific brood parasitism can increase the number of eggs that an individual lays in its own nest.

Intraspecific brood parasitism involves laying eggs in the nest of another individual of the same species without subsequently caring for the eggs or hatchlings. Where individuals lay in their own nest as well as parasitically, previous works predicted that parasitism leads to fewer eggs being laid in an individual's own nest, compared with the equivalent situation without parasitism. This is predicted to occur both to reduce the effects of competition from parasitically laid individuals and because parasitism can be used to reduce competition between siblings. Here, we present a quantitative model of this situation. This model indicates that the brood-reduction prediction does not hold universally. For some plausible parameter combinations, parasitism causes an increase rather than a decrease in the number of eggs laid by an individual in its own nest. This occurs because parasitism becomes a less profitable tactic as more eggs are laid by nest owners due to increasing within-nest competition. Increasing clutch size will also increase competition between the host's own offspring, but can still be advantageous if the induced reduction in parasitism is sufficient.

Animals↗