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PubMed2004

Dispersal, eviction, and conflict in meerkats (Suricata suricatta): an evolutionarily stable strategy model.

Decisions regarding immigration and emigration are crucial to understanding group dynamics in social animals, but dispersal is rarely treated in models of optimal behavior. We developed a model of evolutionarily stable dispersal and eviction strategies for a cooperative mammal, the meerkat Suricata suricatta. Using rank and group size as state variables, we determined state-specific probabilities that subordinate females would disperse and contrasted these with probabilities of eviction by the dominant female, based on the long-term fitness consequences of these behaviors but incorporating the potential for error. We examined whether long-term fitness considerations explain group size regulation in meerkats; whether long-term fitness considerations can lead to conflict between dominant and subordinate female group members; and under what circumstances those conflicts were likely to lead to stability, dispersal, or eviction. Our results indicated that long-term fitness considerations can explain group size regulation in meerkats. Group size distributions expected from predicted dispersal and eviction strategies matched empirical distributions most closely when emigrant survival was approximately that determined from the field study. Long-term fitness considerations may lead to conflicts between dominant and subordinate female meerkats, and eviction is the most likely result of these conflicts. Our model is computationally intensive but provides a general framework for incorporating future changes in the size of multimember cooperative breeding groups.

Animal Migration↗
PubMed2004

Evolutionary stability of mutualism: interspecific population regulation as an evolutionarily stable strategy.

Interspecific mutualisms are often vulnerable to instability because low benefit : cost ratios can rapidly lead to extinction or to the conversion of mutualism to parasite-host or predator-prey interactions. We hypothesize that the evolutionary stability of mutualism can depend on how benefits and costs to one mutualist vary with the population density of its partner, and that stability can be maintained if a mutualist can influence demographic rates and regulate the population density of its partner. We test this hypothesis in a model of mutualism with key features of senita cactus (Pachycereus schottii)-senita moth (Upiga virescens) interactions, in which benefits of pollination and costs of larval seed consumption to plant fitness depend on pollinator density. We show that plants can maximize their fitness by allocating resources to the production of excess flowers at the expense of fruit. Fruit abortion resulting from excess flower production reduces pre-adult survival of the pollinating seed-consumer, and maintains its density beneath a threshold that would destabilize the mutualism. Such a strategy of excess flower production and fruit abortion is convergent and evolutionarily stable against invasion by cheater plants that produce few flowers and abort few to no fruit. This novel mechanism of achieving evolutionarily stable mutualism, namely interspecific population regulation, is qualitatively different from other mechanisms invoking partner choice or selective rewards, and may be a general process that helps to preserve mutualistic interactions in nature.

Animals↗
PubMed1995

The evolutionarily stable strategy under individual condition and tactic frequency.

A proof is presented to show that, when fitnesses from alternative tactics within a population depend on both their frequency and the phenotypic condition of individuals, there will be a unique ESS switchpoint s* that determines both the condition at which an individual will switch between tactics and the resulting frequency of the tactics in the population. For an individual at the ESS s*, the fitnesses of the alternative tactics will be equal. When fitness is averaged over the population, however, the average fitnesses of the alternative tactics will not be equal.

Animals↗
PubMed1997

Evolutionarily stable strategy, stable state, periodic cycle and chaos in a simple discrete time two-phenotype model.

A simple discrete time two-phenotype matrix game model is investigated. In this model, according to the suggestion of Vincent & Fisher (1988, Evolutionary Ecology 2, 321-337), the fitness of an individual is defined to be an exponential function of its expected pay-off value. The results show that : (i) in our model, the static conditions of ESS are only dependent on the properties of pay-off matrix, but not on the specific form of fitness function. This result implies that the ESS conditions on our model are completely identical with the conditions in the two-phenotype model with linear fitness function. (ii) In our model, the relationship between the static conditions of ESS and the dynamic properties of the pure strategy model is that if the interior fixed point of the pure strategy model is not an ESS-equilibrium, then it must be unstable; conversely, if the interior fixed point of the pure strategy model is an ESS-equilibrium, then it can be stable or unstable, and an unstable ESS-equilibrium must correspond to the cyclic or chaotic behaviour of the population state.

Animals↗
PubMed2000

Evolutionarily stable strategy in a sex- and frequency-dependent selection model.

In this paper, a sex-dependent matrix game haploid model is investigated. For this model, since the phenotypes of female and male individuals are determined by alleles located at a single locus and are sex dependent, any given genotype corresponds to a strategy pair. Thus, a strategy pair is an ESS if and only if the allele corresponding to this strategy pair cannot be invaded by any mutant allele. We show that an ESS equilibrium must be locally asymptotically stable if it exists.

Alleles↗
PubMed1992

Niche breadth in parasites: an evolutionarily stable strategy model, with special reference to the protozoan parasite Leishmania.

A parasite's host range essentially defines its niche breadth, which, as foraging theory predicts, is influenced by resource availability. For parasites, the interaction of infection and transmission characteristics with host population dynamics determines host availability. An epidemiological model, involving two host types and describing competition between a "generalist" parasite strain and a related "specialist" strain, is used to examine the interplay among host range, relative host availabilities, and adaptational compromises engendered by increased host range. Results show that the generalist can predominate even when it cannot maintain itself in either host alone, but that the specialist can persist if its reproductive rate attains some threshold relative to either of the generalist's respective rates in its two hosts. The model is in rough, qualitative agreement with observed dynamics of two Leishmania parasite-host systems, and overall results suggest that infection of two species with a common parasite can lead to complex, indirect coevolutionary dynamics.

Adaptation, Biological↗
PubMed2004

Evolutionarily stable strategies for stochastic processes.

The classical definition of evolutionary stability assumes that the fitness of each phenotype is fully determined by the composition of phenotypes in the population and by the strategies of each of these phenotypes. In natural populations, however, stochasticity often plays a crucial role in determining the fitness of an individual and a deterministic fitness function is probably rather rare. For example, choices of a new host plant, prey or oviposition patch are completely stochastic processes. Here we introduce a new definition of ESS that takes into account the effect of stochasticity on individual fitness. Then we show an application of this definition in a realistic system.

Animals↗
PubMed1990

Strong stability and density-dependent evolutionarily stable strategies.

Stability conditions for equilibria of the evolution of population strategies in a single species are developed by comparing frequency and density dependent fitnesses of pairs of strategies. Stability of such equilibria is shown for general haploid frequency and density dynamics. It is also shown that this stability is stronger than that of multispecies population dynamical systems. A biological interpretation of the conditions is provided in terms of the fitness of invading subpopulations.

Animals↗