Patsy Haccou

Statistical analysis of behavioural data : an approach based on time-structured models

Introduction Preliminary inspection of the observations Analysis of time-inhomogeneity Tests for exponentiality Tests of sequential dependency properties Simultaneous tests Analysis based on a (semi)-Markov description Examples of analyses based on continuous-time Markov chain modelling Appendices References Author index Subject index.

Starlings exploiting patches: the effect of recent experience on foraging decisions

Laboratory and field experiments have shown that, as predicted by the marginal value model, starlings, Sturnus vulgaris, stay longer in a food patch when the average travel time between patches is long. A laboratory analogue of a patchy environment was used to investigate how starlings respond to rapidly fluctuating changes in travel time in order to find out the length of experience over which information is integrated. When there was a progressive increase in the amount of work required to obtain successive food items in a patch (experiment 1), birds consistently took more prey after long than after short travel times; travel experience before the most recent had no effect on the number of prey taken. Such behaviour does not maximize the rate of energy intake in this environment. The possibility that this is the result of a simple constraint on crop capacity is rejected as, when successive prey were equally easy to obtain up until a stepwise depletion of the patch (experiment 2), birds took equal numbers of prey per visit after long and short travel times: the rate-maximizing behaviour. A series of models are developed to suggest the possible constraints on optimal behaviour that affect starlings in the type of environment mimicked by experiment 1.

INFORMATION PROCESSING BY FORAGERS: EFFECTS OF INTRA-PATCH EXPERIENCE ON THE LEAVING TENDENCY OF LEPTOPILINA HETEROTOMA

(1) In this paper, the relation between the tendency to leave a patch and the experience in that patch is studied, from a functional point of view. (2) The study is based on empirical data rather than the usual a priori modelling. The relative effects of several factors on patch-leaving decisions are estimated from the data and it is tested which factors have significant effects. Afterwards, we discuss the implications of the effects that were found in a functional context. (3) This approach is an important extension to a priori modelling, since it can indicate the relative importance of several aspects of the natural environment in determining the foraging strategy. (4) Experiments were done with the parasitic wasp Leptopilina heterotoma. In the trials, wasps were deposited in a Petri dish containing a patch of yeast with Drosophila larvae. Their behaviour was continuously recorded until they left the patch for more than 60 s. (5) The data were analysed by means of the proportional hazards model (Cox 1972) for factors affecting the leaving tendency of the parasitoids, i.e. the chance per unit of time that the patch was left. (6) It was found that the leaving tendency decreases with the number of ovipositions. (7) Oviposition rates experienced in the patch also have a strong influence on the tendency of the wasps to leave. As expected, the most recently experienced oviposition rates have the strongest effect. Long foraging times between recent ovipositions produce a high leaving tendency. (8) The number of times the patch has been left before, during periods shorter than 60

Bet hedging or not? A guide to proper classification of microbial survival strategies

Bacteria have developed an impressive ability to survive and propagate in highly diverse and changing environments by evolving phenotypic heterogeneity. Phenotypic heterogeneity ensures that a subpopulation is well prepared for environmental changes. The expression bet hedging is commonly (but often incorrectly) used by molecular biologists to describe any observed phenotypic heterogeneity. In evolutionary biology, however, bet hedging denotes a risk‐spreading strategy displayed by isogenic populations that evolved in unpredictably changing environments. Opposed to other survival strategies, bet hedging evolves because the selection environment changes and favours different phenotypes at different times. Consequently, in bet hedging populations all phenotypes perform differently well at any time, depending on the selection pressures present. Moreover, bet hedging is the only strategy in which temporal variance of offspring numbers per individual is minimized. Our paper aims to provide a guide for the correct use of the term bet hedging in molecular biology.

Effects of intra-patch experiences on patch time, search time and searching efficiency of the parasitoid Leptopilina clavipes (Hartig).

1. This paper considers the effects of intra-patch experiences, such as contact with kairomone, ovipositions and rejections on the searching behaviour of individual female parasitoids of the species Leptopilina clavipes. 2. Behavioural records were analysed by means of the proportional hazards model (Cox 1972) taking effects of fixed as well as time-varying covariates into account. 3. Analyses were carried out at three levels of resolution: (i) patch leaving and return tendencies; (ii) tendencies to stop and start searching while on the patch; and (iii) the encounter rate during search bouts

LEARNING AND COLONIZATION OF NEW NICHES: A FIRST STEP TOWARD SPECIATION

Abstract Learning processes potentially play a role in speciation but are often ignored in speciation models. Learning may, for instance, play a role when a new niche is being colonized, because the learning of niche features may cause niche‐specific assortative mating and a tendency to produce young in this niche. Several animal species learn about their environmental features that may be important in finding or attracting mates. We use a gene‐culture coevolutionary model to look into the effect of such learning on the colonization of new niches and on the genetic divergence between groups using different niches, which are steps necessary in achieving speciation. We assume that density is regulated separately in each of the two niches and that the viability of an individual depends on its genotype as well as on which niche it exploits. Our results show that genetic adaptation to the new niche is enhanced by a high female fecundity and a low viability selection against heterozygotes. Furthermore, when initial colonization (without genetic adaptation) fails, genetic divergence is more difficult when the mating preference is stronger. In contrast, when colonization without genetic adaptation is successful, a stronger mating preference makes genetic divergence easier. An increase in the number of egg‐laying mistakes by females can have a positive or negative effect on the success of genetic adaptation depending on other parameters. We show that genetic divergence can be prevented by a niche shift, which can occur only if viabilities in the two niches are asymmetrical.

The effect of autocorrelation in environmental variability on the persistence of populations: an experimental test

Despite its significance regarding the conservation and management of biological resources, the body of theory predicting that the correlation between successive environmental states can profoundly influence extinction has not been empirically validated. Identical clonal populations from a model experimental system based on the collembolan Folsomia candida were used in the present study to investigate the effect of environmental autocorrelation on time to extinction. Environmental variation was imposed by variable implementation (present/absent) of a culling procedure according to treatments that represented six patterns of environmental autocorrelation. The average number of culling events was held constant across treatments but, as environmental autocorrelation increased, longer runs of both favourable and unfavourable culling tended to occur. While no difference was found among the survival functions for the various treatments, the time taken for 50% of the component populations to become extinct decreased significantly with increasing environmental autocorrelation. Similarly, analysis of all extinct populations demonstrated that time to extinction was shortened as environmental autocorrelation increased. However, this acceleration of extinction can be fully offset if sequential introduction is used in place of simultaneous introduction when founding the populations.

ESS emergence pattern of male butterflies in stochastic environments

SummaryThe evolutionarily stable (or ESS) emergence schedule for males of univoltine butterflies is analysed in an environment in which the female emergence schedule fluctuates stochastically between years. The ESS emergence curve, computed using the mutant invadability criterion, is shown to be the one that maximizes mean logarithmic lifetime mating success in the population in which it dominates. If males have accurate information about the female emergence schedule within each year, their emergence curve would evolve to the one predicted by a deterministic game model. The male emergence curve would then shift between years, closely following year to year changes in the female emergence pattern. If, instead, males have uncertainty about the female emergence schedule, the ESS male emergence curve becomes broader than the one predicted by the deterministic game model and will not track the between-year fluctuation of female emergence well. In a special case, we show how the between-year variation of mean emergence date, the variance of emergence date, the sexual difference in mean emergence dates (protandry) and the between-year correlation of mean emergence dates of both sexes should change with the degree of accuracy of information available to males.

When did it really start or stop: the impact of censored observations on the analysis of duration

Behaviour is often described in terms of bout lengths. Because of censoring, some of these bout lengths may only be observed partially. For instance, when observation is finished after a fixed period the end moment of the last bout remains unknown. The only available information on such a bout length is that it exceeds a certain value. This value is the censored observed bout length. Censored data are quite common in ethology, but the problem is often not recognized. Therefore, the well established statistical methods that account for censoring are rarely used in ethology. We report on the consequences of using standard methods instead of methods adjusted to account for censoring. We demonstrate that the usual methods of dealing with censored observations, such as treating them as uncensored observations or omitting them altogether, leads more often to erroneous conclusions. When an unadjusted test is used for testing the equality of two censored samples of bout lengths, the probability of rejecting the null hypothesis when the samples are different is much lower than when an adjusted test is used. Moreover, especially when censoring patterns differ between samples, the probability of wrongly rejecting the null hypothesis may be increased.

Analysis of time-inhomogeneity in Markov chains applied to mother-infant interactions of rhesus monkeys

Abstract When studying the interaction between mother-infant pairs of rhesus monkeys, inhomogeneities appear to exist during the awake phase of the infant, even under externally constant circumstances. These inhomogeneities are obscured by the stochastic nature of the bout lengths as well as the transitions between the several behavioural acts. An accurate description of the interaction, with the changes in the behaviour during the awake phase included, is necessary in order to be able to quantify the influence of the mother on the social development of the infant and vice versa. A mathematical model is described belonging to the class of continuous time Markov chains. This model gives an adequate characterization of the behavioural processes in a restricted number of ethologically wellinterpretable parameters. New procedures for estimating these parameters are derived, as well as tests on hypotheses concerning the number and magnitude of abrupt behavioural changes of the pairs. The pervasive motivational changes prior to or after napping by infants could be described comprehensively by the parameters developed.