Boldness-aggression syndromes can reduce population density: behavior and demographic heterogeneity

Aggression may be good for the individual but bad for the group. In many species, some individuals have an aggressive “personality” that helps in some circumstances (beating out rivals for a mate) but not in others (staring down a predator). Using mathematical models, we show that the evolution of personalities to a mixture that maximizes individual fitness can reduce the population’s overall abundance. This may increase the risk that the population goes extinct.

Related papers:

title: An evolutionary ecology of individual differences.
abstract: Individuals often differ in what they do. This has been recognised since antiquity. Nevertheless, the ecological and evolutionary significance of such variation is attracting widespread interest, which is burgeoning to an extent that is fragmenting the literature. As a first attempt at synthesis, we focus on individual differences in behaviour within populations that exceed the day-to-day variation in individual behaviour (i.e. behavioural specialisation). Indeed, the factors promoting ecologically relevant behavioural specialisation within natural populations are likely to have far-reaching ecological and evolutionary consequences. We discuss such individual differences from three distinct perspectives: individual niche specialisations, the division of labour within insect societies and animal personality variation. In the process, while recognising that each area has its own unique motivations, we identify a number of opportunities for productive 'cross-fertilisation' among the (largely independent) bodies of work. We conclude that a complete understanding of evolutionarily and ecologically relevant individual differences must specify how ecological interactions impact the basic biological process (e.g. Darwinian selection, development and information processing) that underpin the organismal features determining behavioural specialisations. Moreover, there is likely to be co-variation amongst behavioural specialisations. Thus, we sketch the key elements of a general framework for studying the evolutionary ecology of individual differences.

title: Animal personalities: consequences for ecology and evolution.
abstract: Personality differences are a widespread phenomenon throughout the animal kingdom. Past research has focused on the characterization of such differences and a quest for their proximate and ultimate causation. However, the consequences of these differences for ecology and evolution received much less attention. Here, we strive to fill this gap by providing a comprehensive inventory of the potential implications of personality differences, ranging from population growth and persistence to species interactions and community dynamics, and covering issues such as social evolution, the speed of evolution, evolvability, and speciation. The emerging picture strongly suggests that personality differences matter for ecological and evolutionary processes (and their interaction) and, thus, should be considered a key dimension of ecologically and evolutionarily relevant intraspecific variation.

title: Behavioral syndromes: an ecological and evolutionary overview.
abstract: Recent studies suggest that populations and species often exhibit behavioral syndromes; that is, suites of correlated behaviors across situations. An example is an aggression syndrome where some individuals are more aggressive, whereas others are less aggressive across a range of situations and contexts. The existence of behavioral syndromes focuses the attention of behavioral ecologists on limited (less than optimal) behavioral plasticity and behavioral carryovers across situations, rather than on optimal plasticity in each isolated situation. Behavioral syndromes can explain behaviors that appear strikingly non-adaptive in an isolated context (e.g. inappropriately high activity when predators are present, or excessive sexual cannibalism). Behavioral syndromes can also help to explain the maintenance of individual variation in behavioral types, a phenomenon that is ubiquitous, but often ignored. Recent studies suggest that the behavioral type of an individual, population or species can have important ecological and evolutionary implications, including major effects on species distributions, on the relative tendencies of species to be invasive or to respond well to environmental change, and on speciation rates. Although most studies of behavioral syndromes to date have focused on a few organisms, mainly in the laboratory, further work on other species, particularly in the field, should yield numerous new insights.

title: The mix matters: behavioural types and group dynamics in water striders
abstract: The effect of an individual’s behavioral type (e.g., its boldness or aggressiveness) on fitness likely depends on the environmental context. In many species, an important component of an individual’s environment is its social environment — the mix of individuals in its social group. Accordingly, much of game theory assumes that the mix of behavioral types (BTs) in a social group influences individual fitness and group dynamics. Few experimental studies, however, have directly investigated how the group’s mix of BTs influences individual and group outcomes. Here we manipulated social group composition in the water strider Aquarius remigis and evaluated the effects of our manipulation on individual behavior and various group outcomes (overall group activity, aggression, mating success). We formed 12 groups that differed substantially in average male BT (activity and aggression level), each with a low variance in BT. That is, one group had only the most active and aggressive males, a second group was made up of the next most active and aggressive males, and on down to a group of all very inactive and unaggressive males. All groups also had females. We found that, on average, groups made up of more active-aggressive males continued to be more active than other groups, but that contrary to predictions, these groups did not tend to enjoy higher mating success. Instead, a major factor affecting group mating activity was the presence of hyper-aggressive males. Hyper-aggressive males drove females out of the group and thereby decreased the group’s overall mating activity. We discuss these findings in terms of their importance to the study of behavioral plasticity in social groups and the potential role of keystone individuals in determining group dynamics.

title: A test for correlations among fitness-linked behavioural traits in the spider Agelenopsis aperta (Araneae, Agelenidae)
abstract: The spider Agelenopsis aperta, exhibits a suite of behavioural traits that are functionally dissimilar but which all potentially could be influenced by inherent levels of 'fear' and 'aggression': agonistic behaviour, territory size, foraging behaviour, and anti-predatory behaviour. Previous findings suggest that in A. aperta, agonistic behaviour and territory size are phenotypically correlated at both the individual and population levels, as are foraging and anti-predator behaviour patterns. In this study first anti-predatory and then agonistic trials were completed on two sets of spiders (wild and laboratory-reared F1 generation) from each of two populations (desert grassland and riparian) to test for an inter-connection between these two sets of traits. Spider scores in the anti-predatory fear test were an accurate predictor of the outcome of contests between individuals that were matched for weight but that had different fear scores. This entire set of traits may have the same underlying genetic basis as pleiotropic effects of the same genes. However, quantitative genetic studies are required to test this hypothesis.

title: From mice to men: what can we learn about personality from animal research?
abstract: The author explores the viability of a comparative approach to personality research. A review of the diverse animal-personality literature suggests that (a) most research uses trait constructs, focuses on variation within (vs. across) species, and uses either behavioral codings or trait ratings; (b) ratings are generally reliable and show some validity (7 parameters that could influence reliability and 4 challenges to validation are discussed); and (c) some dimensions emerge across species, but summaries are hindered by a lack of standard descriptors. Arguments for and against cross-species comparisons are discussed, and research guidelines are suggested. Finally, a research agenda guided by evolutionary and ecological principles is proposed. It is concluded that animal studies provide unique opportunities to examine biological, genetic, and environmental bases of personality and to study personality change, personality-health links, and personality perception.

title: An explanatory framework for adaptive personality differences
abstract: We develop a conceptual framework for the understanding of animal personalities in terms of adaptive evolution. We focus on two basic questions. First, why do behavioural types exhibit limited behavioural plasticity, that is, behavioural correlations both across contexts and over time? Second, how can multiple behavioural types coexist within a single population? We emphasize differences in ‘state’ among individuals in combination with state-dependent behaviour. Some states are inherently stable and individual differences in such states can explain stable differences in suites of behaviour if it is adaptive to make behaviour in various contexts dependent on such states. Behavioural stability and cross-context correlations in behaviour are more difficult to explain if individual states are potentially more variable. In such cases stable personalities can result from state-dependent behaviour if state and behaviour mutually reinforce each other by feedback mechanisms. We discuss various evolutionary mechanisms for the maintenance of variation (in states and/or behaviour), including frequency-dependent selection, spatial variation with incomplete matching between habitat and phenotype, bet-hedging in a temporally fluctuating environment, and non-equilibrium dynamics. Although state differences are important, we also discuss how social conventions and social signalling can give rise to adaptive personality differences in the absence of state differences.

title: Behavioral syndromes as evolutionary constraints
abstract: Behaviors are commonly correlated between individuals in so-called "behavioral syndromes." Between-individual correlations of phenotypic traits can change the trajectories of evolutionary responses available to populations and even prevent evolutionary change if underpinned by genetic correlations. Whether behavioral syndromes also influence the course of evolution in this manner remains unknown. Here, we provide the first test of the degree to which evolutionary responses might be affected by behavioral syndrome structure. This test, based on a meta-analysis of additive genetic variance–covariance matrices, shows that behavioral syndromes constrain potential evolutionary responses by an average of 33%. For comparison, correlations between life-history or between morphological traits suggest constraints of 13–18%. This finding demonstrates that behavioral syndromes might substantially constrain the evolutionary trajectories available to populations, prompts novel future directions for the study of behavioral syndromes, emphasizes the importance of viewing syndrome research from an evolutionary perspective, and provides a bridge between syndrome research and theoretical quantitative genetics.

title: Repeatability and heritability of exploratory behaviour in great tits from the wild
abstract: We investigated whether individual great tits, Parus major, vary consistently in their exploratory behaviour in a novel environment and measured the repeatability and heritability of this trait. Wild birds were caught in their natural habitat, tested in the laboratory in an open field test on the following morning, then released at the capture site. We measured individual consistency of exploratory behaviour for recaptured individuals (repeatability) and estimated the heritability with parent–offspring regressions and sibling analyses. Measures of exploratory behaviour of individuals at repeated captures were consistent in both sexes and study areas (repeatabilities ranged from 0.27 to 0.48). Exploration scores did not differ between the sexes, and were unrelated to age, condition at fledging or condition during measurement. Heritability estimates were 0.22–0.41 (parent–offspring regressions) and 0.37–0.40 (sibling analyses). We conclude that (1) consistent individual variation in open field behaviour exists in individuals from the wild, and (2) this behavioural variation is heritable. This is one of the first studies showing heritable variation in a behavioural trait in animals from the wild, and poses the question of how this variation is maintained under natural conditions.

title: THE EVOLUTION OF INDIVIDUAL VARIATION IN COMMUNICATION STRATEGIES
abstract: Communication is a process in which senders provide information via signals and receivers respond accordingly. This process relies on two coevolving conventions: a “sender code” that determines what kind of signal is to be sent given the sender's state; and a “receiver code” that determines the appropriate responses to different signal types. By means of a simple but generic model, we show that polymorphic sender and receiver strategies emerge naturally during the evolution of communication, and that the number of alternative strategies observed at equilibrium depends on the potential for error in signal production. Our model suggests that alternative communication strategies will evolve whenever senders possess imperfect information about their own quality or state, signals are costly, and genetic mechanisms allow for a correlation between sender and receiver behavior. These findings provide an explanation for recent reports of individual differences in communication strategies, and suggest that the amount of individual variation that can be expected in communication systems depends on the type of information being conveyed. Our model also suggests a link between communication and the evolution of animal personalities, which is that individual differences in the production and interpretation of signals can result in consistent differences in behavior.

title: Learning in a game context: strategy choice by some keeps learning from evolving in others
abstract: Behavioural decisions in a social context commonly have frequency-dependent outcomes and so require analysis using evolutionary game theory. Learning provides a mechanism for tracking changing conditions and it has frequently been predicted to supplant fixed behaviour in shifting environments; yet few studies have examined the evolution of learning specifically in a game-theoretic context. We present a model that examines the evolution of learning in a frequency-dependent context created by a producer–scrounger game, where producers search for their own resources and scroungers usurp the discoveries of producers. We ask whether a learning mutant that can optimize its use of producer and scrounger to local conditions can invade a population of non-learning individuals that play producer and scrounger with fixed probabilities. We find that learning provides an initial advantage but never evolves to fixation. Once a stable equilibrium is attained, the population is always made up of a majority of fixed players and a minority of learning individuals. This result is robust to variation in the initial proportion of fixed individuals, the rate of within- and between-generation environmental change, and population size. Such learning polymorphisms will manifest themselves in a wide range of contexts, providing an important element leading to behavioural syndromes.

title: Evolutionary models of metabolism, behaviour and personality
abstract: I explore the relationship between metabolism and personality by establishing how selection acts on metabolic rate and risk-taking in the context of a trade-off between energy and predation. Using a simple time budget model, I show that a high resting metabolic rate is not necessarily associated with a high daily energy expenditure. The metabolic rate that minimizes the time spent foraging does not maximize the net gain rate while foraging, and it is not always advantageous for animals to have a higher metabolic rate when food availability is high. A model based on minimizing the ratio of mortality rate to net gain rate is used to determine how a willingness to take risks should be correlated with metabolic rate. My results establish that it is not always advantageous for animals to take greater risks when metabolic rate is high. When foraging intensity and metabolic rate coevolve, I show that in a particular case different combinations of foraging intensity and metabolic rate can have equal fitness.

title: Risk, resources and state-dependent adaptive behavioural syndromes
abstract: Many animals exhibit behavioural syndromes—consistent individual differences in behaviour across two or more contexts or situations. Here, we present adaptive, state-dependent mathematical models for analysing issues about behavioural syndromes. We find that asset protection (where individuals with more ‘assets’ tend be more cautious) and starvation avoidance, two state-dependent mechanisms, can explain short-term behavioural consistency, but not long-term stable behavioural types (BTs). These negative-feedback mechanisms tend to produce convergence in state and behaviour over time. In contrast, a positive-feedback mechanism, state-dependent safety (where individuals with higher energy reserves, size, condition or vigour are better at coping with predators), can explain stable differences in personality over the long term. The relative importance of negative- and positive-feedback mechanisms in governing behavioural consistency depends on environmental conditions (predation risk and resource availability). Behavioural syndromes emerge more readily in conditions of intermediate ecological favourability (e.g. medium risk and medium resources, or high risk and resources, or low risk and resources). Under these conditions, individuals with higher initial state maintain a tendency to be bolder than individuals that start with low initial state; i.e. later BT is determined by state during an early ‘developmental window’. In contrast, when conditions are highly favourable (low risk, high resources) or highly unfavourable (high risk, low resources), individuals converge to be all relatively bold or all relatively cautious, respectively. In those circumstances, initial differences in BT are not maintained over the long term, and there is no early developmental window where initial state governs later BT. The exact range of ecological conditions favouring behavioural syndromes depends also on the strength of state-dependent safety.

title: Metabolic Rates Can Drive Individual Differences in Information and Insurance Use under the Risk of Starvation
abstract: Variation in how individuals invest in acquiring information (sampling) and in insuring themselves against potential negative consequences of uncertainty (e.g., by storing energy reserves) has been suggested to underlie consistent individual differences in suites of behavioral traits. However, the key drivers of individual differences in information use remain poorly understood. We use dynamic programming to explore how existing variation in metabolic rates (MRs) affects the use of sampling and insurance under starvation risk. Our analysis reveals nonlinear effects of MRs on diurnal patterns of sampling and insurance. Individuals with low MRs accrue reserves quickly, because they invest in sampling and are able to exploit profitable options when they arise. Individuals with intermediate MRs initially lose reserves, because sampling, while optimal, is relatively expensive; however, they later build reserves due to efficient exploitation of alternative foraging options. Sampling rarely pays for individuals with the highest MRs, which show relatively constant levels of energy reserves throughout the foraging period. Thus, individual variation in MRs on the scale observed in natural populations can lead to important differences in investment in sampling and insurance and may underpin consistent individual differences in suites of other behavioral traits, including individual differences in behavioral responsiveness.

title: How noisy information and individual asymmetries can make ‘personality’ an adaptation: a simple model
abstract: Recent attention has been drawn to the existence of individual differences in correlated behaviour across contexts, animal 'personality' (Gosling 2001,  Bulletin, 127, 45-86) and behavioural syndromes (Sih et al. 2004b, Quarterly Review of Biology, 79, 241-277). The causes of these patterns of behaviour are subjects of debate. Here, we present a very simple model of how adaptively managing noisy information, combined with differences in individual state, can lead to evolutionarily stable differences in how individuals respond to environmental cues. When information is very noisy, behavioural syndromes are most likely, but as long as there is some error, some types of individuals display the same behaviour in all contexts. In extreme cases, very few individuals display flexible behaviour, and different stable behavioural types dominate the population.

title: Evolution of trust and trustworthiness: social awareness favours personality differences
abstract: Interest in the evolution and maintenance of personality is burgeoning. Individuals of diverse animal species differ in their aggressiveness, fearfulness, sociability and activity. Strong trade-offs, mutation–selection balance, spatio-temporal fluctuations in selection, frequency dependence and good-genes mate choice are invoked to explain heritable personality variation, yet for continuous behavioural traits, it remains unclear which selective force is likely to maintain distinct polymorphisms. Using a model of trust and cooperation, we show how allowing individuals to monitor each other's cooperative tendencies, at a cost, can select for heritable polymorphisms in trustworthiness. This variation, in turn, favours costly ‘social awareness’ in some individuals. Feedback of this sort can explain the individual differences in trust and trustworthiness so often documented by economists in experimental public goods games across a range of cultures. Our work adds to growing evidence that evolutionary game theorists can no longer afford to ignore the importance of real world inter-individual variation in their models.

title: Evolutionary emergence of responsive and unresponsive personalities
abstract: In many animal species, individuals differ consistently in suites of correlated behaviors, comparable with human personalities. Increasing evidence suggests that one of the fundamental factors structuring personality differences is the responsiveness of individuals to environmental stimuli. Whereas some individuals tend to be highly responsive to such stimuli, others are unresponsive and show routine-like behaviors. Much research has focused on the proximate causes of these differences but little is known about their evolutionary origin. Here, we provide an evolutionary explanation. We develop a simple but general evolutionary model that is based on two key ingredients. First, the benefits of responsiveness are frequency-dependent; that is, being responsive is advantageous when rare but disadvantageous when common. This explains why responsive and unresponsive individuals can coexist within a population. Second, positive-feedback mechanisms reduce the costs of responsiveness; that is, responsiveness is less costly for individuals that have been responsive before. This explains why individuals differ consistently in their responsiveness, across contexts and over time. As a result, natural selection gives rise to stable individual differences in responsiveness. Whereas some individuals respond to environmental stimuli in all kinds of contexts, others consistently neglect such stimuli. Interestingly, such differences induce correlations among all kinds of other traits (e.g., boldness and aggressiveness), thus providing an explanation for environment-specific behavioral syndromes.

title: Life-history trade-offs favour the evolution of animal personalities
abstract: In recent years evidence has been accumulating that personalities are not only found in humans but also in a wide range of other animal species. Individuals differ consistently in their behavioural tendencies and the behaviour in one context is correlated with the behaviour in multiple other contexts. From an adaptive perspective, the evolution of animal personalities is still a mystery, because a more flexible structure of behaviour should provide a selective advantage. Accordingly, many researchers view personalities as resulting from constraints imposed by the architecture of behaviour (but see ref. 12). In contrast, we show here that animal personalities can be given an adaptive explanation. Our argument is based on the insight that the trade-off between current and future reproduction often results in polymorphic populations in which some individuals put more emphasis on future fitness returns than others. Life-history theory predicts that such differences in fitness expectations should result in systematic differences in risk-taking behaviour. Individuals with high future expectations (who have much to lose) should be more risk-averse than individuals with low expectations. This applies to all kinds of risky situations, so individuals should consistently differ in their behaviour. By means of an evolutionary model we demonstrate that this basic principle results in the evolution of animal personalities. It simultaneously explains the coexistence of behavioural types, the consistency of behaviour through time and the structure of behavioural correlations across contexts. Moreover, it explains the common finding that explorative behaviour and risk-related traits like boldness and aggressiveness are common characteristics of animal personalities.

title: Ecological implications of behavioural syndromes.
abstract: Interspecific trait variation has long served as a conceptual foundation for our understanding of ecological patterns and dynamics. In particular, ecologists recognise the important role that animal behaviour plays in shaping ecological processes. An emerging area of interest in animal behaviour, the study of behavioural syndromes (animal personalities) considers how limited behavioural plasticity, as well as behavioural correlations affects an individual's fitness in diverse ecological contexts. In this article we explore how insights from the concept and study of behavioural syndromes provide fresh understanding of major issues in population ecology. We identify several general mechanisms for how population ecology phenomena can be influenced by a species or population's average behavioural type, by within-species variation in behavioural type, or by behavioural correlations across time or across ecological contexts. We note, in particular, the importance of behavioural type-dependent dispersal in spatial ecology. We then review recent literature and provide new syntheses for how these general mechanisms produce novel insights on five major issues in population ecology: (1) limits to species' distribution and abundance; (2) species interactions; (3) population dynamics; (4) relative responses to human-induced rapid environmental change; and (5) ecological invasions.

title: Behavioural syndromes and their fitness consequences in a socially polymorphic spider, Anelosimus studiosus

abstract: The temperate comb-footed spider, Anelosimus studiosus, shows a social behaviour polymorphism: individuals may defend asocial nests against intrusion by conspecifics or cooperate with them in multifemale nests. A suite of behavioural traits, including response to predators and prey, degree of superfluous killing, exploratory behaviour and general level of activity, was examined in laboratory trials to: (1) establish the extent to which these traits are correlated with social phenotype and (2) explore the potential adaptive value of this trait suite to the respective asocial and social phenotypes. Populations from the two latitudes studied, 26° and 36°, showed similar suites of correlated traits or syndromes. The individuals tested generally fell into two groups in the behavioural trials, although the asocial individuals from the mixed-phenotype population at 36° latitude were intermediate with respect to some of the measures. Individuals scored as ‘social’ generally showed less aggressive behaviour towards predatory cues, were less responsive to prey encountering their webs, showed little evidence of superfluous killing of prey and showed lower levels of activity than did most individuals scored as ‘asocial’. These results suggest linkage or pleiotropy between social behaviour and these traits. The behaviour of individuals in staged, mixed-phenotype feeding pairs indicated that social individuals may suffer fitness consequences in polymorphic populations. These results are discussed with respect to the stability and dynamics of the respective phenotypes in polymorphic populations.

title: Personality and the emergence of the pace-of-life syndrome concept at the population level
abstract: The pace-of-life syndrome (POLS) hypothesis specifies that closely related species or populations experiencing different ecological conditions should differ in a suite of metabolic, hormonal and immunity traits that have coevolved with the life-history particularities related to these conditions. Surprisingly, two important dimensions of the POLS concept have been neglected: (i) despite increasing evidence for numerous connections between behavioural, physiological and life-history traits, behaviours have rarely been considered in the POLS yet; (ii) the POLS could easily be applied to the study of covariation among traits between individuals within a population. In this paper, we propose that consistent behavioural differences among individuals, or personality, covary with life history and physiological differences at the within-population, interpopulation and interspecific levels. We discuss how the POLS provides a heuristic framework in which personality studies can be integrated to address how variation in personality traits is maintained within populations.

title: The Developmental, Physiological, Neural, and Genetical Causes and Consequences of Frequency-Dependent Selection in the Wild
abstract: We outline roles of frequency-dependent selection (FDS) in coadaptation and coevolutionary change. Coadaptation and coevolution occur because correlational selection (CS) and correlated evolution couple many traits. CS arises from causal interactions between traits expressed in two or more interactors, which invariably involve different traits (signalers-receivers). Thus, the causes of CS are due to FDS acting on trait interactions. Negative FDS, a rare advantage, is often coupled to positive FDS generating complex dynamics and FD cycles. Neural mechanisms of learning and perception create analogous routes by which traits are reinforced in cognitive and perceptual systems of interactors, substituting for positive FDS. FDS across all levels of biological organization is thus best understood as proximate causes that link interactors and shape genetic correlations within and among interactors on long timescales, or cognitive trait correlations within interactors on short timescales. We find rock-paper-scissors dynamics are common in nature.

title: Behavioral correlations provide a mechanism for explaining high invader densities and increased impacts on native prey.
abstract: The fact that superabundant invasive pests are also sometimes highly aggressive represents an interesting paradox. Strong intraspecific aggression should result in high intraspecific competition and limit the densities reached by exotic species. One mechanism that can allow invaders to attain high densities despite high intraspecific aggression, involves positive correlations between aggression and other behaviors such as foraging activity. We conducted a mesocosm experiment to quantify the ecological implications of correlations between aggressiveness and foraging activity among groups of exotic signal crayfish (Pacifastacus leniusculus) at low and high densities. Our results showed that high invader densities increased intraspecific aggression and per capita interactions between crayfish, but also increased foraging activity and impacts on preferred prey. As a result, exotic crayfish did not show density-dependent reductions in per capita feeding or growth rates. We suggest that the positive correlation between aggression and activity is part of an aggression syndrome whereby some individuals are generally more aggressive/active than others across situations. An aggression syndrome can couple aggressive behaviors important to population establishment of invasive species with foraging activity that enhances the ability of invaders to attain high densities and have large impacts on invaded communities.

title: Social Personality Polymorphism and the Spread of Invasive Species: A Model
abstract: Ecological invasions are a major worldwide problem exacting tremendous economic and ecological costs. Efforts to explain variability in invasion speed and impact by searching for combinations of ecological conditions and species traits associated with invasions have met with mixed success. We use a simulation model that integrates insights from life-history theory, animal personalities, network theory, and spatial ecology to derive a new mechanism for explaining variation in animal invasion success. We show that spread occurs most rapidly when (1) a species includes a mix of life-history or personality types that differ in density-dependent performance and dispersal tendencies, (2) the differences between types are of intermediate magnitude, and (3) patch connections are intermediate in number and widely spread. Within-species polymorphism in phenotype (e.g., life-history strategies or personality), a feature not included in previous models, is important for overcoming the fact that different traits are associated with success in different stages of the invasion process. Polymorphism in sociability (a personality type) increases the speed of the invasion front, since asocial individuals colonize empty patches and facilitate the local growth of social types that, in turn, induce faster dispersal by asocials at the invasion edge. The results hold implications for the prediction of invasion impacts and the classification of traits associated with invasiveness.

title: Are animal personality traits linked to life-history productivity?
abstract: Animal personality traits such as boldness, activity and aggressiveness have been described for many animal species. However, why some individuals are consistently bolder or more active than others, for example, is currently obscure. Given that life-history tradeoffs are common and known to promote inter-individual differences in behavior, we suggest that consistent individual differences in animal personality traits can be favored when those traits contribute to consistent individual differences in productivity (growth and/or fecundity). A survey of empirical studies indicates that boldness, activity and/or aggressiveness are positively related to food intake rates, productivity and other life-history traits in a wide range of taxa. Our conceptual framework sets the stage for a closer look at relationships between personality traits and life-history traits in animals.

title: Consequences of heterogeneity in survival probability in a population of Florida scrub-jays.
abstract: 1. Using data on breeding birds from a 35-year study of Florida scrub-jays Aphelocoma coerulescens (Bosc 1795), we show that survival probabilities are structured by age, birth cohort, and maternal family, but not by sex. Using both accelerated failure time (AFT) and Cox proportional hazard models, the data are best described by models incorporating variation among birth cohorts and greater mortality hazard with increasing age. AFT models using Weibull distributions with the shape parameter > 1 were always the best-fitting models. 2. Shared frailty models allowing for family structure greatly reduce model deviance. The best-fitting models included a term for frailty shared by maternal families. 3. To ask how long a data set must be to reach qualitatively the same conclusions, we repeated the analyses for all possible truncated data sets of 2 years in length or greater. Length of the data set affects the parameter estimates, but not the qualitative conclusions. In all but three of 337 truncated data sets the best-fitting models pointed to same conclusions as the full data set. Shared frailty models appear to be quite robust. 4. The data are not adequate for testing hypotheses as to whether variation in frailty is heritable. 5. Substantial structured heterogeneity for survival exists in this population. Such structured heterogeneity has been shown to have substantial effects in reducing demographic stochasticity.

title: Growth-mortality tradeoffs and 'personality traits' in animals.
abstract: Consistent individual differences in boldness, reactivity, aggressiveness, and other 'personality traits' in animals are stable within individuals but vary across individuals, for reasons which are currently obscure. Here, I suggest that consistent individual differences in growth rates encourage consistent individual differences in behavior patterns that contribute to growth-mortality tradeoffs. This hypothesis predicts that behavior patterns that increase both growth and mortality rates (e.g. foraging under predation risk, aggressive defense of feeding territories) will be positively correlated with one another across individuals, that selection for high growth rates will increase mean levels of potentially risky behavior across populations, and that within populations, faster-growing individuals will take more risks in foraging contexts than slower-growing individuals. Tentative empirical support for these predictions suggests that a growth-mortality perspective may help explain some of the consistent individual differences in behavioral traits that have been reported in fish, amphibians, reptiles, and other animals with indeterminate growth.

title: Demographic and Environmental Stochasticity Concepts and Definitions
abstract: General definitions of demographic and environmental variances as well as demographic covariance are given from first principles. The sum of the environmental variance and the demographic covariance is the covariance betweeen two individuals' contributions to the population growth within a year and corresponds to the coefficient of x2 in the expression for the variance of the change in population size. Hence, this coefficient may actually be negative. The demographic variance is the variance among individuals. It is shown that the definitions are consistent with use of these terms in models with additive effects and in diffusion approximations to population processes. The connection to classical birth and death processes, in which the environmental variance and demographic covariance is always zero, is discussed. The concepts are illustrated by some stochastic simulations.

title: Individual Heterogeneity in Vital Parameters and Demographic Stochasticity
abstract: Most population models assume that individuals have equal opportunities for survival and reproduction, although many natural populations consist of individuals with different vital parameters that remain different over time. Individual heterogeneity in vital parameters, which may depend on age or stage, can alter many population characteristics compared with a homogeneous population, affecting both deterministic and stochastic properties of the population process. Demographic variance is an important parameter influenced by heterogeneity. However, whether heterogeneity leads to increased or decreased demographic variance has been an unresolved question, except for special cases. Here, we present a general stochastic matrix model for a heterogeneous population that allows us to examine effects of heterogeneity on population dynamics, even when the degree of heterogeneity depends on age. Using this model, we found that the demographic variance may increase, decrease, or remain unaltered compared with a homogeneous comparison model, depending on the vital parameter values and on how these are distributed among individuals at each time step. Furthermore, if the reproductive value is the same for all individuals, heterogeneity has no effect on the demographic variance. Thus, we provide a general theoretical framework for analyzing how individual heterogeneity caused by different biological mechanisms affects fluctuations of especially small populations.

title: Unstructured Individual Variation and Demographic Stochasticity
abstract: Author(s): Kendall, Bruce E; Fox, Gordon A | Abstract: Demographic stochasticity increases the variance in the growth rate of small populations, and is an important factor to consider when predicting the fates of such populations. Unfortunately, the concept has been treated inconsistently. It is often defined verbally as representing chance variation among individuals in both traits (such as survival probability) and fates (such as whether the individual survived or not). In practice it is modeled as variation in fates only, with all individuals having identical underlying traits. In previous work we demonstrated that structured (but unmodeled) individual variability in survival traits can reduce the variance in population survivorship associated with demographic stochasticity, but that unstructured random variability in survival traits has no such effect. We implicitly generalized the latter result to fecundity, without offering proof. Robert et al. (2003) have demonstrated, using simulations, that unstructured individual variability in fecundity traits can increase the extinction risk of a small population when demographic stochasticity in fecundity is modeled as following a Poisson distribution. In this paper we extend our earlier theory to correct our mistaken speculations and analytically show the source of Robert et al.’s results. We also provide general predictions about the circumstances under which both structured and unstructured individual trait variation should either increase or decrease the magnitude of demographic stochasticity in the population.

title: Demographic heterogeneity, cohort selection, and population growth.
abstract: Demographic heterogeneity--variation among individuals in survival and reproduction--is ubiquitous in natural populations. Structured population models address heterogeneity due to age, size, or major developmental stages. However, other important sources of demographic heterogeneity, such as genetic variation, spatial heterogeneity in the environment, maternal effects, and differential exposure to stressors, are often not easily measured and hence are modeled as stochasticity. Recent research has elucidated the role of demographic heterogeneity in changing the magnitude of demographic stochasticity in small populations. Here we demonstrate a previously unrecognized effect: heterogeneous survival in long-lived species can increase the long-term growth rate in populations of any size. We illustrate this result using simple models in which each individual's annual survival rate is independent of age but survival may differ among individuals within a cohort. Similar models, but with nonoverlapping generations, have been extensively studied by demographers, who showed that, because the more "frail" individuals are more likely to die at a young age, the average survival rate of the cohort increases with age. Within ecology and evolution, this phenomenon of "cohort selection" is increasingly appreciated as a confounding factor in studies of senescence. We show that, when placed in a population model with overlapping generations, this heterogeneity also causes the asymptotic population growth rate lambda to increase, relative to a homogeneous population with the same mean survival rate at birth. The increase occurs because, even integrating over all the cohorts in the population, the population becomes increasingly dominated by the more robust individuals. The growth rate increases monotonically with the variance in survival rates, and the effect can be substantial, easily doubling the growth rate of slow-growing populations. Correlations between parent and offspring phenotype change the magnitude of the increase in lambda, but the increase occurs even for negative parent-offspring correlations. The effect of heterogeneity in reproductive rate on lambda is quite different: growth rate increases with reproductive heterogeneity for positive parent-offspring correlation but decreases for negative parent-offspring correlation. These effects of demographic heterogeneity on lambda have important implications for population dynamics, population viability analysis, and evolution.

title: Demographic heterogeneity impacts density-dependent population dynamics
abstract: Among-individual variation in vital parameters such as birth and death rates that is unrelated to age, stage, sex, or environmental fluctuations is referred to as demographic heterogeneity. This kind of heterogeneity is prevalent in ecological populations, but is almost always left out of models. Demographic heterogeneity has been shown to affect demographic stochasticity in small populations and to increase growth rates for density-independent populations. The latter is due to “cohort selection,” where the most frail individuals die out first, lowering the cohort’s average mortality as it ages. The importance of cohort selection to population dynamics has only recently been recognized. We use a continuous-time model with density dependence, based on the logistic equation, to study the effects of demographic heterogeneity in mortality and reproduction. Reproductive heterogeneity is introduced in three ways: parent fertility, offspring viability, and parent–offspring correlation. We find that both the low-density growth rate and the equilibrium population size increase as the magnitude of mortality heterogeneity increases or as parent–offspring phenotypic correlation increases. Population dynamics are affected by complex interactions among the different types of heterogeneity, and trade-off scenarios are examined which can sometimes reverse the effect of increased heterogeneity. We show that there are a number of different homogeneous approximations to heterogeneous models, but all fail to capture important parts of the dynamics of the full model.

title: EFFECTS OF INDIVIDUAL HETEROGENEITY IN ESTIMATING THE PERSISTENCE OF SMALL POPULATIONS
abstract: Population viability models are commonly used to estimate the probability of pprsistence of smrll, thrcatened, or endangered populations. Demographic, temporal, spatial, and individual heterogeneity are inlportant factors affecting the probability of persistence of small populations. Bccausc stochvstic process are intractable analytically (Ludwig [lSSG]), computer simulation models are often used for estimating population viability via numerical techniques. Although demographic, spatial, and temporal stochast~city have becrl i~icurpulaLcld ir~tu some populat io~~ viability models, individual heterogeneity has not been included. In this pnpw we include individual heterogeneity in a simulation model and examine probabilities of population persistence a t different levels of heterogeneity and population size. Individual heterogencity may incrceae the probability of pelsisleoce of rrrlall populations. The mechanism for the extension in persistence may be explained by natural selection. Genotypes persisting through a decline may be those that survive better under the conditiurla cauhing tlic decline. These individuals that survive and reproduce in the face of adverse conditions may extend the probability ths t a small popnlat,ion persists. I \ 1 ,)11..1I. I , , \ . I l ' l i i l l . . \ 1 11111\1 11111 . . . . . 2 . . . . , . 1 .; .I , I , I . .I,,.., I . . ,,.1..,1."' 1. I . . : ,,I. I , . . I , . . . I t ~ ~ r . ~ . ~ t . i~.c, . ,! . 1 t,; , . I : I . > . ~

title: Heterogeneity's ruses: some surprising effects of selection on population dynamics.
abstract: "As a cohort of people, animals, or machines ages, the individuals at highest risk tend to die or exit first. This differential selection can produce patterns of mortality for the population as a whole that are surprisingly different from the patterns for subpopulations or individuals. Naive acceptance of observed population patterns may lead to erroneous policy recommendations if an intervention depends on the response of individuals. Furthermore, because patterns at the individual level may be simpler than composite population patterns, both theoretical and empirical research may be unnecessarily complicated by failure to recognize the effects of heterogeneity."

title: On the coevolution of social responsiveness and behavioural consistency
abstract: Recent research focuses on animal personalities, that is individual differences in behaviour that are consistent across contexts and over time. From an adaptive perspective, such limited behavioural plasticity is surprising, since a more flexible structure of behaviour should provide a selective advantage. Here, we argue that consistency can be advantageous because it makes individuals predictable. Predictability, however, can only be advantageous if at least some individuals in the population respond to individual differences. Consequently, the evolution of consistency and responsiveness are mutually dependent. We present a general analysis of this coevolutionary feedback for scenarios that can be represented as matrix games with two pure strategies (e.g. hawk-dove game, snowdrift game). We first show that responsive strategies are favoured whenever some individual differences are present in the population (e.g. due to mutation and drift). We then show that the presence of responsive individuals can trigger a coevolutionary process between responsiveness and consistency that gives rise to populations in which responsive individuals coexist with unresponsive individuals who show high levels of adaptive consistency in their behaviour. Next to providing an adaptive explanation for consistency, our results also link two key features associated with personalities, individual differences in responsiveness and behavioural consistency.

title: On the Evolution of Personalities via Frequency-Dependent Selection
abstract: Personality differences can be found in a wide range of species across the animal kingdom, but why natural selection gave rise to such differences remains an open question. Frequency-dependent selection is a potent mechanism explaining variation; it does not explain, however, the other two key features associated with personalities, consistency and correlations. Using the hawk-dove game and a frequency-dependent foraging game as examples, we here show that this changes fundamentally whenever one takes into account the physiological architecture underlying behavior (e.g., metabolism). We find that the inclusion of physiology changes the evolutionary predictions concerning consistency and correlations: while selection gives rise to inconsistent individuals and stochastically fluctuating behavioral correlations in scenarios that neglect physiology, we find high levels of behavioral consistency and tight and stable trait correlations in scenarios that incorporate physiology. The coevolution of behavioral and physiological traits also gives rise to adaptive physiological differences that are systematically associated with behavioral differences. As well as providing a framework for understanding behavioral consistency and behavioral correlations, our work thus also provides an explanation for systematic physiological differences within populations, a phenomenon that appears to exist in a wide range of species but that, up to now, has been poorly understood.

title: Site-specific group selection drives locally adapted group compositions
abstract: Group selection may be defined as selection caused by the differential extinction or proliferation of groups. The socially polymorphic spider Anelosimus studiosus exhibits a behavioural polymorphism in which females exhibit either a ‘docile’ or ‘aggressive’ behavioural phenotype. Natural colonies are composed of a mixture of related docile and aggressive individuals, and populations differ in colonies’ characteristic docile:aggressive ratios. Using experimentally constructed colonies of known composition, here we demonstrate that population-level divergence in docile:aggressive ratios is driven by site-specific selection at the group level—certain ratios yield high survivorship at some sites but not others. Our data also indicate that colonies responded to the risk of extinction: perturbed colonies tended to adjust their composition over two generations to match the ratio characteristic of their native site, thus promoting their long-term survival in their natal habitat. However, colonies of displaced individuals continued to shift their compositions towards mixtures that would have promoted their survival had they remained at their home sites, regardless of their contemporary environment. Thus, the regulatory mechanisms that colonies use to adjust their composition appear to be locally adapted. Our data provide experimental evidence of group selection driving collective traits in wild populations.

title: The relationship between anti-predator behaviour and aggression among conspecifics in the three-spined stickleback, Gasterosteus Aculeatus

abstract: The response of individual breeding three-spined sticklebacks to territorial intruders of various species was compared with their response to a predator outside the breeding season. The nature of the territorial response to the different intruders, as revealed by factor analysis, was very similar and the level of aggression shown to the different species co-varied across individuals and during each breeding cycle. The level of territorial aggression of the individual fish was positively correlated with their ‘boldness’ towards a predator. These results provide tentative support for the idea that anti-predator behaviour and aggression towards conspecifics are linked in this species. Supporting evidence for and possible adaptive significance of these results are discussed.

title: Frequency-Dependent Success of Cheaters During Foraging Bouts Might Limit Their Spread within Colonies of a Socially Polymorphic Spider
abstract: Although several studies have demonstrated that frequency-dependent effects can promote the maintenance of cooperative behavior in microbes, experimental evidence of frequency-dependent effects in cooperative animal societies is rare. We staged mixed phenotype feeding bouts in the spider Anelosimus studiosus, which shows a within-population social polymorphism, to determine how phenotype frequency affects the foraging success of the social (cooperative) and asocial (cheater) phenotypes. Foraging performance was inferred from average change in percent mass for the respective phenotypes after staged group foraging events. We then performed a field census of multifemale colonies of A. studiosus to determine the phenotypic composition of naturally occurring colonies. Our data indicate that asocial (i.e., cheater) individuals experience negative frequency-dependent foraging success in staged foraging contests. Asocial individuals outperform social individuals when their representation is low, but lose this competitive advantage as their relative numbers increase. Naturally occurring colonies, on average, contained 58.33% social and 41.67% asocial individuals.

title: Similar patterns of frequency‐dependent selection on animal personalities emerge in three species of social spiders
abstract: Frequency‐dependent selection is thought to be a major contributor to the maintenance of phenotypic variation. We tested for frequency‐dependent selection on contrasting behavioural strategies, termed here ‘personalities’, in three species of social spiders, each thought to represent an independent evolutionary origin of sociality. The evolution of sociality in the spider genus Anelosimus is consistently met with the emergence of two temporally stable discrete personality types: an ‘aggressive’ or ‘docile’ form. We assessed how the foraging success of each phenotype changes as a function of its representation within a colony. We did this by creating experimental colonies of various compositions (six aggressives, three aggressives and three dociles, one aggressive and five dociles, six dociles), maintaining them in a common garden for 3 weeks, and tracking the mass gained by individuals of either phenotype. We found that both the docile and aggressive phenotypes experienced their greatest mass gain in mixed colonies of mostly docile individuals. However, the performance of both phenotypes decreased as the frequency of the aggressive phenotype increased. Nearly identical patterns of phenotype‐specific frequency dependence were recovered in all three species. Naturally occurring colonies of these spiders exhibit mixtures dominated by the docile phenotype, suggesting that these spiders may have evolved mechanisms to maintain the compositions that maximize the success of the colony without compromising the expected reproductive output of either phenotype.

title: An introduction to population genetics theory
abstract: An introduction to population genetics theory , An introduction to population genetics theory , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

title: Mass-Action Models of Plant Mating Systems: The Evolutionary Stability of Mixed Mating Systems
abstract: In self-compatible plants the selfing rate is directly related to the relative amounts of self and outcross pollen deposited on receptive stigmas. As a result, the fraction of ovules self-fertilized by a particular plant is a function not only of the fraction of the pollen it produces that is deposited on its own stigma but of the amount of pollen exported by other plants in the population and the probability that exported pollen successfully reaches its receptive stigmas. Thus, the reproductive success of different genotypes is both frequency- and density-dependent. In dense populations in which the probability of successful pollen export is relatively high, complete outcrossing is evolutionarily stable, even in the absence of inbreeding depression. In sparse populations, genotypes that increase the selfing rate in the population may increase in frequency, but genotypes that cause complete selfing can never become fixed, unless reproduction is pollen-limited. Whenever self-fertilization can evolve, mixed mating systems are evolutionarily stable. This model predicts that selfing rates should be both density-dependent and frequency-dependent. The limited data currently available are consistent with both of these predictions, although there are several complications in attempting to apply the mass-action model directly to biotically pollinated plants. These results suggest that the probability of successful outcrossed reproduction plays at least as important a role in determining the mating system of plants as inbreeding depression.

title: Principles of population genetics
abstract: Genetic and Phenotypic Variation Organisation of Genetic Variation Random Genetic Drift Mutation and the Neutral Theory Darwinian Selection Inbreeding, Population Subdivision, and Migration Molecular Population Genetics Evolutionary Quantitative Genetics Population Genomics Human Population Genetics

title: Yolk hormones have sex-specific long-term effects on behavior in the pied flycatcher (Ficedula hypoleuca)
abstract: The hormonal environment during early development, such as maternally derived androgens in bird eggs, shapes the development and phenotype of the offspring in ways that may have important long-term consequences for behaviour. We studied the effects of yolk androgens on multiple behavioural traits in female and male pied flycatchers (Ficedula hypoleuca) by experimentally elevating androgen levels (testosterone and androstenedione) in the eggs. The birds were housed in a common-garden environment in captivity until full independence, after which their behaviour was tested. We found that androgen-treated males were more likely than control males to explore a novel environment and showed higher activity in the presence of a novel object. In response to a simulated predator attack, androgen-treated males mainly showed freezing behaviour, while control males showed escape behaviour. Females from the androgen treatment and control group showed no differences in these behaviours. Androgen treatment did not affect neophobia (latency to approach the novel object) or dominance behaviour in either sex. Behaviour in the novel environment and towards a novel object was repeatable, but behaviours in the different experiments were mostly not inter-correlated. These results indicate that yolk androgens have various long-lasting effects on behaviour, especially in males, but that they do not induce a distinct behavioural syndrome. As behaviour is strongly linked with fitness, our results suggest that yolk androgens may play a role in determining fitness, and thus play a potentially adaptive role.

title: Evolutionarily singular strategies and the adaptive growth and branching of the evolutionary tree
abstract: We present a general framework for modelling adaptive trait dynamics in which we integrate various concepts and techniques from modern ESS-theory. The concept of evolutionarily singular strategies is introduced as a generalization of the ESS-concept. We give a full classification of the singular strategies in terms of ESS-stability, convergence stability, the ability of the singular strategy to invade other populations if initially rare itself, and the possibility of protected dimorphisms occurring within the singular strategy's neighbourhood. Of particular interest is a type of singular strategy that is an evolutionary attractor from a great distance, but once in its neighbourhood a population becomes dimorphic and undergoes disruptive selection leading to evolutionary branching. Modelling the adaptive growth and branching of the evolutionary tree can thus be considered as a major application of the framework. A haploid version of Levene's ‘soft selection’ model is developed as a specific example to demonstrate evolutionary dynamics and branching in monomorphic and polymorphic populations.

title: Nongenomic transmission across generations of maternal behavior and stress responses in the rat.
abstract: In the rat, variations in maternal care appear to influence the development of behavioral and endocrine responses to stress in the offspring. The results of cross-fostering studies reported here provide evidence for (i) a causal relationship between maternal behavior and stress reactivity in the offspring and (ii) the transmission of such individual differences in maternal behavior from one generation of females to the next. Moreover, an environmental manipulation imposed during early development that alters maternal behavior can then affect the pattern of transmission in subsequent generations. Taken together, these findings indicate that variations in maternal care can serve as the basis for a nongenomic behavioral transmission of individual differences in stress reactivity across generations.

title: Epigenetic programming by maternal behavior
abstract: Here we report that increased pup licking and grooming (LG) and arched-back nursing (ABN) by rat mothers altered the offspring epigenome at a glucocorticoid receptor (GR) gene promoter in the hippocampus. Offspring of mothers that showed high levels of LG and ABN were found to have differences in DNA methylation, as compared to offspring of 'low-LG-ABN' mothers. These differences emerged over the first week of life, were reversed with cross-fostering, persisted into adulthood and were associated with altered histone acetylation and transcription factor (NGFI-A) binding to the GR promoter. Central infusion of a histone deacetylase inhibitor removed the group differences in histone acetylation, DNA methylation, NGFI-A binding, GR expression and hypothalamic-pituitary-adrenal (HPA) responses to stress, suggesting a causal relation among epigenomic state, GR expression and the maternal effect on stress responses in the offspring. Thus we show that an epigenomic state of a gene can be established through behavioral programming, and it is potentially reversible.

title: Dealing with death data: individual hazards, mortality and bias
abstract: In ecology and evolution, we have barely begun to tap the information available in survival data. Who lives or dies, and why, is a large part of natural selection. In ecology, these are key questions for building better individual-based models of population and community dynamics. Powerful analytical tools exist to answer them, but the literature is scattered across disciplines, and its relevance is often obscured by inconsistent terminology and technical presentation. Here, we evaluate methods for the application of such tools to ecology and evolution. Analyses based on individual hazards of death are particularly promising, especially in combination with improvements in sampling design. The same methods can also reduce the largely unrecognized biases that plague population-level estimates of mortality rates.

title: A Complete Classification of Darwinian Extinction in Ecological Interactions
abstract: The evolution of a population by individual‐level natural selection can result in the population’s extinction. Selection causes the spread of phenotypes with higher relative fitness, but at the same time, selection can also indirectly produce changes in the physical, biotic, or genotypical environment through population interactions (e.g., environment modification, interspecific interactions, and genomic conflict). Because fitness is environment dependent, this can cause mean fitness to decrease, resulting in extinction. I call this process “Darwinian extinction.” Examples of Darwinian extinction include a variety of dynamics and modes of extinction, but the variation is constrained. I determine the complete classification of possible dynamics and modes of Darwinian extinction due to ecological interactions, using bifurcation theory and models with ecological and evolutionary changes occurring on different timescales. This classification is also extended to extinctions due to interactions within the population. The mode of extinction may be either sudden or gradual (requiring additional stochastic processes), and each mode has specific types of dynamics associated with it. Darwinian extinction is a robust and normal phenomenon, and this reasonably complete classification can help us understand more thoroughly its role in nature.

title: Evolution in Stage-Structured Populations
abstract: For many organisms, stage is a better predictor of demographic rates than age. Yet no general theoretical framework exists for understanding or predicting evolution in stage-structured populations. Here, we provide a general modeling approach that can be used to predict evolution and demography of stage-structured populations. This advances our ability to understand evolution in stage-structured populations to a level previously available only for populations structured by age. We use this framework to provide the first rigorous proof that Lande’s theorem, which relates adaptive evolution to population growth, applies to stage-classified populations, assuming only normality and that evolution is slow relative to population dynamics. We extend this theorem to allow for different means or variances among stages. Our next major result is the formulation of Price’s theorem, a fundamental law of evolution, for stage-structured populations. In addition, we use data from Trillium grandiflorum to demonstrate how our models can be applied to a real-world population and thereby show their practical potential to generate accurate projections of evolutionary and population dynamics. Finally, we use our framework to compare rates of evolution in age- versus stage-structured populations, which shows how our methods can yield biological insights about evolution in stage-structured populations.

title: Reproductive consequences of male body mass and aggressiveness depend on females’ behavioral types
abstract: Relatively few investigations explicitly test for concordant versus conflicting selection pressures from intrasexual versus intersexual selection. Here, we examine the effects of male body mass and behavioral type (BT) on reproductive success in the spider Anelosimus studiosus, with emphasis placed on the potential interaction between intrasexual and intersexual selection influences. Female A. studiosus exhibit either an aggressive-active or docile-passive BT, both of which co-occur in multifemale colonies. Males, in contrast, exhibit a more continuous distribution of behavioral tendencies. We investigated the male traits favored by females in five trial types: one docile female, one aggressive female, four docile females, four aggressive females, and two docile and two aggressive females. Male reproductive success was estimated by the number eggs produced by females following staged mating trials. In previous work, it was established that large aggressive males are favored in male–male contests, an intrasexual effect. However, large aggressive males were not universally favored here. We failed to detect an effect of male body mass or aggressiveness on reproductive success in trials with all docile females; however, in situations involving aggressive females, large aggressive males experienced diminished reproductive success relative to small docile males. Large, aggressive males were also more likely to be attacked and killed by aggressive females in the first 20 min of staged encounters and were more likely to be found dead after 72 h of unobserved interactions. Taken together, our data suggest that the reproductive consequences of male traits differ based on (1) the aspect of sexual selection being considered (intrasexual versus intersexual) and (2) the BT of their prospective mates: large aggressive males enjoy advantages in intrasexual selection and when courting docile females and small docile males experience reduced risk of cannibalism and increased reproductive success with aggressive females.

title: Intimidating courtship and sex differences in predation risk lead to sex-specific behavioural syndromes
abstract: Behavioural correlations between mating behaviour and antipredator behaviour are expected when sexual behaviour increases predation risk. However, the correlation would be different between males and females, particularly when the sexes experience different levels of predation risk. Here, we tested this idea using a water strider species, Gerris gracilicornis (Heteroptera: Gerridae). G. gracilicornis males employ an unusual intimidating courtship strategy capitalizing on predator behaviours and female response to predators. Since mounted females are more vulnerable than males to predatory attacks from below, we predicted that changes in female mating behaviours across predation contexts (boldness in a mating context) should be associated with female antipredator behaviours (boldness in a nonmating context), but that the correlation would be weaker for male mating behaviours. In a series of behavioural assays, we measured water striders' (1) mating behaviour in the absence of predators, (2) mating behaviour in the presence of predation risk, (3) boldness in the mating context (changes in female mating behaviour after predator attacks) and (4) boldness in the nonmating context. We found that females behaved more cautiously around predators in both the mating and nonmating contexts. We also found that females' boldness in the mating context was significantly correlated with their boldness in the nonmating context. In contrast to females, antipredator behaviour of males in the nonmating context did not correlate with their boldness in the mating context. Thus we suggest that sex differences in boldness across predation contexts appear to cause sex-specific behavioural syndromes.

title: A behavioral syndrome linking courtship behavior toward males and females predicts reproductive success from a single mating in the hissing cockroach, Gromphadorhina portentosa
abstract: Suites of correlated behaviors, or "behavioral syndromes," have been shown to occur throughout the animal kingdom. Behavioral syndromes involving sexual selection are expected to have significant evolutionary ramifications, but few studies have linked behavioral syndromes to sexual selection. We measured the behavior of male hissing cockroaches (Gromphadorhina portentosa) during male--male competition, female choice, and 3 other ecologically relevant contexts and quantified between-context correlations in behavior. We found that aggression directed toward an opponent and retreat and courtship elicited from an opponent were repeatable among males, suggesting that individuals exhibit stable behavioral types in the context of male--male interaction. Our analyses also revealed a "fast--slow" syndrome, linking behavior in a self-righting context to behavior in a foraging context. In contrast to data from several other species, fast--slow scores in hissing cockroaches were not correlated with aggression in a male--male context. Finally, we identified a new type of behavioral syndrome, which we call "libido." Libido was defined by a positive relationship between courtship directed toward opponents in a male--male context and courtship directed toward potential mating partners in a male--female context. Among males that copulated, libido scores predicted reproductive success. We conclude that the libido syndrome, coupled with sexual selection favoring high courtship intensity in a male--female context, may be responsible for the persistence of male--male courtship behavior in this population.

title: Four ways in which data-free papers on animal personality fail to be impactful
abstract: The literature on animal personality is dominated by papers lacking any data. These papers, which we will call ‘data-free’ papers, are cited and recognized twice as much as comparable empirical studies. In this data-free paper, we highlight 4 common data-free contributions that often fail to have an impact on the topic: a) novel conceptual frameworks suggesting novel avenues of research or hypotheses, b) papers prescribing novel terminologies, c) syntheses revisiting older theories, and d) papers introducing novel statistical methods. We argue that conceptual papers presenting a novel hypothesis probably could almost always be replaced by robust empirical studies actually testing the hypotheses of interest. We hope this paper will stimulate discussion on what makes a data-free paper on animal personality impactful, beyond simply being highly cited.

title: Commentary: Four ways in which data-free papers on animal personality fail to be impactful
abstract: Four ways in which data-free papers on animal personality fail to be impactful. In a recent Frontiers in Ecology and Evolution paper, DiRienzo and Montiglio (2015) suggest that " the literature on animal personality is dominated by papers lacking any data " and that additional data-free papers do little to move the field forward. Here, we present our quantitative analysis of data-free papers in the animal personality and behavioral ecology literature, as well as discuss the value of such articles. We found that data-free papers composed 20% of all publications on animal personalities in the last decade. We further determined the prevalence of data-free papers within the top-ten most cited papers in other behavioral ecology fields, showing that animal personality did not have an unusual excess of highly cited data-free papers when compared to other subfields of animal behavior. Regarding the impact of data-free papers, we argue that impactful data-free papers provide coherent syntheses and reviews of current knowledge, integrate different fields of thought in novel ways, or identify important future directions within a framework beyond the scope typical of empirical papers. Ultimately, we suggest that a combination of robust empirical studies and effectual data-free papers is vital to advance a field. To quantify the frequency of data-free papers in the animal personality literature, we conducted a web search using Web of Science (BIOSIS Previews). Specifically, we used the search terms " behavio * syndrome * " OR " animal personalit * " for the period 2005–2014, which follows Sih et al.'s influential papers in 2004 (Sih et al., 2004a,b). Our search differed from DiRienzo and Montiglio's (" individual behavioral variation ") because we felt that ours more accurately assessed the overall animal personality literature; however, searches using any combination of these terms yielded the same conclusions. By reading the title and abstract for each paper, we determined whether it contained data. We classified data-free papers into sub-categories: literature reviews, hypothetical ideas/concepts, and general methods. Maintaining consistency with DiRienzo and Montiglio's definition of data-free, all statistical methods, meta-analyses, simulations, or mathematical modeling papers were not considered data-free as they generate quantitative analyses. We excluded papers not explicitly related to behavioral ecology and animal personality (e.g., human studies). We obtained 473 papers, of which 20% were data-free. Of these data-free papers, 70% were literature reviews, and 19% were hypothetical ideas/conceptual papers. Many of these reviews and idea papers sought to: …