Egg limitation and individual variation in parasitization risk among hosts in host–parasitoid dynamics

Egg limitation is known to destabilize host–parasitoid dynamics. This study reexamines the effect of egg limitation in light of the individual variation in parasitization risk among hosts (e.g., some hosts are more likely to be parasitized than others). Previous studies have considered egg limitation (predicted as a destabilizing factor) and individual variation among hosts (predicted as a stabilizing factor) in isolation; however, their interaction is not known. An individual‐based model was used to examine the effects of each factor and their interaction. The model‐based analysis shows a clear interaction between egg limitation and individual variation in risk among hosts. Egg limitation can both stabilize and destabilize host–parasitioid dynamics depending on the presence and absence of the risk variation. The result suggests that the population‐dynamic consequences of egg limitation are more complex than previously thought and emphasizes the importance of the simultaneous consideration of multiple ecological factors (with individual‐level details) to uncover potential interactions among them.     

Intraindividual variability in behavior shapes fitness landscapes

Although intraindividual variability (IIV) in behavior is fundamental to ecological dynamics, the factors that contribute to the expression of IIV are poorly understood. Using an individual‐based model, this study examined the effects of stochasticity on the evolution of IIV represented by the residual variability of behavior. The model describes a population of prey with nonoverlapping generations, in which prey take refuge upon encountering a predator. The strategy of a prey is characterized by the mean and IIV (i.e., standard deviation) of hiding duration. Prey with no IIV will spend the same duration hiding in a refuge at each predator encounter, while prey with IIV will have variable hiding durations among encounters. For the sources of stochasticity, within‐generation stochasticity (represented by random predator encounters) and between‐generation stochasticity (represented by random resource availability) were considered. Analysis of the model indicates that individuals with high levels of IIV are maintained in a population in the presence of between‐generation stochasticity even though the optimal strategy in each generation is a strategy with no IIV, regardless of the presence or absence of within‐generation stochasticity. This contradictory pattern emerges because the mean behavioral trait and IIV do not independently influence fitness (e.g., the sign of the selection gradient with respect to IIV depends on the mean trait). Consequently, even when evolution eventually leads toward a strategy with no IIV (i.e., the optimal strategy), greater IIV may be transiently selected. Between‐generation stochasticity consistently imposes such transient selection and maintain high levels of IIV in a population.     

Variation in foraging success among predators and its implications for population dynamics

The effects of the expected predation rate on population dynamics have been studied intensively, but little is known about the effects of predation rate variability (i.e., predator individuals having variable foraging success) on population dynamics. In this study, variation in foraging success among predators was quantified by observing the predation of the wolf spider Pardosa pseudoannulata on the cricket Gryllus bimaculatus in the laboratory. A population model was then developed, and the effect of foraging variability on predator–prey dynamics was examined by incorporating levels of variation comparable to those quantified in the experiment. The variability in the foraging success among spiders was greater than would be expected by chance (i.e., the random allocation of prey to predators). The foraging variation was density‐dependent; it became higher as the predator density increased. A population model that incorporates foraging variation shows that the variation influences population dynamics by affecting the numerical response of predators. In particular, the variation induces negative density‐dependent effects among predators and stabilizes predator–prey dynamics.     

Optimisation of the mean boat velocity in rowing

In rowing, motor learning may be facilitated by augmented feedback that displays the ratio between actual mean boat velocity and maximal achievable mean boat velocity. To provide this ratio, the aim of this work was to develop and evaluate an algorithm calculating an individual maximal mean boat velocity. The algorithm optimised the horizontal oar movement under constraints such as the individual range of the horizontal oar displacement, individual timing of catch and release and an individual power–angle relation. Immersion and turning of the oar were simplified, and the seat movement of a professional rower was implemented. The feasibility of the algorithm, and of the associated ratio between actual boat velocity and optimised boat velocity, was confirmed by a study on four subjects: as expected, advanced rowing skills resulted in higher ratios, and the maximal mean boat velocity depended on the range of the horizontal oar displacement.     

Measurement of the time required for termites to pass each other in tunnels of different curvatures

Subterranean termites construct complex tunnel networks for foraging. During travel in the tunnels, termites often encounter one another when passing in opposite directions. Such encounters are likely to affect the “movement efficiency,” which is the time required for a termite to travel a certain distance in a tunnel. In this study, we explored how individual–individual encounters affect movement efficiency in tunnels by measuring the time (τ) taken by two termites to pass one another in tunnels of different curvatures. Artificial tunnels of 5 cm in length and variable widths (W) of 2, 3, or 4 mm were made. Tunnel distance (D) was 2, 3, 4, or 5 cm. When D had a higher value, curvature was lower. When W = 2, τ was significantly shorter in the tunnel with D = 5 than in tunnels of D = 2, 3, or 4, whereas τ was statistically the same for D = 2, 3 and 4. When W = 3, τ was shorter in the tunnel with D = 5 than for D = 3 and 4, while τ was longer in the tunnel with D = 2 than for D = 3 and 4. When W = 4, τ was longer in the tunnels with D = 2 and 3 than for D = 4 and 5. Based on these observations, 3 types of termite behavior were identified: biased walking, backward walking, and zigzag walking. We considered these results in relation to foraging efficiency.     

布氏田鼠社会行为对光周期的适应格局

对实验室内不同光周期条件下的布氏田鼠陌生成体—亚成体间社会行为模式的初步研究显示:不同光周期下成体对亚成体（特别是对雄性亚成体）的行为反应具性二型特征,长光照周期下（light:dark,14L:10D)成体与亚成体同性组合间的争斗较异性组合间的明显,容忍性低,其中成体雄对亚成体雄尤甚。短光照周期下（light:dark,10L:14D）成体雄对亚成体雄、成体雌对亚成体雌及亚成体雄的相容性均较成体雄对亚成体雌的容忍性低,尤成体雌对亚成体雄的排斥表现更为突出,其容忍性也较长光照条件下对应组的低。结果表明,不同光周期条件下布氏田鼠成体与亚成体间的社会行为模式不同。在自然条件下,这些行为模式是其对环境季节变化的一种有效适应,它影响种群中未成年个体存活、补充、扩散重组以及社群结构、种群空间格局季节变化,对该鼠的生存和繁殖有利。     

Seasonal and diel plasticity of song type use in individual ovenbirds (Seiurus aurocapilla)

Animal communication is an important aspect of ecology across taxa, and there is a growing area of research that examines how animals plastically adjust their signals to account for both abiotic and biotic factors. Song type use and the temporal plasticity of song have been described in many bird species, but as of yet, few studies have examined how song type use may change across both seasonal and diel timeframes, and no studies have considered individual-level variation in plasticity. Using a hierarchical framework, we examined temporal patterns of primary and flight song use in ovenbirds (Seiurus aurocapilla; N = 21 individuals). We recorded ovenbird songs (N = 99,259) with autonomous recorders over 24-hr periods once per week across a breeding season near Sault Ste. Marie, Canada. As predicted, the occurrence and frequency of both song types significantly decreased over the season and showed temporal separation over diel periods. Primary songs peaked at dawn and declined throughout the day, while flight songs peaked at dusk and night. Our results support that primary songs have multiple functions as they remained more frequent during dawn and morning across the breeding season, while flight songs likely serve an intersexual function as they decreased similarly for all diel periods as mating opportunities decreased. Individuals were consistent in how frequently they sang their primary songs, but not their flight songs, suggesting that flight songs are more plastically expressed. We highlight the importance of examining plasticity in animal communication at the individual level as we show that males significantly differed in both their song behaviours (random intercepts) and the seasonal plasticity (random slopes) in these behaviours. Integrating themes such as song type use, temporal plasticity, and individual variation will be important for examining the evolutionary mechanisms that shape animal communication systems.     

Decomposing demographic contributions to the effective population size with moose as a case study

Levels of random genetic drift are influenced by demographic factors, such as mating system, sex ratio and age structure. The effective population size (N_e) is a useful measure for quantifying genetic drift. Evaluating relative contributions of different demographic factors to N_e is therefore important to identify what makes a population vulnerable to loss of genetic variation. Until recently, models for estimating N_e have required many simplifying assumptions, making them unsuitable for this task. Here, using data from a small, harvested moose population, we demonstrate the use of a stochastic demographic framework allowing for fluctuations in both population size and age distribution to estimate and decompose the total demographic variance and hence the ratio of effective to total population size (N_e/N) into components originating from sex, age, survival and reproduction. We not only show which components contribute most to N_e/N currently, but also which components have the greatest potential for changing N_e/N. In this relatively long‐lived polygynous system we show that N_e/N is most sensitive to the demographic variance of older males, and that both reproductive autocorrelations (i.e., a tendency for the same individuals to be successful several years in a row) and covariance between survival and reproduction contribute to decreasing N_e/N (increasing genetic drift). These conditions are common in nature and can be caused by common hunting strategies. Thus, the framework presented here has great potential to increase our understanding of the demographic processes that contribute to genetic drift and viability of populations, and to inform management decisions.     

Intraspecific genetic variation and competition interact to influence niche expansion

Theory and empirical evidence show that intraspecific competition can drive selection favouring the use of novel resources (i.e. niche expansion). The evolutionary response to such selection depends on genetic variation for resource use. However, while genetic variation might facilitate niche expansion, genetically diverse groups may also experience weaker competition, reducing density-dependent selection on resource use. Therefore, genetic variation for fitness on different resources could directly facilitate, or indirectly retard, niche expansion. To test these alternatives, we factorially manipulated both the degree of genetic variation and population density in flour beetles (Tribolium castaneum) exposed to both novel and familiar food resources. Using stable carbon isotope analysis, we measured temporal change and individual variation in beetle diet across eight generations. Intraspecific competition and genetic variation acted on different components of niche evolution: competition facilitated niche expansion, while genetic variation increased individual variation in niche use. In addition, genetic variation and competition together facilitated niche expansion, but all these impacts were temporally variable. Thus, we show that the interaction between genetic variation and competition can also determine niche evolution at different time scales.     

From sneaker to bourgeois male: Long-term observations on recognized tompot blenny Parablennius gattorugine individuals reveal new information on their biology

The behaviour of the tompot blenny Parablennius gattorugine was studied by underwater observation and photography on the south-west coast of the UK over an 11 year period, with >50 individuals identified at two locations by their distinctive skin markings. Observations showed males engaging in rapid swimming behaviour when approached by a female, and younger males using alternative ‘sneaker’ tactics before becoming ‘bourgeois’ territory-holders. The noninvasive recognition technique also facilitated detailed observations on territory retention (up to 7 years) and agonistic behaviours among both males and females.     

Long-term memory of individual identity in ant queens

Remembering individual identities is part of our own everyday social life. Surprisingly, this ability has recently been shown in two social insects. While paper wasps recognize each other individually through their facial markings, the ant, Pachycondyla villosa, uses chemical cues. In both species, individual recognition is adaptive since it facilitates the maintenance of stable dominance hierarchies among individuals, and thus reduces the cost of conflict within these small societies. Here, we investigated individual recognition in Pachycondyla ants by quantifying the level of aggression between pairs of familiar or unfamiliar queens over time. We show that unrelated founding queens of P. villosa and Pachycondyla inversa store information on the individual identity of other queens and can retrieve it from memory after 24h of separation. Thus, we have documented for the first time that long-term memory of individual identity is present and functional in ants. This novel finding represents an advance in our understanding of the mechanism determining the evolution of cooperation among unrelated individuals.     

Quantifying synchrony among reproductive or other states

Synchrony among reproductive or other states is a widespread phenomenon of significance in evolutionary theory. A model is presented for use in the measurement of the degree of synchrony in any set of behavioral or biological states, such as menstrual cycling, pregnancy, or lactation. At a given time, maximum group synchrony occurs when all members of a group are in a single state, minimum synchrony occurs when equal numbers are in all states, and intermediate values of synchrony occur for other proportional representations of the states. The model yields group synchrony scores ranging from 0 to 100 by standardizing the average of the absolute deviations among frequencies of occurrence in pairs of states. In addition, individual synchrony is characterized by the proportion of others who share an individual's state at a specified set of times. Properties of the model are discussed, simplified calculation procedures are presented, and the method's usefulness for comparative purposes is illustrated. © 1995 Wiley-Liss, Inc.     

Adjustments and adaptations to indoor and outdoor environments: Continuity and change in young adult rhesus monkeys

Optimal environments for captive primates are assumed to be those which simulate certain ecological features and elicit a wide range of species-typical behavior patterns. Outdoor environments are often thought to be more suitable than indoor environments in that they provide more space and potentially higher levels of stimulation. The purpose of this study was to compare the long-term behavioral responses of several groups of animals that had been reared identically during the first two years of life and then exposed to different environments. Two groups were moved into separate “enriched” indoor pens while one group was moved to an outdoor area covering approximately 5 acres. The monkeys were observed during the first year of life and again in these different environments between the ages of 6 and 10. Although behaviorally similar during the first year of life, monkeys developed different response patterns to indoor and outdoor environments. Contrary to commonly held views, indoor monkeys were not more aggressive, nor did they show higher levels of stereotypical behavior. Instead, indoor monkeys exhibited higher levels of grooming, sexual posturing, tactile/oral exploration, and passive visual behavior than their outdoor counterparts. These differences are consistent with the reconciliation model of de Waal. Individual monkeys also showed remarkable stability in certain traits over the 5-year period. © 1992 Wiley-Liss, Inc.     

Owl dusk chorus is related to the quality of individuals and nest‐sites

Dawn and dusk choruses represent one of the most investigated topics in avian vocal behaviour, but their underlying basis remains unclear. As with the dawn chorus in passerines, dusk chorus in owls seems to support the mate and rival assessment hypothesis and happens during the most constraining period, as individuals have not yet fed and, under the handicap principle, dusk chorus is likely to reveal inter‐individual differences in competitive ability, body condition and/or habitat quality. Here, a study of vocal displays at dusk of 14 Eurasian Eagle Owls Bubo bubo revealed a temporal succession in the order in which males began their vocalizations. The vocalization order appeared to be related to both the quality of the nesting territory (based upon mean number of fledged young and proportion of rats in the diet) and the male's individual quality, as revealed by haematocrit values and the brightness of the white throat patch.     

Variation in social rank acquisition influences lifetime reproductive success in black-capped chickadees

Dominance relationships structure many animal societies, yet the process of rank attainment is poorly understood. We investigated acquisition of social dominance in winter flocks and its fitness consequences in male black-capped chickadees (Poecile atricapillus) over a 10-year period. Age was the best predictor of rank, and paired comparisons showed high-ranked males to be older than their low-ranked flock-mates. When controlling for age, morphological variables did not predict male social rank, but high-ranked males were heavier, had lower fat scores and were in leaner condition than low-ranked males. Males that survived between years tended to increase in rank over time; however, the rate of rank advancement varied individually. Rank reversals between familiar contestants were rare, and changes in male social rank were associated with changes in flock membership. Average lifetime reproductive success (LRS) of males and females was variable and best predicted by lifespan. Male rank history also influenced realized reproductive success. Birds with higher average rank over their lifespan were more likely to reproduce successfully. However, among successful birds, average rank did not significantly predict LRS. Thus, birds that lived longer and attained high social rank earlier had higher fitness, but this effect was not manifested as fine-scale differences among successful individuals. Taken together, these findings demonstrate the importance of social factors influencing individual fitness.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 85–95.     

Individual differences in children's innovative problem-solving are not predicted by divergent thinking or executive functions

Recent studies of children''s tool innovation have revealed that there is variation in children''s success in middle-childhood. In two individual differences studies, we sought to identify personal characteristics that might predict success on an innovation task. In Study 1, we found that although measures of divergent thinking were related to each other they did not predict innovation success. In Study 2, we measured executive functioning including: inhibition, working memory, attentional flexibility and ill-structured problem-solving. None of these measures predicted innovation, but, innovation was predicted by children''s performance on a receptive vocabulary scale that may function as a proxy for general intelligence. We did not find evidence that children''s innovation was predicted by specific personal characteristics.