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.     

Incorporating variability in simulations of seasonally forced phenology using integral projection models

Phenology models are becoming increasingly important tools to accurately predict how climate change will impact the life histories of organisms. We propose a class of integral projection phenology models derived from stochastic individual‐based models of insect development and demography. Our derivation, which is based on the rate summation concept, produces integral projection models that capture the effect of phenotypic rate variability on insect phenology, but which are typically more computationally frugal than equivalent individual‐based phenology models. We demonstrate our approach using a temperature‐dependent model of the demography of the mountain pine beetle (Dendroctonus ponderosae Hopkins), an insect that kills mature pine trees. This work illustrates how a wide range of stochastic phenology models can be reformulated as integral projection models. Due to their computational efficiency, these integral projection models are suitable for deployment in large‐scale simulations, such as studies of altered pest distributions under climate change.     

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.     

Host use dynamics in a heterogeneous fitness landscape generates oscillations in host range and diversification

Colonization of novel hosts is thought to play an important role in parasite diversification, yet little consensus has been achieved about the macroevolutionary consequences of changes in host use. Here, we offer a mechanistic basis for the origins of parasite diversity by simulating lineages evolved in silico. We describe an individual‐based model in which (i) parasites undergo sexual reproduction limited by genetic proximity, (ii) hosts are uniformly distributed along a one‐dimensional resource gradient, and (iii) host use is determined by the interaction between the phenotype of the parasite and a heterogeneous fitness landscape. We found two main effects of host use on the evolution of a parasite lineage. First, the colonization of a novel host allowed parasites to explore new areas of the resource space, increasing phenotypic and genotypic variation. Second, hosts produced heterogeneity in the parasite fitness landscape, which led to reproductive isolation and therefore, speciation. As a validation of the model, we analyzed empirical data from Nymphalidae butterflies and their host plants. We then assessed the number of hosts used by parasite lineages and the diversity of resources they encompass. In both simulated and empirical systems, host diversity emerged as the main predictor of parasite species richness.     

Consistency pays: sex differences and fitness consequences of behavioural specialization in a wide-ranging seabird

Specialists and generalists often coexist within a single population, but the biological drivers of individual strategies are not fully resolved. When sexes differ in their foraging strategy, this can lead them to different environmental conditions and stability across their habitat range. As such, sexual segregation, combined with dominance, may lead to varying levels of specialization between the sexes. Here, we examine spatial and temporal niche width (intraindividual variability in aspects of foraging behaviour) of male and female black-browed albatrosses (Thalassarche melanophrys), and its consequences for fitness. We show that females, where maximum foraging range is under fluctuating selection, exhibit more variable behaviours and appear more generalist than males, who are under directional selection to forage close to the colony. However within each sex, successful birds had a much narrower niche width across most behaviours, suggesting some specialization is adaptive in both sexes. These results demonstrate that while there are sex differences in niche width, the fitness benefit of specialization in spatial distribution is strong in this wide-ranging seabird.     

Habitat restoration will help some functional plant types persist under climate change in fragmented landscapes

In the next century, global climate change is predicted to have large influences on species' distributions. Much of the research in this area has focused on predicting the areas where conditions will be suitable for the species in future, and thus the potential distribution of the species. However, it is equally important to predict the relative abilities of species to migrate into new suitable areas as conditions shift, while accounting for dynamic processes, such as dispersal, maturation, mortality, and reproduction, as well as landscape characteristics, such as level of habitat fragmentation and connectivity. In this study, we developed a spatially explicit individual‐based model that addresses these factors. As a motivating case study, we based aspects of the model on southwest Australia, a global biodiversity hotspot, but stress that the results obtained are generalizable beyond this region. Using the model, we enhanced current understanding of climate change impacts by investigating how and to what extent the functional traits of plant species affect their ability to move with climate change across landscapes with various levels of fragmentation. We also tested the efficacy of strategic restoration, such as planting corridors to increase connectivity among fragments. We found that even if the landscape is fully intact, only an average of 34.2% of all simulated functional groups had a good chance of successfully tracking climate change. However, our study highlights the power of strategic restoration as a tool for increasing species persistence. Corridors linking fragments increased species persistence rates by up to 24%. The lowest persistence rates were found for trees, a functional group with high dispersal but also long generation times. Our results indicate that for trees intervention techniques, such as assisted migration might be required to prevent species losses.     

A study of Choughs'' vocal repertoire: variability related to individuals, sexes and ages

Summary The calls uttered by Choughs (Pyrrhocorax pyrrhocorax) on Islay (S-W Scotland) were recorded during the breeding season. We analysed the vocal repertoire and the degree of call variation, among and within individuals. Eight structurally different calls were identified in Choughs' vocal repertoire. Significant differences in temporal and frequency variables of calls were found between fledglings and adults, whereas females' and males' calls turned out to differ only in two parameters of the commonest call type (chwee-ow). Despite sex-related differences in this call, partners appeared to utter similar versions of it, which suggests that mate vocal mimicry might occur. A certain degree of individuality, i.e. a greater among than within individuals variability, was found in three call types, but the reverse was found in the commonest call of the species. Accordingly, we hypothesise that this call might promote effective species recognition, whereas the other call types would be involved in individual recognition.

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Das stimmliche Repertoire der Alpenkrähe: individuelle, geschlechtliche und altersabhängige Variabilität

Zusammenfassung Während der Brutzeit 1996 wurde das Rufinventar von Alpenkrähen (Pyrrhocorax pyrrhocorax) auf der Insel Islay (SW Schottland) aufgenommen und hinsichtlich individueller Variation und Unterschieden zwischen verschiedenen Individuen analysiert. Acht grundsätzlich verschiedene Rufe wurden unterschieden. Signifikante Unterschiede bestanden zwischen flüggen Jungvögeln und Altvögeln in der Ruffrequenz und der zeitlichen Abfolge der Rufe. Männchen und Weibchen unterschieden sich dagegen nur geringfügig in dem am häufigsten vorgetragenen Ruf. Ungeachtet dieser geringen sexuellen Unterschiede riefen Paarpartner sehr ähnlich, was als Hinweise auf eine Stimmenmimikrie angesehen wird. In drei Ruftypen fand sich eine gewisse Individualität mit größerer Variablität zwischen verschiedenen als innerhalb eines Rufers, wogegen der häufigste Ruf von allen Individuen sehr ähnlich vorgetragen wurde. Es wird geschlossen, daß dieser Ruf der Arterkennung dient, die anderen dagegen mehr der individuellen Erkennung.

     

Seasonality,species richness and poor dispersion mediate intraspecific trait variability in stonefly community responses along an elevational gradient

相似文献   

Temporal effects of disturbance on community composition in simulated stage‐structured plant communities

In an era of global environmental change, understanding how disturbance affects the dynamics of ecological communities is crucial. However, few studies have theoretically explored the potential influence of disturbance including both intensity and frequency on compositional change over time in communities with stage structure. A spatially explicit, individual‐based model was constructed incorporating the various demographic responses to disturbance of plants at two different growth stages: seedlings and adults. In the model, we assumed that individuals within each stage were demographically equivalent (neutral) but differed between stages. We simulated a common phenomenon that seedlings suffered more from disturbance such as grazing and fire than adults. We showed how stage‐structured communities of seedlings and adults responded to disturbance with various levels of disturbance frequency and intensity. In “undisturbed” simulations, the relationship between average species abundance (defined here as the total number of individuals divided by species richness) and community composition turnover (measured by the Bray–Curtis similarity index) was asymptotic. However, in strongly “disturbed” simulations with the between‐disturbance intervals greater than one, this relationship became unimodal. Stage‐dependent response to disturbance underlay the above discrepancy between undisturbed and disturbed communities.     

The fitness threshold model: Random environmental change alters adaptive landscapes

We used a probabilistic optimization model to explore the joint evolutionary effects of random phenotypic and environmental variation. Two forms of environmental noise were defined in which the optimal phenotype remained constant but all organisms experienced either the same proportionate or the same absolute fitness gains and losses. There was no evolutionary effect of proportionate fitness fluctuations. In contrast, the optimal genotype varied with absolute fitness fluctuations, despite the environmental effect being phenotype-independent. We refer to such phenotype-independent fluctuation in absolute fitness as the fitness threshold model, because shared fitness effects determine the zero-fitness points (i.e. the baseline) on an intrinsic fitness function. Thus, environmental effects that are unrelated to a focal trait can cause peak shifts in the genetic optimum for the trait. Changes in the fitness threshold not only changed peak locations, but also altered the slopes defining the peaks, and so should alter the rate of evolution towards optima. This model pertains to evolution in any system, unless there is no phenotypic or environmental variance, or the selection function and distribution of phenotypic error assume similar shapes. Our results have many basic and applied implications for topics such as the maintenance of genetic variation, the canalization of development and the management of natural populations.     

Seed predators exert selection on the subindividual variation of seed size

Subindividual variation among repeated organs in plants constitutes an overlooked level of variation in phenotypic selection studies, despite being a major component of phenotypic variation. Animals that interact with plants could be selective agents on subindividual variation. This study examines selective pressures exerted during post‐dispersal seed predation and germination on the subindividual variation of seed size in hawthorn (Crataegus monogyna). With a seed offering experiment and a germination test, we estimated phenotypic selection differentials for average and subindividual variation of seed size due to seed predation and germination. Seed size affects germination, growth rate and the probability of an individual seed of escaping predation. Longer seeds showed higher germination rates, but this did not result in significant selection on phenotypes of the maternal trees. On the other hand, seed predators avoided wider seeds, and by doing so exerted phenotypic selection on adult average and subindividual variation of seed size. The detected selection on subindividual variation suggests that the levels of phenotypic variation within individual plants may be, at least partly, the adaptive consequence of animal‐mediated selection.     

Introducing efficiency into the analysis of individual lifetime performance variability: a key to assess herd management

Lifetime performance variability is a powerful tool for evaluating herd management. Although efficiency is a key aspect of performance, it has not been integrated into existing studies on the variability of lifetime performance. The goal of the present article is to analyse the effects of various herd management options on the variability of lifetime performance by integrating criteria relative to feed efficiency. A herd model developed for dairy goat systems was used in three virtual experiments to test the effects of the diet energy level, the segmentation of the feeding plan and the mean production potential of the herd on the variability of lifetime performance. Principal component analysis showed that the variability of lifetime performance was structured around the first axis related to longevity and production and the second related to the variables used in feed efficiency calculation. The intra-management variability was expressed on the first axis (longevity and production), whereas the inter-management variability was expressed on the second axis (feed efficiency) and was mainly influenced by the combination of the diet energy level and the mean production potential. Similar feed efficiencies were attained with different management options. Still, such combinations relied on different biological bases and, at the level of the individual, contrasting results were observed in the relationship between the obtained pattern of performance (in response to diet energy) and the reference pattern of performance (defined by the production potential). Indeed, our results showed that over-feeding interacted with the feeding plan segmentation: a high level of feeding plan segmentation generated a low proportion of individuals at equilibrium with their production potential, whereas a single ration generated a larger proportion. At the herd level, the diet energy level and the herd production potential had marked effects on production and efficiency due to dilution of fixed production costs (i.e. maintenance requirements). Management options led to similar production and feed efficiencies at the herd level while giving large contrasts in the proportions of individuals at equilibrium with their production potential. These results suggested that analysing individual variability on the basis of criteria related to production processes could improve the assessment of herd management. The herd model opens promising perspectives in studying whether individual variability represents an advantage for herd performance.     

Evolutionary advantage of small populations on complex fitness landscapes

Recent experimental and theoretical studies have shown that small asexual populations evolving on complex fitness landscapes may achieve a higher fitness than large ones due to the increased heterogeneity of adaptive trajectories. Here, we introduce a class of haploid three-locus fitness landscapes that allow the investigation of this scenario in a precise and quantitative way. Our main result derived analytically shows how the probability of choosing the path of the largest initial fitness increase grows with the population size. This makes large populations more likely to get trapped at local fitness peaks and implies an advantage of small populations at intermediate time scales. The range of population sizes where this effect is operative coincides with the onset of clonal interference. Additional studies using ensembles of random fitness landscapes show that the results achieved for a particular choice of three-locus landscape parameters are robust and also persist as the number of loci increases. Our study indicates that an advantage for small populations is likely whenever the fitness landscape contains local maxima. The advantage appears at intermediate time scales, which are long enough for trapping at local fitness maxima to have occurred but too short for peak escape by the creation of multiple mutants.     

Rethinking the nature of intraspecific variability and its consequences on species coexistence

Intraspecific variability (IV) has been proposed to explain species coexistence in diverse communities. Assuming, sometimes implicitly, that conspecific individuals can perform differently in the same environment and that IV increases niche overlap, previous studies have found contrasting results regarding the effect of IV on species coexistence. We aim at showing that the large IV observed in data does not mean that conspecific individuals are necessarily different in their response to the environment and that the role of high‐dimensional environmental variation in determining IV has largely remained unexplored in forest plant communities. We first used a simulation experiment where an individual attribute is derived from a high‐dimensional model, representing “perfect knowledge” of individual response to the environment, to illustrate how large observed IV can result from “imperfect knowledge” of the environment. Second, using growth data from clonal Eucalyptus plantations in Brazil, we estimated a major contribution of the environment in determining individual growth. Third, using tree growth data from long‐term tropical forest inventories in French Guiana, Panama and India, we showed that tree growth in tropical forests is structured spatially and that despite a large observed IV at the population level, conspecific individuals perform more similarly locally than compared with heterospecific individuals. As the number of environmental dimensions that are well quantified at fine scale is generally lower than the actual number of dimensions influencing individual attributes, a great part of observed IV might be represented as random variation across individuals when in fact it is environmentally driven. This mis‐representation has important consequences for inference about community dynamics. We emphasize that observed IV does not necessarily impact species coexistence per se but can reveal species response to high‐dimensional environment, which is consistent with niche theory and the observation of the many differences between species in nature.     

Variation in floral morphology within a population of Aster hispidus var. tubulosus (Asteraceae,Astereae)

The family Asteraceae has a particular inflorescence, the capitulum, consisting of ray florets and disc florets. The ray florets function as petals that attract pollinators. Marked variation in the ray floret morphology is known in a natural population of Aster hispidus var. tubulosus (Asteraceae). We analyzed the variation and found two distinct types in the ray florets, the long tubular ray floret and the ligulate ray floret. In this species, therefore, the variation in floral morphology among capitula, each of which is the basic pollination unit, is caused by the variation in the composition of the two ray floret types among capitula. We evaluated the sources of the observed variation in the floral morphology among capitula within a population using a hierarchical analysis that separated within‐individual (i.e. among capitula within each individual) and between‐individual components of the variation. We found that the main source of the variation lay at the between‐individual level, not at the between‐capitulum level nested within individuals. This finding will provide the basic knowledge that enables future study exploring whether the between‐individual variation in floral morphology caused by the compositional variation of the ray floret types leads to differential pollination success of individual plants in species of Asteraceae.     

Leaf and stem economics spectra drive diversity of functional plant traits in a dynamic global vegetation model

Functional diversity is critical for ecosystem dynamics, stability and productivity. However, dynamic global vegetation models (DGVMs) which are increasingly used to simulate ecosystem functions under global change, condense functional diversity to plant functional types (PFTs) with constant parameters. Here, we develop an individual‐ and trait‐based version of the DGVM LPJmL (Lund‐Potsdam‐Jena managed Land) called LPJmL‐ flexible individual traits (LPJmL‐FIT) with flexible individual traits) which we apply to generate plant trait maps for the Amazon basin. LPJmL‐FIT incorporates empirical ranges of five traits of tropical trees extracted from the TRY global plant trait database, namely specific leaf area (SLA), leaf longevity (LL), leaf nitrogen content (N_area), the maximum carboxylation rate of Rubisco per leaf area (), and wood density (WD). To scale the individual growth performance of trees, the leaf traits are linked by trade‐offs based on the leaf economics spectrum, whereas wood density is linked to tree mortality. No preselection of growth strategies is taking place, because individuals with unique trait combinations are uniformly distributed at tree establishment. We validate the modeled trait distributions by empirical trait data and the modeled biomass by a remote sensing product along a climatic gradient. Including trait variability and trade‐offs successfully predicts natural trait distributions and achieves a more realistic representation of functional diversity at the local to regional scale. As sites of high climatic variability, the fringes of the Amazon promote trait divergence and the coexistence of multiple tree growth strategies, while lower plant trait diversity is found in the species‐rich center of the region with relatively low climatic variability. LPJmL‐FIT enables to test hypotheses on the effects of functional biodiversity on ecosystem functioning and to apply the DGVM to current challenges in ecosystem management from local to global scales, that is, deforestation and climate change effects.     

kernelpop,a spatially explicit population genetic simulation engine

Individual‐based, spatially explicit models provide a mechanism to understand distributions of individuals on the landscape; however, few models have been coupled with population genetics. The primary benefits of such a combination is to assess performance of population‐genetic estimators in realistic situations. kernelpop represents a flexible framework to implement almost any arbitrary population‐genetic and demographic model in a spatially explicit context using a variety of dispersal kernels. Estimates of type I error associated with genome scans in metapopulations are provided as an illustration of this software's utility.     

Rapid within‐ and transgenerational changes in thermal tolerance and fitness in variable thermal landscapes

Phenotypic plasticity may increase the performance and fitness and allow organisms to cope with variable environmental conditions. We studied within‐generation plasticity and transgenerational effects of thermal conditions on temperature tolerance and demographic parameters in Drosophila melanogaster. We employed a fully factorial design, in which both parental (P) and offspring generations (F1) were reared in a constant or a variable thermal environment. Thermal variability during ontogeny increased heat tolerance in P, but with demographic cost as this treatment resulted in substantially lower survival, fecundity, and net reproductive rate. The adverse effects of thermal variability (V) on demographic parameters were less drastic in flies from the F1, which exhibited higher net reproductive rates than their parents. These compensatory responses could not totally overcome the challenges of the thermally variable regime, contrasting with the offspring of flies raised in a constant temperature (C) that showed no reduction in fitness with thermal variation. Thus, the parental thermal environment had effects on thermal tolerance and demographic parameters in fruit fly. These results demonstrate how transgenerational effects of environmental conditions on heat tolerance, as well as their potential costs on other fitness components, can have a major impact on populations’ resilience to warming temperatures and more frequent thermal extremes.     

Social dynamics and individual plasticity of infant care behavior in cooperatively breeding cotton‐top tamarins

Individual variation in infant caretaking behavior is prevalent among marmoset and tamarin monkeys. Although most group members participate in infant care, the timing and amount provided differs greatly. In this study, we quantified general trends in infant carrying behavior by using a longitudinal database that included 11 years of instantaneous scan observations following 80 births of cotton‐top tamarins. Using detailed focal observations on a subset of the same families (10 births) we identified influences that affected expression of infant care at the group and individual levels. Fathers were the primary carriers and paternal carry time gradually decreased with increasing infant age. Paternal carry time also decreased significantly with an increasing number of older sibling helpers. Most fathers began to carry on the first day postpartum. However, we report circumstances in which fathers delayed carrying until almost a month postpartum. Fathers retrieved infants the most, although adult brothers' rates of retrievals peaked and surpassed fathers' rates during week 4 postpartum. Fathers delayed rejection of infants until week 4, whereas mothers rejected infants immediately and throughout the eight weeks. Nonetheless, infants climbed onto their mothers more than onto any other family member. Mothers showed a high initial investment in carrying during the first two weeks, decreasing quickly thereafter. Maternal contributions to infant carrying remained low and relatively consistent regardless of group size. However, mothers dramatically increased their infant carrying behavior in families in which fathers were absent. Older siblings cared for infants more than did younger siblings, and brothers retrieved and carried infants more than did sisters. Individual expression of infant care changed to accommodate infant needs and changed according to varying social dynamics and circumstances across litters. Am. J. Primatol. 72:296–306, 2010. © 2009 Wiley‐Liss, Inc.