Eco‐evolutionary dynamics in response to selection on life‐history

Understanding the consequences of environmental change on ecological and evolutionary dynamics is inherently problematic because of the complex interplay between them. Using invertebrates in microcosms, we characterise phenotypic, population and evolutionary dynamics before, during and after exposure to a novel environment and harvesting over 20 generations. We demonstrate an evolved change in life‐history traits (the age‐ and size‐at‐maturity, and survival to maturity) in response to selection caused by environmental change (wild to laboratory) and to harvesting (juvenile or adult). Life‐history evolution, which drives changes in population growth rate and thus population dynamics, includes an increase in age‐to‐maturity of 76% (from 12.5 to 22 days) in the unharvested populations as they adapt to the new environment. Evolutionary responses to harvesting are outweighed by the response to environmental change (~ 1.4 vs. 4% change in age‐at‐maturity per generation). The adaptive response to environmental change converts a negative population growth trajectory into a positive one: an example of evolutionary rescue.     

Constraints on growth and allocation patterns of Silphium integrifolium (Asteraceae) caused by a cynipid gall wasp

Summary Life-history traits of 101 clones from two populations of Daphnia magna were measured under controlled environmental conditions in the laboratory. Some individuals had four juvenile instars, others had five. This depended on their length at birth and on the population they came from. Females in the group with five juvenile instars were smaller at birth but larger and older at maturity than those with four juvenile instars. Within groups of females with equal numbers of preadult instars (instar groups) age and size at maturity increased with size at birth. This relationship differed significantly among instar groups for both age and size at maturity. Significant differences in age and size at maturity between two populations became non-significant when size at birth was used as a covariable in AN-COVA. Within populations, size at birth depended on the clone and on the parity of the clutch. First-clutch offspring were considerably smaller than those from later clutches. The results suggest that variability in life-history traits is common within and between clones, but that most of this variation can be accounted for by size at birth and the number of pre-adult instars.     

Are gardens effective in butterfly conservation? A case study with the pipevine swallowtail, <Emphasis Type="Italic">Battus philenor</Emphasis>

Gardens with nectar sources and larval host plants have been proposed to stem the decline in butterfly abundance caused by habitat loss. However, no study has provided evidence that gardens benefit butterflies. We examined the use of natural sites and gardens in the San Francisco bay area by the butterfly, Battus philenor. We found that natural sites were more likely to attract adult B. philenor, received more oviposition, and had higher juvenile survival than gardens sites. Butterflies were more likely to be present in gardens with established populations of the host plant, Aristolochia californica, growing in the sun. Battus philenor are unlikely to visit gardens with host plants planted within the past 7 years. Gardens between the ages of 8–40 years received oviposition, but did not always support completion of larval development of B. philenor. In gardens with host plants over 40 years of age, B. philenor consistently survived from egg to the adult stage. Natural enemy induced mortality of eggs did not differ between garden and natural sites, but overall egg survival was lower in gardens than at natural sites. It is unlikely that gardens serve as 'refugia' for B. philenor in years when populations in natural sites experience low survival or low fecundity. Even in gardens capable of supporting larvae to maturity, the density of eggs and survival rates were lower than in natural populations of the host plant suggesting that gardens were not optimal habitats. Therefore, without evidence that juvenile abundance and survival rates in gardens matches or exceeds that in natural sites, it is most likely that gardens act as population sinks for B. philenor.     

The influence of persistent individual differences and age at maturity on effective population size

Ratios of effective populations size, N(e), to census population size, N, are used as a measure of genetic drift in populations. Several life-history parameters have been shown to affect these ratios, including mating system and age at sexual maturation. Using a stochastic matrix model, we examine how different levels of persistent individual differences in mating success among males may affect N(e)/N, and how this relates to generation time. Individual differences of this type are shown to cause a lower N(e)/N ratio than would be expected when mating is independent among seasons. Examining the way in which age at maturity affects N(e)/N, we find that both the direction and magnitude of the effect depends on the survival rate of juveniles in the population. In particular, when maturation is delayed, lowered juvenile survival causes higher levels of genetic drift. In addition, predicted shifts in N(e)/N with changing age at maturity are shown to be dependent on which of the commonly used definitions of census population size, N, is employed. Our results demonstrate that patterns of mating success, as well as juvenile survival probabilities, have substantial effects on rates of genetic drift.     

The effects of productivity and seasonality on life history: comparing age at maturity among moose (Alces alces) populations

The productivity hypothesis in respect of an animal species’ geographical range predicts that whereas higher productivity at the equatorial periphery of a species’ range favours superior competitors, lower productivity at the centre of a species’ range favours high reproduction and reduced competitive traits. I test whether life‐history patterns follow this hypothesis, using demographic data from 15 Canadian moose (Alces alces) populations. Two models are contrasted; the first assumes that intraspecific variation in age at maturity is explained proximately by density and juvenile mortality. Age at maturity was found to increase with decreasing juvenile mortality (P = 0.01) and increasing density (P = 0.006). To test the productivity hypothesis, the second model additionally included primary productivity and seasonality as geographical explanatory variables that would ultimately influence age at maturity via juvenile mortality and density. Path analysis indicated that including productivity and seasonality improved the model predictions of variation in age at maturity (R_a² 0.56 and 0.85). In bivariate comparisons, seasonality was negatively associated (P = 0.01) with age at maturity. In the best model, however, primary productivity was the environmental variable that explained 25% of the variance in age at maturity, and forest cover replaced seasonality as an explanatory variable. The positive association between primary productivity and age at maturity is consistent with the productivity hypothesis. Relative to populations that lived at the centre of the species’ range (51°N), moose populations living in relatively high productivity and low seasonality environments (equatorial periphery of species’ range; 48°N) experienced less juvenile mortality, more variable year‐to‐year density, higher relative density and slower life history (slower growth rate, later age at maturity, lower fecundity).     

Effects of experimental manipulations on the life history pattern of Lymnaea stagnalis appressa say (pulmonata: lymnaeidae)

Field sampling of an Iowa population of Lymnaea stagnalis appressa Say indicated an annual generation pattern, with survivorship to maturity of i percent or less. Estimates of adult fecundity ranged from about 300 to 800 eggs.Density and food manipulations were performed to determine whether density dependent limitation of growth rates, maturation, or fecundity occurs in this fresh water pulmonate snail. Addition of a high quality food resource, spinach, accelerated growth rates, but did not drastically accelerate maturity, nor increase fecundity. Density increments lowered growth rates, delayed maturity, and lowered fecundity, and the addition of spinach did not counteract high densities. Adult densities are fairly low in the field population, and adults are randomly dispersed, indicating little density dependent regulation of fecundity in this population. However, the low survivorship to maturity, response in growth rates with food addition, and increasing survivorship with age and size indicate that juvenile mortality may play an important role in structuring life history patterns in this population.     

Comparative survival and recovery of Ross's and lesser snow geese from Canada's central arctic

Large increases in several populations of North American arctic geese have resulted in ecosystem-level effects from associated herbivory. Consequently, some breeding populations have shown density dependence in recruitment through declines in food availability. Differences in population trajectories of lesser snow geese (Chen caerulescens caerulescens; hereafter snow geese) and Ross's geese (C. rossii) breeding in mixed-species colonies south of Queen Maud Gulf (QMG), in Canada's central arctic, suggest that density dependence may be limiting snow goose populations. Specifically, long-term declines in age ratios (immature:adult) of harvested snow geese may have resulted from declines in juvenile survival. Thus, we focused on juvenile (first-year) survival of snow and Ross's geese in relation to timing of reproduction (annual mean nest initiation date) and late summer weather. We banded Ross's and snow geese from 1991 to 2008 in the QMG Migratory Bird Sanctuary. We used age-structured mark-recapture models to estimate annual survival rates for adults and juveniles from recoveries of dead birds. Consistent with life history differences, juvenile snow geese survived at rates higher than juvenile Ross's geese. Juvenile survival of both species also was lower in late seasons, but was unrelated to arctic weather measured during a 17-day period after banding. We found no evidence of density dependence (i.e., a decline in juvenile survival over time) in either species. We also found no interspecific differences in age-specific hunting vulnerability, though juveniles were more vulnerable than adults in both species, as expected. Thus, interspecific differences in survival were unrelated to harvest. Lower survival of juvenile Ross's geese may result from natural migration mortality related to smaller body size (e.g., greater susceptibility to inclement weather or predation) compared to juvenile snow geese. Despite lower first-year survival, recruitment by Ross's geese may still be greater than that by snow geese because of earlier sexual maturity, greater breeding propensity, and higher nest success by Ross's geese. © 2012 The Wildlife Society.     

Interpopulation variation in growth and life-history traits of the introduced sunfish, pumpkinseed Lepomis gibbosus, in southern England

We examined attributes of growth and reproduction in 19 populations of pumpkinseed (Lepomis gibbosus) introduced into southern England in order to: (i) assess variability of these traits in a northern European climate; (ii) assess inter‐relationships among these variables; and (iii) compare these attributes with populations from other parts of Europe where pumpkinseeds have been introduced. Growth rates varied considerably among populations, but juvenile growth rates and adult body sizes were generally among the lowest in Europe. Mean age at maturity ranged from 2.0 to 3.9, and was strongly predicted by the juvenile growth rate (earlier maturity with faster juvenile growth). Other population parameters that also displayed significant negative associations with mean age at maturity were gonadosomatic index, body condition, and adult body size (total length, TL at age 5). Mean TL at maturity and the adult growth increment showed no significant associations with any of the other growth or life‐history variables. Pumpkinseed populations in England matured significantly later than those introduced into warmer, more southerly areas of the continental Europe. All of these data suggest that a combination of cool summer temperatures and resource limitation is the cause of slow growth, small adult body size and delayed maturity relative to introduced populations on the European mainland.     

Life-history traits and potential invasiveness of introduced pumpkinseed Lepomis gibbosus populations in northwestern Europe

To evaluate the potential invasiveness of pumpkinseed Lepomis gibbosus introduced to northwestern European inland waters, growth and reproduction traits were examined in ten populations along a trajectory spanning northwestern Europe (Norway, England, Holland, Belgium and France) and evaluated in light of published dataset from Europe. In the 848 pumpkinseed captured, maximum age was 3–4 years, with a sex ratio near unity in all but one population. Significant variations with increasing latitude were observed in adult growth (age 2–3 increment in total length, TL) and mean age at maturity (A _M), with non-significant variations observed in juvenile growth (TL at age 2), sex ratio and gonado-somatic index. As observed elsewhere in Europe, mean A _M decreased significantly with increasing TL at age 2. Using this relationship, which has been proposed elsewhere as a potential predictive model of pumpkinseed invasiveness, eight of the ten populations could be provisionally categorized as ‘non-invasive’ (five populations), ‘transitional’ (one population) and ‘potentially invasive’ (two populations), with two populations not categorized due to insufficient data. Based on the available knowledge on each population, the relationship between juvenile growth and age at maturity appeared to predict reasonably the status of pumpkinseed in northwestern Europe and its applicability to other species should be tested.     

The island syndrome in isolated populations of a tropical forest rodent

I examined population traits of eight isolated populations of a tropical forest rodent (Proechimys semispinosus, the Central American spiny rat) for 1 year in central Panamá. Populations were sampled by monthly live-trapping, and seven traits (density, population growth rate, adult survival, reproductive effort, age structure, sex ratio, and body mass) were compared among populations. I also compared results with published data from nearby mainland populations. Each isolated population showed characteristics typical of island populations when compared with mainland populations, including higher and more stable densities, reduced reproductive effort, and greater body mass. Densities were the highest yet recorded for this species, and biomass of these island populations was among the highest of any tropical rodent yet studied. Population traits varied not only between island and mainland populations but also among island populations. P. semispinosus have traits that allow individuals in a population to rapidly respond to temporal changes in habitat quality or resource abundance. These traits include a high reproductive rate and an ability to adjust reproductive effort to changes in density. P. semispinosus are therefore able to quickly reach and maintain high densities under favorable conditions, thereby allowing close tracking of temporally and spatially varying resources. This flexibility is predicted for habitat generalists and presumably promotes abundance and persistence in temporally and spatially heterogeneous environments. P. semispinosus, often the most abundant and widely distributed species of rodent in forests throughout their geographic range, therefore have traits that are similar to those of generalist rodents in temperate forests.     

Effects of extra food on Peromyscus and Clethrionomys populations in the southern Yukon

Summary If food supply limits density in rodent populations, the addition of supplemental food ought to increase population size. From May to September we added food on 2-hectare areas of white spruce forest in the southern Yukon. In 1977, we used oats with no measurable impact. In 1978 and 1979 we used sunflower seeds and doubled or tripled the population densities of Peromyscus maniculatus and Clethrionomys rutilus. Supplemental feeding with sunflower seeds increased juvenile production in both species, probably by increasing early juvenile survival. The breeding season ended at the same time on experimental and control areas, and the onset of maturity in juveniles was not affected by feeding. Survival of adult rodents was not improved by feeding. Immigration into sunflower seed areas was very high, and was the major factor producing the increase in population density. Body weight was not changed by feeding. Food supply is thus one factor limiting population density in these subarctic small mammals, but we do not know why supplemental food produces no more than a 2- to 3-fold effect on densities.Dedicated to Dr. Springer and Prof. Evenari     

The effect of forest management operations on population performance of Vaccinium myrtillus on a landscape-scale

We have studied the variation in average performance of Vaccinium myrtillus L. among local populations within an intensively managed boreal forest landscape in southeast Norway. Our aim was to identify whether forest disturbance history was an important factor controlling the variation in average plant performance. We used three measures of forest maturity (maturity class, tree biomass and number of trees) as variables reflecting disturbance history. These variables were used in our analysis together with measured environmental conditions (soil moisture, pH, nitrogen, and elevation) a priori known to affect plant performance. To quantify plant performance, we used multiple measures of the local V. myrtillus populations, including percentage cover, average ramet age, height, diameter, biomass, growth, and sexual reproduction (number of fruits and number of mature seeds per fruit). Most of the explained variation in our performance variables could be related to our environmental variables, but disturbance history was also an important determinant of the performance of V. myrtillus. All performance variables were higher in younger, less mature stands, except ramet age, which was highest in mature stands. The increase in performance after clear cutting indicates that this period is of high importance for the population dynamics and persistence of V. myrtillus in intensively managed boreal forest landscapes.     

Demographic response of snake-necked turtles correlates with indigenous harvest and feral pig predation in tropical northern Australia

Species that mature late, experience high levels of survival and have long generation times are more vulnerable to chronic increases in mortality than species with higher fecundity and more rapid turnover of generations. Many chelonians have low hatchling survival, slow growth, delayed sexual maturity and high subadult and adult survival. This constrains their ability to respond quickly to increases in adult mortality from harvesting or habitat alteration. In contrast, the northern snake-necked turtle Chelodina rugosa (Ogilby 1890) is fast-growing, early maturing and highly fecund relative to other turtles, and may be resilient to increased mortality. Here we provide correlative evidence spanning six study sites and three field seasons, indicating that C. rugosa is able to compensate demographically to conditions of relatively low subadult and adult survival, caused by pig Sus scrofa (Linnaeus 1758) predation and customary harvesting by humans. Recruitment and age specific fecundity tended to be greater in sites with low adult and subadult survival (and thus reduced densities of large turtles), owing to higher juvenile survival, a smaller size at onset of maturity and faster post-maturity growth. These patterns are consistent with compensatory density-dependent responses, and as such challenge the generality that high subadult and adult survival is crucial for achieving long-term population stability in long-lived vertebrates such as chelonians. We posit that long-lived species with 'fast' recruitment and a capacity for a compensatory demographic response, similar to C. rugosa, may be able to persist in the face of occasional or sustained adult harvest without inevitably threatening population viability.     

Effects of temperature on two Mediterranean population of Dinophilus gyrociliatus (Polychaeta: Dinophilidae): II. Effects on demographic parameters

The effects of temperature on demographic characteristics of two populations from Ravenna and Genoa of the polychaete Dinophilus gyrociliatus were investigated. Temperature affects age-specific survival and fecundity and all the demographic parameters often to a different degree in the two populations. Individuals from Ravenna survive longer than those from Genoa. The most evident differences in the age-specific fecundity curves of the experimental groups are related to age at maturity and the duration of the reproductive period that are in inverse proportion to temperature. In both populations of D. gyrociliatus, the maximum daily fecundity is observed at intermediate temperatures. In all cases, the Genoa females mature earlier, attain their maximum fecundity more quickly and have a shorter reproductive period than their Ravenna counterparts.Age at maturity, fecundity during the first reproductive events and juvenile survival are by far the most important characteristics in determining the fitness of the two populations at the tested temperatures. Even though the greatest net growth rates and highest expectation of life were recorded at 12 °C in the Ravenna population, the delay in the attainment of sexual maturity means that, at this temperature, the population growth rate is lowest. The higher juvenile survivorship and the greater fecundity observed at 24 °C is counter-balanced by the early attainment of sexual maturity induced at 30 °C. The comparison of the population growth rate calculated in laboratory with field data suggests that temperature is one of the main environmental parameters determining the fitness of D. gyrociliatus.     

Estimating density dependence in time-series of age-structured populations

For a life history with age at maturity alpha, and stochasticity and density dependence in adult recruitment and mortality, we derive a linearized autoregressive equation with time-lags of from 1 to alpha years. Contrary to current interpretations, the coefficients for different time-lags in the autoregressive dynamics do not simply measure delayed density dependence, but also depend on life-history parameters. We define a new measure of total density dependence in a life history, D, as the negative elasticity of population growth rate per generation with respect to change in population size, D = - partial differential lnlambda(T)/partial differential lnN, where lambda is the asymptotic multiplicative growth rate per year, T is the generation time and N is adult population size. We show that D can be estimated from the sum of the autoregression coefficients. We estimated D in populations of six avian species for which life-history data and unusually long time-series of complete population censuses were available. Estimates of D were in the order of 1 or higher, indicating strong, statistically significant density dependence in four of the six species.     

基于标志重捕法的高原鼢鼠种群动态及其环境影响因子

高原鼢鼠（Eospalax baileyi）是青藏高原优势地下啮齿动物,研究其种群数量变化规律及其与环境因子关系,对于保护高寒草地生物多样性和科学防控草原鼠害具有重要意义。于2014-2019年在天祝县抓喜秀龙乡高原鼢鼠分布区,采用标志重捕法调查每年5月和10月高原鼢鼠种群密度、存活率、补充量及体重,利用样方法调查各植物功能群地上、地下生物量,并从中国气象数据中心获取同期气象数据。通过灰色关联度分析,探究高原鼢鼠种群特征变化与环境因子关联程度。结果表明：高原鼢鼠种群数量存在年际和季节性变化规律,年际间高原鼢鼠种群数量总体呈下降趋势,秋季高原鼢鼠种群数量高于春季种群数量;灰色关联分析表明,春季高原鼢鼠种群数量变化与降雨量、极端温度和杂类草生物量关联程度较高,而秋季高原鼢鼠种群数量与环境因子关联程度较低。研究结果不仅为今后构建高原鼢鼠种群数量预测预报模型提供基础依据,也为适时防控高原鼢鼠危害提供有益参考。     

Viability and Management of an Endangered Capercaillie (Tetrao urogallus) Metapopulation in the Jura Mountains, Western Switzerland

The populations of Capercaillie (Tetrao urogallus), the largest European grouse, have seriously declined during the last century over most of their distribution in western and central Europe. In the Jura mountains, the relict population is now isolated and critically endangered (about 500 breeding adults). We developed a simulation software (TetrasPool) that accounts for age and spatial structure as well as stochastic processes, to perform a viability analysis and explore management scenarios for this population, capitalizing on a 24 years-long series of field data. Simulations predict a marked decline and a significant extinction risk over the next century, largely due to environmental and demographic stochasticity (average values of life-history parameters would otherwise allow stability). Variances among scenarios mainly stem from uncertainties about the shape and intensity of density dependence. Uncertainty analyses suggest to focus conservation efforts on enhancing, not only adult survival (as often advocated for long-lived species), but also recruitment. The juvenile stage matters when local populations undergo extinctions, because it ensures connectivity and recolonization. Besides limiting human perturbations, a silvicultural strategy aimed at opening forest structure should improve the quality and surface of available patches, independent of their size and localization. Such measures are to be taken urgently, if the population is to be saved.     

Demography and dynamics of three wild horse populations in the Australian Alps

Wild horses (Equus caballus) are a non‐native species occupying over 2800 km² of the nationally significant Australian Alps National Parks. We estimated key demographic parameters (fecundity, adult and juvenile survival and annual finite population growth rate) over 3 years and related these to horse body condition and available food for three populations under natural conditions, and found a trend consistent with food limitation. The populations were independent, with different site characteristics and occupied areas, identified by land managers, as areas of concern about possible conservation impacts. Annual fecundity and juvenile survival varied across sites averaging between 0.21 and 0.31 female young per adult female, and 0.83 and 0.90 per annum, respectively, and annual adult survival was consistent across sites averaging 0.91 per annum. One population was increasing (λ = 1.09 year^?1; 95% CI 1.04–1.14) and two populations were stable (λ ～ 1.0 year^?1). Mean body condition of horses was positively correlated with mean pasture biomass rank. Across the three populations, fecundity, recruitment, body condition and annual finite population growth rate were lowest when mean pasture biomass rank was lowest and conversely highest when pasture rank was highest. We conclude that food limitation appears to be operating across these three sites. We used our results to assess the sensitivity of annual finite rate of increase (λ) to changes in key demographic parameters and found that λ was most sensitive to a change in adult survival, with the second most sensitive parameter being fecundity. Thus, if the aim of management is to reduce the size of the wild horse population then targeting adult survival is most important, followed by fecundity. Finally, we estimated the linear, negative, numerical response for wild horses between annual λ and horses per unit pasture biomass.     

Variations in age‐ and sex‐specific survival rates help explain population trend in a discrete marine mammal population

Understanding the drivers underlying fluctuations in the size of animal populations is central to ecology, conservation biology, and wildlife management. Reliable estimates of survival probabilities are key to population viability assessments, and patterns of variation in survival can help inferring the causal factors behind detected changes in population size. We investigated whether variation in age‐ and sex‐specific survival probabilities could help explain the increasing trend in population size detected in a small, discrete population of bottlenose dolphins Tursiops truncatus off the east coast of Scotland. To estimate annual survival probabilities, we applied capture–recapture models to photoidentification data collected from 1989 to 2015. We used robust design models accounting for temporary emigration to estimate juvenile and adult survival, multistate models to estimate sex‐specific survival, and age models to estimate calf survival. We found strong support for an increase in juvenile/adult annual survival from 93.1% to 96.0% over the study period, most likely caused by a change in juvenile survival. Examination of sex‐specific variation showed weaker support for this trend being a result of increasing female survival, which was overall higher than for males and animals of unknown sex. Calf survival was lower in the first than second year; a bias in estimating third‐year survival will likely exist in similar studies. There was some support first‐born calf survival being lower than for calves born subsequently. Coastal marine mammal populations are subject to the impacts of environmental change, increasing anthropogenic disturbance and the effects of management measures. Survival estimates are essential to improve our understanding of population dynamics and help predict how future pressures may impact populations, but obtaining robust information on the life history of long‐lived species is challenging. Our study illustrates how knowledge of survival can be increased by applying a robust analytical framework to photoidentification data.     

Sex ratio and sexual dimorphism in the dioecious Borderea pyrenaica (Dioscoreaceae)

Sex ratio and sexual dimorphism of Borderea pyrenaica, a long-lived dioecious geophyte endemic to the Pyrenees (north-east Iberian Peninsula), were examined in three alpine populations. In this species, age can be estimated and the sex of nonreproductive adult plants identified. Male plants attain sexual maturity earlier, flower more frequently and grow faster than female plants, whereas females allocate a higher biomass to reproduction than males. These results support the hypothesis that female plants incur a higher cost of sexual reproduction and that this higher cost is measurable as reduced vegetative growth and lower flowering frequency. Variation of sex ratio among young, intermediate and old adults within populations suggests, however, that this higher female reproductive investment does not result in sexual differences in mortality. The overall male-biased sex ratio in B. pyrenaica is mainly a consequence of the tendency of males to reproduce at an earlier age and more frequently than females.