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It has recently been recognised that populations are rarely in demographic equilibrium, but rather in a 'transient' state. To examine how transient dynamics influence our empirical understanding of the links between changes in demographic rates and population growth, we conducted a 32-year study of Columbian ground squirrels. The population increased rapidly for 10 years, followed by a 2-year crash, and a gradual 19-year recovery. Transient life table response experiment (LTRE) analysis showed that demographic stochasticity accounted for approximately one-fourth of the variation in population growth, leaving the majority to be explained by environmental influences. These relatively small rodents appeared to have a slow pace of life. But unlike the general pattern for large mammals with slow life histories, ground squirrel survival did not exhibit low variation associated with environmental 'buffering'; instead, survival varied substantially over time and contributed substantially (78%) to changes in abundance over the long-term study, with minor contributions from reproduction and unstable stage structure., (© 2024 John Wiley & Sons Ltd.)

Demography of herbivorous mammal populations may be affected by changes in predation, population density, harvesting, and climate. Whereas numerous studies have focused on the effect of single environmental variables on individual demographic processes, attempts to integrate the consequences of several environmental variables on numerous functional traits and demographic rates are rare. Over a 32-year period, we examined how forage availability (vegetation assessed through NDVI) and population density affected the functional traits and demographic rates of a population of Columbian ground squirrels (Urocitellus columbianus), a herbivorous hibernating rodent. We focused on mean population phenology, body mass, breeding success, and survival. We found a negative effect of population density on demographic rates, including on breeding success and pup and adult survival to the next year. We found diverging effects of vegetation phenology on demographic rates: positive effects of a later start of the growing season on adult and yearling female survival, and juvenile survival, but no clear effect on male survival. Interestingly, neither population density nor vegetation affected population phenology or body condition in the following year. Vegetative growth rate had a positive influence on female mass gain (somatic investment) over a season, but both vegetative growth rate and biomass, surprisingly, had negative effects on the survival of young through their first hibernation. Thus, ground squirrels appeared to benefit more from later timing of vegetation than increases in vegetative biomass per se. Our study provides evidence for complex ecological effects of vegetation and population density on functional traits and demographic rates of small mammal populations., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The measurement of glucocorticoid (GC) hormones provides us with a window into the stress physiology of vertebrates and the adaptative responses they use to cope with predictable and unpredictable changes in the environment. Baseline GCs inform us about the metabolic demands they are subject to at that point in their yearly life-history stage, whereas GC changes (often increases) in response to acute challenges inform us on their capacity to cope with more immediate environmental challenges. However, baseline GC levels and the kinetics of GC responses to acute stressors can vary substantially among and within species, depending on individual characteristics (age, sex, condition, life-history stage). In addition, a thorough understanding of the stress status of an animal requires moving beyond the measurement of GCs alone by focusing on downstream measures of metabolic activation, such as oxidative stress. Here, we evaluated the changes in blood cortisol and oxidative stress markers in wild adult Columbian ground squirrels (Urocitellus columbianus), following a 30-min capture-handling stress performed in mid-late June. Measurements were taken when males were post-reproductive and preparing for hibernation and adult females were weaning litters. We found three key results. First, the time-course of GC increase was markedly slower (by an order of magnitude) than what is currently reported in the literature for most species of mammals, birds and reptiles. Second, there were marked differences in the male and female response, linked to differences in life-history stage: females close to weaning had abolished GC responses, whereas post-reproductive males did not. Third, there were mild to moderate increases in oxidative damage and decreases in oxidative defenses in response to our short-term challenge, consistent with the idea that short-term acute metabolic activation may carry physiological costs. However, these changes were not correlated to the changes in GCs, a novel result suggesting a disconnect between the hormonal stress response and oxidative damage., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Seasonal animal dormancy is widely interpreted as a physiological response for surviving energetic challenges during the harshest times of the year (the physiological constraint hypothesis). However, there are other mutually non-exclusive hypotheses to explain the timing of animal dormancy, that is, entry into and emergence from hibernation (i.e. dormancy phenology). Survival advantages of dormancy that have been proposed are reduced risks of predation and competition (the 'life-history' hypothesis), but comparative tests across animal species are few. Using the phylogenetic comparative method applied to more than 20 hibernating mammalian species, we found support for both hypotheses as explanations for the phenology of dormancy. In accordance with the life-history hypotheses, sex differences in hibernation emergence and immergence were favored by the sex difference in reproductive effort. In addition, physiological constraint may influence the trade-off between survival and reproduction such that low temperatures and precipitation, as well as smaller body mass, influence sex differences in phenology. We also compiled initial evidence that ectotherm dormancy may be (1) less temperature dependent than previously thought and (2) associated with trade-offs consistent with the life-history hypothesis. Thus, dormancy during non-life-threatening periods that are unfavorable for reproduction may be more widespread than previously thought., Competing Interests: TC, FD, CH, SG No competing interests declared, (© 2023, Constant et al.)

Parentage analyses via molecular markers have revealed multiple paternity within the broods of polytocous species, reshaping our understanding of animal behavior, ecology, and evolution. In a meta-analysis of multiple paternity in bird and mammal species, we conducted a literature search and found 138 bird and 64 mammal populations with microsatellite DNA paternity results. Bird populations averaged 19.5% multiple paternity and mammals more than twice that level (46.1%). We used a Bayesian approach to construct a null model for how multiple paternity should behave at random among species, under the assumption that all mated males have equal likelihood of siring success, given mean brood size and mean number of sires. We compared the differences between the null model and the actual probabilities of multiple paternity. While a few bird populations fell close to the null model, most did not, averaging 34.0-percentage points below null model predictions; mammals had an average probability of multiple paternity 13.6-percentage points below the null model. Differences between bird and mammal species were also subjected to comparative phylogenetic analyses that generally confirmed our analyses that did not adjust for estimated historical relationships. Birds exhibited extremely low probabilities of multiple paternity, not only compared to mammals but also relative to other major animal taxa. The generally low probability of multiple paternity in birds might be produced by a variety of factors, including behaviors that reflect sexual selection (extreme mate guarding or unifocal female choice) and sperm competition (e.g., precedence effects favoring fertilization by early or late matings)., (© 2024 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)

Desynchrony of phenological responses to climate change is a major concern for ecological communities. Potential uncoupling between one of the most fundamental divisions within populations, males and females, has not been well studied. To address this gap, we examined sex-specific plasticity in hibernation phenology in two populations of Columbian ground squirrels ( Urocitellus columbianus ). We find that both sexes display similar phenological plasticity to spring snowmelt dates in their timing of torpor termination and behavioural emergence from hibernation. As a result of this plasticity, the degree of protandry (i.e. males' emergences from hibernation preceding those of females) did not change significantly over the 27-year study. Earlier male behavioural emergence, relative to females, improved the likelihood of securing a breeding territory and increased annual reproductive success. Sexual selection favouring earlier male emergence from hibernation may maintain protandry in this population, but did not contribute to further advances in male phenology. Together, our results provide evidence that the sexes should remain synchronized, at least in response to the weather variation investigated here, and further support the role of sexual selection in the evolution of protandry in sexually reproducing organisms.

To combat mosquito-borne diseases, a variety of vector control tools have been implemented. Estimating age structure in populations of vector species is important for understanding transmission potential. Age-grading techniques have been used as critical methods for evaluating the efficacy of vector control tools. However, methods like mark-release-recapture and ovarian dissection are laborious and require a high level of training. For decades, scientists have discussed the wide array of acoustic signatures of different mosquito species. These distinguishable wingbeat signatures with spatiotemporal classification allow mosquitoes of the same species to locate one another for mating. In recent years, the use of sensitive acoustic devices like mobile phones have proved effective. Wingbeat signatures can be used to identify mosquito species without the challenge of intensive field collections and morphological and molecular identifications. In this study, laboratory Aedes aegypti (L.) female and male wingbeats were recorded using mobile phones to determine whether sex and age differences with chronological time, and across different physiological stages, can be detected. Our results indicate significantly different wingbeat signatures between male and female Ae. aegypti, and a change of wingbeat frequencies with age and reproduction stage in females., (© 2023 Royal Entomological Society.)

Inclement weather can rapidly modify the thermal conditions experienced by animals, inducing changes in their behavior, body condition, and stress physiology, and affecting their survival and breeding success. For animals living in variable environments, the extent to which they have adapted to cope with inclement weather is not established, especially for hibernating species with a short active season that are constrained temporally to breed and store energy for subsequent hibernation. We examined behavioral (foraging activity) and physiological (body mass and fecal cortisol metabolites) responses of Columbian ground squirrels (Urocitellus columbianus), small hibernating rodents inhabiting open meadows in Rocky Mountains, to 3 events of inclement weather (two snow storms in May 2021 and May 2022, one heavy rainfall in June 2022). We found that individuals adapted to inclement weather conditions by (1) reducing above-ground activity, including foraging, (2) decreasing the mobilization of stored resources as indicated by a decrease in the activity of the hypothalamo-pituitary-adrenal (HPA) axis and lower fecal cortisol metabolites in the hours/days following periods of inclement weather; and (3) compensating through increased foraging and more local activity when favorable conditions resumed. As a result, body mass and growth did not decrease following short periods of inclement weather. Columbian ground squirrels were well-adapted to short periods of inclement weather, coping via modifications of their behavior and the activity of the HPA axis., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2023. Published by Elsevier Inc.)

Telomeres, the terminal repetitive DNA sequences at the ends of linear chromosomes, have strong associations with longevity in some major taxa. Longevity has been linked to rate of decline in telomere length in birds and mammals, and absolute telomere length seems to be associated with body mass in mammals. Using a phylogenetic comparative method and 30 species of birds, we examined longevity (reflected by maximum lifespan), absolute telomere length, the rate of change in telomere length (TROC), and body mass (often strongly associated with longevity) to ascertain their degree of association. We divided lifespan into two life-history components, one reflected by body size (measured as body mass) and a component that was statistically independent of body mass. While both lifespan and body mass were strongly associated with a family tree of the species (viz., the phylogeny of the species), telomere measures were not. Telomere length was not significantly associated with longevity or body mass or our measure of mass-independent lifespan. TROC, however, was strongly associated with mass-independent lifespan, but only to a much lesser degree at best with body mass-predicted lifespan. Our results supported an association of TROC and longevity, in particular longevity that was independent of body size and part of the pace-of-life syndrome of life histories., (© 2022 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)

Social interactions are a ubiquitous feature of the lives of vertebrate species. These may be cooperative or competitive, and shape the dynamics of social systems, with profound effects on individual behavior, physiology, fitness, and health. On one hand, a wealth of studies on humans, laboratory animal models, and captive species have focused on understanding the relationships between social interactions and individual health within the context of disease and pathology. On the other, ecological studies are attempting an understanding of how social interactions shape individual phenotypes in the wild, and the consequences this entails in terms of adaptation. Whereas numerous studies in wild vertebrates have focused on the relationships between social environments and the stress axis, much remains to be done in understanding how socially-related activation of the stress axis coordinates other key physiological functions related to health. Here, we review the state of our current knowledge on the effects that social interactions may have on other markers of vertebrate fitness and health. Building upon complementary findings from the biomedical and ecological fields, we identify 6 key physiological functions (cellular metabolism, oxidative stress, cellular senescence, immunity, brain function, and the regulation of biological rhythms) which are intimately related to the stress axis, and likely directly affected by social interactions. Our goal is a holistic understanding of how social environments affect vertebrate fitness and health in the wild. Whereas both social interactions and social environments are recognized as important sources of phenotypic variation, their consequences on vertebrate fitness, and the adaptive nature of social-stress-induced phenotypes, remain unclear. Social flexibility, or the ability of an animal to change its social behavior with resulting changes in social systems in response to fluctuating environments, has emerged as a critical underlying factor that may buffer the beneficial and detrimental effects of social environments on vertebrate fitness and health., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Telomeres are specialized non-coding DNA sequences located at the end of chromosomes and that protect genetic information. Telomere loss over lifespan is generally viewed as a phenomenon associated with aging in animals. Recently, telomere elongation after hibernation has been described in several mammals. Whether this pattern is an adaptation to repair DNA damage caused during rewarming from torpor or if it coevolved as a mechanism to promote somatic maintenance in preparation for the upcoming reproductive effort remains unclear. In a longitudinal study measuring telomere length using buccal swabs, we tested if telomere elongation was related to reproductive success in wild adult female Columbian ground squirrels (Urocitellus columbianus) that were monitored from emergence from hibernation to the end of the reproductive season. We found three key results. First, female telomere length increased at the start of the breeding season, both in breeding and non-breeding individuals. Second, post-emergence telomere lengthening was unrelated to female future reproductive output. Third, telomere length decreased in breeding females during lactation, but remained stable in non-breeding females over a similar period. Within breeders, telomeres shortened more in females producing larger and heavier litters. We concluded that telomere lengthening after hibernation did not constrain immediate female reproductive capacities. It was more likely to be part of the body recovery process that takes place after hibernation. Telomere erosion that occurs after birth may constitute a physiological cost of female reproduction., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Social environments can profoundly affect the behavior and stress physiology of group-living animals. In many territorial species, territory owners advertise territorial boundaries to conspecifics by scent marking. Several studies have investigated the information that scent marks convey about donors' characteristics (e.g., dominance, age, sex, reproductive status), but less is known about whether scents affect the behavior and stress of recipients. We experimentally tested the hypothesis that scent marking may be a potent source of social stress in territorial species. We tested this hypothesis for Columbian ground squirrels (Urocitellus columbianus) during lactation, when territorial females defend individual nest-burrows against conspecifics. We exposed lactating females, on their territory, to the scent of other lactating females. Scents were either from unfamiliar females, kin relatives (a mother, daughter, or sister), or their own scent (control condition). We expected females to react strongly to novel scents from other females on their territory, displaying increased vigilance, and higher cortisol levels, indicative of behavioral and physiological stress. We further expected females to be more sensitive to unfamiliar female scents than to kin scents, given the matrilineal social structure of this species and known fitness benefits of co-breeding in female kin groups. Females were highly sensitive to intruder (both unfamiliar and kin) scents, but not to their own scent. Surprisingly, females reacted more strongly to the scent of close kin than to the scent of unfamiliar females. Vigilance behavior increased sharply in the presence of scents; this increase was more marked for kin than unfamiliar female scents, and was mirrored by a marked 131% increase in free plasma cortisol levels in the presence of kin (but not unfamiliar female) scents. Among kin scents, lactating females were more vigilant to the scent of sisters of equal age, but showed a marked 318% increase in plasma free cortisol levels in response to the scent of older and more dominant mothers. These results suggest that scent marks convey detailed information on the identity of intruders, directly affecting the stress axis of territory holders., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Parental allocation of resources into male or female offspring and differences in the balance of offspring sexes in natural populations are central research topics in evolutionary ecology. Fisher (Fisher, R. A. 1930. The genetical theory of natural selection, Clarendon Press, Oxford, UK) identified frequency-dependent selection as the mechanism responsible for an equal investment in the sexes of offspring at the end of parental care. Three main theories have been proposed for explaining departures from Fisherian sex ratios in light of variation in environmental (social) and individual (maternal condition) characteristics. The Trivers-Willard model (Trivers, R., and D. Willard. 1973. Natural selection of parental ability to vary the sex ratio of offspring. Science 179:90-92) of male-biased sex allocation by mothers in the best body condition is based on the competitive ability of male offspring for future access to mates and thus superior reproduction. The local resource competition model is based on competitive interactions in matrilines, as occur in many mammal species, where producing sons reduces future intrasexual competition with daughters. A final model invokes advantages of maintaining matrilines for philopatric females, despite any increased competition among females. We used 29 yr of pedigree and demographic data to evaluate these hypotheses in the Colombian ground squirrel (Urocitellus columbianus), a semisocial species characterized by strong female philopatry. Overall, male offspring were heavier than female offspring at birth and at weaning, suggesting a higher production cost. With more local kin present, mothers in the best condition biased their offspring sex ratio in favor of males, and mothers in poor condition biased offspring sex ratio in favor of females. Without co-breeding close kin, the pattern was reversed, with mothers in the best condition producing more daughters, and mothers in poor condition producing more sons. Our results do not provide strong support for any of the single-factor models of allocation to the sexes of offspring, but rather suggest combined influences of relative maternal condition and matriline dominance on offspring sex ratio., (© 2021 by the Ecological Society of America.)

Longevity is highly variable among animal species and has coevolved with other life-history traits, such as body size and rates of reproduction. Telomeres, through their erosion over time, are one of the cell mechanisms that produce senescence at the cell level and might even have an influence on the rate of aging in whole organisms. However, uneroded telomeres are also risk factors of cell immortalization. The associations of telomere lengths, their rate of change, and life-history traits independent of body size are largely underexplored for birds. To test associations of life-history traits and telomere dynamics, we conducted a phylogenetic meta-analysis using studies of 53 species of birds. We restricted analyses to studies that applied the telomere restriction fragment length (TRF) method, and examined relationships between mean telomere length at the chick ( Chick TL ) and adult ( Adult TL ) stages, the mean rate of change in telomere length during life ( TROC ), and life-history traits. We examined 3 principal components of 12 life-history variables that represented: body size (PC1), the slow-fast continuum of pace of life (PC2), and postfledging parental care (PC3). Phylogeny had at best a small-to-medium influence on Adult and Chick TL ( r 2  = .190 and .138, respectively), but a substantial influence on TROC ( r 2  = .688). Phylogeny strongly influenced life histories: PC1 ( r 2  = .828), PC2 (.838), and PC3 (.613). Adult TL and Chick TL were poorly associated with the life-history variables. TROC , however, was negatively and moderate-to-strongly associated with PC2 (unadjusted r  = -.340; with phylogenetic correction, r  = -.490). Independent of body size, long-lived species with smaller clutches, and slower embryonic rate of growth may exhibit less change in telomere length over their lifetimes. We suggest that telomere lengths may have diverged, even among closely avian-related species, yet telomere dynamics are strongly linked to the pace of life., Competing Interests: None declared., (© 2021 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)

The Arctic is undergoing rapid and accelerating change in response to global warming, altering biodiversity patterns, and ecosystem function across the region. For Arctic endemic species, our understanding of the consequences of such change remains limited. Spectacled eiders ( Somateria fischeri ), a large Arctic sea duck, use remote regions in the Bering Sea, Arctic Russia, and Alaska throughout the annual cycle making it difficult to conduct comprehensive surveys or demographic studies. Listed as Threatened under the U.S. Endangered Species Act, understanding the species response to climate change is critical for effective conservation policy and planning. Here, we developed an integrated population model to describe spectacled eider population dynamics using capture-mark-recapture, breeding population survey, nest survey, and environmental data collected between 1992 and 2014. Our intent was to estimate abundance, population growth, and demographic rates, and quantify how changes in the environment influenced population dynamics. Abundance of spectacled eiders breeding in western Alaska has increased since listing in 1993 and responded more strongly to annual variation in first-year survival than adult survival or productivity. We found both adult survival and nest success were highest in years following intermediate sea ice conditions during the wintering period, and both demographic rates declined when sea ice conditions were above or below average. In recent years, sea ice extent has reached new record lows and has remained below average throughout the winter for multiple years in a row. Sea ice persistence is expected to further decline in the Bering Sea. Our results indicate spectacled eiders may be vulnerable to climate change and the increasingly variable sea ice conditions throughout their wintering range with potentially deleterious effects on population dynamics. Importantly, we identified that different demographic rates responded similarly to changes in sea ice conditions, emphasizing the need for integrated analyses to understand population dynamics., Competing Interests: The authors indicate there are no competing interests., (© 2021 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)

Parentage analyses via microsatellite markers have revealed multiple paternity within the broods of polytocous species of mammals, reptiles, amphibians, fishes and invertebrates. The widespread phenomenon of multiple paternity may have attending relationships with such evolutionary processes as sexual selection and kin selection. However, just how much multiple paternity should a species exhibit? We developed Bayesian null models of how multiple paternity relates to brood sizes. For each of 114 species with published data on brood sizes and numbers of sires, we compared our null model estimates to published frequencies of multiple paternity. The majority of species fell close to our null model, especially among fish and invertebrate species. Some species, however, had low probabilities of multiple paternity, far from the predictions of the null model, likely due to sexual selection and environmental constraints. We suggest a major division among species' mating systems between those with close to random mating and high levels of multiple paternity, and those with constraints that produce low levels of multiple paternity., (© 2021 Wiley Periodicals LLC.)

Temporal variation in natural selection is predicted to strongly impact the evolution and demography of natural populations, with consequences for the rate of adaptation, evolution of plasticity, and extinction risk. Most of the theory underlying these predictions assumes a moving optimum phenotype, with predictions expressed in terms of the temporal variance and autocorrelation of this optimum. However, empirical studies seldom estimate patterns of fluctuations of an optimum phenotype, precluding further progress in connecting theory with observations. To bridge this gap, we assess the evidence for temporal variation in selection on breeding date by modeling a fitness function with a fluctuating optimum, across 39 populations of 21 wild animals, one of the largest compilations of long-term datasets with individual measurements of trait and fitness components. We find compelling evidence for fluctuations in the fitness function, causing temporal variation in the magnitude, but not the direction of selection. However, fluctuations of the optimum phenotype need not directly translate into variation in selection gradients, because their impact can be buffered by partial tracking of the optimum by the mean phenotype. Analyzing individuals that reproduce in consecutive years, we find that plastic changes track movements of the optimum phenotype across years, especially in bird species, reducing temporal variation in directional selection. This suggests that phenological plasticity has evolved to cope with fluctuations in the optimum, despite their currently modest contribution to variation in selection., Competing Interests: The authors declare no competing interest.

Low mortality rate is often associated with slow life history, and so far, has mainly been assessed through examinations of specific adaptations and lifestyles that limit mortality risk. However, the organization of activity time budgets also needs to be considered, since some activities and the time afforded for performing them may expose animals to higher mortality risks such as increased predation and/or increased metabolic stress. We examined the extent of activity time budgets contribution to explaining variation in life history traits in mammals. We specifically focused on hibernating species because of their marked seasonal cycle of activity/inactivity associated with very different mortality risks. Hibernation is considered a seasonal adaptation to prolonged periods of food shortage and cold. This inactivity period may also reduce both extrinsic and intrinsic mortality risks, by decreasing exposure to predators and drastically reducing metabolic rate. In turn, reduction in mortality may explain why hibernators have slower life history traits than non-hibernators of the same size. Using phylogenetically controlled models, we tested the hypothesis that longevity was positively correlated with the hibernation season duration (the time spent between immergence and emergence from the hibernaculum or den) across 82 different mammalian species. We found that longevity increased significantly with hibernation season duration, an effect that was particularly strong in small hibernators (<1.5 kg) especially for bats. These results confirm that hibernation not only allows mammals to survive periods of energy scarcity, but further suggest that activity time budgets may be selected to reduce mortality risks according to life history pace., (Copyright © 2020 Constant, Giroud, Viblanc, Tissier, Bergeron, Dobson and Habold.)

Studies of multiple paternity in mammals and other animal species generally report proportion of multiple paternity among litters, mean litter sizes, and mean number of sires per litter. It is shown how these variables can be used to produce an estimate of the probability of reproductive success for a male that has mated with a female. This estimate of male success is more informative about the mating system that alternative measures, like the proportion of litters with multiple paternity or the mean number of sires per litter. The probability of success for a mated male can be measured both theoretically and empirically, and gives an estimate of the intensity of sperm competition and of a male's "confidence of paternity" upon mating. The probability of success for mated males for ten "exemplar" species of mammals is estimated and they are compared for insights into the functioning of their mating systems., (© 2019 WILEY Periodicals, Inc.)

Biological responses to climate change have been widely documented across taxa and regions, but it remains unclear whether species are maintaining a good match between phenotype and environment, i.e. whether observed trait changes are adaptive. Here we reviewed 10,090 abstracts and extracted data from 71 studies reported in 58 relevant publications, to assess quantitatively whether phenotypic trait changes associated with climate change are adaptive in animals. A meta-analysis focussing on birds, the taxon best represented in our dataset, suggests that global warming has not systematically affected morphological traits, but has advanced phenological traits. We demonstrate that these advances are adaptive for some species, but imperfect as evidenced by the observed consistent selection for earlier timing. Application of a theoretical model indicates that the evolutionary load imposed by incomplete adaptive responses to ongoing climate change may already be threatening the persistence of species.

Parasites affect many aspects of host physiology and behavior, and thus are generally thought to negatively impact host fitness. However, changes in form of short-term parasite effects on host physiological markers have generally been overlooked in favor of fitness measures. Here, we studied flea ( Oropsylla idahoensis and Oropsylla opisocroistis tuberculata ) parasitism on a natural population of Columbian ground squirrels ( Urocitellus columbianus ) in Sheep River Provincial Park, AB, Canada. Fleas were experimentally added to adult female U. columbianus at physiologically demanding times, including birth, lactation and weaning of their young. The body mass of adult females, as well as their oxidative stress and immunity were recorded multiple times over the active season under flea-augmented and control conditions. We also measured the prevalence of an internal parasite ( Trypanosoma otospermophili ). Doubly labeled water (DLW) was intra-peritoneally injected at peak lactation to examine energy expenditure. Effects of parasites on oxidative stress were only observed after offspring were weaned. There was no direct effect of experimentally heightened flea prevalence on energy use. A short-term 24 h mass loss (-17 g) was detected briefly after parasite addition, likely due to U. columbianus preferentially allocating time for grooming. Our parasite augmentation did not strongly affect hosts and suggested that short-term physiological effects were unlikely to culminate in long-term fitness consequences. Columbian ground squirrels appear to rapidly manage parasite costs, probably through grooming., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2019. Published by The Company of Biologists Ltd.)

Many cooperative social attributes are being linked to characteristics of mating systems, particularly to the rate of multiple paternity that typifies a population. Under the logic that greater offspring production by females should engender greater competition among males to mate with females, it is predicted that multiple paternity should increase with litter sizes. We tested the predicted positive association of multiple paternity and litter size with a meta-analysis of 59 species of mammals. The probability of multiple paternity and mean litter size were positively correlated, but not significantly ( Zr = 0.202). Also, the mean number of sires of litters increased with mean litter size, but not significantly ( Zr = 0.235). We developed a combinatorial formula for the influence of number of male mates and litter size on the probability of multiple paternity. We used Bayesian Markov chain Monte Carlo simulations to generate an expectation for the form of the relationship between the probability of multiple paternity and mean litter size. Under the assumption of random samplings of numbers of mates, the expected association of the probability of multiple paternity and mean litter sizes among species was positive, curvilinear and relatively high. However, the empirical probabilities of multiple paternities were much less than expected, suggesting that behavioural factors (such as mating-associated behaviours) or ecological characteristics (such as population density) probably limit the number of male mates for reproductive females. The probability of multiple paternity in a population is an estimate of mating patterns that does not closely reflect the number of sires of individual litters. We suggest use of the estimated probability of mating success for males as an alternative measure of their contribution to the mating system., (© 2018 The Author(s).)

Sexual selection and social selection are two important theories proposed for explaining the evolution of colorful ornamental traits in animals. Understanding signal honesty requires studying how environmental and physiological factors during development influence the showy nature of sexual and social ornaments. We experimentally manipulated physiological stress and immunity status during the molt in adult king penguins ( Aptenodytes patagonicus ), and studied the consequences of our treatments on colourful ornaments (yellow-orange and UV beak spots and yellow-orange auricular feather patches) known to be used in sexual and social contexts in this species. Whereas some ornamental features showed strong condition-dependence (yellow auricular feather chroma, yellow and UV chroma of the beak), others were condition-independent and remained highly correlated before and after the molt (auricular patch size and beak UV hue). Our study provides a rare examination of the links between ornament determinism and selection processes in the wild. We highlight the coexistence of ornaments costly to produce that may be honest signals used in mate choice, and ornaments for which honesty may be enforced by social mediation or rely on genetic constraints.

A major question for conservationists and evolutionary biologists is whether natural populations can adapt to rapid environmental change through micro-evolution or phenotypic plasticity. Making use of 17 years of data from a colony of a long-distant migratory seabird, the common tern ( Sterna hirundo ), we examined phenotypic plasticity and the evolutionary potential of breeding phenology, a key reproductive trait. We found that laying date was strongly heritable (0.27 ± 0.09) and under significant fecundity selection for earlier laying. Paradoxically, and in contrast to patterns observed in most songbird populations, laying date became delayed over the study period, by about 5 days. The discrepancy between the observed changes and those predicted from selection on laying date was explained by substantial phenotypic plasticity. The plastic response in laying date did not vary significantly among individuals. Exploration of climatic factors showed individual responses to the mean sea surface temperature in Senegal in December prior to breeding: Common terns laid later following warmer winters in Senegal. For each 1°C of warming of the sea surface in Senegal, common terns delayed their laying date in northern Germany by 6.7 days. This suggests that warmer waters provide poorer wintering resources. We therefore found that substantial plastic response to wintering conditions can oppose natural selection, perhaps constraining adaptation.

Energetic trade-offs in resource allocation form the basis of life-history theory, which predicts that reproductive allocation in a given season should negatively affect future reproduction or individual survival. We examined how allocation of resources differed between successful and unsuccessful breeding female Columbian ground squirrels to discern any effects of resource allocation on reproductive and somatic efforts. We compared the survival rates, subsequent reprodction, and mass gain of successful breeders (females that successfully weaned young) and unsuccessful breeders (females that failed to give birth or wean young) and investigated "carryover" effects to the next year. Starting capital was an important factor influencing whether successful reproduction was initiated or not, as females with the lowest spring emergence masses did not give birth to a litter in that year. Females that were successful and unsuccessful at breeding in one year, however, were equally likely to be successful breeders in the next year and at very similar litter sizes. Although successful and unsuccessful breeding females showed no difference in over winter survival, females that failed to wean a litter gained additional mass during the season when they failed. The next year, those females had increased energy "capital" in the spring, leading to larger litter sizes. Columbian ground squirrels appear to act as income breeders that also rely on stored capital to increase their propensity for future reproduction. Failed breeders in one year "prepare" for future reproduction by accumulating additional mass, which is "carried over" to the subsequent reproductive season.

The social environment has potent effects on individual phenotype and fitness in group-living species. We asked whether the presence of kin might act on energy allocation, a central aspect of life-history variation. Using a 22-year data set on reproductive and somatic allocations in Columbian ground squirrels (Urocitellus columbianus), we tested the effects of co-breeding and non-breeding kin on the fitness and energy allocation balance between reproduction and personal body condition of individual females. Greater numbers of co-breeding kin had a positive effect on the number of offspring weaned, through the mechanism of altering energy allocation patterns. On average, females with higher numbers of co-breeding kin did not increase energy income but biased energy allocation towards reproduction. Co-breeding female kin ground squirrels maintain close nest burrows, likely providing a social buffer against territorial invasions from non-kin ground squirrels. Lower aggressiveness, lower risks of infanticide from female kin and greater protection of territorial boundaries may allow individual females to derive net fitness benefits via their energy allocation strategies. We demonstrated the importance of kin effects on a fundamental life-history trade-off., (© 2016 The Authors. Journal of Animal Ecology © 2016 British Ecological Society.)

The influence of climate change on the fitness of wild populations is often studied in the context of the spring onset of the reproductive season. This focus is relevant for climate influences on reproductive success, but neglects other fitness-relevant periods (e.g., autumn preparation for overwintering). We examined variation in climate variables (temperature, rainfall, snowfall, and snowpack) across the full annual cycle of Columbian ground squirrels (Urocitellus columbianus) for 21 years. We investigated seasonal climate variables that were associated with fitness variables, climate variables that exhibited directional changes across the study period, and finally observed declines in fitness (-0.03 units/year; total decline = 37%) that were associated with directional changes in climate variables. Annual fitness of adult female ground squirrels was positively associated with spring temperature (r = 0.69) and early summer rainfall (r = 0.56) and negatively associated with spring snow conditions (r = -0.44 to -0.66). Across the 21 years, spring snowmelt has become significantly delayed (r = 0.48) and summer rainfall became significantly reduced (r = -0.53). Using a standardized partial regression model, we found that directional changes in the timing of spring snowmelt and early summer rainfall (i.e., progressively drier summers) had moderate influences on annual fitness, with the latter statistically significant (ρ = -0.314 and 0.437, respectively). The summer period corresponds to prehibernation fattening of young and adult ground squirrels. Had we focused on a single point in time (viz. the onset of the breeding season), we would have underestimated the influences of climate change on our population. Rather, we obtained a comprehensive understanding of the influences of climate change on individual fitness by investigating the full lifecycle.

King penguins exhibit mutual color ornamentation of feathers and beak color. They breed in dense colonies and produce a single chick every 2 years. Thus, males and females must choose partners carefully to be reproductively successful, and auricular patches of males and UV coloration of beak spots have been shown to influence mate choice. Position in the breeding colony is also important to reproductive success, with pairs on the edge of the colony less successful than those in the center. We studied the mutual ornaments, individual condition, and position of pairs in their breeding colony. Males were significantly larger than females in size, body mass, and auricular patch size. Within pairs, auricular patch size of males and females were significantly correlated, and male auricular patch size and body mass were significantly associated, suggesting a link between this ornament and male body condition. Moving from the edge to the center of the colony, pairs had larger yellow-orange auricular patches, indicating a link between this ornament and settlement in higher quality territories in the center of the colony. Pairs were also less brightly brown colored on the breast and less saturated in UV color of the beak spot. Since we observed pairs that were settling for egg laying, location in the colony may have reflected aspects of pair condition, rather than later jockeying for positioning using ornaments as signals of behavioral dominance., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Parasites play an important role in the evolution of host traits via natural selection, coevolution and sexually selected ornaments used in mate choice. These evolutionary scenarios assume fitness costs for hosts. To test this assumption, we conducted an ectoparasite removal experiment in free-living Columbian ground squirrels (Urocittelus columbianus) in four populations over three years. Adult females were randomly chosen to be either experimentally treated with anti-parasite treatments (spot-on solution and flea powder, N = 61) or a sham treatment (control, N = 44). We expected that experimental females would show better body condition, increased reproductive success and enhanced survival. Contrary to our expectations, body mass was not significantly different between treatments at mating, birth of litter or weaning of young. Further, neither number nor size of young at weaning differed significantly between the two treatments. Survival to the next spring for adult females and juveniles was not significantly different between experimental and control treatments. Finally, annual fitness was not affected by the treatments. We concluded that females and their offspring were able compensate for the presence of ectoparasites, suggesting little or no fitness costs of parasites for females in the different colonies and during the years of our experiments., (© 2015 The Author(s) Published by the Royal Society. All rights reserved.)

A major question in ecology is how age-specific variation in demographic parameters influences population dynamics. Based on long-term studies of growing populations of birds and mammals, we analyze population dynamics by using fluctuations in the total reproductive value of the population. This enables us to account for random fluctuations in age distribution. The influence of demographic and environmental stochasticity on the population dynamics of a species decreased with generation time. Variation in age-specific contributions to total reproductive value and to stochastic components of population dynamics was correlated with the position of the species along the slow-fast continuum of life-history variation. Younger age classes relative to the generation time accounted for larger contributions to the total reproductive value and to demographic stochasticity in "slow" than in "fast" species, in which many age classes contributed more equally. In contrast, fluctuations in population growth rate attributable to stochastic environmental variation involved a larger proportion of all age classes independent of life history. Thus, changes in population growth rates can be surprisingly well explained by basic species-specific life-history characteristics.

Predation is one of the major selective agents influencing evolution of color patterns. Cryptic color patterns decrease detection probability by predators, but their concealing function depends on the background against which patterns are seen; therefore, habitat use and color patterns are tightly linked. In many anole species, females exhibit variation in dorsal color patterns; the drab and perhaps cryptic colors of the patterns suggest a predator avoidance function behind this polymorphism. We tested whether these different color patterns experience different predation rates depending on their microhabitat. We expected each pattern to form at least one optimal combination with a typically used micro-habitat that would result in lower predation compared to other morphs in the same micro-habitat. We tested this hypothesis for anoles at La Selva, Costa Rica, using clay models resembling a common species at this site: Norops humilis. The first experiment tested for variation in predation on various substrates. We included leaf litter, live leaves, and two size classes of woody stems, using 44 models for each pattern substrate combination. A second experiment tested effects of perch height (10 and 60cm) and diameter (< 2 cm and > 5 cm), with 50 models for each pattern perch combination. We found differences in predation rates between the morphs depending on their micro-habitat. Specifically, the striped morph had a significant advantage over the others on green leaves. In the second experiment, striped morphs showed significantly lower predation on low than on high perches, irrespective of perch diameter. Reticulated models had an advantage over other morphs on thin stems for the first experiment, where models were placed about 60cm high. Diameter did not have a significant effect on predation for reticulated morphs when height classes were combined. Dotted models did not experience an advantage over the other morphs in any of the treatments. In leaf litter and on thick perches no morph had any advantage over another, and leaf litter predation rates were generally low. These results support a role for predation in maintaining multiple female morphs within small Costa Rican anoles, such as N. humilis.

The most commonly reported ecological effects of climate change are shifts in phenologies, in particular of warmer spring temperatures leading to earlier timing of key events. Among animals, however, these reports have been heavily biased towards avian phenologies, whereas we still know comparatively little about other seasonal adaptations, such as mammalian hibernation. Here we show a significant delay (0.47 days per year, over a 20-year period) in the hibernation emergence date of adult females in a wild population of Columbian ground squirrels in Alberta, Canada. This finding was related to the climatic conditions at our study location: owing to within-individual phenotypic plasticity, females emerged later during years of lower spring temperature and delayed snowmelt. Although there has not been a significant annual trend in spring temperature, the date of snowmelt has become progressively later owing to an increasing prevalence of late-season snowstorms. Importantly, years of later emergence were also associated with decreased individual fitness. There has consequently been a decline in mean fitness (that is, population growth rate) across the past two decades. Our results show that plastic responses to climate change may be driven by climatic trends other than increasing temperature, and may be associated with declines in individual fitness and, hence, population viability.

Empirical and theoretical studies have supported kin selection by demonstrating nepotism or modelling its conditions and consequences. As an alternative, we previously found that female Columbian ground squirrels had greater direct fitness when more close kin were present. Extending those results, we used population matrix methods to calculate minimum estimates of individual fitness, estimated direct and indirect components of fitness, estimated inclusive fitness by adding the direct fitness (stripped of estimated influences of the social environment) and indirect fitness components together, and finally looked for inclusive fitness benefits of associations with close kin who seem to be 'genial neighbours'. We examined the estimated fitness of a sample of 35 females for which complete lifetimes were known for themselves, their mothers and their littermate sisters. Six of these females had no cosurviving adult close kin, and their direct fitness was significantly lower than 29 females with such kin (λ = 0.66 vs. λ = 1.23). The net fitness benefit of the presence of close kin was thus 0.57. The estimated indirect component of fitness through benefits to the direct fitness of close kin was 0.43. Thus, estimated inclusive fitness for females with cosurviving close kin (λ = 1.09) was significantly greater than that for females without surviving close kin (viz., λ = 0.66). The presence of closely related and philopatric female kin appeared to result in considerable fitness benefits for female ground squirrels, perhaps through the behavioural mechanisms of lowered aggression and other forms of behavioural cooperation., (© 2011 Blackwell Publishing Ltd.)

Philopatry and dispersal result in selection of habitat locations that may differ in resources and social environment and thus should influence fitness components like survival and reproduction. We examined short-distance movements of young and adult females from natal or previous nesting sites within a colony of Columbian ground squirrels (Urocitellus columbianus) in the Rocky Mountains of Alberta, Canada, over a 17-year period. Females of all ages were strongly philopatric, yet a few (10-15%) exhibited movements that took them to new home ranges. We tested three hypotheses to explain the pattern of female natal and breeding movements: (1) that movements of philopatric females promote proximity to close kin; (2) that range shifts favour close kin via bequeathal of territory and (3) that dispersers move to lower density areas where competition for resources is lower. Tests of these three hypotheses revealed that: (1) philopatry and movements of young and older philopatric females led to proximity to mothers and local presence of close kin; (2) breeding dispersal did not result in bequeathal of home range to daughters, but movements of philopatric females suggested that they shared space with close kin and (3) adult females moved to new ranges with lower local densities, though dispersing females also left ranges where local density was significantly lower than for philopatric females. Natal and breeding movements among years produced two opportunities for territorial females: close spatial proximity to close kin via short philopatric movements, and habitats with fewer competitors via longer dispersal movements., (© 2011 Blackwell Publishing Ltd.)

Understanding which life-history variables have the greatest influence on population growth rate has great ecological and conservation importance. Applying models of population regulation and demographic mechanisms can aid management and conservation of both wild and captive populations. By comparisons of sensitivity, elasticity, and life-table response analyses, we identified demographic processes that were most likely to produce changes in population size (via prospective analyses) and the traits that actually influenced population changes (via retrospective analyses) among sexes, zoological facilities, and generations of captive squirrel monkey populations (Saimiri sciureus). Variation in life-history traits occurs within each group analyzed. Those traits that vary the most include age at maturity, age at last reproduction, and fertility. Zoos with increasing population growth rates maintain earlier ages of maturity, later ages of last reproduction, high rates of juvenile and adult survival, and most importantly greater fertility, reflecting shorter inter-birth intervals. Using prospective analyses, juvenile and adult survivals were predicted to be demographic traits with the greatest effect on population growth. Surprisingly, and despite predictions, retrospective analyses revealed that fertility was the life-history characteristic trait that contributed the most to changes in population size., (© 2011 Wiley-Liss, Inc.)

The life history schedules of wild organisms have long attracted scientific interest, and, in light of ongoing climate change, an understanding of their genetic and environmental underpinnings is increasingly becoming of applied concern. We used a multi-generation pedigree and detailed phenotypic records, spanning 18 years, to estimate the quantitative genetic influences on the timing of hibernation emergence in a wild population of Columbian ground squirrels (Urocitellus columbianus). Emergence date was significantly heritable [h(2) = 0.22 ± 0.05 (in females) and 0.34 ± 0.14 (in males)], and there was a positive genetic correlation (r(G) = 0.76 ± 0.22) between male and female emergence dates. In adult females, the heritabilities of body mass at emergence and oestrous date were h(2) = 0.23 ± 0.09 and h(2) = 0.18 ± 0.12, respectively. The date of hibernation emergence has been hypothesized to have evolved so as to synchronize subsequent reproduction with upcoming peaks in vegetation abundance. In support of this hypothesis, although levels of phenotypic variance in emergence date were higher than oestrous date, there was a highly significant genetic correlation between the two (r(G) = 0.98 ± 0.01). Hibernation is a prominent feature in the annual cycle of many small mammals, but our understanding of its influences lags behind that for phenological traits in many other taxa. Our results provide the first insight into its quantitative genetic influences and thus help contribute to a more general understanding of its evolutionary significance., (© 2011 The Authors. Journal of Evolutionary Biology © 2011 European Society For Evolutionary Biology.)

Since W. D. Hamilton's seminal work on the evolution of sociality, a large body of research has accumulated on how kin selection might explain the evolution of cooperation in many group-living species. Our study examined the evolutionary basis of philopatry and cooperation; specifically, whether individuals benefit from the presence of close kin. We applied an individual fitness approach to a 16-year study of Columbian ground squirrels (Urocitellus columbianus) to investigate potential causal paths by which the presence of kin might act on individual fitness. Our results indicate that individual fitness benefits resulted from associations of philopatric female kin, and support the hypothesis that increased tolerance of proximity of kin is a proximate mechanism for these benefits. The major life-history influence of kin on individual fitness was through improved reproductive success, and this benefit may have been owing to philopatric settlement of kin that were recognized through familiarization in the natal burrow. Thus, we demonstrated an evolutionary basis necessary for ongoing kin-selected cooperation in Columbian ground squirrels, though the mechanism of familiarity may determine which kin individuals benefit from cooperative behaviours.

The dynamics of an age-structured population in a fluctuating environment is determined by the stochastic individual contributions from annual survival and fecundity to the total reproductive value of the population the next year. All parameters required to describe the population dynamics are simple properties of the distribution of these individual demographic contributions, which we call individual reproductive value. The asymptotic population growth rate in the average environment and the demographic and environmental variances are respectively the mean individual reproductive value over individuals through time and the variance within and between years. Our approach leads to an intuitive understanding of demographic and environmental variances in age-structured populations and their decomposition into additive age-specific components due to survival and reproduction. We show how to apply this approach to estimate the demographic and environmental variances and their components. The estimates are based on yearly random samples of individual vital rates and require no information about the total population size.

Comparative analyses of survival senescence by using life tables have identified generalizations including the observation that mammals senesce faster than similar-sized birds. These generalizations have been challenged because of limitations of life-table approaches and the growing appreciation that senescence is more than an increasing probability of death. Without using life tables, we examine senescence rates in annual individual fitness using 20 individual-based data sets of terrestrial vertebrates with contrasting life histories and body size. We find that senescence is widespread in the wild and equally likely to occur in survival and reproduction. Additionally, mammals senesce faster than birds because they have a faster life history for a given body size. By allowing us to disentangle the effects of two major fitness components our methods allow an assessment of the robustness of the prevalent life-table approach. Focusing on one aspect of life history - survival or recruitment - can provide reliable information on overall senescence.

Results of the study by Blackburn et al. (2004a) of avifauna on oceanic islands suggest that distance from the mainland and time since European colonization have major influences on species extinctions and that island area is a significant but secondary contributing factor. After augmenting the data of the study on geographical properties for some of the islands they examined, we used a causal analysis approach with structural equation modeling to reexamine their conclusions. In our model geographical properties of islands, such as island area and isolation, were considered constraints on biological factors, such as the number of introduced mammalian predators and existing number of avifauna, that can directly or indirectly influence extinction. Of the variables we tested, island area had the greatest total influence on the threat of extinction due to its direct and indirect effects on the size of island avifauna. Larger islands had both a greater number of threatened bird species and more avifauna, increasing the number of species that could become threatened with extinction. Island isolation also had a significant, positive, and direct effect on threats to island avifauna because islands farther from the mainland had fewer current extant avifauna. Time since European colonization had a significant negative, but relatively weaker, influence on threats compared with the traditional biogeographic factors of island area and distance to the mainland. We also tested the hypothesis that the amount of threat is proportionally lower on islands that have had more extinctions (i.e., there is a "filter effect"). Because the proportion of bird extinctions potentially explained only 2.3% of the variation in the proportion of threatened species on islands, our results did not support this hypothesis. Causal modeling provided a powerful tool for examining threat of extinction patterns of known and hypothesized pathways of influence.

We studied litter size variation in a population of Richardson's ground squirrels (Spermophilus richardsonii) in Alberta, Canada, from 1987 to 2004. Litter size at first emergence of juveniles from the natal burrow ranged from 1 to 14; the most common litter sizes, collectively accounting for 41.0% of 999 litters, were 6 and 7. The number of offspring surviving to adulthood (attained on emergence from hibernation as yearlings) increased with increasing litter size, a result that was not predicted by Lack's "optimal litter size" hypothesis, Mountford's "cliff-edge" effect, or the "bad-years" effect. Contrary to the negative effects predicted by the "cost of reproduction" hypothesis, litter size had no significant influence on survival of mothers to the subsequent year or on the size of the subsequent litter. Rather, our results best fit the predictions of the "individual optimization" hypothesis, which suggests that litter size is determined by the body condition and environmental circumstances of each mother. Supporting this hypothesis, survival of individual offspring was not significantly associated with litter size. Additionally, year-to-year changes in maternal body mass at mating were positively associated with concurrent changes in litter size (r = 0.56), suggesting that litter size depends on the body condition of the mother. Because the mean number of recruits to adulthood increased as litter size increased (r2 = 0.96) and litter size increased with maternal condition, offspring productivity was greater for mothers in better body condition.

The historical debate of the 1960s between group and individual selection hinged on how the slow breeding of seabirds could be explained. While this debate was settled by the ascendance of individual selection, championed by David Lack, explanations for slow breeding in seabirds remain to be tested. We examined the slowest breeding of these birds, the albatrosses and petrels (order Procellariiformes), using analyses that statistically controlled for variations in body size and phylogeny. Incubation and fledging periods appeared strongly correlated, but this turned out to be largely explained by phylogeny. Nonetheless, developmental and reproductive rates were associated with the distance to the foraging range, as predicted under the hypothesis of ecological constraints on breeding pairs, and these results were independent of body size and phylogeny. Slower breeding in these seabirds appeared associated with the rigors of farther pelagic feeding, as Lack originally hypothesized.

The relative importance of life-history variables to population growth rate (lambda) has substantial consequences for the study of life-history evolution and for the dynamics of biological populations. Using life-history data for 142 natural populations of mammals, we estimated the elasticity of lambda to changes in age at maturity (alpha), age at last reproduction (omega), juvenile survival (Pj), adult survival (Pa), and fertility (F). Elasticities were then used to quantify the relative importance of alpha, omega, Pj, Pa, and F to lambda and to test theoretical predictions regarding the relative influence on lambda of changes in life-history variables. Neither alpha nor any other single life-history variable had the largest relative influence on lambda in the majority of the populations, and this pattern did not change substantially when effects of phylogeny and body size were statistically removed. Empirical support for theoretical predictions was poor at best. However, analyses of elasticities on the basis of the magnitude (F) and onset (alpha) of reproduction revealed that alpha, followed by F, had the largest relative influence on lambda in populations characterized by early maturity and high reproductive rates, or when F/alpha > 0.60. When maturity was delayed and reproductive rates were low, or when F/alpha < 0.15, survival rates were overwhelmingly most influential, and reproductive parameters (alpha and F) had little relative influence on lambda. Population dynamic consequences of likely responses of biological populations to perturbations in life-history variables are examined, and predictions are made regarding the numerical dynamics of age-structured populations on the basis of values of the F/alpha ratio.