Dominique Berteaux

Wavelet analysis of ecological time series

Wavelet analysis is a powerful tool that is already in use throughout science and engineering. The versatility and attractiveness of the wavelet approach lie in its decomposition properties, principally its time-scale localization. It is especially relevant to the analysis of non-stationary systems, i.e., systems with short-lived transient components, like those observed in ecological systems. Here, we review the basic properties of the wavelet approach for time-series analysis from an ecological perspective. Wavelet decomposition offers several advantages that are discussed in this paper and illustrated by appropriate synthetic and ecological examples. Wavelet analysis is notably free from the assumption of stationarity that makes most methods unsuitable for many ecological time series. Wavelet analysis also permits analysis of the relationships between two signals, and it is especially appropriate for following gradual change in forcing by exogenous variables.

Keeping Pace with Fast Climate Change: Can Arctic Life Count on Evolution?

Abstract Adaptations to the cold and to short growing seasons characterize arctic life, but climate in the Arctic is warming at an unprecedented rate. Will plant and animal populations of the Arctic be able to cope with these drastic changes in environmental conditions? Here we explore the potential contribution of evolution by natural selection to the current response of populations to climate change. We focus on the spring phenology of populations because it is highly responsive to climate change and easy to document across a wide range of species. We show that evolution can be fast and can occur at the time scale of a few decades. We present an example of reproductive phenological change associated with climate change (North American red squirrels in the Yukon), where a detailed analysis of quantitative genetic parameters demonstrates contemporary evolution. We answer a series of frequently asked questions that should help biologists less familiar with evolutionary theory and quantitative genetic methods to think about the role of evolution in current responses of ecological systems to climate change. Our conclusion is that evolution by natural selection is a pertinent force to consider even at the time scale of contemporary climate changes. However, all species may not be equal in their capacity to benefit from contemporary evolution.

MATERNAL EFFECTS AND THE POTENTIAL FOR EVOLUTION IN A NATURAL POPULATION OF ANIMALS

Abstract Maternal effects are widespread and can have dramatic influences on evolutionary dynamics, but their genetic basis has been measured rarely in natural populations. We used cross‐fostering techniques and a long‐term study of a natural population of red squirrels, Tamiasciurus hudsonicus, to estimate both direct (heritability) and indirect (maternal) influences on the potential for evolution. Juvenile growth in both body mass and size had significant amounts of genetic variation (mass h2= 0.10; size h2= 0.33), but experienced large, heritable maternal effects. Growth in body mass also had a large positive covariance between direct and maternal genetic effects. The consideration of these indirect genetic effects revealed a greater than three‐fold increase in the potential for evolution of growth in body mass (h t2= 0.36) relative to that predicted by heritability alone. Simple heritabilities, therefore, may severely underestimate or overestimate the potential for evolution in natural populations of animals.

BREEDING DISPERSAL IN FEMALE NORTH AMERICAN RED SQUIRRELS

Although natal dispersal has received considerable attention from animal ecologists, the causes and consequences of breeding dispersal have remained largely unexplored. We used telemetry, direct observation, and long-term mark–recapture (9 yr) to study breeding dispersal in the North American red squirrel (Tamiasciurus hudsonicus) at Kluane, Yukon, Canada. We recorded the postbreeding behavior (keep the territory, share it with juveniles, or bequeath it to juveniles) of mothers from 485 litters, and monitored the fates of eight cohorts of weaned juveniles (680 individuals). The proportion of mothers that bequeathed their territory to one of their offspring was roughly one-third of that keeping or sharing it. Breeding dispersal was a recurrent phenomenon that characterized a fraction of the population of reproductive females every year. Dispersing females did not improve the quality of their breeding environment. In contrast, by leaving their territory, mothers allowed some offspring to stay on the natal site, which increased juvenile survival. Breeding dispersal by female red squirrels was thus a form of parental investment. Dispersing females were older than others, had higher numbers of juveniles at weaning, and moved their breeding sites more frequently after reproducing when food availability was high. These patterns are consistent with the major predictions of parental investment theories. We detected no difference in survivorship or future reproduction between dispersing and resident mothers. Juvenile males dispersed more often than females, but not farther. The sex of offspring did not influence whether mothers dispersed or not. Although we showed that breeding dispersal can have major impacts on the dynamics of squirrel populations, the relative implications of natal and breeding dispersal for the genetic structure and demography of populations and the social evolution of species remain unknown.

Repeatability of daily field metabolic rate in female Meadow Voles (Microtus pennsylvanicus)

1. Repeated measurements of daily field metabolic rate (FMR) were made on 11 Meadow Voles (Microtus pennsylvanicus Ord.) by means of the doubly labelled water technique. The objective was to quantify the individual consistency of FMR by calculating the repeatability of successive measures on the same individuals. One more general goal was to test whether FMRs are sufficiently repeatable to be convenient for field studies of natural selection. 2. Voles were all non-reproductive females, 5-7-months old. They were maintained individually in outdoor enclosures 25m 2 and were injected 1-3 times with doubly labelled water. Two to six measures of daily FMR were thus obtained per individual (x = 4.09, SD = 1.51, n = 11) over a period of 42 days in July and August 1994. 3. Body mass and rate of change in body mass accounted for 31.6% of the observed variation in FMR; ground-temperature variations had no significant effect on FMR, probably owing to the small range of temperatures experienced by voles. 4. Repeatability of mass-corrected log 10 FMR measurements was low (r=0.261). This low repeatability was very consistent with the results of a previous study on consistency of mass-specific daily energy expenditures of caged pouched mice. 5. A partition of the total variance observed in mass-corrected FMR showed that 63.0% of the variance originated from differences within individuals, 27.6% from differences among individuals, and 9.4% from measurement error. FMR was not consistently higher or lower on the first or second day of measurement, indicating no clear effect of handling stress. 6. A practical implication of these results is that single measurements of daily field metabolic rates are not necessarily a good predictor of the average 24 h energy budget for a given individual. On a more theoretical basis, these results indicate that, although the ability of an animal to manage its energy economics may largely determine its selective value, daily FMR seems to be a poor candidate variable to relate this ability to individual fitness in experimental studies. 7. We suggest that future studies of repeatability of FMR should concentrate on energetically constraining periods. This would allow further evaluation of the potential role of interindividual differences in FMR as a tool for understanding evolutionary pathways that shaped energy economics of animals.

Historical and ecological determinants of genetic structure in arctic canids

Wolves (Canis lupus) and arctic foxes (Alopex lagopus) are the only canid species found throughout the mainland tundra and arctic islands of North America. Contrasting evolutionary histories, and the contemporary ecology of each species, have combined to produce their divergent population genetic characteristics. Arctic foxes are more variable than wolves, and both island and mainland fox populations possess similarly high microsatellite variation. These differences result from larger effective population sizes in arctic foxes, and the fact that, unlike wolves, foxes were not isolated in discrete refugia during the Pleistocene. Despite the large physical distances and distinct ecotypes represented, a single, panmictic population of arctic foxes was found which spans the Svalbard Archipelago and the North American range of the species. This pattern likely reflects both the absence of historical population bottlenecks and current, high levels of gene flow following frequent long‐distance foraging movements. In contrast, genetic structure in wolves correlates strongly to transitions in habitat type, and is probably determined by natal habitat‐biased dispersal. Nonrandom dispersal may be cued by relative levels of vegetation cover between tundra and forest habitats, but especially by wolf prey specialization on ungulate species of familiar type and behaviour (sedentary or migratory). Results presented here suggest that, through its influence on sea ice, vegetation, prey dynamics and distribution, continued arctic climate change may have effects as dramatic as those of the Pleistocene on the genetic structure of arctic canid species.

Food choice by white-tailed deer in relation to protein and energy content of the diet: a field experiment

Abstract Optimality models of food selection by herbivores assume that individuals are capable of assessing forage value, either directly through the currency used in the model or indirectly through other variables correlated with the currency. Although energy and protein are the two currencies most often used, controversy exists regarding their respective influence on food choice. Part of the debate is due to the difficulty of teasing apart these two nutrients, which are closely correlated in most natural forages. Here we offer a test of the assumption that energy and protein contents of the forage are both currencies that large mammalian herbivores can use when selecting their food. We observed feeding behavior of 47 wild white-tailed deer (Odocoileusvirginianus) during winter while individuals were presented with four experimental foods representing two levels of energy and protein (dry matter digestibility: 40–50%; crude protein: 12–16%). Using experimental foods allowed us to separate the influences of energy and protein and clearly distinguish between the roles of these two nutrients. Deer discriminated between foods through partial selection, and selected diets higher in energy but lower in protein. The observed choices appeared consistent with physiological needs of deer wintering at the study site, where digestible energy was in short supply in the natural environment while protein was probably not. Results are in good agreement with recent findings on domesticated ruminants. They support a basic assumption of optimality models of food selection that use energy and/or protein as a currency, although the physiological mechanisms behind the food selection process remain unclear. We urge students of food selection by herbivores to replicate our experiment with other foods and/or in other circumstances before more general conclusions are drawn.

Integrating Traditional Ecological Knowledge and Ecological Science: a Question of Scale

The benefits and challenges of integrating traditional ecological knowledge and scientific knowledge have led to extensive discussions over the past decades, but much work is still needed to facilitate the articulation and co-application of these two types of knowledge. Through two case studies, we examined the integration of traditional ecological knowledge and scientific knowledge by emphasizing their complementarity across spatial and temporal scales. We expected that combining Inuit traditional ecological knowledge and scientific knowledge would expand the spatial and temporal scales of currently documented knowledge on the arctic fox (Vulpes lagopus) and the greater snow goose (Chen caerulescens atlantica), two important tundra species. Using participatory approaches in Mittimatalik (also known as Pond Inlet), Nunavut, Canada, we documented traditional ecological knowledge about these species and found that, in fact, it did expand the spatial and temporal scales of current scientific knowledge for local arctic fox ecology. However, the benefits were not as apparent for snow goose ecology, probably because of the similar spatial and temporal observational scales of the two types of knowledge for this species. Comparing sources of knowledge at similar scales allowed us to gain confidence in our conclusions and to identify areas of disagreement that should be studied further. Emphasizing complementarities across scales was more powerful for generating new insights and hypotheses. We conclude that determining the scales of the observations that form the basis for traditional ecological knowledge and scientific knowledge represents a critical step when evaluating the benefits of integrating these two types of knowledge. This is also critical when examining the congruence or contrast between the two types of knowledge for a given subject.

LIFETIME SELECTION ON HERITABLE LIFE-HISTORY TRAITS IN A NATURAL POPULATION OF RED SQUIRRELS

Abstract Despite their importance in evolutionary biology, heritability and the strength of natural selection have rarely been estimated in wild populations of iteroparous species or have usually been limited to one particular event during an organisms lifetime. Using an animal‐model restricted maximum likelihood and phenotypic selection models, we estimated quantitative genetic parameters and the strength of lifetime selection on parturition date and litter size at birth in a natural population of North American red squirrels, Tamiasciurus hudsonicus. Litter size at birth and parturition date had low heritabilities (h2= 0.15 and 0.16, respectively). We considered potential effects of temporal environmental covariances between phenotypes and fitness and of spatial environmental heterogeneity in estimates of selection. Selection favored early breeders and females that produced litter sizes close to the population average. Stabilizing selection on litter size at birth may occur because of a trade‐off between number of offspring produced per litter and offspring survival or a trade‐off between a females fecundity and her future reproductive success and survival.

Best squirrels trade a long life for an early reproduction

Age at primiparity plays a crucial role in population dynamics and life-history evolution. Long-term data on female North American red squirrels were analysed to study the fitness consequences of delaying first reproduction. Early breeders were born earlier, had a higher breeding success and achieved a higher lifetime reproductive success than females who delayed their first reproduction, which suggests a higher quality of early breeders. However, early breeders had similar mass when tagged, and similar number of food caches available at one year of age as late breeders. Nevertheless, we found evidence of survival costs of early primiparity. Early breeders had a lower survival between one and two years of age than late breeders and a lower lifespan. Our study points out that two reproductive tactics co-occurred in this population: a tactic based on early maturity at the cost of a lower survival versus a tactic based on delayed maturity and long lifespan. High quality individuals express the most profitable tactic by breeding early whereas low quality individuals do the best of a bad job by delaying their first reproduction.