Steeve D. Côté

Of glaciers and refugia: a decade of study sheds new light on the phylogeography of northwestern North America

Glacial cycles have played a dominant role in shaping the genetic structure and distribution of biota in northwestern North America. The two major ice age refugia of Beringia and the Pacific Northwest were connected by major mountain chains and bordered by the Pacific Ocean. As a result, numerous refugial options were available for the regions taxa during glacial advances. We reviewed the importance of glaciations and refugia in shaping northwestern North America’s phylogeographic history. We also tested whether ecological variables were associated with refugial history. The recurrent phylogeographic patterns that emerged were the following: (i) additional complexity, i.e. refugia within refugia, in both Beringia and the Pacific Northwest; and (ii) strong evidence for cryptic refugia in the Alexander Archipelago and Haida Gwaii, the Canadian Arctic and within the ice‐sheets. Species with contemporary ranges that covered multiple refugia, or those with high dispersal ability, were significantly more likely to have resided in multiple refugia. Most of the shared phylogeographic patterns can be attributed to multiple refugial locales during the last glacial maximum or major physiographic barriers like rivers and glaciers. However, some of the observed patterns are much older and appear connected to the orogeny of the Cascade‐Sierra chain or allopatric differentiation during historic glacial advances. The emergent patterns from this review suggest we should refine the classic Beringian‐southern refugial paradigm for northwestern North American biota and highlight the ecological and evolutionary consequences of colonization from multiple refugia.

Early onset of vegetation growth vs. rapid green-up: impacts on juvenile mountain ungulates.

Seasonal patterns of climate and vegetation growth are expected to be altered by global warming. In alpine environments, the reproduction of birds and mammals is tightly linked to seasonality; therefore such alterations may have strong repercussions on recruitment. We used the normalized difference vegetation index (NDVI), a satellite-based measurement that correlates strongly with aboveground net primary productivity, to explore how annual variations in the timing of vegetation onset and in the rate of change in primary production during green-up affected juvenile growth and survival of bighorn sheep (Ovis canadensis), Alpine ibex (Capra ibex), and mountain goats (Oreamnos americanus) in four different populations in two continents. We indexed timing of onset of vegetation growth by the integrated NDVI (INDVI) in May. The rate of change in primary production during green-up (early May to early July) was estimated as (1) the maximal slope between any two successive bimonthly NDVI values during this period and (2) the slope in NDVI between early May and early July. The maximal slope in NDVI was negatively correlated with lamb growth and survival in both populations of bighorn sheep, growth of mountain goat kids, and survival of Alpine ibex kids, but not with survival of mountain goat kids. There was no effect of INDVI in May and of the slope in NDVI between early May and early July on juvenile growth and survival for any species. Although rapid changes in NDVI during the green-up period could translate into higher plant productivity, they may also lead to a shorter period of availability of high-quality forage over a large spatial scale, decreasing the opportunity for mountain ungulates to exploit high-quality forage. Our results suggest that attempts to forecast how warmer winters and springs will affect animal population dynamics and life histories in alpine environments should consider factors influencing the rate of changes in primary production during green-up and the timing of vegetation onset.

Individual variation in reproductive costs of reproduction: high-quality females always do better

1. Although life-history theory predicts substantial costs of reproduction, individuals often show positive correlations among life-history traits, rather than trade-offs. The apparent absence of reproductive costs may result from heterogeneity in individual quality. 2. Using detailed longitudinal data from three contrasted ungulate populations (mountain goats, Oreamnos americanus; bighorn sheep, Ovis canadensis; and roe deer, Capreolus capreolus), we assessed how individual quality affects the probability of detecting a cost of current reproduction on future reproduction for females. We used a composite measure of individual quality based on variations in longevity (all species), success in the last breeding opportunity before death (goats and sheep), adult mass (all species), and social rank (goats only). 3. In all species, high-quality females consistently had a higher probability of reproduction, irrespective of previous reproductive status. In mountain goats, we detected a cost of reproduction only after accounting for differences in individual quality. Only low-quality female goats were less likely to reproduce following years of breeding than of nonbreeding. Offspring survival was lower in bighorn ewes following years of successful breeding than after years when no lamb was produced, but only for low-quality females, suggesting that a cost of reproduction only occurred for low-quality females. 4. Because costs of reproduction differ among females, studies of life-history evolution must account for heterogeneity in individual quality.

DOMINANCE HIERARCHIES IN FEMALE MOUNTAIN GOATS: STABILITY, AGGRESSIVENESS AND DETERMINANTS OF RANK

To investigate the importance of dominance relationships in the social organization of large mammals, I studied the aggressive behaviour of marked adult female mountain goats ( Oreamnos americanus ) during four years in west-central Alberta, Canada. Despite large group size, the 38-45 adult females in the population were organized in a strong and very stable linear hierarchy. Social rank was strongly related to age and did not decrease for the oldest females. The presence of a kid did not affect the aggressive behaviour of females, suggesting that aggressiveness probably did not evolve for offspring defense in mountain goats. Initiators won most encounters, except when the receiver was an older female. When age was accounted for, body mass, horn length, and body size were not related to female rank. A new measure of aggressiveness, controlling for the number of opportunities for interactions, revealed that aggressiveness towards younger adult females increased with both age and social rank. On the other hand, age and social rank did not affect aggressiveness towards other females of the same age or older. Goats interacted more often with individuals of similar ranks than with individuals that were distant in the dominance hierarchy. Social rank of adult daughters was not related to the social rank of mothers. Although central positions in a group may decrease predation risk, dominant females did not occupy central positions more often than subordinates. Because age was the main determinant of rank, the only effective way to increase social rank was to survive.

Reproductive success in female mountain goats: the influence of age and social rank

In mammals, reproductive success may be positively correlated with both maternal age and social rank. Because social rank often increases with age, however, the effects of rank and age on reproductive success are difficult to separate. We studied a marked population of mountain goats, Oreamnos americanus, to assess the relative effects of maternal age and social rank on kid production and survival. Adult females formed a linear and stable dominance hierarchy. Kid production increased with both age-specific maternal social rank and age, but decreased slightly after 9 years of age. The influence of dominance was particularly important among 3- to 5-year-old females, and the positive effect of dominance on kid production decreased with increasing female age. Age-specific social rank and maternal age did not affect kid survival to autumn or to 1 year. Kids whose mothers were heavy for their age had a higher probability of surviving to weaning and to 1 year than kids born to light females. When age was accounted for, female survival was not related to social rank. Social rank appears to be an important determinant of reproductive success for female mountain goats, especially among young females.

Individual quality, early‐life conditions, and reproductive success in contrasted populations of large herbivores

Variations among individuals in phenotypic quality and fitness often confound analyses of life-history strategies assessed at the population level. We used detailed long-term data from three populations of large herbivores with generation times ranging from four to nine years to quantify heterogeneity in individual quality among females, and to assess its influence on mean annual reproductive success over the lifetime (MRS). We also determined how environmental conditions in early life shaped individual quality and tested A. Lomnickis hypothesis that variance in individual quality should increase when environmental conditions deteriorate. Using multivariate analyses (PCA), we identified one (in sheep and deer) or two (in goats) covariations among life-history traits (longevity, success in the last breeding opportunity, adult mass, and social rank) as indexes of individual quality that positively influenced MRS of females. Individual quality was reduced by unfavorable weather, low resource availability, and high population density in the year of birth. Early-life conditions accounted for 35-55% of variation in individual quality. In roe deer, we found greater variance in individual quality for cohorts born under unfavorable conditions as opposed to favorable ones, but the opposite was found in bighorn sheep and mountain goats. Our results demonstrate that heterogeneity in female quality can originate from environmental conditions in early life and can markedly influence the fitness of females in species located at different positions along the slow-fast continuum of life-history strategies.

Life-history effects of chemical immobilization and radiocollars on mountain goats

To assess the potential effect of our research activities on mountain goats (Oreamnos americanus), we tested for long-term behavioral, reproductive, and survival effects of immobilizing and radiocollanng goats in an unhunted population in Alberta, Canada. Chemical immobilization of females with xylazine hydrochloride 1-5 months before rut decreased kid production the following year for 3 and 4 year olds (P = 0.02), but not for older females (P = 0.67). Following capture, drugged females abandoned their kids more often than undrugged females (16 vs. 2%; P = 0.02), and abandonment decreased kid survival (P 0.10). Chemical immobilization did not affect survival, foraging efficiency, or time spent alert for either sex (P > 0.20). Radiocollars had no effect on kid production or female dominance status and did not affect survival, foraging efficiency, or time spent alert for either sex (P > 0.10). Overwinter survival of captured and uncaptured kids did not differ. Kids with radiocollars appeared to have lower survival than uncollared kids, but the effect was not significant (P = 0.16). Our results suggest that handling affected reproduction and survival of mountain goats and underline the need to test for similar effects in wildlife field studies. We provide guidelines to reduce unwanted life-history effects on captured mountain goats.

Responses of woodland caribou to winter ecotourism in the Charlevoix Biosphere Reserve, Canada

Abstract We assessed the impact of ecotourist visits during winter on woodland caribou Rangifer tarandus caribou time budgets in the Charlevoix Biosphere Reserve, Canada. We compared the behaviour of caribou during and after ecotourist visits with their behaviour during days without visits. In the presence of ecotourists, caribou increased time spent vigilant and standing, mostly at the expense of time spent resting and foraging. After visits, caribou tended to rest more than during control days. Caribou reduced time spent foraging during ecotourist visits as the number of observers increased. The impact of ecotourists appeared to decrease as winter progressed. Visits were short ( x =39.3 min) and caribou never left their winter quarters because of human presence. However, caribou abandoned their wintering area twice in response to wolf presence. Although winter is a difficult period of the year for caribou, our results suggest that with proper precautions caribou in Charlevoix can tolerate ecotourist visits.

Feedback effects of chronic browsing on life-history traits of a large herbivore.

1. Increasing ungulate populations are affecting vegetation negatively in many areas, but few studies have assessed the long-term effects of overbrowsing on individual life-history traits of ungulates. 2. Using an insular population of white-tailed deer (Odocoileus virginianus Zimmermann; Anticosti, Québec, Canada) introduced in 1896, and whose density has remained high since the first evidence of severe browsing in the 1930s, we investigated potential feedbacks of long-term and heavy browsing on deer life-history traits. 3. We assessed whether chronic browsing contributed to a decline of the quality of deer diet in early autumn during the last 25 years, and evaluated the impacts of reduced diet quality on deer body condition and reproduction. 4. Rumen nitrogen content declined 22% between two time periods, 1977-79 and 2002-04, indicating a reduction in diet quality. 5. After accounting for the effects of year within the time period, age and date of harvest in autumn, peak body mass of both sexes declined between the two time periods. At the end of November, males were on average 12% heavier and adult does 6% heavier in 1977-79 than in 2002-04. Hind foot length did not vary between time periods. 6. The probability of conception increased 15% between the two time periods, but litter size at ovulation declined 7%, resulting in a similar total number of ovulations in 2002-04 and in 1977-79. 7. Our results suggest that following a decline in diet quality, white-tailed deer females modified their life-history strategies to maintain reproduction at the expense of growth. 8. Deer appear to tolerate drastic reductions in diet quality by modifying their life history traits, such as body mass and reproduction, before a reduction in density is observed. Such modifications may contribute to maintain high population density of large herbivores following population irruption.

Integrative use of spatial, genetic, and demographic analyses for investigating genetic connectivity between migratory, montane, and sedentary caribou herds

Genetic differentiation is generally assumed to be low in highly mobile species, but this simplistic view may obscure the complex conditions and mechanisms allowing genetic exchanges between specific populations. Here, we combined data from satellite‐tracked migratory caribou (Rangifer tarandus), microsatellite markers, and demographic simulations to investigate gene flow mechanisms between seven caribou herds of eastern Canada. Our study included one montane, two migratory, and four sedentary herds. Satellite‐tracking data indicated possibilities of high gene flow between migratory herds: overlap of their rutting ranges averaged 10% across years and 9.4% of females switched calving sites at least once in their lifetime. Some migratory individuals moved into the range of the sedentary herds, suggesting possibilities of gene flow between these herds. Genetic differentiation between herds was weak but significant (FST = 0.015): migratory and montane herds were not significantly distinct (FST all ≤ 0.005), whereas sedentary herds were more differentiated (FST = 0.018–0.048). Geographical distances among sedentary herds limited gene flow. Historical estimates of gene flow were higher from migratory herds into sedentary herds (4Nm all > 9) than vice‐versa (4Nm all < 5), which suggests migratory herds had a demographic impact on sedentary herds. Demographic simulations showed that an effective immigration rate of 0.0005 was sufficient to obtain the empirical FST of 0.015, while a null immigration rate increased the simulated FST to > 0.6. In conclusion, the weak genetic differentiation between herds cannot be obtained without some genetic exchanges among herds, as demonstrated by genetic and spatial data.