Mattis Pelletier
Master student
Department of Biology
Laval University

Co-supervised by:

Steeve Côté (Regular member)

Research project description

Impact of cohort effects on the biodemographic components of migratory caribou

Introduction: Environmental conditions experienced during early development are particularly likely to generate long-term consequences on the fitness of individuals. Environmental conditions affect all individuals in a cohort simultaneously and can generate cohort effects, i.e. variations observed in the characteristics and behavior of a given generation of individuals compared to previous or subsequent generations. For example, cohorts experiencing favorable conditions may demonstrate higher fitness than those experiencing unfavorable conditions early in life. It therefore becomes crucial to determine which environmental conditions experienced early in life have an impact on the short- and long-term fitness of different caribou cohorts, and to quantify this impact.Objectives: The study aims to understand the impact of environmental conditions on the condition of yearling caribou and their long-term survival. The first objective examines which environmental conditions experienced during the calves' first year of life influence their condition. Three distinct periods of the fawn's first year of life are identified (gestation, pre-weaning and post-weaning) to determine which period(s) is/are critical for fawns. The second objective explores the long-term consequences on survival and longevity, with two hypotheses: better long-term survival for cohorts born under favorable conditions, or viability selection favoring those who survived despite difficult conditions. The third objective studies the interaction between environmental conditions in early life and adulthood on survival. This hypothesis suggests that similar conditions at both stages favor fitness. Study sites: In northern Quebec and Labrador, migratory caribou (Rangifer tarandus), represented mainly by the Rivière-aux-Feuilles (RAF) and Rivière-George (RG) herds, have suffered dramatic declines in numbers (68% and 99% respectively) over the past 25 years. Numbering over a million individuals in the 1990s, these herds have declined rapidly, a situation similar to that of most migratory caribou populations around the Arctic Circle. The causes of this decline are multifactorial, with increasing threats from human disturbance and climate change. The current situation of the RG, whose abundance was estimated at around 8 100 caribou (± 486) in 2020, is precarious. At present, it is impossible to assess the prospects for its recovery. The RAF was estimated at around 199 000 (± 15 920) in 2016, and the population is still considered to be in decline.Material and methods: The study uses capture data and satellite-telemetry tracking of females. Captures targeted individuals of known age (0.5 to 1 year) to measure their body condition. The females were then tracked with satellite collars, providing data on their annual survival. Environmental variables, extracted for each season and year, included temperature, precipitation, snow accumulation and cover, and the North Atlantic Oscillation index. Population size and migration distance are also assessed. Seasonal food resources are represented by NDVI, with meteorological data obtained from NARR. Statistical analyses, such as linear mixed models and Cox models, will be used to assess relationships between environmental conditions, yearling body condition and annual survival.Expected results: Our study will determine the effect of environmental and population conditions on the condition of yearling migratory caribou, but also the long-term effects on survival and longevity. I expect that environmental and population conditions influencing travel-related energy expenditure will generate cohort effects. Cohorts experiencing favorable conditions will have better annual survival and increased longevity than cohorts experiencing constraining conditions. I expect the inter-cohort differences in annual survival to dissipate over time, as is generally the case with large herbivores. Finally, I expect similar conditions at both stages to have no impact on the fitness of this population, which would be in line with the literature.

Research Site Coordinates

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