Model Links High-Density Moose Dynamics to Density Dependence, Calf Predation and Dispersal

February 18, 2026

A wild female moose standing in the Jacques-Cartier River in Quebec

Research · Ecology

A new population model suggests that rising density strongly reshaped survival, reproduction and dispersal in North American moose (Alces alces americana) in Quebec, Canada’s Forillon National Park, where gray wolves are absent. Survival and reproduction showed negative density dependence, while movement across the park boundary also changed as the population grew. The model further indicates that American black bears (Ursus americanus) and coyotes (Canis latrans) caused substantial calf mortality each year, while winter ticks had only a slight effect on calf survival.

The open-access study was published online in Ecological Modelling on 18 February 2026. Its authors developed a model structured by sex and age to explain nearly four decades of observed change in a protected population that reached high density without its apex predator.

Map of Forillon National Park and graph of moose density from 1982 to 2020 — Study area in Quebec and moose density in Forillon National Park from 1982 to 2020, estimated from late-winter aerial surveys. Figure 1 from Tassi et al. (2026), CC BY 4.0.

Wolves were absent, but calf predation remained substantial

Forillon differs from many moose systems because gray wolves are absent. That removes a major source of adult and juvenile mortality, but it does not mean predation disappears. Black bears and coyotes remain capable of killing calves, and animals can move across the park boundary into a landscape where hunting and other human pressures differ.

Many existing moose models were developed for lower-density populations or systems with wolves. The researchers therefore built a sex- and age-structured simulation suited to Forillon’s circumstances. They used pattern-oriented modelling, comparing simulated population patterns with observations to identify combinations of demographic rates that could plausibly reproduce the historical record.

Density affected several demographic processes

The most plausible simulations showed strong density dependence in survival, reproduction and dispersal. Calf winter survival was especially sensitive to both population density and winter severity, while adult survival was more buffered. As food competition increased, the model also required lower reproduction and changing rates of movement out of the park to reproduce the observed population trajectory.

Density dependence can emerge when animals compete more strongly for food or when habitat quality declines under heavy browsing. It can also interact with disease, condition and movement. The study’s result does not mean that one single mechanism was measured directly; it identifies a combination of demographic responses that best reproduced the observed changes.

The dominant pressures changed as the population grew

The model did not assign the same importance to every driver throughout the 38 years. Winter conditions and predation appeared to have greater influence before 2000, when moose density was still relatively low. After 2000, density dependence became the leading influence. Winter climate also interacted with density and winter-tick burden, helping explain why calf survival varied more strongly than adult survival.

Calf predators still mattered

Although wolves were absent, the model attributed substantial annual calf mortality to black bears and coyotes. These alternative predators therefore remained an important part of the population’s early-life dynamics.

Winter ticks, by contrast, produced only a slight effect on calf survival in the most plausible model. This differs from findings in some other parts of northeastern North America, where heavy tick infestations have been associated with severe calf losses.

The model also suggested that changes in the population’s sex ratio were mainly explained by sex-biased dispersal. Overall emigration increased through time, apart from a temporary decrease in 2009–2016, and males were proportionally more likely to leave than females; yearling males made up the largest group of emigrants. Immigration also increased and consisted mainly of females, especially yearlings.

Movement across the protected-area boundary also exposed animals to hunting outside Forillon. Modelled hunting mortality increased through time in all sex and age classes, while autumn survival was lower and declined more strongly in males than in females and calves. Hunting is prohibited inside the national park, so this mortality reflects the consequences of animals moving into the surrounding hunted landscape rather than hunting within the protected area.

The model identifies a plausible combination of mechanisms

Pattern-oriented modelling does not identify one observed cause in the same way as a controlled experiment. It tests which combinations of mechanisms can reproduce several features of the real population at once. The resulting sequence of vital rates is described as the most plausible among those evaluated, not as the only possible history.

Sources and image credit

Tassi, L., Etcheverry, P., Bauduin, S., & St-Laurent, M.-H. (2026). While the wolf is away: Modelling the dynamics of a moose population in a protected area. Ecological Modelling, 515, 111528. https://doi.org/10.1016/j.ecolmodel.2026.111528Primary peer-reviewed open-access article available online 18 February 2026 under CC BY 4.0. The sex- and age-structured model reproduced 38 years of change in the Forillon National Park moose population and identified negative density dependence, calf predation and sex-biased dispersal as components of the most plausible parameter sequence.

Image: Cephas — wild female moose (Alces alces) in Jacques-Cartier National Park, Quebec, Canada, 28 June 2009; representative Quebec image, not an animal from the Forillon study. Source: Wikimedia Commons. · CC BY-SA 3.0 — https://creativecommons.org/licenses/by-sa/3.0/ · Source

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Moose Alces alces Explore species

Coyote Canis latrans Explore species

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