A slow life in hell or a fast life in heaven: demographic analyses of contrasting roe deer populations
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- 1Environmental conditions shape population growth through their impact on demographic parameters. While knowledge has accumulated concerning the effects of population density and climatic conditions, a topical question now concerns how predation and harvest influence demographic parameters and population growth (λ).
- 2We performed a comparative demographic analysis based on projection matrix models for female roe deer. Population-specific matrices were parameterized based on longitudinal data from five intensively monitored populations in Norway and France, spanning a large variability in environmental characteristics such as densities of large predators, hunter harvest and seasonality.
- 3As expected for a large iteroparous vertebrate, temporal variation was invariably higher in recruitment than in adult survival, and the elasticity of adult survival was consistently higher than that of recruitment. However, the relative difference in elasticity of λ to recruitment and adult survival varied strongly across populations, and was closely correlated with adult survival.
- 4Different traits accounted for most of the variance in λ in different ecological settings. Adult survival generally contributed more in populations with low mean adult survival and low mean growth rate during the study period. Hunters and predators (Eurasian lynx and red foxes) occurred in two of our study populations and contributed substantially to the variance in λ, accounting for a total of 35% and 70% in the two populations respectively.
- 5Across populations, we did not find any evidence that roe deer increased their reproductive output when faced with harsh conditions, resulting in some populations having negative growth rates.
- 6Generation time, a measure of the speed of the life-history cycle, increased from less than 4 years in the most productive population (‘roe deer heaven’) to more than 6 years in declining populations facing predation from lynx, red fox and hunters (‘roe deer hell’), and was tightly and inversely correlated with λ. Such a deceleration of the life cycle in declining populations might be a general feature in large herbivores.
- 7Our results shows that the plethora of environmental conditions faced by populations of large herbivores also induce high intraspecific variation in their ranking along the ‘fast–slow’ continuum of life-history tactics.