Abstract
Climate seasonality is a predominant constraint on the lifecycles of species in alpine and polar biomes. Assessing the response of these species to climate change thus requires taking into account seasonal constraints on populations. However, interactions between seasonality, weather fluctuations, and population parameters remain poorly explored as they require long‐term studies with high sampling frequency. This study investigated the influence of environmental covariates on the demography of a corvid species, the alpine chough Pyrrhocorax graculus, in the highly seasonal environment of the Mont Blanc region. In two steps, we estimated: (1) the seasonal survival of categories of individuals based on their age, sex, etc., (2) the effect of environmental covariates on seasonal survival. We hypothesized that the cold season—and more specifically, the end of the cold season (spring)—would be a critical period for individuals, and we expected that weather and individual covariates would influence survival variation during critical periods. We found that while spring was a critical season for adult female survival, it was not for males. This is likely because females are dominated by males at feeding sites during snowy seasons (winter and spring), and additionally must invest energy in egg production. When conditions were not favorable, which seemed to happen when the cold season was warmer than usual, females probably reached their physiological limits. Surprisingly, adult survival was higher at the beginning of the cold season than in summer, which may result from adaptation to harsh weather in alpine and polar vertebrates. This hypothesis could be confirmed by testing it with larger sets of populations. This first seasonal analysis of individual survival over the full life cycle in a sedentary alpine bird shows that including seasonality in demographic investigations is crucial to better understand the potential impacts of climate change on cold ecosystems.
Highlights
High latitudes and high elevations are the regions on Earth most exposed to current and future climate change (Nogués‐Bravo, Araujo, Errea, & Martinez‐Rica, 2007; Pepin et al, 2015; Yoccoz, Delestrade, & Loison, 2010)
Predicting the impact of climate change on long‐lived terrestrial vertebrates living in highly seasonal environments is difficult due to the combination of immediate and delayed consequences of seasonality on demographic traits
| 12533 individuals to be greater during the harsh or “critical” seasons; (c) dominated adults to have lower survival than dominating adults during the harsh/critical seasons; (d) winter flock size to negatively influence cold season survival, as intraspecific competition for food is strongly correlated with the relative size of a flock, despite the numerous advantages of living in a group (Clutton‐Brock et al, 1999; Lehtonen & Jaatinen, 2016); and (e) seasonal survival rates to be influenced by weather conditions such as temperature and precipitation, through direct or carry‐over effects, especially during critical survival periods
Summary
High latitudes and high elevations are the regions on Earth most exposed to current and future climate change (Nogués‐Bravo, Araujo, Errea, & Martinez‐Rica, 2007; Pepin et al, 2015; Yoccoz, Delestrade, & Loison, 2010). Predicting the impact of climate change on long‐lived terrestrial vertebrates living in highly seasonal environments is difficult due to the combination of immediate and delayed consequences of seasonality on demographic traits Estimating such parameters in marked free‐living populations over the long‐term is the most reliable way to identify critical survival periods for individuals and the determinants of temporal variation on survival. A flock has a strong hierarchical social structure, with adults dominating immature individuals, and males dominating females on clumped food resources (Delestrade, 1993b) Given these characteristics, and the general pattern of survival observed in long‐lived species, we expected: (a) the end of the winter season (the spring in alpine environments) to be the most critical period of the year in terms of survival for all individuals (due to low food income, high requirements and lower levels of fat reserves); (b) differences in survival between adults and younger. | 12533 individuals to be greater during the harsh or “critical” seasons (winter and especially spring in this case); (c) dominated adults (females and small individuals) to have lower survival than dominating adults during the harsh/critical seasons; (d) winter flock size to negatively influence cold season survival, as intraspecific competition for food is strongly correlated with the relative size of a flock, despite the numerous advantages of living in a group (Clutton‐Brock et al, 1999; Lehtonen & Jaatinen, 2016); and (e) seasonal survival rates to be influenced by weather conditions such as temperature (warm summers, cold winters, or springs) and precipitation, through direct or carry‐over effects, especially during critical survival periods
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