Variation in Demography and Life-History Strategies Across the Range of a Declining Mountain Bird Species

Arnaud G Barras,Raphaël Arlettaz,Sébastien Blache,Michael Schaub

doi:10.3389/fevo.2021.780706

Abstract

Species- and population-specific responses to their environment may depend to a large extent on the spatial variation in life-history traits and in demographic processes of local population dynamics. Yet, those parameters and their variability remain largely unknown for many cold-adapted species, which are exposed to particularly rapid rates of environmental change. Here, we compared the demographic traits and dynamics for an emblematic bird species of European mountain ecosystems, the ring ouzel (Turdus torquatus). Using integrated population models fitted in a Bayesian framework, we estimated the survival probability, productivity and immigration of two populations from the Western European Alps, in France (over 11 years) and Switzerland (over 6 years). Juvenile apparent survival was lower and immigration rate higher in the Swiss compared to the French population, with the temporal variation in population growth rate driven by different demographic processes. Yet, when compared to populations in the northwestern part of the range, in Scotland, these two Alpine populations both showed a much lower productivity and higher adult survival, indicating a slower life-history strategy. Our results suggest that demographic characteristics can substantially vary across the discontinuous range of this passerine species, essentially due to contrasted, possibly locally evolved life-history strategies. This study therefore raises the question of whether flexibility in life-history traits is widespread among boreo-alpine species and if it might provide adaptive potential for coping with current environmental change.

Highlights

The evolution of diversity in life-history strategies is a central topic in evolutionary ecology (Partridge and Harvey, 1988)
Our results suggest that demographic characteristics can substantially vary across the discontinuous range of this passerine species, essentially due to contrasted, possibly locally evolved life-history strategies
It has become increasingly important from a conservation biology perspective, as understanding the type and flexibility of lifehistory strategies contributes to the estimation of the adaptive potential (Forcada et al, 2008), which will be decisive for accurately predicting the responses of biodiversity to environmental change (Reed et al, 2011; Swab et al, 2015)

Summary

Introduction

The evolution of diversity in life-history strategies is a central topic in evolutionary ecology (Partridge and Harvey, 1988). We might expect that intraspecific differences in life-history traits contribute to spatially heterogeneous sensitivity (Jiguet et al, 2007; Swab et al, 2015), which would have important implications for conservation management (Caswell, 2000; Reed et al, 2011; Schwartz et al, 2021) This calls for more local studies to understand which ecological and demographic processes matter at the population level across latitudinal and elevational gradients (Chamberlain et al, 2012; Lehikoinen et al, 2019; Lundblad and Conway, 2020; Schwartz et al, 2021). This knowledge would help to improve predictions of population resilience or resistance to new environmental circumstances (Pearson et al, 2014; Swab et al, 2015; Boyle et al, 2016)

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