Drivers of large‐scale spatial demographic variation in a perennial plant

Gesa Römer,Kasper Reitzel,Johan Ehrlén,Kristoffer Hylander,Ditte M Christiansen,Owen R Jones,Hendrik De Buhr,Sonia Merinero,Johan P Dahlgren

doi:10.1002/ecs2.3356

Abstract

AbstractTo understand how the environment drives spatial variation in population dynamics, we need to assess the effects of a large number of potential drivers on vital rates (survival, growth, and reproduction) and explore these relationships over large geographical areas and broad environmental gradients. In this study, we examined the effects of a wide variety of abiotic and biotic environmental factors on the demography of the forest understory herb Actaea spicata between 2017 and 2019 at 40 sites across Sweden, including the northern range margin of its distribution. We assessed the effects of potential environmental drivers on vital rates using generalized linear mixed models (GLMMs) and then quantified the impact of each important driver on population growth rate (λ) using integral projection models (IPMs). Population dynamics of A. spicata were mostly driven by environmental factors affecting survival and growth, such as air humidity, soil depth, and forest tree species composition, and thus, those drivers jointly determined the realized niche of the species. Soil pH had a strong effect on the flowering probability, while the effect on λ was relatively small. In addition to identifying specific drivers for A. spicata’s population dynamics, our study illustrates the impact that spatial variation in environmental conditions can have on λ. Assessing the effects of a broad range of potential drivers, as done in this study, is important not only to quantify the relative importance of different drivers for population dynamics but also to understand species distributions and abundance patterns.

Highlights

Abiotic and biotic environmental conditions such as climate and competition vary across time and space and drive the population dynamics of species through effects on vital rates such as survival, growth, and reproduction (Bruna and Oli2005, Doak and Morris 2010)
We examined the effects of a wide variety of abiotic and biotic environmental factors on the demography of the forest understory herb Actaea spicata between 2017 and 2019 at 40 sites across Sweden, including the northern range margin of its distribution
We assessed the effects of potential environmental drivers on vital rates using generalized linear mixed models (GLMMs) and quantified the impact of each important driver on population growth rate (λ) using integral projection models (IPMs)

Summary

Introduction

Abiotic and biotic environmental conditions such as climate and competition vary across time and space and drive the population dynamics of species through effects on vital rates such as survival, growth, and reproduction (Bruna and Oli2005, Doak and Morris 2010). To achieve an in-depth understanding of the population dynamics of a species, and to describe and predict distributions and abundances, we need to assess how environmental variation is linked to demographic variation (Ehrlen and Morris 2015). Using environmentally explicit demographic models allows us to disentangle which vital rates are most affected by the environment, and how those vital rates contribute to population growth rate (λ). Such a more mechanistic understanding of the processes underlying a species’ distribution and abundance allows for more accurate predictions of species responses to environmental and climate changes Explicit demographic models provide a means to identify the drivers of the short-term dynamics and of the realized niches of species

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Results

Conclusion