Climatic niche position predicts population dynamics in Mediterranean shrubs after drought
TL;DR
It is found that proximity to the niche centroid increased population growth, especially for H. halimifolium, and population fitness is shaped by climatic niche position, with higher fitness generally closer to their niche centroid.
Abstract
Climate change is altering plant population dynamics by increasing drought frequency and intensity in many regions. The climatic niche (i.e. the range of climatic conditions under which a species persists) offers a powerful framework to link the effects of climate on population performance with species‐specific tolerances. However, how the population's position within its species' climatic niche influences population fitness remains poorly understood. We investigated demographic responses to climatic niche position in two Mediterranean shrubs, Halimium halimifolium and Lavandula stoechas, following an extreme drought in Doñana National Park (SW Spain). Using individual demographic data from 2019 to 2022, we modelled survival, growth and reproduction as functions of distance to each species' climatic niche centroid and of drought‐induced vegetation die‐off. We then integrated these vital rates into integral projection models (IPMs) to assess population growth. We found that proximity to the niche centroid increased population growth, especially for H. halimifolium. In contrast, L. stoechas exhibited a more complex pattern, with population growth peaking near the niche centroid but remaining high farther away. These patterns were driven mainly by increased recruitment near the niche centroid, together with reduced seedling survival, suggesting demographic compensation. In both species, small shifts in niche position within the observed range led to substantial demographic changes. Importantly, vegetation die‐off further modulated demographic responses to niche position. Population growth in H. halimifolium was highest at moderate die‐off, likely balancing facilitation and competition. In contrast, L. stoechas reached its highest population growth under high die‐off, possibly due to competitive release. Perturbation analysis pointed out that changes in population growth in L. stoechas were driven mainly by the influence of niche position on early life‐stage processes, especially recruitment and seedling survival, whereas in H. halimifolium they were mainly influenced by adult survival and growth responses to niche position. Synthesis. Our results show that population fitness is shaped by climatic niche position, with higher fitness generally closer to their niche centroid. Niche metrics capture species‐specific climatic tolerances and requirements; by incorporating them into demographic models, we can better assess population responses to climatic variability across species and ecosystems.