Variable species establishment in response to microhabitat indicates different likelihoods of climate-driven range shifts

Abstract

Climate change is causing geographic range shifts globally, and understanding the factors that influence species’ range expansions is crucial for predicting future changes in biodiversity. A common, yet untested, assumption in forecasting approaches is that species will shift beyond current range edges into new habitats as they become macroclimatically suitable, even though microhabitat variability could have overriding effects on local population dynamics. We aim to better understand the role of microhabitat in range shifts through its impacts on establishment by i) examining microhabitat variability along large macroclimatic gradients, ii) testing which of these microhabitat variables explain plant recruitment and seedling survival, and iii) predicting microhabitat suitability beyond species range limits. We transplanted seeds of 25 common tree, shrub, forb, and graminoid species across and beyond their current elevational ranges in the Washington Cascade Range, USA, along a large elevational gradient spanning a broad range of macroclimates. Over five years, we recorded recruitment, survival, and microhabitat characteristics rarely measured in biogeographic studies. We asked whether microhabitat variables correlate with elevation, which variables drive species establishment, and whether microhabitat variables important for establishment are already suitable beyond leading range limits. We found that only 30% of microhabitat parameters covaried in the expected way with elevation. We further observed extremely low recruitment and moderate seedling survival in our study system, and these were generally only weakly explained by microhabitat. Moreover, species and life stages responded in contrasting ways to soil biota, soil moisture, temperature, and snow duration. Microhabitat suitability predictions suggest that distribution shifts are likely to be species-specific, as different species have different suitabilities, and availabilities, of microhabitat beyond their present ranges, thus calling into question large-scale macroclimatic projections that will miss such complexities. We encourage further research on species responses to microhabitat and the inclusion of microhabitat in range shift forecasts.

Possible extinction of Eversmannia subspinosa in Eastern Alborz by 2060 due to climate change: A MaxEnt study

“…In their comprehensive 2021 study, Steven R. Beissinger and Eric A. Riddell highlight the crucial role of physiological traits of species and the availability of suitable habitats in determining the speed and direction of species range shifts (Beissinger et al, 2021). Chardon et al (2023) found that microhabitat variables weakly predict recruitment and seedling survival, with varied responses to environmental factors across species and life stages (Chardon et al, 2023). Adding to this complexity, a recent research has highlighted the importance of considering intraspeci c ecological variation when predicting species distributions for conservation and climate change impact assessment (Varaldo et al, 2023).…”