Comparing climatic suitability and niche distances to explain populations responses to extreme climatic events

Abstract

Habitat suitability calculated from species distribution models (SDMs) has been used to assess population performance, but empirical studies have provided weak or inconclusive support to this approach. Novel approaches measuring population distances to niche centroid and margin in environmental space have been recently proposed to explain population performance, particularly when populations experience exceptional environmental conditions that may place them outside of the species niche. Here, we use data of co-occurring species' decay, gathered after an extreme drought event occurring in the southeast of the Iberian Peninsula which highly affected rich semiarid shrubland communities, to compare the relationship between population decay (mortality and remaining green canopy) and 1) distances between populations' location and species niche margin and centroid in the environmental space, and 2) climatic suitability estimated from frequently used SDMs (here MaxEnt) considering both the extreme climatic episode and the average reference climatic period before this. We found that both SDMs-derived suitability and distances to species niche properly predict populations performance when considering the reference climatic period; but climatic suitability failed to predict performance considering the extreme climate period. In addition, while distance to niche margins accurately predict both mortality and remaining green canopy responses, centroid distances failed to explain mortality, suggesting that indexes containing information about the position to niche margin (inside or outside) are better to predict binary responses. We conclude that the location of populations in the environmental space is consistent with performance responses to extreme drought. Niche distances appear to be a more efficient approach than the use of climate suitability indices derived from more frequently used SDMs to explain population performance when dealing with environmental conditions that are located outside the species environmental niche. The use of this alternative metrics may be particularly useful when designing conservation measures to mitigate impacts of shifting environmental conditions.

Monitoring of species’ genetic diversity in Europe varies greatly and overlooks potential climate change impacts

“…To address the importance of environmental gradients to the conservation of genetic diversity, we distinguish here between populations that are geographically peripheral with regard to a range centroid and populations that are environmentally marginal, occurring towards the limit of their realized environmental niche. Relative geographic position can present little relationship to variation at functional loci, while relative environmental niche marginality of populations can predict variation at these loci and demographic events in populations near niche limits 41 , 45 . The establishment, adaptation and persistence of populations at environmental niche margins may depend on baseline genetic diversity, the steepness of environmental gradients, the rates of gene flow from non-marginal populations and stochastic processes 20 , 46 .…”

Climate change may alter the signal of plant facilitation in Mediterranean drylands

“…Second, we characterized the univariate niche and the niche‐derived indices by following Broennimann et al (2021) and Perez‐Navarro et al (2022). Briefly, to construct the species niche, a one‐dimensional density function was adjusted, based on all the outcomes of the climate (mean annual precipitation) of Q. ilex subsp.…”

Plant canopies promote climatic disequilibrium in Mediterranean recruit communities

“…We then characterized the climatic niche surface and optimum of each species in the multivariate climatic space by translating species occurrences into the two-dimensional climatic space (Broennimann et al, 2012). To do so, we followed the procedure described in Perez-Navarro et al (2022) and in Appendix S3. Accordingly, species' climatic niche corresponded to the 2d occurrence density surface, and niche optimum to the centre of mass of this surface.…”