Less favourable climates constrain demographic strategies in plants

Abstract

Correlative species distribution models are based on the observed relationship between species’ occurrence and macroclimate or other environmental variables. In climates predicted less favourable populations are expected to decline, and in favourable climates they are expected to persist. However, little comparative empirical support exists for a relationship between predicted climate suitability and population performance. We found that the performance of 93 populations of 34 plant species worldwide – as measured by in situ population growth rate, its temporal variation and extinction risk – was not correlated with climate suitability. However, correlations of demographic processes underpinning population performance with climate suitability indicated both resistance and vulnerability pathways of population responses to climate: in less suitable climates, plants experienced greater retrogression (resistance pathway) and greater variability in some demographic rates (vulnerability pathway). While a range of demographic strategies occur within species’ climatic niches, demographic strategies are more constrained in climates predicted to be less suitable.

Extensive mismatches between species distributions and performance and their relationship to functional traits

“…Our analyses show that mismatches between species’ distributions and density or demographic rates along the SWB gradient are common, but highly variable among species. These results extend a growing body of research, suggesting that patterns in occurrence do not necessarily match current patterns in density and demographic rates (Diez et al ; Thuiller et al ; Csergő et al ; Pironon et al ). Because current densities of long‐lived species are determined by past demographic performance, any factors that lead to changes in performance over time may lead to mismatches between current performance and distributions.…”

“…Although there is again mixed evidence among species and studies, recruitment patterns are generally not well matched to adult distributions, and the differences do not tend to suggest directional migration in response to changing climate (Zhu et al ; Serra‐Diaz et al ; Wason & Dovciak ). Studies comparing distributions to predicted population growth rates have also shown significant mismatches between where species are present and where they are predicted to perform well (Diez et al ; Merow et al ; Csergő et al ). Overall, these studies offer significant evidence that species are not always distributed where they perform best, but the mechanisms and generality of these relationships remain poorly understood.…”

Addressing common pitfalls does not provide more support to geographical and ecological abundant‐centre hypotheses

“…A3), the smaller the set of species the higher the probability the hypothesis is supported by chance. Similarly, studies focusing on environmental suitability and demographic rates in plants found contrasting results (Thuiller et al 2014, Pironon et al 2015, Csergő et al 2017. Here we estimated geographic and niche measures on the entire geographic range of the species, therefore presumably better capturing the centrality/marginality patterns.…”

Climate change is likely to affect the distribution but not parapatry of the Brazilian marmoset monkeys (Callithrixspp.)

“…These trimmed models were generated through a pixel‐by‐pixel analysis to prevent large overlaps between species’ distributions. First, we rescaled the predicted suitability values (from the ENMs analysis) within untrimmed models to range between 0 and 1, in order to make predictions comparable across species (Csergő et al, ). Then, within the overlapping area of a species pair, the species with the higher (rescaled) suitability score was considered as present in the pixel at the expense of the other.…”