The niche is not the range: Dispersal and persistence shape mismatches between ecological niches and geographic distributions of plants

Abstract

The ecological niche of a species describes the variation in population growth rates along environmental gradients that drives geographic range dynamics. Niches are thus central for understanding and forecasting species' geographic distributions. However, theory predicts that migration limitation, source-sink dynamics and time-lagged local extinction can cause mismatches between niches and geographic distributions. It is still unclear how relevant these niche-distribution mismatches are for biodiversity dynamics and how they depend on species life history traits. This is mainly due to a lack of the comprehensive, range-wide demographic data needed to directly infer ecological niches for multiple species. Here we quantify niches from extensive demographic measurements along environmental gradients across the geographic ranges of 26 plant species (Proteaceae; South Africa). We then test whether life history explains variation in species' niches and niche-distribution mismatches. Niches are generally wider for species with high seed dispersal or persistence abilities. Life history traits also explain the considerable interspecific variation in nichedistribution mismatches: poorer dispersers are absent from larger parts of their potential geographic ranges, whereas species with higher persistence ability more frequently occupy environments outside their ecological niche. Our study thus identifies major demographic and functional determinants of species' niches and geographic distributions. It highlights that the inference of ecological niches from geographical distributions is most problematic for poorly dispersed and highly persistent species. We conclude that the direct quantification of ecological niches from demographic responses to environmental variation is a crucial step towards a better predictive understanding of biodiversity dynamics under environmental change.

Functional traits explain the Hutchinsonian niches of plant species

“…Species-specific demographic responses to environmental gradients were analysed with hierarchical demographic response models (Pagel et al, 2019) Table S3]. The response of each demographic rate to the different environmental variables k = 1 … K was described by a multiplication of Gaussian curves of the…”

“…Niche characteristics were derived from combining range-wide variation in key demographic rates and demographic niche models that estimated the responses of population growth rates to environmental variation in a Bayesian framework (see Materials and Methods section; Pagel et al, 2019). The surface depicts the response of intrinsic population growth rate (r 0 ) to two environmental variables [minimum winter temperature (T min ) and maximum summer temperature (T max )].…”

“…The surface depicts the response of intrinsic population growth rate (r 0 ) to two environmental variables [minimum winter temperature (T min ) and maximum summer temperature (T max )]. Niche characteristics were derived from combining range-wide variation in key demographic rates and demographic niche models that estimated the responses of population growth rates to environmental variation in a Bayesian framework (see Materials and Methods section; Pagel et al, 2019). The orange point on the vertical axis is the global maximum population growth rate (r max ).…”

“…Hutchinsonian niches (the global maximum population growth rate, r max , as well as niche optima and widths along individual environmental dimensions; Figure 1) that were derived from demographic responses to major environmental gradients (aridity, maximum summer and minimum winter temperature, soil fertility and fire disturbance; Pagel et al, 2019). Our main objective is to examine how species-mean trait values and intraspecific trait variation relate to these characteristics of species' niches.…”

“…) [Colour figure can be viewed at wileyonlinelibrary.com] that responses of adult fire survival rates to environmental variation were modelled for resprouter species only (because non-sprouters have low fire survival, with very little intraspecific variation;Treurnicht et al, 2016). Further details on the model structure, formulation of density dependence and Bayesian parameter estimation are provided byPagel et al (2019).…”