Individual fitness is decoupled from coarse‐scale probability of occurrence in North American trees

Abstract

Habitat suitability estimated with probability of occurrence in species distribution models (SDMs) is used in conservation to identify geographic areas that are most likely to harbor individuals of interest. In theory, probability of occurrence is coupled with individual fitness so that individuals have higher fitness at the centre of their species environmental niche than at the edges, which we here define as 'fitness-centre' hypothesis. However, such relationship is uncertain and has been rarely tested across multiple species. Here, we quantified the relationship between coarse-scale probability of occurrence projected with SDMs and individual fitness in 66 tree species native of North America. We used 1) field data of individuals' growth rate (height and diameter standardized by age) available from the United States Forest Inventory Analysis plots; and 2) common garden data collected from 23 studies reporting individual growth rate, survival, height and diameter of individuals originated from different provenances in United States and Canada. We show 'fitness-centre' relationships are rare, with only 12% and 11% of cases showing a significant positive correlation for field and common garden data, respectively. Furthermore, we found the 'fitness-centre' relationship is not affected by the precision of the SDMs and it does not depend upon dispersal ability and climatic breath of the species. Thus, although the 'fitness-centre' relationship is supported by theory, it does not hold true in nearly any species. Because individual fitness plays a relevant role in buffering local extinction and range contraction following climatic changes and biotic invasions, our results encourage conservationists not to assume the 'fitness-centre' relationship when modelling species distribution.

High resolution species distribution and abundance models cannot predict separate shrub datasets in adjacent Arctic fjords

“…However, specifically assessing differences in SDM versus SAM predictions has, to our knowledge, not been carried out in the Arctic. Regardless of model type, it remains contentious to what degree model outputs are related to empirical measures of population performance, such as population persistence (Araújo & Williams, 2000), abundance (Dallas & Hastings, 2018; Midolo et al, 2021; Weber et al, 2017), and demographic rates (Csergő et al, 2017; Thuiller et al, 2014). Furthermore, examples of SDMs incorrectly predicting observed distributional trends (e.g., Sofaer et al, 2018) point to the more fundamental questions of how well these models can accurately capture spatial patterns across the landscape and how to best validate this (e.g., Santini et al, 2021).…”

Changes in the climate suitability and growth rates of trees in eastern North America

“…In fact, the main sources of variability for suitability and growth were different: the highest proportion of variance for suitability is at the plot, genus and species levels, whereas growth variance was mostly concentrated at the year and family levels (Supporting information). Midolo et al (2021) found that predicted suitabilities from SDM and species fitness relationships are rare (although they only evaluated spatial variation and they did not assess temporal variation), and van der Maaten et al (2017) found that predictions of SDMs were related to temporal growth variation but not to spatial growth variation. Furthermore, we recognize some limitations specific to our SDM and suitability calculations.…”

Can suitability indices predict plant growth in the invaded range? The case of Acacias species

“…Despite the high accuracy of our models, we did not observe an association between suitability and tree growth. Midolo et al (2021) suggested that an implicit and scarcely tested assumption in niche models is that individual fitness should be higher at the center of the environmental niche, what they called the "fitness-centre" hypothesis. However, they found that the support for this hypothesis in actual data was scarce (Midolo et al, 2021).…”

“…Midolo et al (2021) suggested that an implicit and scarcely tested assumption in niche models is that individual fitness should be higher at the center of the environmental niche, what they called the "fitness-centre" hypothesis. However, they found that the support for this hypothesis in actual data was scarce (Midolo et al, 2021). Similarly, Bernal-Escobar et al (2022) said that, according to the fitnesssuitability hypothesis, there should be a positive relationship between climate suitability and tree growth rates.…”