The weakness of evidence supporting tropical niche conservatism as a main driver of current richness–temperature gradients

Abstract

Aim Geographical variations in species richness are highly correlated with current temperature. The tropical niche conservatism hypothesis proposes that this relationship is driven by the evolutionarily conserved ancestral tolerances of species to the warm environments in which most clades originated. The hypothesis predicts that the slope of the richness–temperature gradient is positively related to the temperature of the period during which the clade originated. Here, we test this prediction for bird and mammal families in the Americas and by revisiting a global analysis of 343 groups of organisms (Romdal et al., 2013, Global Ecology and Biogeography, 22, 344–350). Location The Americas and world‐wide. Methods We computed the slope of the species richness–current temperature relationship within each bird and mammal family in the Americas. We used palaeoclimate reconstructions to estimate temperature at the time of the family's origination, taken from the fossil record. We then tested how much of the among‐family variance in the richness–temperature slope could be explained by the temperature at the time of family origination. We repeated this test for the 343 groups of organisms world‐wide. Results Contrary to the prediction of tropical niche conservatism, the temperature at which bird and mammal families originated does not explain variations in the richness–temperature relationships. Similarly, we show that, although the predicted relationship was statistically detected in a broad range of groups of organisms in a previous study, it in fact statistically explains only 1.2–2.9% of the variance among groups in the slope of richness gradients. Main conclusions We found evidence inconsistent with the hypothesis that tropical niche conservatism is the main mechanism underlying the ubiquitous richness–climate relationship.

Geographical variation in the evolutionary diversity of tree communities across southern South America

“…By not analysing local communities, these studies have been unable to adequately assess the potential influence of environmental factors on SR, PD or lineage diversity (cf. Boucher‐Lalonde et al ., ). Those studies that have taken a community approach have had sparse sampling across the Southern Hemisphere, particularly in South America (e.g.…”

“…In contrast, Boucher‐Lalonde et al . () found that once positive relationships between species richness and current climate are taken into account, the temperature and presumably latitude, at which a clade originates has little influence on its species richness, which the authors take as evidence against the TCH. Other studies have also found results that are contradictory to patterns expected under the TCH, both at a global scale (Jansson et al ., ) and in South America (Segovia et al ., ; Qian, ; Tiede et al ., ).…”

“…However, Boucher‐Lalonde et al . () have shown that analyses of mean family ages may be insufficient to test hypotheses around niche conservatism. As an alternative, studies of the evolutionary diversity of ecological communities can be used to test the potential role for niche conservatism in determining spatial patterns of biodiversity (cf.…”

“…Forest et al ., ; Honorio Coronado et al ., ). As species richness is strongly influenced by current climate (Kreft & Jetz, ; Boucher‐Lalonde et al ., ), it is often of interest to assess whether communities show more or less PD than expected given their SR. One particularly common metric to measure this departure from expectation is the standardized effect size of PD (ses.PD), which we refer to as lineage diversity ( sensu Honorio Coronado et al ., ). In this study, in our analyses of the evolutionary diversity of forest tree communities across southern South America, we focus on measuring phylogenetic diversity sensu stricto and lineage diversity as well as other commonly employed metrics of phylogenetic diversity.…”

Historical factors shaped species diversity and composition of Salix in eastern Asia

“…Specifically, this hypothesis predicts that species diversity for a given clade will be low in regions where the climate conditions deflect from the clade’s ancestral niche, because species have difficulties to evolve adaptions to new climatic niches 8 9 10 . According to niche conservatism hypothesis, species originated in tropical regions tend to show strong positive diversity-temperature relationship while clades originated in temperate regions show negative diversity-temperature relationship 11 12 13 . However, it still remains controversial whether contemporary climate drives species diversity through the control of ambient energy or through niche conservatism.…”