Biogeographic anomalies in the species richness of Chilean forests: Incorporating evolution into a climatic – historic scenario

Abstract

Broad‐scale richness gradients are closely associated with temperature and water availability. However, historical and evolutionary processes have also contributed to shape current diversity patterns. In this paper we focus on the potential influences of Pleistocene glaciation and phylogenetic niche conservatism (the tendency for traits to be maintained during diversification) on the tree diversity gradient in Chile, and we quantify its primary climatic correlates. Tree species richness is greatest at mid latitudes, particularly in the Andes and Coastal ranges, and decreases abruptly to the south and north. Regression tree analysis identified annual precipitation and annual temperature as the primary probable drivers of this gradient. Ice cover during the Last Glacial Maximum was also identified as an ‘important’ variable, but the contemporary and historical predictors are strongly collinear. Geographically weighted regression indicated that the relationships between richness and environmental variables vary regionally: the relationship between tree richness and precipitation is stronger in north‐central Chile, whereas tree richness and temperature are most strongly associated in south‐central Chile. By assigning each species the age of the family to which it belongs and averaging all species in each geographical unit, we also found that species from the oldest families are distributed mainly in mid to high latitudes and species from younger families are distributed mainly at lower latitudes. This pattern is closely associated with annual precipitation. Thus, the ecological component of tree richness follows contemporary climatic gradients of both energy and water, but the aridification of the Atacama Desert was an important driver over evolutionary time. The influence of recent Pleistocene glaciation remains unresolved but it cannot be discounted.

Decoupled evolution of foliar freezing resistance, temperature niche and morphological leaf traits in Chilean Myrceugenia

“…In the case of south‐central Chile, a significant and positive correlation between diversity of tree species and annual temperature has been documented (Segovia et al . ). This pattern would also result from cold tolerance conservatism, but operating at lower taxonomic levels.…”

“…Indeed, in Chile, mean annual precipitation and mean annual temperature are highly and negatively correlated (Segovia et al . ).…”

“…As predicted by this hypothesis, Hawkins et al (2014) showed that North American tree species from higher latitudes belong to younger families than trees species from lower latitudes. In the case of south-central Chile, a significant and positive correlation between diversity of tree species and annual temperature has been documented (Segovia et al 2013). This pattern would also result from cold tolerance conservatism, but operating at lower taxonomic levels.…”

“…It is well known that drought and cold stress can generate similar response in plants (Chaves, Maroco & Pereira 2003), and therefore, the observed relationships between temperature and leaf traits in Myrceugenia could be confused with response to precipitation. Indeed, in Chile, mean annual precipitation and mean annual temperature are highly and negatively correlated (Segovia et al 2013).…”

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

“…() 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, most previous studies have largely focussed on the Northern Hemisphere when interpreting results (Segovia & Armesto, ).…”