Biogeographic anomalies in the species richness of Chilean forests: Incorporating evolution into a climatic – historic scenario
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Segovia, Ricardo A.
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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.
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Austral Ecology (2013) 38, 905–914
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