'Out of the tropics' sheds light on latitudinal gradients in clade ages
of climbers, China
Abstract
We aim to test hypotheses on the patterns of clade age of climbing
plants under climatic variations along the latitudinal gradients in
China. Specifically, we uncover their general patterns of mean family
age (MFA) and their climatic drivers. We evaluate the extents to which
both the tropical niche conservatism hypothesis (TNC) and the out of the
tropics hypothesis (OTT) can account for the MFA of climbing plants
respectively. A dataset including 2487 climbing species was used to
quantify geographical patterns of MFA across China. Spatial regression
analyses with information-theoretical multi-model selections were
performed to estimate the importance of climatic variables. There were
generally increasing trends of MFA from low to high latitudes for all
types of climbers. For woody climbers, MFA was negatively correlated
with minimum temperature, annual mean precipitation but positively with
seasonal temperature and precipitation, and was mostly influenced by
mean temperature of the coldest quarter. For herbaceous vines, MFA
pattern showed relatively insignificant correlations with all the
climatic variables. Our results highlight that the OTT hypothesis offers
a promising explanation for the latitudinal MFA gradients of climbers in
China (especially for woody climbers), which turn out to be contrary to
the TNC predictions.