BIOTIC SEED DISPERSAL, BUT NOT BIOTIC POLLINATION, CONVEYS EXTINCTION RESISTANCE IN NEOGENE PLANT LINEAGES OF WESTERN, BUT NOT EASTERN, NORTH AMERICA

Multiple studies link modes of pollination and seed dispersal to trends in diversification and extinction, but the influence of pollination and seed dispersal modes on emergent patterns that drive diversification, such as community composition through time, is unclear. We here update our 2017 GSA exploration of the correlation of seed dispersal and pollination modes with survival and range contraction of taxa in western (WNA) and eastern North American (ENA) floras in the face of climatic change from the Miocene to the present, using collections from 27 Miocene and Pliocene floras from across the contiguous United States.

We found that, in WNA, taxa possessing animal-mediated seed dispersal have lower extinction rates, while biotic dispersal has no correlation with survival in in ENA. This correlation also dominates North America as a whole, although this may be driven by the larger sample size caused by greater sampling effort in WNA. We did not detect any statistically significant correlations between biotic pollination and extinction; however, non-significant trends suggest that biotic pollination may reduce extinction in WNA, but increase it in ENA.

We hypothesize that the intensity of climate change in WNA resulted in fewer, more widely-separated refugia than in ENA. This selected against plants without extreme long-distance dispersal capabilities in WNA, while the less severe climate change in ENA relaxed the pressure that plants in WNA experienced. Insect pollination may also have contributed to making smaller populations viable in isolated WNA refugia. Both of these proposals make predictions that could be tested in future research.