Modern Quaternary plant lineages promote diversity through facilitation of ancient Tertiary lineages

Abstract

One of the most important floristic sorting periods to affect modern plant communities occurred during the shift from the wet Tertiary period to the unusually dry Quaternary, when most global deserts developed. During this time, a wave of new plant species emerged, presumably in response to the new climate. Interestingly, most Tertiary species that have been tracked through the fossil record did not disappear but remained relatively abundant despite the development of a much more unfavorable climate for species adapted to moist conditions. Here we find, by integrating paleobotanical, ecological, and phylogenetic analyses, that a large number of ancient Tertiary species in Mediterranean-climate ecosystems appear to have been preserved by the facilitative or ''nurse'' effects of modern Quaternary species. Our results indicate that these interdependent relationships among plants have played a central role in the preservation of the global biodiversity and provided a mechanism for stabilizing selection and the conservation of ecological traits over evolutionary time scales.Mediterranean-type ecosystems ͉ Mexical shrubland ͉ phylogenetic niche conservatism ͉ plant facilitation ͉ stabilizing selection T he evolutionary processes that drive speciation and create biological diversity are central to the natural sciences, but we know little regarding the historical ecological processes that have eliminated species from communities or allowed them to persist (1). Current plant communities are the product of historical sorting processes and, therefore, include mixtures of floristic elements originating in different geological times and, presumably, under different ecological scenarios (2). Many extant plant species are millions of years old (3) and, therefore, have persisted through dramatic changes in global climate. Biogeographic and paleontological evidence indicates that communities are derived from species that have originated in different geological times and places, and that these taxa have been mixed and culled independently of each other through various sorting processes (2, 3). The perception that interdependent processes among plant species are insignificant over evolutionary time frames has been central to the idea that communities are ''merely a coincidence'' (4) and the development of neutral model theory on biodiversity (5). Therefore, with few exceptions (6, 7), plant communities are not thought to possess stable properties determined by plant-plant interactions.In contrast to existing theory, our observations of ecological relationships among species in semiarid communities around the world suggest that powerful facilitative ecological interactions among plant species have been a crucial component of the historical and sorting processes responsible for the composition and diversity of contemporary plant communities. Facilitative interactions appear to have been particularly important during the shift from mesic Tertiary period to the unusually dry Quaternary when global deserts developed. Desertification pr...

Fine-scale spatial patterns of the Tertiary relict Zelkova abelicea (Ulmaceae) indicate possible processes contributing to its persistence to climate changes

“…Our assumption is in agreement with Valiente-Banuet et al (2006) who reported that a large number of Tertiary relict species in Mediterranean climate ecosystems appear to have been preserved by the facilitative effects of other species. Nevertheless, whether A. sempervirens is a modern Quaternary plant lineage is not clear.…”

Steady diversification of derived liverworts under Tertiary climatic fluctuations

“…In addition, some clades may have been more diverse in the past but were subsequently replaced by members of sister clades that diversified in later periods of the Cenozoic. The replacement of species by close relatives from the same genera or family where similar ecologies already exist is thought to be a significant contribution to the persistence and stability of plant communities over significant time periods (DiMichele & Philips 1996;Valiente et al 2006).…”

Shading and litter mediate the effects of soil fertility on the performance of an understorey herb

“…For example, we found that Trientalis occurrence is highly related to overstorey cover rather than topographic microclimate, suggesting that small shifts in climate may have little effect on distribution if overstorey cover does not significantly change, whereas loss of overstorey due to increasingly severe or frequent fires could have much more drastic consequences. Facilitative effects of canopy cover may also explain patterns such as persistence of species with 'cool-adapted' traits through long-term drying trends (Valiente-Banuet et al, 2006) and the positive effect of forest density on tree regeneration niche (Dobrowski et al, 2015). These results also imply that changes in biotic conditions independent of climate could lead to shifts in distribution and abundance that were not predicted by climate-based models.…”