At a time when global warming is making many regions of our planet hotter and drier, deserts are relatively new biomes that have grown substantially over the past 30 million years, with vast arid areas like those covering much of North America emerging only during the past five to seven million years. Thus, a better understanding of how several species of plants have invaded these harsh environments and were able to survive could help predict how ecosystems will fare in a drier, hotter future.
According to a new study led by the University of California, Berkeley, plants that invaded deserts millions of years ago, such as rock daisies, had already developed adaptations to deal with heat and water stress before. These plants adapted while living on exposed rock outcroppings within older, moist areas or even tropical forests, which made it easier for them to invade expanding deserts.
“If you think about aridity only as a stimulus to plant evolution, then in many cases people could say these plants are survivors, they are adaptable, and they will be fine. They will take advantage of these new conditions, and they will thrive,” said study lead author Isaac Lichter-Marck, plant taxonomist, biogeographer, and evolutionary ecologist at UC Berkeley.
However, the history of rock daisies shows that, when deserts emerged, “plants that had the necessary preadaptations to take advantage of new conditions were the ones that thrived. Adding more aridification to the system doesn’t necessarily mean more rapid adaptive evolution will occur. There’s a limited source of lineages that can take advantage of new levels of aridity, and that is important for understanding the effect of climate change on biodiversity.”
By collecting and analyzing hundreds of rock daisy specimens from the deserts of Arizona, California, Texas, and Mexico, and comparing them to fossilized daisies, the scientists managed to develop a timeline of the evolution of these plants’ characteristics as they eventually invaded expanded deserts. The investigation revealed that most rock daisies – particularly the genus Laphamia, which was the first to move into deserts — had already adapted to the multiple stresses of heat, sun, aridity, and wind by growing on cliffs before invading deserts.
“This is a clear empirical demonstration of what was originally Axelrod’s hypothesis – of a desert plant group originating in dry microclimates prior to the widespread emergence of desert habitats. What this means is that the strategies for drought tolerance that are so characteristic of desert vegetation might not actually represent responses to the dry conditions found in deserts. Instead, they could be traits that evolved earlier in association with much older and more stable dry microclimates, such as rock outcrops in tropical settings,” Lichter-Marck concluded.
The study is published in the journal Proceedings of the National Academy of Sciences.
Image Credit: Isaac Lichter-Marck
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