A big part of evolution is competition – when resources are limited, plants and animals must fight for nutrients, mates, and places to live. This means that the flower-covered grasslands of China’s Hengduan Mountains were an evolutionary mystery – there are dozens of closely related rhododendron species all living in harmony. To figure out why, scientists spent a summer carefully documenting the flowering patterns of 34 Rhododendron species, and they discovered the reason plants could co-exist: they burst into bloom at different times of the season so they didn’t have to compete for pollinators.
“There’s this basic idea in niche ecology, that a species’ way of life, like what it eats and how it fits into the environment, can’t be duplicated in the same community. If two species with the same lifestyle live in the same space, they will compete with each other, so one or both will adapt to have different, non-overlapping lifestyles, or they will disappear,” says Rick Ree, curator at the Field Museum in Chicago and lead author of the new study in the Journal of Ecology. “Since there are so many closely related species of rhododendrons all living together in these mountains, we wanted to understand how they could co-exist.”
Rhododendrons are flowering shrubs; you’ve probably seen some species (like azaleas) for sale at the garden center. The Hengduan Mountains, adjacent to the Qinghai-Tibet Plateau, are what biologists call a biodiversity hotspot: an ecologically fragile place with an unusually high number of different species. “They form thickets along the sides of the mountains, it looks like an ocean of flowers,” says Qin Li, postdoctoral researcher at the Field Museum and lead author of the paper.
“The Rhododendron the diversity in this area is caused in part by speciation, which is when new species diverge from a common ancestor,” says Ree. more distant.” This means that the closely related rhododendrons in the Hengduan Mountains should be even more likely to compete for resources.
When plants compete with each other, they can adapt in many ways to be able to coexist. “They can become very different in terms of preferences for soil, light and moisture, very basic physiological functional traits. They can also develop differences to reduce this potential for cross-pollination or competition for pollinators. would manifest as differences in flower shape, size or color, or may manifest when they make their flowers available to pollinators,” Ree explains. “By partitioning this timeline, they can reduce their chances of wasting their pollen and resources that go into reproduction.”
All of these evolutionary strategies were on the table to explain why rhododendrons had not driven themselves to extinction. To determine which was occurring, Li led a two-month field expedition to Mount Gongga in China, chosen as a study area for detailed investigation after a four-month trip to Rhododendron the previous year through the wider Hengduan Mountains.
“I had never done fieldwork in southwest China before, but we were actually quite close to my hometown in Sichuan province,” Li says. “With my field assistant and co -author Ji Wang of Sichuan University, I spent more than two months visiting more than 100 sites, and we visited each of these sites four times during the season.” After months of documenting the plants’ ecological characteristics, including leaf and flower size and shape and plant flowering dates, Li and his colleagues analyzed the data, using statistical approaches to find trends. They determined that the key factor allowing the plants to coexist was that they all flower at different times.
“Going in, we had a hunch the timing would be important, but we weren’t quite sure,” says Ree. “It is quite obvious that there is a long season when you can see flowers in the Himalayan region – there are some species that produce striking flowers against the backdrop of the snow field, and others that wait late summer. Our analysis of the data confirms this suspicion.”
The study results help shed light on one of the many ways plants can diversify without driving each other to extinction. But confirmation that timing is key to Mount Gongga Rhododendron the diversity also means that the climate crisis poses an additional threat to these plants.
“There is plenty of evidence that the pace of climate change is disrupting flowering times in plants, causing population declines and extinctions,” Ree says. “The question is, how will plant communities around the world respond? Weather is part of what signals them to bloom, and since climate change affects weather, it is likely to alter that competitive landscape. When the environment change, species have three choices: you move, you adapt or you die. Climate change is accelerating this dynamic.”
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Material provided by Field Museum. Note: Content may be edited for style and length.
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