Seed Size May Help Predict Climate Change Impact

Oct. 21, 2008 -- Plants closer to the equator are more likely to have larger seeds, a fact that could help predict the risk that climate change poses to native plants, according to an Australian researcher.

Evolutionary biologist Angela Moles of the University of New South Wales will this week receive an Australian Institute of Policy and Science Tall Poppy award for her research, which looks at how climate and other factors influence plant traits across the world.

Moles argues a better understanding of the impact of climate on plant traits will help pinpoint which plants have traits that will be an advantage or disadvantage under future climate changes.

"A lot of the time we just protect them in national parks and hope for the best but with all of these changes happening it's not clear that is going to work," she said.

Moles and colleagues searched the literature on more than 11,000 species of native plants from around the world to identify what factors influence the size of their seeds.

They found tropical plants had overall bigger seeds.

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"Seeds are 320 times bigger at the equator than at 60 degree latitude," said Moles.

She says this is largely because trees have bigger seeds than shrubs or herbs, and make up a larger proportion of plant life in the tropics.

These seeds are typically found in fleshy fruits and are dispersed by big animals, ranging from monkeys to giant birds, which are also more plentiful in the tropics.

By contrast in the Arctic, seeds tend to be small and wind-dispersed.

Moles said the largest seeds are those of the double coconut, which weigh up to 27 kilograms (60 pounds) each and "look like giant bums."

The smallest seeds are those of orchids, which look like little bits of dust, and weigh less than a millionth of a gram, she said.