Evolution, ecology and volcanoes

There are many questions one can ask that link evolution and ecology to volcanoes…


Let’s start at a small scale in both space and time. Are plants and animals growing on and near active volcanoes different from those growing elsewhere? Yes, they are! Volcanic soils are rich in certain minerals (though poor in humus), and plants like coffee grow particularly well there. Thus, because plant species each have their own requirements for temperature, nutrients, moisture and light—the abiotic part of their ‘ecological niche’—the plants growing on volcanoes are different. There is also a time aspect. Immediately after an eruption, the lava is too hot for any living thing to live on it. Once it has cooled down, pioneer species arrive, and then ecological succession takes place, as one set of (typically ‘weedy’) organisms occupy the area, change it, and are then overtaken by further sets of (less and less ‘weedy’, more and more longer-lived) organisms. If the volcano erupts very seldom, this process of succession may lead to a ‘climax community’, which undergoes no further change, until the next eruption. But if it erupts more often, then a kind of ecological snakes and ladders takes place, with succession being interrupted at wherever it has reached by the time of the next eruption. These processes are, however, all just ecology; that is, we can understand them while regarding each species as unchanging in itself.

Does evolution have a significant role in the differences between life on volcanoes and life elsewhere? While it is often easy to see ecology at work, finding out about evolution is harder. One relevant piece of evidence would be finding organisms that occurred only in association with volcanic activity. The most famous example are microbes called ‘thermophiles’. The name means ‘heat lovers’, and they live in hot springs, such as those in Yellowstone National Park, and in deep sea hydrothermal vents, both places where the Earth’s liquid core lies close to the top of the Earth’s crust. Unlike terrestrial and most aquatic life, which relies on photosynthesis and therefore on energy from the sun, thermophiles use a variety of energy sources that come from the earth’s core, such as elemental sulphur. There are whole communities of organisms based around this alternative source of energy, and some biologists believe that life began in this way, with photosynthesis evolving later. Another way to study evolutionary effects on volcanic life would be to compare organisms that live on volcanoes with others of the same species that live elsewhere: collecting the samples sounds like a nice project!

One of the best things about biology is that there are always curious examples, whatever you choose to look into, and here’s one about life on volcanoes. We expect the first colonists on cooling lava to be small: often they are lichen. But in Hawaii the very first colonist is often an insect—the ‘lava cricket’ Caconemobius fori. No one knows why a reasonable-sized animal is first, but a team led by the famous behavioural ecologist Marlene Zuk are currently trying to find out. Surprisingly, while mating, the female lava cricket drinks haemolymph (the insect version of blood) from the male’s leg. He can lose a substantial fraction of his body mass in this way. Biologists suspect this is a ‘nuptial gift’: the lava is hot, the female will be able to produce more eggs if she has more fluid, and the extra offspring may make the male’s loss worthwhile for him: but the biologists aren’t sure, and so will need to keep going back to Hawaii…

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Alan Grafen

Professor Alan Grafen, Tutorial Fellow in Quantitative Biology
I teach population biology in the first year, and statistics and behavioural ecology in the second and third years of the Biological Sciences course.  I also teach Animal Behaviour to Human Scientists at St John’s. My research involves applying mathematical and logical theorising to evolutionary problems. My current research program is my ‘formal Darwinism project’, which aims to capture Darwin’s central argument about evolution by natural selection in a mathematical framework.