Nice example of "ecosystem engineering" or "niche construction". It's increasingly considered to be an important evolutionary mechanism.<p><a href="http://en.wikipedia.org/wiki/Niche_construction" rel="nofollow">http://en.wikipedia.org/wiki/Niche_construction</a><p>One of the most significant inadvertent "engineering" events was the biologically-induced oxygenation of Earth's atmosphere:<p><a href="http://en.wikipedia.org/wiki/Great_Oxygenation_Event" rel="nofollow">http://en.wikipedia.org/wiki/Great_Oxygenation_Event</a>
I'm reminded of a similarly circular phenomenon, known as "fairy ring," where mushrooms grow in a circle. They appeared on our lawn in Saskatchewan from time to time; apparently it happens all over the world.<p><a href="http://en.wikipedia.org/wiki/Fairy_ring" rel="nofollow">http://en.wikipedia.org/wiki/Fairy_ring</a>