21 April 2010

Why are there no single-celled terrestrial organisms? Part 2

In response to the Part 1 of this series, our friend and regular reader Carl Christensen e-mailed an article all the way from Hawaii early this morning. The article1 has in its title the words "free-living terrestrial microorganisms" and is about the human-mediated dispersal of testate amoebae that live in the soil. While reading it I was reminded of a much older paper2 in my collection with the intriguing title "Colpoda cucullus: a terrestrial aquatic". That paper is about the ciliate C. cucullus, which also lives in the soil as well as on various plants.

Despite the authors' use of the qualifier terrestrial in referring to their subject protists, the latter are not terrestrial in the sense I was discussing in this post. They may live in soil or on the surfaces of plants, but they are active only when fully immersed in water. They are obligately aquatic. They may be called "terrestrial aquatic" only because their watery habitats in the terra firma are often too small in volume to be noticeable by humans.

To be continued.

1David M. Wilkinson. 2010. Have we underestimated the importance of humans in the biogeography of free-living terrestrial microorganisms? Journal of Biogeography 37:393–397.
2Mueller & Mueller. 1970. Colpoda cucullus: a terrestrial aquatic. American Midland Naturalist 84:1-12.

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