Saturday, January 13, 2007

The Rules of Engagement

Ideally I would like to discover the identity of all the organisms living in my garden. Since I read here however that "There are more organisms in one gram of soil than there are human beings on this Earth!" (does anyone out there have a comment on whether this is fact, speculation or exaggeration?) I guess I am going to have to set some constraints on my search:

I'm going to start with (a somewhat arbitary) Rule 1 therefore: I'll record any organism with a bodily dimension of more than 5mm.

Rule 2 is simpler: if it's alive in my garden I want to know about it. Birds, flowers, mosses, insects, lichens, spiders, trees, mushrooms....they're all 'fair game'

This immediately leads me to speculate over how many organisms I'm eventually going to find.

At this stage I really have no idea!

I am going to take a wild guess and say 250.

I'd be interested to invite comment on this number from readers of this blog. I'll describe some salient features of my garden in the next posting.

4 comments:

Roger B. said...

>"There are more organisms in one gram of soil than there are human beings on this Earth!"

I think that's probably an exaggeration, even when you include bacteria.

According to Wikipedia "there are typically 40 million bacterial cells in a gram of soil".

That's a lot of organisms, but still fewer than the total human population (6.6 billion).

Henry Walloon said...

Many thanks for the comment Roger. Not least as you have the high honour of being my very first blog commentator.

The Wikipedia article is enlightening...to a point. As you rightly point out, the main article quotes "40 million" and gives a reference ("[2]").

Following the reference however leads to a paper that states (in connection with table 2):

"For forest soils, the number of prokaryotes in the top 1 m was 4 × 10^7 cells per gram of soil, and
in 1-8 m, it was 10^6 cells per gram of soil (16). For other soils, the number of prokaryotes in the top 1 m was 2 × 10^9 cells per gram of soil, and in 1-8 m, it was 108 cells per gram of soil (18)."

"2 x 10^9" is 2 billion (I think) - on a par with the human population. If there's other "living stuff" in there as well, maybe the original suggestion is correct?

How these figures relate to the Wikipedia "40 million..." statement isn't immediately clear to me?

Laura said...

Henry! This is a fantastic challenge you have set yourself. I will follow with great interest and wonder. Thanks for your visit.

R2K said...

""There are more organisms in one gram of soil than there are human beings on this Earth!""

That is a bit much, but expand that to a cubic yard of soil and I would accept that. However, there are far fewer species in a gram of soil than that would suggest. Almost certainly fewer than 1000 species. And if you ignore bacteria and viruses, you have a much more manageable number. I suspect that your yard, if carefully explored, probably contains 250 - 750 species, and that would still be mostly small things like nematodes and mites. Stick to visible animals and plants? You would do well to find 75 species, so that is something you can handle!