What am I treading on?

I was saved by a whisker, from the temptation to pick up that can of pesticides and relieve my plants from masses of aphids.  Well, by a paper in Nature actually- a scientific and statistical study on organic farming ("Organic agriculture promotes evenness and natural pest control" by Crowder et al., Nature 466, 1 July 2010, 109-112).

The authors studied two aspects of species variance in controlled plots of land - species richness (the number of species) and species evenness (the relative abundance of each species).  While several people have noted a decrease in species richness in conventional farms, few have paid attention to species evenness.  This paper shows that organic farming promotes both richness and evenness and a higher evenness (not possible in chemically treated land) results in better natural pest control (and an increase in plant size).

A plant pest, at different stages of its life cycle, is susceptible to different predators and pathogens which might be in the form of other insects, nematodes or even fungus.  Thus a rich web of interactions is spun on and around the plants above and below the ground and this controls the pests more efficiently than the conventional method of destroying large numbers of species indiscriminately (often resulting in the evolution of a pesticide-resistant creature whose natural predators have been destroyed).  The authors also showed that different predator groups did not compete with other predator groups (but just within their own species) for survival and that they had a synergistic effect on pest reduction.  There seem to be ecological niches which remain under-utilized when species evenness falls and then the ecosystem cannot function optimally. 

Thus one can conceive of an intriguing, interactive environment in a farmland or garden.  "Where on earth have you been?" the beetle Hippodamia convergens might say to a passing nematode, "Let's meet."
"Ha!  Ha!  Damn funny," the earthworm might reply scathingly.

Or one could imagine a  rich orchestra of soil and air and moisture, with noted players such as Beauveria bassiana (the fearful fungus) or the duo of Nabis alternatus and Geocoris bullatus (predator bugs of the mighty potato beetle Leptinotarsa decemlineata).  And wonder what kind of chaos one inflicts when one reaches out for that can of pesticides...  Before we stamp out all that has taken years to form, let us ask ourselves what it is we tread upon.

I think of Karel Capek's words as I write-

"...When mother in her young days was telling her fortune from cards she always whispered over one pile: "What am I treading on?"  Then I could not understand why she was so interested in what she was treading on.  Only after many years did it begin to dawn on me.  I discovered that I was treading on the earth.
 
In fact, one does not care what one is treading on; one rushes somewhere like mad, and at most one notices what beautiful clouds there are, or what a beautiful horizon it is, or how beautifully blue the hills are; but one does not look under one's feet to note and praise the beautiful soil that is there.  You must have a garden, though it be no bigger than a pocket handkerchief; you must have one bed at least to know what you are treading on.  Then, dear friend, you will see that not even clouds are so diverse, so beautiful, and terrible as the soil under your feet.  You will know the soil as sour, tough, clayey, cold, stony and rotten; you will recognize the mould puffy like pastry, warm, light, and good like bread, and you will say of this that it is beautiful, just as you say so of women or of clouds...

And from that time on you will not go over the earth unconscious of what you are treading on..."