Monday, January 9, 2012

A Tiny Dying Such as This – Is There an Ongoing Mini Mass Extinction of Soil Invertebrates in the Midwest?

My latest 3quarksdaily column

A short note in which I conjecture on a potentially vast local extinction event of Midwestern soil organisms especially of those inhabiting the leaf litter of woodlands.

In our evolutionary progression humans scrambled from the leafy treetops about half way down the length of the trunk.  We now live perched between treetop and root ball on that convenient platform we call the soil.  If physicists can give themselves vertiginous shivers by imagining those Microarth_mosaicempty atomic spaces that constitute the seeming sturdiness of ordinary things then it is surprising that soil ecologists ever leave their homes knowing as they do how vastly crenulated, fissured, fractured and porous is the soil.

Ours is the exceptional ecological enterprise since more organisms live in the soil in those porous and interstitial lodgings than on the soil.  We are not directly equipped for flight, we rarely burrow, we are condemned to walk upon the dirt until at last we may complete our descent into the ground, toppling into that large furrow excavated for our remains.  A soil pore will have us after all.   

If we had been just a little smaller and had migrated just a little further down the length of that primordial tree we’d be living in one of the most biologically diverse and ecologically active compartments of the biosphere.  The upper ten centimeters or so of soil teems with living things.  The organisms living in Earth’s thin and hyperactive rind are phylogenetically diverse, trophically heterogeneous, functionally assorted, highly variable in size, dissimilar in longevity, variegated in morphology, behaviorally divergent, adapted to different soil horizons, disparately pigmented, but are united in their reliance on death.  Specifically, soil organisms are all similar in that they feed on detritus (i.e., dead organic matter).  As I discussed in a recent column, collectively the action of these organisms within detrital-based food webs results in the breakdown of dead organic matter and the mineralization of organic compounds that makes key nutrient available to the living. 

Examine your foot a moment.  If it is like mine when shod it measures roughly 30 cm in length (yes, a foot) by about 9 cm wide (your foot, of course, may not be quite so rectangular!).  A pair of feet such as these out for a stroll treads minimally upon the bodies as 270,000 protozoa, 135 mites, 3 springtails, and a one or more large earthworms with each footfall.  In places of high animal density the injury toll would be higher by several orders of magnitude.  If you were sallying along a woodland path in the temperate zone these crushed critters will be representative of about 30 distinct and species of which up to half may be previously undescribed by taxonomists.  Scaled up there can be as many as 200 species of soil insects and 1000 species of soil animals in total in every 1 m2 of soil.

Read on at 3quarksdaily here

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