Diversity varies with climate at diverse sizes:
One of the frustrating things about the issue of kinship and fertility is that the postulates that require the relationship should apply to plants as well as animals.  But while evidence is mountain high in animals, plants seem to be coy on the issue.

The best argument I can adduce from plants is that at high latitudes there are fewer plant species than in tropical or temperate zones.  And those cold-hardy species that do occur do not form the dense forest canopies seen in warmer places.  Of course the wooded areas of the north tend to be confined to riparian zones which are better sheltered and overall more fertile.  But the distance over which these river bank woods extend are vast and the breadth of one strip is much like the breadth of another far away.  This suggests that the forest community is managing its gene pool size by avoiding canopies while tropical forests manage theirs by having species diversity. 

All that is easy to say, but putting it on a quantitative basis is problematic.  Another could look at the same aerial views and deny it.  Making a quantitative prediction is problematic.  And of course there is the view that far northern forests have been wiped out by ice ages and have not had time to develop species diversity.

I speak of northern forests.  There is less land at high southern latitudes.

Now high altitude tends to follow the same pattern as high latitude; less diversity.  But I do not see the same canopy fragmentation at the timberline that I do in northern forests.  This is a puzzler. 

So if this relationship between species diversity and climate holds for large plants and animals, should it also hold for microorganisms?  At first blush one would doubt it.  Microorganisms should be able to evolve much faster than large life forms; one would not be surprised that their species diversity had already recovered from the most recent great ice age.  And besides, a lot of microorganisms reproduce simply by dividing, at least most of the time, so the pressure to limit population size ought to be absent.  But I really can’t derive it from first principles.

At all events the facts now seem to be in.  (CA Diversity Defined SCIENCE vol. 333 no. 6038 July 1, 2011 page 15 citing Stomp et al. ECOLOGY 92, 10.1890/10-1023.1(2011))  Yes, microscopic diversity is more diverse where large organisms are more diverse.  All right.  Maybe the little ones are more diverse because the big ones are more diverse. 
Anyway, it does not look like a promising line of evidence at this moment.

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