Is Everything Everywhere?
In 1807, Alexander von Humboldt wrote “The nearer we approach the tropics, the greater the increase in the variety of structure, grace of form, and mixture of colors, as also in perpetual youth and vigor of organic life”. The increase in numbers of animal and plant species from the poles toward the equator is one of the most pervasive patterns of life on earth. Although known at least since the early 1800s, this pattern still lacks a consensus explanation. And although well documented in large, multicellular animals and plants, this pattern is reported to be relatively weak or absent in morphospecies of unicellular organisms. The lack of apparent geographic pattern has been attributed to high abundances, frequent and long-distance dispersal, and low extinction rates. This argument would suggest that bacteria, even smaller, more abundant, and more readily dispersed than protists, would also show little or no latitudinal gradient of diversity. This idea is expressed in microbiology as “Everything is everywhere; the environment selects“. But is everything everywhere?
A latitudinal diversity gradient in planktonic marine bacteria. PNAS USA, May 28, 2008
For two centuries, biologists have documented a gradient of animal and plant biodiversity from the tropics to the poles but have been unable to agree whether it is controlled primarily by productivity, temperature, or historical factors. Recent reports that find latitudinal diversity gradients to be reduced or absent in some unicellular organisms and attribute this to their high abundance and dispersal capabilities would suggest that bacteria, the smallest and most abundant organisms, should exhibit no latitudinal pattern of diversity. We used amplified ribosomal intergenic spacer analysis whole-assemblage genetic fingerprinting to quantify species richness in 103 near-surface samples of marine bacterial plankton, taken from tropical to polar in both hemispheres. We found a significant latitudinal gradient in richness. The data can help to evaluate hypotheses about the cause of the gradient. The correlations of richness with latitude and temperature were similarly strong, whereas correlations with parameters relating to productivity (chlorophyll, annual primary productivity, bacterial abundance) and other variables (salinity and distance to shore) were much weaker. Despite the high abundance and potentially high dispersal of bacteria, they exhibit geographic patterns of species diversity that are similar to those seen in other organisms. The latitudinal gradient in marine bacteria supports the hypothesis that the kinetics of metabolism, setting the pace for life, has strong influence on diversity.
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Tags: Bacteria, Biology, Environment, Microbiology, Science
Interesting post. Although unrelated, I remember a passage from Jared Diamond’s book Guns, Germs, and Steel, in which he theorizes why people nearer to the poles invented more sophisticated technology. His theory was that the people near the poles had more time to burn inside from the weather to invent and that people near the poles had more of what they needed and could obtain it easily without sophisticated technology.
Sea currents, geomagnetic flux of earth may have some influence on ‘dispersal’.
Corollary of the Second Law of Thermodynamics – which states that “everything takes longer and costs more” (well, loosely speaking, anyway) – is the maxim “everything goes faster and makes more mistakes”. When it’s warm, that is. Which allows more generations and more mistakes in a given time.
Or just MORE.
I like the evidence that one can get the same generic bugs out of wells that go deep underneath Paris, and sediment dredged up from abyssal depths in the Pacific. Not only “everything, everywhere”, but everything, everyWHEN.