Tuesday, June 18, 2013

Most species originate in the tropics

Yesterday was the first really good day of 2013 to swim in a pond – two months later than in 2012 – and today is the first supertropical day of the otherwise cloudy year 2013 with temperatures reaching 35 °C in Pilsen where the warmth has its headquarters. Prague was colder but 33.5 °C was still enough (by 0.3 °C) to beat the record for this day which didn't occur in 2012 but in... 1934. ;-) A tropical topic may therefore be appropriate.

Because Slovak geologist Mr Adam Tomášových is among the 8 authors of the paper, the science section of the Slovak daily Sme.sk reviewed the article
Out of the tropics, but how? Fossils, bridge species, and thermal ranges in the dynamics of the marine latitudinal diversity gradient
written by David Jablonski et al. and published in PNAS. See also futurity.org.

They looked at three slices of Cenozoic (from 66 million AD through now) and decided that most marine genera originated in the tropics. You may view the paper as a followup to the "out of the tropics" mechanism coined by Jablonski and others in 2006.

They were also interested in the way how these tropics-born species migrate into the moderate zone. A heat wave is probably necessary for such a migration while intraspecies adaptation and the diversification rate of a species is helpful to allow a new species to migrate out of the tropics.

I think that most of us will find these statements somewhat uncontroversial and plausible. Tropics is where the concentration of life is maximized. Moreover, the Sun and heat probably tends to increase the mutation rates over there which is why the percentage of the species originated in the tropics is likely to be even greater, probably much greater, than the percentage of the individual organisms that actually live there today.

Tropics are the place with the highest biodiversity and it's no coincidence. Their research shows that this has been the case at many distant moments in the past, too.

An interesting concept promoted by the paper are the bridge species. A seemingly sensible yet naive assumption known as "niche conservatism" is that species tend to live in similar habitats as their relatives. However, according to this paper, many jumps (in some analogy, jumps over the river) have occurred and they were extremely important. For these jumps to be possible, one needed one of the rare special species, the bridge species, that allowed life to spread to less hospitable (essentially cooler) places. Just to be sure, "niche conservatism" will be obeyed in most cases if you look at random animals and their ancestors. However, this "niche conservatism" assumption prevents you from explaining the origin of the bulk of biodiversity on Earth.

There are only one or two bridge species per evolutionary lineage – a small percentage of all species – and all these bridge species seem to have originated in the tropics themselves. The paper also finds something you may view as counterintuitive: the most widespread species are not those that tolerate the largest temperature swings. In fact, those that tolerate a narrow interval are (at least in the case of bivalves) the most widespread ones. But it's not so illogical as you might think because the narrow tolerated interval may be adjusted by evolution, too. Moreover, the tropics represent a significant part of the Earth and the temperature over there is rather constant so too much tolerance isn't needed.

The global warming alarmist censors must have misunderstood the paper completely because they couldn't stop the publication of this paper despite the fact that according to these loons, liars, and demagogues, a warmer weather is hurting (and is probably going to destroy) life on Earth. ;-)

More seriously, if the tropics offer the best temperature for life on Earth, we may calculate how much the temperature should rise (uniformly over the globe: an assumption) for the life's well-being to be optimized over the globe. Clearly, it would be better for the optimum temperature to be found in the moderate zone – which has a greater area and which is currently about 20 °C cooler than the optimum tropics. It follows that the optimum global temperature rise for life is at least 20 °C. I say "at least" because there are no available data that would directly or indirectly imply that the optimum temperature for life isn't even higher than the current temperature of the tropics. Compare this scientific fact – that a 20 °C temperature rise would be beneficial for life – with the insane fearmongering about a 2 °C warming (from which only 0.7 °C or so was realized in the last 100 years).

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