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# Why are there more species in the tropics than at the poles?

I was just curious to get your intuitions and opinions about this unanswered question in Ecology and if there are ecologists here how close are we to an answer?

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1.

Naive idea: there's more energy coming in from solar radiation?

I may have read somewhere (I'll try to check) that stable conditions favour biodiversity. I guess there are not too many fluctuations near the equator, every day is roughly the same.

Perhaps one should look into the reasons for differentiation of species and for the conditions that the different branches can survive.

Comment Source:Naive idea: there's more energy coming in from solar radiation? I may have read somewhere (I'll try to check) that stable conditions favour biodiversity. I guess there are not too many fluctuations near the equator, every day is roughly the same. Perhaps one should look into the reasons for differentiation of species and for the conditions that the different branches can survive.
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2.

This is purely pulled out of the air, but I've seen TV documentaries that suggest that a given "annular slice" around the pole is only habitable for a given portion of the year, and that almost everything migrates to-and-fro yearly (unlike elsewhere with milder changes where some species migrate and some stay put). So one fator might be just that the "effective area" of the poles is much smaller than when viewed purely as a region on a globe.

Comment Source:This is purely pulled out of the air, but I've seen TV documentaries that suggest that a given "annular slice" around the pole is only habitable for a given portion of the year, and that almost everything migrates to-and-fro yearly (unlike elsewhere with milder changes where some species migrate and some stay put). So one fator might be just that the "effective area" of the poles is much smaller than when viewed purely as a region on a globe.
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3.

More energy was my first instinctual thought as well! so maybe they migrate where there are stable conditions for the moment . So what do you think are the reasons for differentiation of species in time and in space?

The other thing I thought about was, precisely the opposite that living conditions around the harsh living conditions might favor species collaboration more than competition in the tropics. But that fell on the fact that its hard to know which is more harsh - arctic or tropics. But I thought that like David mentions that it was regulated by migration, so it still might be valid.

Comment Source:More energy was my first instinctual thought as well! so maybe they migrate where there are stable conditions for the moment . So what do you think are the reasons for differentiation of species in time and in space? The other thing I thought about was, precisely the opposite that living conditions around the harsh living conditions might favor species collaboration more than competition in the tropics. But that fell on the fact that its hard to know which is more harsh - arctic or tropics. But I thought that like David mentions that it was regulated by migration, so it still might be valid.
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4.

If I remember correctly for differentiation you need some kind of ecological barrier such that random genetic variations can influence one particular subgroup and turn it into a new species (simplistically speaking). In between there has to be some selection pressure which favours the new expression above the old one of course. The stronger the selection pressure, the more quickly new traits will spread through the population (I think).

About cooperation and competition, I think both are more likely the more species are present.

I think the problem with harsh is that we automatically think of harsh in human terms.

Life needs food so in that respect the poles are more harsh, except for sea life due to upwelling nutrient-rich water in the North pole.

I believe there are some bacteria who use radioactive energy to go and multiply but for some reason this doesn't favour large organisms (too many genetic variations due to the radiation, I suppose).

Comment Source:If I remember correctly for differentiation you need some kind of ecological barrier such that random genetic variations can influence one particular subgroup and turn it into a new species (simplistically speaking). In between there has to be some selection pressure which favours the new expression above the old one of course. The stronger the selection pressure, the more quickly new traits will spread through the population (I think). About cooperation and competition, I think **both** are more likely the more species are present. I think the problem with **harsh** is that we automatically think of harsh in human terms. Life needs food so in that respect the poles are more harsh, except for sea life due to upwelling nutrient-rich water in the North pole. I believe there are some bacteria who use radioactive energy to go and multiply but for some reason this doesn't favour large organisms (too many genetic variations due to the radiation, I suppose).
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5.

Btw, I've heard somewhere that estimation of species biodiversity is often done by counting beetles.

Comment Source:Btw, I've heard somewhere that estimation of species biodiversity is often done by counting beetles.
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6.
edited March 2011

Biodiversity seciton "Number of species sizes making up various phyla" shows that, if you just care about number of variants, insects (including beetles) make up the vast majority of biodviersity.

Comment Source:[[Biodiversity]] seciton "Number of species sizes making up various phyla" shows that, if you just care about number of variants, insects (including beetles) make up the vast majority of biodviersity.
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7.

If I remember correctly for differentiation you need some kind of ecological barrier such that random genetic variations can influence one particular subgroup and turn it into a new species (simplistically speaking). In between there has to be some selection pressure which favours the new expression above the old one of course. The stronger the selection pressure, the more quickly new traits will spread through the population (I think).

You seem to be confusing two processes - adaptation and speciation. Adaptation happens in a single population. Speciation is (or at least involves) the splitting of one population into two. They may be very entangled processes in particular cases, but they are very different things.

I believe there are some bacteria who use radioactive energy to go and multiply but for some reason this doesn't favour large organisms (too many genetic variations due to the radiation, I suppose).

I never heard of that. Some bacteria (and archaea and some big things too near hot vents) use geothermal or geochemical energy which is derived from radioactivity in the Earth rather than energy from the sun.

Comment Source:> If I remember correctly for differentiation you need some kind of ecological barrier such that random genetic variations can influence one particular subgroup and turn it into a new species (simplistically speaking). In between there has to be some selection pressure which favours the new expression above the old one of course. The stronger the selection pressure, the more quickly new traits will spread through the population (I think). You seem to be confusing two processes - [adaptation](http://en.wikipedia.org/wiki/Adaptation) and [speciation](http://en.wikipedia.org/wiki/Speciation). Adaptation happens in a single population. Speciation is (or at least involves) the splitting of one population into two. They may be very entangled processes in particular cases, but they are very different things. > I believe there are some bacteria who use radioactive energy to go and multiply but for some reason this doesn't favour large organisms (too many genetic variations due to the radiation, I suppose). I never heard of that. Some bacteria (and archaea and some big things too near hot vents) use geothermal or geochemical energy which is derived from radioactivity in the Earth rather than energy from the sun.
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8.

Graham said:

You seem to be confusing two processes

Thanks for the links! My explanation wasn't accurate, but I have heard of this distinction before.

I never heard of that.

I suppose I heard of these:

Bacteria Use Radioactive Uranium To Convert Water Molecules To Useable Energy

but indeed, they don't directly use radiation as an energy source, despite the suggestive title!.

Firmicutes species are the producers, capturing the energy of radiation-borne hydrogen gas to support microbial communities.

Comment Source:Graham said: > You seem to be confusing two processes Thanks for the links! My explanation wasn't accurate, but I have heard of this distinction before. > I never heard of that. I suppose I heard of these: [Bacteria Use Radioactive Uranium To Convert Water Molecules To Useable Energy](http://www.sciencedaily.com/releases/2006/10/061019192814.htm) but indeed, they don't directly use radiation as an energy source, despite the suggestive title!. > Firmicutes species are the producers, capturing the energy of radiation-borne hydrogen gas to support microbial communities.
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9.

i think i understand adaption and speciation but so how is this "confusion" important for the difference in numbers of species ?

I just read in Everetts book "Critical Transitions in Nature and society" see Recommended reading, that the long debate on why there are so many species (Huthcinson,May..) the Hutchinson argument on phyto--plancton abundance is in non-equilibrium initially has been verified. He also mentions an experiment he did another thing to explain stable species coexistence which started out with lumps of species with random sizes, resulted in a convergence towards coexistence of species that are more similar. And this is supported empirically by lake plancton, beetles, homo sapiens and several bird communities. So what does this have to do with my question? I'll come to that later...

Comment Source:i think i understand adaption and speciation but so how is this "confusion" important for the difference in numbers of species ? I just read in Everetts book "Critical Transitions in Nature and society" see [[Recommended reading]], that the long debate on why there are so many species (Huthcinson,May..) the Hutchinson argument on phyto--plancton abundance is in non-equilibrium initially has been verified. He also mentions an experiment he did another thing to explain stable species coexistence which started out with lumps of species with random sizes, resulted in a convergence towards coexistence of species that are more similar. And this is supported empirically by lake plancton, beetles, homo sapiens and several bird communities. So what does this have to do with my question? I'll come to that later...
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10.

the Hutchinson argument on phyto-plankton abundance is in non-equilibrium initially has been verified.

What's the Hutchinson argument?

Comment Source:> the Hutchinson argument on phyto-plankton abundance is in non-equilibrium initially has been verified. What's the Hutchinson argument?
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11.
edited April 2011

Everett refers two papers by Hutchinson and the first is "Hommage to Santa-Rosalia or why are there so many species" (on conditions for coexistence). The latter is "The paradox of the Plankton" he mentions that the fact that high diversity of phytoplankton in equilibrium would be limited (the number of species cannot be greater than the number of resources in that case). But he claimed that the phytoplankton started out in non-eq. it was verified by U. Sommer 1984 (ed) and MA Huston "Biological Diversity : the Coexistence of Species on Changing Landscapes"

Everett continues and writes:

Intrinsic chaos can do the same job.

Comment Source:Everett refers two papers by Hutchinson and the first is "Hommage to Santa-Rosalia or why are there so many species" (on conditions for coexistence). The latter is "The paradox of the Plankton" he mentions that the fact that high diversity of phytoplankton in equilibrium would be limited (the number of species cannot be greater than the number of resources in that case). But he claimed that the phytoplankton started out in non-eq. it was verified by U. Sommer 1984 (ed) and MA Huston "Biological Diversity : the Coexistence of Species on Changing Landscapes" Everett continues and writes: > Intrinsic chaos can do the same job.
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12.

Here is a Wikipedia article on this with a lot of hypotheses and critique Latitudinal gradients in species diversity

what a wonderful name :-)

Comment Source:Here is a Wikipedia article on this with a lot of hypotheses and critique [Latitudinal gradients in species diversity](http://en.wikipedia.org/wiki/Latitudinal_gradients_in_species_diversity) what a wonderful name :-)