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## The influence of area on the number of species

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### The influence of area on the number of species

Yello everyone,

So my biology book states (free translation) : " The surface area of an area influences the biodiversity. The number of species doubles when the area grows ten times. Or the other way; when the area reduces to 10% the number of species drop to half."

That's cool and all..but I can't wrap my mind around it. If the area is only 10% of what is used to be, how can the amount of species be even half? I can't see the mathematical pattern here:0 I hope someone can explain this in a way that a noob like me can understand.
Chiabete
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Because it's the same like when you grow area 10-times (10% -> 100%) and get double number of species.
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JackBean
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OK I'm no mathematican but if you say increasing an area ten times simply doubles the number of species then it seems to me that reducing an area to a tenth would reduce the number of species to a 20th of the species that were in the original area.
animartco
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really? So when going from x m2 with y species to 10x m2 with 2y, it's different than when going from 10x m2 to x m2?
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JackBean
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### Re:

JackBean wrote:really? So when going from x m2 with y species to 10x m2 with 2y, it's different than when going from 10x m2 to x m2?

I don't do maths, but using logic instead, it seems that if you only get double the number by muliplying by ten, when dividing by ten you would get a catastrophic drop.
animartco
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### Re: Re:

animartco wrote:I don't do maths, but using logic instead, it seems that if you only get double the number by muliplying by ten, when dividing by ten you would get a catastrophic drop.
If you have an area of ten with two species, then an area of one hundred has four species. How many species if you divide one hundred by ten?
ughaibu
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The point is that if you have two species and you multiply the area by ten you should using basic maths get 20 species. But you only get four. So the actual equation that applies is one that is far more complicated than simple mathematics.
animartco
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The mathematical pattern is simply: 10 x area = 2 x no. of species, but I think you get that.

I take it what your struggling to get your head around is the fact that only 10% of the area could still support half of the original species?

It is just a generalization, so don't take it as gospel. I think it works because as area increases the number of niches doesn't increase at the same rate. You get a certain amount of redundancy build up as area increases and the same species fill up more area. If you cut the area down to 10% you might still have 50% of the niches available for different species to exploit and so you keep 50% of the species. Like I say it is just a general rule so it's not always correct.

For real life examples, if you look at the diversity on oceanic islands, such as the Hawaii or the Pacific islands, they are still very diverse and have high concentrations of species in small areas. When you go onto continents, the diversity doesn't increase linearly with area because many of the habitats are the same and you get the same or similar combinations of species in different areas.
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BasicBiology
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