Naked Science Forum

Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: Don_1 on 26/11/2009 13:37:54

Title: What causes dwarves and giants?
Post by: Don_1 on 26/11/2009 13:37:54

Many species of animals come in a range of sizes, the cat family are good example, from our small domestic species to the Tiger. The whale family ranges from the Hector's Dolphin, at under 5ft long, to the Blue Whale, at over 100ft. A Hermann Tortoise will grow no bigger than a side plate, while the Aldabra and Galapagos species are big enough to ride on.

Then there are these:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.bbc.co.uk%2Flastchancetosee%2Fsites%2Fanimals%2Fimages%2F226%2Fmark_madagascar_11.jpg&hash=12a48235642db49d1dbd45bee9ee86f3)(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.shoarns.com%2Fparsons%2520chameleon%2520small%2520.jpg&hash=1b26c74044feb00b9c5580b44d4b6e80)
The Pygmy Chameleon                  The Parsons Chameleon

One is no bigger than your thumb nail, the other can be over 2ft long.

What is the cause of these, sometimes tremendous, differences in size? Is it food availability, habitat, predators (or the lack of them), or just strange quirks of evolutionary nature?

What's your opinion?

Title: What causes dwarves and giants?
Post by: Nizzle on 26/11/2009 13:59:00

It's probably food availability, habitat, (lack of) predators AND genetics.

Title: What causes dwarves and giants?
Post by: Don_1 on 27/11/2009 15:25:51

In the case of the two chameleons above, both are from the rain forests of Madagascar, so both have much the same food availability, climate, habitat and predators. So why and how did one become so small and the other so big?

Is there a limit to the difference in size between the smallest and largest species of an order or family group?

Title: What causes dwarves and giants?
Post by: Nizzle on 01/12/2009 07:10:34

Yes there are limits. If food is abundant, climate is ideal and there are no predators around, genetics will have an upper limit to the size of the species in the sense of: The biggest animal of the species will have the most effective alleles of  most of the growth-involved genes. His kin can become larger only if by breeding, it will have even more growth-involved genes at maximum potential.

So there's a theoretical limit to the size of an animal where ALL the growth-involved genes are at maximum effectiveness. Then again, mutations can either increase or decrease the theoretical limit of size