Henry Gee takes a look at why there are so few big animal species
There are several answers to why there are just a few huge animals, says Helen Gee.
The first is simply that the earliest organisms in any group tend to be small, and remain small – only a few evolve larger sizes.
The second is that large organisms take a lot of energy to maintain. So they require larger spaces to live in, and competition with other large animals will ensure that there are fewer of them.
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The third is that larger creatures often run into problems of heat loss and support not suffered by smaller animals.
Yet a fourth is that larger animals tend to have fewer offspring, keeping populations small and survival precarious.
The fifth is that once they have become big, they need a huge standing stock of smaller creatures to feed on. It’s no wonder that the biggest creatures evolve in the sea – where the territories are vast, and problems of support and heat loss are minimised – and graze on enormous quantities of plankton that are further down the food-chain and easy to harvest.
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