The primitive food chain is mutually exclusive, so that different species can continue to survive in nature, piranhas have a nemesis even if they are fierce.

If you're in a vast expanse of desert, unless you can find water straight away, you'll be lucky to meet a camel. And it's not just the traditional image of the 'desert boat' that makes this animal so interesting - as a herbivore, they are almost never known to have natural predators in nature.