eli5: Why are herbivorous animals usually fatter/bigger than carnivorous animals?
In: 119
First of all, I don’t think this is true. Many herbivorous animals are tiny. You’re probably not thinking about the sizes of all animals – you’re probably noticing that most of the largest animals are herbivores.
The main advantage of being large are:
– you don’t need to be able to run or hide from as many predators, or from any, if you are large enough.
– you probably don’t need to find food every day, as you can store some reserves as fat. (Small animals can do this too, but their energy requirements are actually higher *relative to their body size*, so they usually can’t go as long without food, unless they have ways of drastically slowing their metabolism and becoming inactive.)
The disadvantages are:
– above a certain size, you’re less fast and agile
– you will need loads of food in total to maintain your size
For some herbivores, the disadvantages aren’t very strong. If they live somewhere where their food is plentiful and easy to find, then being large is an option. And you don’t have to be fast or agile to eat fruits, leaves or grass. For carnivores however, these disadvantages quickly become huge. Imagine a carnivorous elephant trying to catch an antelope, and needing to catch lots to survive, and you’ll see the problem.
For carnivores, the cons of being large tend to outweigh the pros for very large body sizes. For some herbivores, the pros still outweigh the cons up to a higher ceiling.
For many animals, including herbivores, it still makes more sense to be small, it’s just that the ceiling for how large you potentially can be tends to be higher for herbivores.
There are other factors too (e.g. you can read about r vs K reproductive strategies), but this is a good start.
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