Learn Spanish (Latin America): Los animales se dan la defensa mutuamente contra el depredador. - The animals give each other defense against the predator.

The pronoun se can be either reflexive ('to themselves') or reciprocal ('to each other'). Without mutuamente, Los animales se dan la defensa could technically mean the animals give defense to themselves. Adding mutuamente (mutually) removes the ambiguity and makes it completely clear that they are defending each other.

Could I use el uno al otro instead of mutuamente in this sentence?

Yes! You could say Los animales se dan la defensa los unos a los otros (using the plural because we are talking about animals in general, though el uno al otro works if there are exactly two). Both expressions do the exact same job here: they clarify that the action is reciprocal rather than reflexive.

Why does Spanish use la defensa when the English translation just says 'defense'?

In Spanish, when you talk about an abstract concept or a general noun, you almost always need the definite article (el, la, los, las). While English drops the word 'the' for general concepts like 'defense', Spanish requires it, making it la defensa.

Is darse la defensa a common way to say 'defend each other'?