dative of φύσει to mean "by nature" ?

M. unit 21, exercise II.5 is to translate “Lions are by nature strong and terrible, …”
The answer key gives: “οἱ λέοντες φύσει ισχυροι και δεινοι εισιν…”
“φθσει” is the dative singular of “nature”. I’ve reviewed “uses of the dative” in M., (p.87-88), but I can’t find a fit for this translation, except perhaps “dative of means”, but it seems far-fetched.
Please comment.
Thanks to all.

The dative singular of phusis means ‘by nature’ (Middle Liddell).

Thanks - Mastronarde does not mention the “by” part in the vocabulary.

But I remain puzzled by the sentence construction. It’s as if the word was an adverb, i.e., “naturally”. And why does it have to be dative?

It seems a bit unfair of Mastronarde to throw this at you, but you can find the answer in Smyth. In 1516 he says “The dative of manner may denote the particular point of view from which a statement is made. This occurs chiefly with intransitive adjectives but also with intransitive verbs (Dative of Respect).”

One of his examples: ἀσθενὴς τῷ σώματι (weak in body) seems like a similar usage.