So to repeat back the quote that I pasted above, I hear you talking about advantage in a way that sounds correct, but then you take that away with your conclusion that that "justice" is involved, because there was never any agreement with those rabbits in the first place.
If the people in the community AGREE to protect a species, then this is their agreement and it's THEIR posited justice, not because they owe a duty to the rabbits but because they owe an agreement to each other. (I think a similar case is argued byLucretius when he discussed the origin of friendship, and he said that people agreed to not harm those weaker than themselves--what comes to mind is my autistic niece who is non-verbal, but elders in the community have agreed to protect her)
Then, too, did neighbours ‘gin to league as friends,
Eager to wrong no more or suffer wrong,
And urged for children and the womankind
Mercy, of fathers, whilst with cries and gestures
They stammered hints how meet it was that all
Should have compassion on the weak.
So the source for Hermarchus is Porphyry