[Perceval]

Yes, that's one example, but it's not the only way that species adapt to resource availability.

Ecologists have hypothesized r-selected and K-selected species as differing responses to resources: https://en.wikipedia.org/wiki/R/K_selection_theory

Homo sapiens may be r-selected. Different cultures of homo sapiens may lean more toward r- or more towards K- (this is part of the thesis of Eric Jones's The European Miracle https://en.wikipedia.org/wiki/The_European_Miracle).

Insofar as Tolkien's work is a fantasy and Hobbits are not real, would it strain our credulity to imagine that they are K-selected?