  We provide a moduli-dependent definition of species scale in quantum gravity
based on black hole arguments. Concretely, it is derived from of a lower bound
on the entropy of extremal black holes with higher curvature corrections, which
ensures that the black hole can be reliably described within the effective
theory. By demanding that our definition coincides with a recent proposal for a
moduli-dependent species scale motivated from the topological string, we
conclude that the conjecture $\mathcal{Z}_{BH} = |\mathcal{Z}_{\rm top}|^2$
relating the black hole to the topological string partition functions should
hold, at least within the regime of validity of our analysis.
