When analyzing reproductive fitness, what perspective is critical beyond simply looking at the size of the current brood?

Answer

The lifetime output relative to the energy expended

Fitness must be assessed over the organism's entire lifespan. A strategy investing heavily in a few offspring with high survival rates (iteroparity) may yield higher lifetime fitness than massive output in a single event if environmental stability is low.

When analyzing reproductive fitness, what perspective is critical beyond simply looking at the size of the current brood?
reproductionEcologyevolutionfactorstrategy