Why must predators in ecosystems with low npp cover huge ranges to survive?

NPP is the actual available energy that's produced by primary producers for other organisms to obtain energy from. When a predator lives in a ecosystem that has a low NPP, it means that the predator will have to cover a much wider range in order to have all the needed energy that's produced by those primary producers. If the there was a high NPP the need to search for those primary producers was much diminished as there would be enough energy available close by.