In an ecosystem, say there are two species in a predator-prey relationship. What is the most typical ratio of these species' population densities? For instance, it could be that for every fox, there are ten rabbits. Actually, the precise ratios are somewhat irrelevant; mostly I would like to know if we can say that the number of prey is generally larger than the number of predators.
I would like references to articles, textbooks, etc. that contain information about such ratios.
Note that this is aimed at the number of species within a single ecosystem. However, if this information is hard to quantify (perhaps because it is hard to define where an ecosystem ends), global populations could be used as an estimate.
Forgive me if this is ill-defined or trivial, I'm a physicist by training.