10% rule (efficiency between trophic levels): limits how long an ecosystem's food chain can be
Predator/prey cost benefit analysis (i.e. foraging) -- cost is risk of being eaten or killed along the way, benefit is energy/nourishment obtained: limits distribution of predator v. prey
Immigration/Emigration with other populations and ecosystems
Island biogeography: size of land and distance from another population/ecosystem (mainland): limits population size and variability on island