How do energetic considerations affect the structure of populations? communities? ecosystems?

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