What determines the carrying capacity of an ecosystem?

What determines the carrying capacity of an ecosystem is simply a number out of the population in the ecosystem; whether is be a quarter of it, half of it, all of it, it's a population that can be supported by the the needs of the organisms living in the ecosystem. Say "food", say there is over 300,000 fish in a swamp with 300 gators. Each gator eats 2000 fish a year. There is not enough fish to feed all 300 gators. So let's say the carrying capacity of this ecosystem is 200. 

It allows water to resist freezing and thawing cycle.

Mechanical energy from wind nonrenewable resource