What are the critical factors required for the maintenace of natural ecosystem functions?

Question

What I've come up with so far isn't really cutting it so I need a little help on this for a college assignment. Please cite sources if you have an answer for me :) If if comes from personal knowledge add your name and I will use that as a reference if I use part of your answer.

Answer 1

Here's a minimalist way to look at it, and I'm not sure this is what you prof is looking for - this is just my way of thinking:

A hypothetical autotrophic system would require:
* organisms that convert energy to biomass (plants)
* water
* nutrients
* suitable atmosphere
* suitable temperatures

A minimal heterotropic system would need the above plus decomposers

A complete ecosystem adds more trophic levels to the previous two components:
*herbivores
*carnivores - primary & secondary
*omnivores