Spore wouldn't be a bad place to start for this... Each planet had ecology spots for animals based on how suited for life it was. Ignoring the fact that there was only 1 suited for life (more on that later), you could do something similar.
(by for every and there's 1, I mean type, and this is obviously an example)
For every 2 shrubs, there's 1 tree and 1 small herbivore.
For every 2 trees, there's 1 large herbivore
For every 2 small herbivores, there's 1 small predator
For every 5 large herbivores, there's 1 large predator
Then look at the earth biomass indicators
Each 5 lions requires 1 herd of antelopes. (Or someat) something similar could be done.
Fun ways to break this are omnivores (bears take up a large herbivore slot and 1 small predator slot), hibernators (giant worms sleep for 4 years at a time and thus take up 1/4 of a large predator biomass slot). Carnivorous plants provide a shrub, but act as a small predator.
Suited for life:
While I'm not a trekkie, this is
useful to read It's basically common suspension of disbelief.
Other fun:
AstrobiologyHabitability : Actually, this site has LOTS of neat links
Theorized Life supporting atmospheres:
Ammonia
Methane
I'll admit to being a carbon chauvenist, but silicon is also an option, and the softer you want to get, the farther from carbon on the table you can go.
initial scan data
[starname]-[orbit ordinal] CLASS [class]
Atmosphere : [atmosphere]
Weather : [weather activity] (Could be 'active' with winds, 'chemical rains' or whatever)
Geology : [geology type] (liquid core? dead planet? unknown?)
Biological Suitability : [biosuit] (Looks like you like heavy life planets. This is a best guess for how deep the tree is)
Detected Life: (Detected life would just be whatever showed up on the terrain scan. If you establish that 1 Large herbivore implies that there's enough biodiversity to support a small predator, you'll know that's out there too.)
1 shrub
1 tree
1 large herbivore
As you scan new plants and animals, they'd be added to this list. Also, after you scan the first plant or animal, the life on planet section is filled in:
Plants on XXX
Plants have evolved the use of chlorophyl to derive power from the sun. (Ok, my botany is crap)
Animals on XXX
Large animals usually have [defining characteristics.]
Anyway my two cents... Sorry for the mind dump