for what its worth my (now 12) youngest daughter overheard me explaining my homegrown Traveller universe to my (now soon to be ex) wife while we were driving around one day. Later that night Sarah asked me if she could see (she was 10 then) my "new video game"? I told her it was really not a video game but an old-school RPG I had been running since 1977 back when you had to just have a big game of "let's pretend".
So I dragged out all my materials and explained hot to play it. She was enthralled and rolled up a scout named Lady Victoria Challenger. Because she wants to grow up to be a vet and enjoys drawing and making up animals (she now posts her drawings to her Devianart page) I decided to run her in a solo game where the plot was that Scout Vickie found a new world and explored it while cataloging all the new species on it. So Sarah would randomly roll up a creature, and we would work out together what it was like as her scout "studied" it. And example was this:
http://freelancetraveller.com/features/animals/rsrunner.html
She gave up as her attention wandered, as kids do, to other things after a few moths but I'm still writing up some of the various critters. My point is that you cold run the game as a similar adventure where the players help roll up the animals and you then feed them some info at a time as you polish what the flora/fauna are based on the rolls. A player could roll up a set of creatures and then you work on what they are fully like before the next session while working them into the ongoing adventure.
For example, "Vicky" would release several small animal capture 'bots (large enough to dart and capture a rabbit) each night and then see what they came back with the next morning. One morning one of them didn't come back and its transponder showed it was a couple of kilometers away - much, much farther than it could get to on its own. She loaded up the air/raft and set off to find it. Sarah had already rolled up some potential scary predators so I has decided one of these had snatched the 'bot up and carried off in the night as a way to get Scout Vicky out into possible danger - which is what happened. My daughter got to find out all about the stalk/capture strategies of a particularly dangerous flyer when her character had to climb up some rocks to get the 'bot.
Anyway, that whole mini-campaign helped me flesh out a good portion of a new world's ecosystem while giving Sarah a good education in how animals interact with the same. And that not every animal has to be this horrifying ripper-claw-giant teeth-killer like hers all started out as. The universe needs pigs for the above beasties to eat, too. You might consider something similar for a naturalist campaign to help reduce your workload a bit - the players roll the dice and you supply the details.
And don't forget the safari ship, elephant guns, and native bearers who scatter at the first sign of danger.