I chose time originally over space because of the length of time that evolution has been around, the excessive time it took for life to mutate beyond a unicellular point and because there are small enclosed areas, such as caves, that do hold a variety of life, albeit a limited variety.
Watching a bit of 'State of the Planet - David Attenborough - UKTV History' today did make me reconsider this point though. He referred to an effect that mankind is having on biodiversity known as 'islandisation'. Basically; the detrimental affect that something as simple as a road through a jungle can have by dividing the natural environment into smaller parcels.
For instance there is a little bird that steals insects from army ants, the army ants need a large amount of jungle to survive, when the army ants run out of insects in their bit of jungle they are quite happy to cross the road to find more insects but the bird, never having had a lesson on road safety, won't.
All along these man made boundaries both the plant and animal diversity is lessened.
Weigh this against an animal heavyweight such as the crocodile, a reptile that stopped evolving a long time ago because it had reached an apex for its environment.
If your bot has stopped evolving I would suggest a quick game of 'Darwin’s Finches'. Change the environment, if it has stopped mutating then it probably (having reached the ‘crocodile point’) doesn't need to any more.
I am changing my original answer from time, (although important in its own right) to space, environment and genetic pool.
PS
In Africa, many of the original game reserves are now considered too small, the solution they are now thinking about is joining many of these game reserves using ‘corridors’, much like the affect hedgerows used to have on biodiversity here in England and the reason that we now have laws about the removal of hedgerows.
This reminds me of the internet sharing idea that has never been fully implemented, diverse environments joined by an internet pipeline.