Surely this will depend on the organisms involved. If you were dealing with thrips, or most flying insects, then there is no limit. If you are working with snails or even plants, then there are limits. Also the altitude at which the organism normally lives may determine what altitude it can colonise....So, essentially, which group of organisms are you examining in this context?

Thanks Christine,

I am working for plants.

This will depend on the plant. Coastal plants will need hardly any elevation; for lowland plants it would depend on size, altitude and substrate; for plants restricted to higher elevations higher altitudes are required. I hope this helps.