Finally after several versions of the composition, I have come up with something I'm happy with.
The process for this was…… After drawing out all the different animals I scanned them into the computer turned them into silhouettes and placed them onto the landscape; I spent a lot of time thinking about the grouping and how the animals related to each other. I moved the individuals around until they felt right together. I think this is where having seen them in the wild helps, as you have better understanding of how they use the landscape and move with each other in a group.
To help me with the feeling of recession, so that I could judge sizing better, I lightened the silhouettes of the zebras and Thompson's gazelles. I also placed silhouettes onto a size grid, on a separate document, to better understand the difference in height between the species.
Once in place, I have now printed it out and will now transfer this to the painting. Doing this element of the composition on the computer, for me, speeds the process up. I don't know what I'd do without it now.