QuestionI own two box turtles and one Russian tortoise. I was wondering if they could co-exist in one tank due to space constraints.
AnswerIt is not a good idea to mix animals from different continents (because of disease intolerance issues), and it is not a good idea to mix animals from different habitats.
Russians are from the grassy scrubs with rather nasty winters, sort of like the Ornate Box, but very different than the Eastern or Three-Toe Boxes.
If this is a big back-yard habitat with lots of different micro-climates, or even a really big (8'x4') tortoise table, I might not be so worried, but you said 'tank', which usually means pretty small.
Heck, even Box Turtles really SHOULD be in a 4'x4' space whenever possible!
Try http://www.tortoisetrust.org for more details.