How do we call a region of low carrying capacity?
If you ask about quantity/numbers only, I would suggest using "the zone of low population density" or "intermittent zone" which in turn borders the "buffer zone" and "the zone of intermediate/high population density". 

The "buffer zone" is the zone between two different populations where the number of the animals in question is zero. 

J.Potts, M.Lewis "How do animal territories form and change? Lessons from 20 years of mechanistic modelling"

There are other classifications based on the "main usage" of the territories.