== "living on the margins of livable horse habitat" == 

 For me it was difficult to understand that "The ancestors of most modern ponies developed small stature due to living on the margins of livable horse habitat." means that (I had to read a Russian language version to understand this) these animals lived in an environment where there was too little food, hence being small helped them to survive. 

 Is there a certain term, idiom or grammar construct which I should know, which would make it easier to parse that sentence?