Question about ape trees and ape lore

[thivid08]

I know that jungle trees can spawn apes, but how does this work? Do they have a chance of spawning randomly depending on the number of trees, or can you force one to spawn by shaking the tree or some other way? The next questions are more about ape lore, so, (sorry for so many questions)

1- why do they spawn from trees? They seem too big to climb them. Do they raise their young there?

2- What is the history of these three subspecies that seem to coexist in harmony?

3- What is their personality, are they just aggressive brutes or are they sensible creatures who just try to defend their home from invaders? 

4- why are apes the only fauna in pure jungle islands? What happened to other animals? 

Finally, why do apes only attack nichelings and not any other animal? In islands that are a mix of grassland and jungle, apes ignore every animal except for the nichelings.