The prepositional phrase "of being" is defining "levels." I can't be sure without more context, but I think the point that then author wants to make is that species need large populations of individuals to survive.

It's not totally clear. 'Levels of being' might refer to creatures/biological entities of varying degrees of complexity and awareness. Like bacteria, insects, reptiles, mammals, humans, etc have 'levels of being' that are of increasing complexity.

In the given sentence, the phrase "scale and levels of being" refers to different degrees or levels of existence or reality. The use of "of being" here emphasizes the various states or degrees of existence within life. So, the sentence is suggesting that life cannot function without these different scales or levels of existence; they are integral to how life operates or functions. The "of being" is used to describe the nature or quality of these scales and levels within the context of existence.