It is a support, it says that the species have constraints which arise by interacting with the environment, yet mechanisms develop. So, if mechanisms develop, then every species can do something with its natural (innate) capacity of population growth. Since the statement has a positive meaning, the population should grow (enhance the population doesn’t make sense), thus the species should surpass its natural capacity. (D)
I feel like I am telling a story 
, someone pls help! I feel its (D)
It’s E
A quick overview of the sentence indicates that the blank should be filled with a verb that indicates what a successful species does with its “innate capacity for population growth” in the face of certain constraints on that growth. This analysis suggests that the correct answer will have something to do with adjusting that capacity in the face of these constraints. Of the choices given, “reconcile” is closest to that meaning. None of the other options make for a meaningful, coherent sentence. “Enhance,” for example, may fit nicely with “its innate capacity,” but it does not make sense with “constraints.”
Thus, the correct answer is reconcile (Choice E).
Oh your explanation makes a lot more sense @keenabdulbasit Nice one 