What do scientists think might cause the universe to stop expanding and collapse in the big crunch? dark energy dark matter cosmic background radiation gravity

Newtonian gravity is what scientists believe will stop the universe’s expansion. This attraction would have to overcome the propulsive force of dark energy expansion, thus causing the compression of all the matter in the universe back into a small, hyperdense singularity.

This is the most closely resembles the model. 

Interacting group of various species in a common location. for example, a forest of trees and undergrowth plants, inhabited by animals and rooted in soil containing bacteria and fungi, constitutes a biological community.