If you are talking about a community of like animals then they depend on each other because some animals could be in the same food chain to survive for food , if 1 species died out then most would be impacted by it and maybe die out too. Hope it makes sense and helps...!
Populations (all members of one type of organism living in an ecosystem) in a community (several populations living in an ecosystem) depend on each other because different species in various population could be sharing a similar food chain and depending on each other for survival.
if one population dies out in a community then all the populations that depend on that species for food may also die out. Hence a change in one population affects the entire community because all the populations in a community depends on each other.
