ecological communities consistent all interacting species populations with any legal system most species populations within an established community such as the african savanna hare interacted with one another over a long period of time the interactions that occur between populations in the commuiny fall into three major categories competition in which populetions compete for limited resources predation in which organissms have one species kill and eat those of another and symbiosis in which two species population live together in close association with one another to the benefit of one or both of the species all these interactions act as forces have natural selection on the species populatinn invalved bus populations given biological community are intertwined with one another in it intricate coevolutionar process howerer these self-sustainning balance communities developed through changes occurring over long periods of time during these periods of changge one type a community gives way to another until a balanced self-sustaining community is established for example none of the earths majeslic forests originally began as forest up huge trees rather the land they now cover was initially inhabited by rarather the land they now cover was initially inhabiled by lichen washes grasses and low growing shurubs it was only after a long period of time that the established forest ecosystems we see todey were formad the process by which ecosystems slowly change into balanced self-sustalning communities is called succession what's now take a cioser look at the selective forces of competition predation and sybiosis as well as how self- sustaining communities are created through succession