Populations of species do not exist in a vacuum. They interact with other populations. The myriad of species interacting in a given area is a biological community. Communities are often identified by their most conspicuous plants or animals, but they also include all of the fungi, protists, and bacteria. A major focus of community ecology explores interactions between species such as predator-prey relationships, competition, and mutualism. Another area of community ecology looks at how the composition of species in an area changes over time (succession). In this section there are models simulating classic studies of interactions between species.