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Communities and Ecosystems



Species living together form what's referred to as an ecological community. When nonliving things such as rocks and soil are added, this forms an ecosystem. Ecosystems are bigger than a community. Within an ecosystem or community, interactions can occur. These interactions can be food-related—where the survival of one organism is dependent on the presence of another organism in the region—and they can influence organismal relationships according to the way they behave in an environment. Both ecological and geological disturbances can also affect the community or ecosystem, often altering the distribution of species.

At A Glance

  • From ecological disturbances to geological changes, there are many biogeographic factors shaping the distribution of organisms and biodiversity in an ecosystem.
  • A group of species living together is an ecological community in which they grow, reproduce to create offspring, and survive through periods of succession in their own habitat.
  • In primary succession, living organisms colonize an area for the first time (e.g., newly formed rock from a lava flow), whereas in secondary succession, an existing community responds to a disturbance in the environment (e.g., a forest fire).
  • Within a community, food chains and food webs are models used to describe how energy flows as it first begins with self-feeding autotrophs, or producers, and ends with high-level consumers such as carnivores.
  • Many positive interactions take place in an ecosystem in which organisms live in symbiosis, a beneficial ecological relationship between two or more organisms living in direct contact with each other.
  • In mutualism, all species interacting with one another will benefit.
  • In commensalism, one species benefits, but the other is not affected either positively or negatively by the interaction.
  • Sometimes only one organism or species benefits from an interaction at the expense of another organism or species. This type of negative ecological interaction can come in different forms, such as predation or competition.
  • One organism consumes another in predation.
  • When two or more species compete for limited resources, it is known as interspecific competition.