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Living organisms interact with one another



Biology Is Studied at Many Levels of Organization Life’s properties emerge when DNA and other molecules are organized in cells. Energy flows through all the biological levels shown here
1.6 Biology Is Studied at Many Levels of OrganizationLife’s properties emerge when DNA and other molecules are
organized in cells. Energy flows through all the biological levels shown here  
The internal hierarchy of the individual organism is matched by the external hierarchy of the biological world (Figure 1.6). Organisms do not live in isolation. A group of individuals of the same species that interact with one another is a population, and populations of all the species that live and interact in the same area are called a community. Communities together with their abiotic environment constitute an ecosystem. Individuals in a population interact in many different ways. Animals eat plants and other animals (usually members of another species) and compete with other species for food and other resources. Some animals will prevent other individuals of their own species from exploiting a resource, whether it be food, nesting sites, or mates. Animals may also cooperate with members of their species, forming social units such as a termite colony or a flock of birds. Such interactions have resulted in the evolution of social behaviors such as communication. Plants also interact with their external environment, which includes other plants, animals, and microorganisms. All terrestrial plants depend on complex partnerships with fungi, bacteria, and animals. Some of these partnerships are necessary to obtain nutrients, some to produce fertile seeds, and still others to disperse seeds. Plants compete with each other for light and water, and they have ongoing evolutionary interactions with the animals that eat them, evolving anti-predation adaptations or ways to attract the animals that assist in their reproduction. The interactions of populations of different plant and animal species in a community are major evolutionary forces that produce specialized adaptations. Communities interacting over a broad geographic area with distinguishing physical features form ecosystems; examples might include an Arctic tundra, a coral reef, or a tropical rainforest.

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