In ecology, a community refers to

Step 1: Analyze the question The question asks for the ecological definition of a community.

Step 2: Explain the concept Ecology works with levels of organization, from smallest to largest:

• Individual: one organism
• Population: individuals of the same species in an area
• Community: all the different populations (species) living and interacting in the same habitat
• Ecosystem: the community plus the non-living (abiotic) environment
• Biosphere: all ecosystems on Earth

Step 3: Check each option

• A. A number of individuals of a given species: This describes a population, not a community.
• B. Groups of different organisms living in a habitat: This is correct. A community is made up of different species (plants, animals, microbes) living and interacting in one habitat.
• C. Existing species in an abandoned farmland: This is too specific. It describes one particular place, not the general definition. It also hints at ecological succession.
• D. The dominant species in a habitat: This is just the dominant species, not the whole community.

Step 4: Answer

Tip: Remember "Population = Pne species" (same species only), while "Community = Collection of different species." If the option mentions different organisms together in one place, it is usually the community.