What ecological concept encompasses the variety of life forms in a given ecosystem?

The correct answer is biodiversity, which refers to the variety of life forms present in a given ecosystem. This concept includes not only the different species of plants, animals, and microorganisms but also the genetic diversity within these species and the variety of ecosystems themselves. Biodiversity is crucial for the stability of ecosystems, as it contributes to resilience against environmental changes, supports ecosystem services such as pollination and nutrient cycling, and enhances the overall health of the planet.

Ecosystem resilience pertains to the ability of an ecosystem to recover from disturbances but does not specifically define the variety of life forms. Population density refers to the number of individuals of a particular species in a given area, and while it can provide some information about species, it does not encompass the full range of life present in an ecosystem. Species richness specifically refers to the number of different species in an area, but it is only one aspect of the broader concept of biodiversity, which also considers the abundance of species and the genetic variation within them. Thus, biodiversity is the most comprehensive term describing the variety of life in an ecosystem.