Final answer:
Ecosystem diversity refers to the variety of ecosystems on Earth and is the characteristic feature for the variety of organisms within an ecosystem.
Step-by-step explanation:
Species diversity refers to the number of different species in an ecosystem or on Earth as a whole. This is the commonest way to measure biodiversity. Genetic diversity refers to the variation in genes within all these species.
Ecosystem diversity refers to the variety of ecosystems on Earth. An ecosystem is a system formed by populations of many different species interacting with each other and their environment.
Therefore, the variety of organisms within an ecosystem is characteristic of ecosystem diversity.