Environment & Ecology · Environment

With reference to ecology, consider the following species: I. Sea otter is regarded as a keystone species in kelp forest ecosystems. II. Beaver is regarded as a keystone species because it significantly modifies habitat through dam-building activity. III. Water hyacinth is regarded as a keystone species in freshwater ecosystems. IV. Indian star tortoise is generally recognised as a keystone species in its ecosystem. V. Certain starfish species (e.g., Pisaster ochraceus) have been cited as keystone species in marine ecosystems. How many of the statements given above are correct?