A expressão “its host” está substituindo:

                               TEXTO I

      Ecology and History of the Amazon Rain Forest

Biodiversity and Symbiosis of South America's Vulnerable Habitat 

No place on Earth is as full of diverse life and landscape as the Amazon Rainforest. It spreads its tall trees and rich biodiversity over 40% of the South American continent. The Amazon River shares its name with its host, and is 11 times the volume of the Mississippi river. The massive water system begins in the Andes Mountains and winds its way 4,080 miles eastward to the Atlantic Ocean, rushing through the forests with tremendous force. The annual outflow of the river is responsible for 1/5 of the entire world’s freshwater flow. Everything about this habitat is super-sized.

(http://www.suite101.com/content/lungs-of-the-earth-a55287)