Ecosystem 

A biological community of interacting organisms and their physical environment. 

Keystone Species 

 A species on which other species in an ecosystem largely depend, such that if it were removed the ecosystem would change drastically. 

Producer 

an organism, either a green plant or bacterium, which is part of the first level of a food chain

Predator

are wild animals that hunt, or prey on, other animals.

Pneumatocystin

gas-containing lesions of unknown etiology.