Answer:
Conservationist
Step-by-step explanation:
What is a conservationist?
A person who advocates or promotes conservation, especially of natural resources
What is a abolitionist?
- Especially prior to the Civil War, a person who advocated or supported the abolition of slavery in the U.S. 
 - A person who favors the abolition of any law or practice deemed harmful to society
 
What is a federalist?
Adjective:
- Pertaining to or of the nature of a union of states under a central government distinct from the individual governments of the separate states, as in federal government; federal system
 - Of, relating to, or nothing such a central government
 
Noun:
- An advocate of federation or federalism
 - A federalist
 
What is a optimist?
- An optimistic person
 - A person who holds the belief or the doctrine of optimism 
 
Optimism is usually defined as:
A disposition or tendency to look on the more favorable side of events or conditions and to expect the most favorable outcome.