bottom-feeder vs scavenger

bottom-feeder and scavenger both are nouns.

Word	Noun	Adjective	Verb	Adverb
bottom-feeder	Yes	No	No	No
scavenger	Yes	No	No	No

As nouns, scavenger is a hypernym of bottom-feeder; that is, scavenger is a word with a broader meaning than bottom-feeder:

bottom-feeder: a scavenger that feeds low on the food chain
scavenger: any animal that feeds on refuse and other decaying organic matter

bottom-feeder (noun)	scavenger (noun)
a fish that lives and feeds on the bottom of a body of water	any animal that feeds on refuse and other decaying organic matter
a scavenger that feeds low on the food chain	someone who collects things that have been discarded by others
	a chemical agent that is added to a chemical mixture to counteract the effects of impurities