1. Symbiosis Commensalism

2. A titan triggerfish creates feeding opportunities for smaller fish by moving large rocks too
big for them to shift themselves.
http://upload.wikimedia.org/wikipedia/commons/thumb/c/ca/Titan_Tr
iggerfish.jpg/220px-Titan_Triggerfish.jpg

3. Barnacles benefit by having a place to stay, leaving the scallop presumably unaffected.
http://upload.wikimedia.org/wikipedia/commons/thumb/5/51/Barnacles_in
_tidepools.JPG/220px-Barnacles_in_tidepools.JPG

4. This one relates?
http://www.cartoonstock.com/newscartoons/cartoonists/cga/lowres/cgan2240l.jpg