Which example illustrates commensalism and not mutualism?
a
hippo dung is eaten by a large species of catfish native to african lakes. the catfish typically follow the hippo herds.
b
cattle have protozoa living in their gut that digest cellulose. the cows are able to feed on grass, while the protozoa are sheltered inside the cow.
c
oxpeckers remove parasitic fly larvae from the skin of buffalo. in exchange, they are protected from predatory cats, who will not challenge a buffalo.
d
ants 'farm' aphid insects like cattle. aphids suck the sap out of trees, which ants also feed on. in turn, the ants sting predators that attack the aphids.