Subject: Why is asexual reproduction common in Angiosperms but not Chordates

A student came up with this in a lesson on cloning! Most angiosperms appear to 
reproduce both sexually and asexually with the sexual reproduction providing 
genetic variety and the asexual enabling them to colonise favourable 
environments and acting as a "backup" if not pollinated. (Most) Chordates and 
most other animals appear exclusively sexual although Aphids & Daphnia seem to 
be a bit "plant like" in their reproductive strategy. So why are such dual 
strategies rare in animals? It could be argued that some animal populations 
such as top predators can be highly dispersed which could make finding a mate 
difficult. It might also be argued that plants may have more "need" of genetic 
variation because they cannot move to a more favourable environment though 
animals may be able to. The more I thought about the student's question the 
better it seemed - so I am asking you, "Why is asexual reproduction  rare in 
animals and particularly the Chordates but common in plants alongside sexual 
reproduction?"

Re: Why is asexual reproduction common in Angiosperms but not Chordates