Animals that chew tubers (6)
I believe the answer is:
brutes
'animals' is the definition.
('brute' can be a synonym of 'animal')
'chew tubers' is the wordplay.
'chew' indicates an anagram (I've seen 'chewed' mean this).
'tubers' is an anagram of 'BRUTES'.
'that' acts as a link.
(Other definitions for brutes that I've seen before include "Savagely violent men or animals" , "Savages" , "Animals other than humans (6)" , "Beasts" .)