Struggle to survive in desert heat (3,4)
I believe the answer is:
rat race
'struggle to survive' is the definition.
(I've seen this before)
'desert heat' is the wordplay.
'desert' becomes 'rat' (abandon treacherously).
'heat' becomes 'race' (I've seen this in another clue).
'rat'+'race'='RAT-RACE'
'in' acts as a link.
(Other definitions for rat race that I've seen before include "Competitive struggle for wealth or power" , "Continual routine of highly competitive activity" , "keen contest" , "constant effort to get ahead" , "The struggle for success" .)