Desert lizard is an ectotherm (poikilotherm) whose body temperature varies according to environmental temperature. So at 15ºC T(L) will fall due to fall in T(M) While mouse is an endotherm (Homeotherm) whose body temperature remains constant always due to variation is metabolic rate In homeotherms metabolic rate is inversely proportional to environmental temperature. So at 15ºC T(M) remain same and M((M) will increased.