Used domain here is Animals, and in Forest there will be other animals along with lions.
Ax(p(x)->q(x)) it means, for all x, if x is a lion then he is fierce.
Ax(p(x) AND q(x)) it means for all x, every x is lion and he is fierce.
But every x is not lion in the forest, there are other animals also. hence we need to say if x is lion then he is fierce.