We consider a smooth area-preserving Anosov diffeomorphism
$f\colon \mathbb T^2\rightarrow \mathbb T^2$
homotopic to an Anosov automorphism L of
$\mathbb T^2$
. It is known that the positive Lyapunov exponent of f with respect to the normalized Lebesgue measure is less than or equal to the topological entropy of L, which, in addition, is less than or equal to the Lyapunov exponent of f with respect to the probability measure of maximal entropy. Moreover, the equalities only occur simultaneously. We show that these are the only restrictions on these two dynamical invariants.