  In this work we exhibit a new criteria for ergodicity of diffeomorphisms
involving conditions on Lyapunov exponents and general position of some
invariant manifolds. On one hand we derive uniqueness of SRB-measures for
transitive surface diffeomorphisms. On the other hand, using recent results on
the existence of blenders we give a positive answer, in the $C^1$ topology, to
a conjecture of Pugh-Shub in the context of partially hyperbolic conservative
diffeomorphisms with two dimensional center bundle.
