  The ground and first excited 0+ states of the {156-172}Er isotopes are
analyzed in the framework of the generator coordinate method. The shape
parameter beta is used to generate wave functions with different deformations
which together with the two-quasiparticle states built on them provide a set of
states. An angular momentum and particle number projection of the latter spawn
the basis states of the generator coordinate method. With this ansatz and using
the separable pairing plus quadrupole interaction we obtain a good agreement
with the experimental spectra and E2 transition rates up to moderate spin
values. The structure of the wave functions suggests that the first excited 0+
states in the soft Er isotopes are dominated by shape fluctuations, while in
the well deformed Er isotopes the two-quasiparticle states are more relevant.
In between both degrees of freedom are necessary .
