  We derive, by means of an extended Gutzwiller wavefunction and within the
Gutzwiller approximation, the phase diagram of the Kondo lattice model. We find
that generically, namely in the absence of nesting, the model displays an
$f$-electron Mott localization accompanied by a discontinuous change of the
conduction electron Fermi surface as well as by magnetism. When the non
interacting Fermi surface is close to nesting, the Mott localization
disentangles from the onset of magnetism. First the paramagnetic heavy fermion
metal turns continuously into an itinerant magnet - the Fermi surface evolves
smoothly across the transition - and afterwards Mott localization intervenes
with a discontinuous rearrangement of the Fermi surface. We find that the
$f$-electron localization remains even if magnetism is prevented, and is still
accompanied by a sharp transfer of spectral weigth at the Fermi energy within
the Brillouin zone. We further show that the Mott localization can be also
induced by an external magnetic field, in which case it occurs concomitantly
with a metamagnetic transition.
