  The BCS to BEC evolution has been recently the focus of studies in
superconductors and cold atomic gases. For a d-wave system, we show that a
Lifshitz transition occurs at a critical particle density which separates two
topologically distinct phases: a BCS-like gapless superconductor/superfluid in
the higher density limit and a BEC-like fully gapped superconductor/superfluid
in the lower density limit. This transition is second order according to
Ehrenfest's classification, but it occurs without a change in the symmetry of
the order parameter, and thus can not be classified under Landau's scheme. To
illustrate the nature of the transition, we compute the compressibility and the
superfluid density as functions of particle density.
