  We study the spectrum of the QCD Dirac operator by means of the valence quark
mass dependence of the chiral condensate in partially quenched Chiral
Perturbation Theory (pqChPT) in the supersymmetric formulation of Bernard and
Golterman. We consider valence quark masses both in the ergodic domain ($m_v
\ll E_c$) and the diffusive domain ($m_v \gg E_c$). These domains are separated
by a mass scale $E_c \sim F^2/\Sigma_0 L^2$ (with $F$ the pion decay constant,
$\Sigma_0$ the chiral condensate and $L$ the size of the box). In the ergodic
domain the effective super-Lagrangian reproduces the microscopic spectral
density of chiral Random Matrix Theory (chRMT). We obtain a natural explanation
of Damgaard's relation between the spectral density and the finite volume
partition function with two additional flavors. We argue that in the ergodic
domain the natural measure for the superunitary integration in the pqChPT
partition function is noncompact. We find that the tail of the two-point
spectral correlation function derived from pqChPT agrees with the chRMT result
in the ergodic domain. In the diffusive domain we extend the results for the
slope of the Dirac spectrum first obtained by Smilga and Stern. We find that
the spectral density diverges logarithmically for nonzero topological
susceptibility. We study the transition between the ergodic and the diffusive
domain and identify a range where chRMT and pqChPT coincide.
