  We study spectral statistics in systems with a mixed phase space, in which
regions of regular and chaotic motion coexist. Increasing their density of
states, we observe a transition of the level-spacing distribution P(s) from
Berry-Robnik to Wigner statistics, although the underlying classical
phase-space structure and the effective Planck constant remain unchanged. This
transition is induced by flooding, i.e., the disappearance of regular states
due to increasing regular-to-chaotic couplings. We account for this effect by a
flooding-improved Berry-Robnik distribution, in which an effectively reduced
size of the regular island enters. To additionally describe power-law level
repulsion at small spacings, we extend this prediction by explicitly
considering the tunneling couplings between regular and chaotic states. This
results in a flooding- and tunneling-improved Berry-Robnik distribution which
is in excellent agreement with numerical data.
