  The rate of phase-space exploration in the decay of isovector and isoscalar
giant quadrupole resonances in $^{40}$Ca is analyzed. The study is based on the
time dependence of the survival probability and of the spectrum of generalized
entropies evaluated in the space of 1p-1h and 2p-2h states. If the 2p-2h
background shows the characteristics typical for chaotic systems, the isovector
excitation evolves almost statistically while the isoscalar excitation remains
largely localized, even though it penetrates the whole available phase space.
