  We analyze the entanglement distribution and the two-qubit residual
entanglement in multipartite systems. For a composite system consisting of two
cavities interacting with independent reservoirs, it is revealed that the
entanglement evolution is restricted by an entanglement monogamy relation
derived here. Moreover, it is found that the initial cavity-cavity entanglement
evolves completely to the genuine four-partite cavities-reservoirs entanglement
in the time interval between the sudden death of cavity-cavity entanglement and
the birth of reservoir-reservoir entanglement. In addition, we also address the
relationship between the genuine block-block entanglement form and qubit-block
form in the interval.
