Radiation is the evolutionary process of diversification of a single species into multiple forms. It includes the physiological and ecological diversity within a rapidly multiplying lineage. There are many types of radiation including adaptive, concordant, and discordant radiation however escape and radiate coevolution does not always follow those specific types.
Ehrlich and Raven's original paper did not clearly answer why ecological escape leads to increased diversification, however several explanations have been proposed. Once a novel defense has been acquired, the attacking organism which had evolved adaptations that allowed it to predate is now up against a new defense that it has not yet been evolved to encounter. This gives the defending organism the advantage, and therefore time to rapidly multiply unopposed by the previously attacking organism. This ultimately leads to the physiological and ecological diversity within the rapidly multiplying lineage, hence radiation.