14. A computer program product for managing collaborations, the computer program product comprising: one or more computer-readable tangible storage devices, and program instructions stored on the storage devices, the program instructions comprising: program instructions to receive a request for collaboration on a topic; program instructions to identify, for a collaboration, a plurality of experts that have expertise in the topic, wherein at least two of the plurality of experts have a different one of a plurality of different threshold levels of a likelihood of participation in the collaboration, wherein the likelihood of participation in the collaboration is the percentage based estimation that the expert will participate in the collaboration based on a relative location of the expert to a collaboration site and whether the expert belongs to an organization hosting the collaboration, and wherein the plurality of experts are identified using a number of collections of information; program instructions to set the plurality of different threshold levels according to a level of expertise of the plurality of experts; and program instructions to identify particular experts of the plurality of experts that have a respective particular likelihood of participation that exceeds one of the plurality of different threshold levels.
14. A computer program product for managing collaborations, the computer program product comprising: one or more computer-readable tangible storage devices, and program instructions stored on the storage devices, the program instructions comprising: program instructions to receive a request for collaboration on a topic; program instructions to identify, for a collaboration, a plurality of experts that have expertise in the topic, wherein at least two of the plurality of experts have a different one of a plurality of different threshold levels of a likelihood of participation in the collaboration, wherein the likelihood of participation in the collaboration is the percentage based estimation that the expert will participate in the collaboration based on a relative location of the expert to a collaboration site and whether the expert belongs to an organization hosting the collaboration, and wherein the plurality of experts are identified using a number of collections of information; program instructions to set the plurality of different threshold levels according to a level of expertise of the plurality of experts; and program instructions to identify particular experts of the plurality of experts that have a respective particular likelihood of participation that exceeds one of the plurality of different threshold levels. 19. The computer program product of claim 14 further comprising: program instructions to send out a set of invitations for the collaboration to the particular experts.