Resource fragmentation hypothesis
Appearance
The resource fragmentation hypothesis was first proposed by Janzen & Pond (1975), and says that as species richness becomes large there is not a linear increase in the number of parasitoid species that can be supported. The mechanism for this hyperbolic relationship is suggested to be that each of the new host species are too rare to support the evolution of specialist parasitoids (Janzen & Pond, 1975).
References:
Janzen, D.H. & Pond, C.M. (1975) A comparison by sweep sampling of the arthropod fauna of secondary vegetation in Michigan, England, and Costa Rica. Transactions of the Royal Entomological Society of London, 127, 33-50.