Physical dormancy-break by predispersal insect seed predators and a discussion of insect x seed (bitrophic) interactions on population growth of legumes.

Physical dormancy can be broken in nature by insect seed predation. Bruchid beetles and various other insects are predispersal seed predators on physically-dormancy (PY) seeds, especially those of legumes (Fabaceae). Although many of the predated seeds are nonviable, some of them may be viable, nondormant and germinable. Our primary aim was to review the literature on the effect of predispersal seed predation on PY-break/germination in this bitrophic system. We found information on the bitrophic interactions between insects and seeds of 46 plant species in 43 "case studies". Seeds in 30 case studies had PY (mostly legumes), five were nondormant (ND) and in eight PY vs. ND was not determined because there was no intact seed control. In 16 of the 29 (55.2%) case studies in which seeds had PY, insect-infested seeds germinated to a higher percentage than intact (control) seeds, indicating that damage by insect seed predators broke PY. Thus, we conclude that predispersal seed predation by insects is a way in which PY is broken in nature. Further, we evaluate the possible demographic consequences of predispersal insect seed predation on legumes with PY seeds and conclude that they appear to have little or no effect of population growth (λ).