Mutualism between grasses and grazers: an evolutionary hypothesis

Grasses and grazers have evolved mutualism to an extent that one group would not have been possible without the other. The recent discovery (Dyer 1980) that saliva produced by grazers stimulates grass growth is interpreted as a mutualistic adaptation by which both grass and grazer benefit. Other such adaptations include a basal meristem which is out of reach of most grazers, high palatability of grass leaves and shoots and vegetative reproduction, all of which, we suggest, are responses to selection by grazers and which increase the fitness of individual grass plants. Grazers and grasses evolved together in the Miocene. Selection pressure from grazers has produced large, long-lived grasses which are completely adapted to grazing. Grasses do not "defend" themselves from grazers; rather they encourage them, possibly also regulating the level of consumption.