Rhinanthus minorL. is an annual grassland hemiparasite often found where other annuals are rare or absent. In addition to its invasive abilities,R.minorhas other characteristics seldom found in annuals: virtual lack of a seed bank; few seeds per plant; seeds too big to be readily dispersed under natural conditions; and a Deevey type I or II survivorship curve. A combination of correlative and experimental studies was performed to investigate the variables influencing fecundity and survivorship inR.minor. Fecundity is positively correlated with surrounding vegetation biomass and negatively withR.minordensity. Survivorship is negatively correlated with surrounding vegetation biomass and withR.minordensity. Presumably,R.minoris an effective invader in relatively unproductive grassland because its finite rate of increase is a nonlinear function of the biomass of the surrounding vegetation, being maximized when the surrounding vegetation is dense enough to allow effective root parasitism (increasingR.minorfecundity) but not so dense that youngR.minorplants are outcompeted for light (decreasingR.minorsurvivorship).
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