PARENTAL ENVIRONMENTAL-EFFECTS AND CYCLICAL DYNAMICS IN PLANT-POPULATIONS

Parental environmental effects have been widely reported in plants, bu t these effects are often weak relative to direct effects of current e nvironmental conditions. Few studies have asked when consideration of such effects is necessary to understand long-term plane population dyn amics. In this article, I show that inclusion of effects of parental d ensity on offspring mass fundamentally changes population dynamics mod els by making recruitment a function of population size in two previou s generations (Nt+1 = f(N-1, Nt-1)), rather than one (Nt+1 = f(N-t)). Models without parental density effects predict either stable populati on dynamics or sharp crashes from high to low population size (flip bi furcations). When parental effects are at least one-third the size of direct density effects, gradual cycles from high to low population siz e (Hopf bifurcations) are possible. In this study, I measured effects of parental and offspring density on offspring quality in an annual pl ant, Cardamine pensylvanica, by manipulating plant density independent ly in parent and offspring generations and by comparing the effects of parent and offspring density on offspring performance. Parental densi ty effects were detectable but were noticeably weaker than offspring d ensity effects. Nonetheless, the parental effect was large enough to c hange population dynamics predictions. Thus, parental effects may be a n important component of the numerical dynamics of plant populations.