Apical Dominance and the Simulation of Metapopulation Dynamics in Lycopodium annotinum

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Abstract
Individual branched systems of the modular plant Lycopodium annotinum L. were studied in Swedish Lapland. Survival and fecundity of horizontal modules varied with module age and the health of the apical growing points. The negative relationship found between survival and reproduction is explained as the effects of released dominance, since more daughter-modules are generally produced behind dead, or dying apices than behind living apices. Apical dominance also controlled the size of sub-dominant modules. Behind an unhealthy main dominant apex, the closest daughter-module to be produced was always horizontal. It is suggested that this increases the possibilites for the continuation of the life of the plant, since differentiation into only vertical modules would terminate the growth of the axis. When the main apex dies, opportunistic branching occurs and widens the potential zone of exploitation, thereby increasing the chance of survival of the plant. Simulations of age-class distributions of horizontal modules using transition probability matrices showed that the stable age class distributions coincides with that found in the field, except for the younger age classes. This may be due to the difficulties in identifying young horizontal modules in the field. The survivorship of horizontal modules shows a Deevey type II curve, characteristic of perennial plant species. An elasticity analysis indicated that survival is more important than fecundity in determining population growth rate.