A resource budget model to explain intraspecific variation in mast reproductive dynamics

Ecological research 23: 3-10.

Abstract

Rowan, Sorbus aucuparia L., exhibits conspicuous geographic variation in inter-annual patterns of reproduction across southern Norway. Along the southern west coast trees flower and produce clusters of succulent berries every other year, while in the east trees mast every three years. We investigate two hypotheses for this variation: local adaptation to environmental conditions that favors different reproductive schedules at different locations or variation arising from a single stereotyped reproductive strategy in the face of a geographic variation in productivity. To assess the theoretical plausibility of each of these hypotheses, we develop a refined resource budget model for mast reproduction. The refined model assumes that there is a lower bound on the amount of resource that may be allocated to reproduction, which allows to predict relation between reproductive schedules and productivity. From the analysis of the model, we found that the observed geographic transition in rowan mast is caused either if productivity in the east is smaller than that in the west or if plants in eastern populations have evolved to pause reproduction until energy reserves are replenished to higher levels. The prediction by the productivity gradient hypothesis matched with the empirical finding that the productivity is in fact likely to be smaller in the east than the west, although we lack empirical data to test the likelihood of the local adaptation hypothesis. There is a need for experimental studies to clarify the validity of the local adaptation hypothesis.

Key words: masting, mast seeding, geographic variation, local adaptation, productivity, reproductive allocation, life history.