A quantitative approach to the sexual reproductive biology and population structure in some arctic flowering plants: Dryas integrifolia, Silene acaulis and Ranunculus nivalis

Abstract

The population ecology of three species in northwest Greenland (Dryas integrifolia, Silene acaulis and Ranunculus nivalis) was studied in two consecutive seasons. Flowering phenology, population structure, flowering biology (including numbers of pollen grains per anther, germinated pollen grains per stigma, ovules per gynoecium, seeds per fruit), pollination and insect activity were the main features investigated.
 They were related to the micro- and macroclimatic conditions.
 The results can be summarized as follows:
 
 The unpredictability of the quality and length of the growing season makes the success of the reproductive cycle (i.e. production of mature seeds) very uncertain.
 There are seedlings at the studied sites of the three species.
 Most of the seedlings disappear.
 Population structure results indicate that seedlings become established in at least some years, but input of new individuals is episodic.
 Of the three species studied, R. nivalis allocates most resources to reproduction.
 Percentage normal pollen varies mostly between plants, less between days and sites (D. integrifolia).
 All three species are self-compatible.
 Full seed set is obtained only after insect visits.
 In S. acaulis seed set may be limited by the number of pollen grains reaching the stigmas.
 The flowers provide food (pollen and nectar) for the insects. They also provide shelter, warmth, and a mating place for them.
 There are sufficient insect visits per flower to ensure seed set, except possibly in S. acaulis.
 About 1 % of total pollen grain production is found as germinated pollen grains on stigmas.
 The utilization of pollen and stigmas varies between the three species. R. nivalis is the most efficient, whereas D. integrifolia is the most extravagant.
 A cold and rainy summer in 1976 resulted in conspicuously lower seed set in 1977 in spite of the latter summer being comparatively dry and warm.
 A 'reproductive budget' quantifying the various steps in the reproductive cycle is presented.