Pollen riskers vs. seed riskers

Dryas octopetala
1 - Dryas octopetala (Rosaceae)
1 - Dryas octopetala (Rosaceae)
Ranunculus glacialis
2 - Ranunculus glacialis (Ranunculaceae)
2 - Ranunculus glacialis (Ranunculaceae)

Early and late flowering species

early or late flowering
Antennaria dioica
3 - Antennaria dioica (Asteraceae)
3 - Antennaria dioica (Asteraceae)
Silene suecica
4 - Silene suecica (Caryophyllaceae)
4 - Silene suecica (Caryophyllaceae)

Based on a study of flowering phenology in 137 arctic-alpine species, Molau (1993) proposed that plant reproduction in this life zone is associated with two opposing risks related to life history strategy.

  • A pollen risk strategy in early flowering species (too cold for pollinator visits, but sufficient time for seed maturation).
  • A seed risk strategy in late flowering species (safe pollination, but not enough time for seed maturation).

Molau found low fruit/flower and seed/ovule ratios in early flowering species and the opposite situation in late-flowering species (see Figure). In early flowering species seed set is low every year due to high abortion rate, and in late-flowering species seed set is reduced in some years because of climatic reasons.

The relationship between flowering phenology and breeding systems is particularly interesting. Early flowering is associated with breeding systems favoring high outbreeding, while late flowering species frequently are selfers or species with agamospermy and vivipary.

relative reproductive success
5 - The Relative reproductive success (product of fruit/flower and seed/ovule ratios) in three groups of subarctic-alpine plants species differing in flowering phenology (Molau 1993).