RELATIONSHIPS BETWEEN FLOWERING PHENOLOGY AND LIFE-HISTORY STRATEGIES IN TUNDRA PLANTS

Temperate plants show high correlations between life history strategies (e.g., along the r-K continuum), mating systems (in terms of pollen:ovule, seed: ovule, and fruit:flower ratios), and genetic population structure. In the tundra, nearly all plants would be categorized as being K-strategists if we use life history traits alone (life span, resource allocation patterns, etc.). However, there is immense variation among species with regard to reproductive traits, such as seed:ovule and fruit: flower ratios, and thus there is a decoupling of the relationships that are valid in other biota. Instead, the reproductive strategies of arctic and alpine plants show strong correlations with flowering phenology, and thereby also with snow cover duration. Early-flowering species show high outbreeding rates and low seed: ovule ratios, and most of the genetic variation is found within local populations; the opposite situation applies in late-flowering species. These two cases are the extremes of a continuum, but arctic plants can be as readily categorized in this model as temperate plants are in the r-K model. Gynodioecious and dioecious breeding systems are abundant only among early-flowering species, whereas apomixis and vivipary are restricted to the late-flowering species. The variation in ploidy levels among species increase from early- to late-flowering. According to the kind of bet-hedging with the resources spent on reproduction, the early- and late-flowering groups are recognized as pollen-risk and seed-risk strategists, respectively.