Variation in generation time in Frasera speciosa (Gentianaceae), a long-lived perennial monocarp
- 68 Downloads
The perennial monocarp Frasera speciosa (Gentianaceae) flowers at a wide range of sizes and ages with consequent variation in generation time (T), net replacement rate (Ro) and intrinsic rate of increase (r). Values of r were calculated for hypothetical cohorts composed of individuals flowering at the same age. Maximum rates of r are achieved by plants which flower at the earliest possible age. Although older plants produce more flowers, this increase is not sufficient to compensate for the effect of increased T on r. Few plants in each population flower at the youngest possible age, and for the majority reproduction is delayed, generation times are longer and r lower than achieved by plants flowering at younger ages. Delayed reproduction may be favored by greater seed set, due to pollinator attraction to larger flower stalks, as well as broader seed dispersal which could increase the probability of seedling establishment. Delays greater than those observed may be selected against by decreasing probability of survival, a decrease in the rate of addition of flowers with increasing size, and slower transitions between leaf number classes in larger plants. Staggered reproduction by an individual's offspring, whether environmentally or genetically determined, has the effect of insuring survival in an environment with high variability in pollinator effectiveness (see d set), germination, and seedling establishment.
KeywordsGeneration Time Seed Dispersal Seedling Establishment Number Class Leaf Number
Unable to display preview. Download preview PDF.
- Beattie A, Breedlove DE, Ehrlich PR (1973) The ecology of the pollinators and predators of Frasera speciosa. Ecology 54:81–91Google Scholar
- Ehrlich PR, Breedlove DE, Brussard PF, Sharp MA (1972) Weather and the “regulation” of subalpine populations. Ecology 53:243–257Google Scholar
- Harper JL (1977) Population biology of plants, Academic Press: New York p 892Google Scholar
- Lewontin RC (1965) Selection for colonizing ability. In: HG Baker and GL Stebbins (eds) The genetics of colonizing species. Academic Press: New York p 77–94Google Scholar
- May RM (1976) Estimating r: a pedagogical note. Am Nat 110:496–499Google Scholar
- Pelton J (1956) A study of seed dormancy in eighteen species of high altitude Colorado plants. Butler University Botanical Studies 13:74–84Google Scholar
- Schaffer WM (1974) Optimal reproductive effort in fluctuating environments. Am Nat 103:783–790Google Scholar
- Schaffer WM, Schaffer MW (1977) The adaptive significance of variations in reproductive habit in Agavaceae. In: B. Stonehouse and C Perrins (eds) Evolutionary ecology, University Park Press: Baltimore p 261–276Google Scholar
- Stearns SC (1976) Life history tactics: a review of the ideas. Q Rev Biol 51:3–47Google Scholar
- Stearns SC (1977) The evolution of life history traits. Ann Rev Ecol Syst 8:145–171Google Scholar