Chapter 3 Plant Life Histories: Of Birds and Bees

Chapter Outline

Introduction
Seed Germination and Seedling Establishment
   Seed dormancy
      Mechanisms
      Seed banks
   Seedling establishment
      Nurse plants
Annuals and Perennials
   Ephemerals (annuals)
   Perennials
      Iteroparous reproduction
      Semelparous reproduction
Pollination
   Wind pollination
   Animal-mediated pollination
Seed Dispersal
   Safe sites
   Seed dispersers as seed predators
   Dispersal distances
Reproductive Options
   Pliant flowering
   Self-pollination and apomixis
   Vegetative (clonal) reproduction

Web Resources

Desert in Bloom provides information about the wildflower season and desert wildflower blooming. From Desert USA.

Yucca and Its Moth explores the remarkable relationship between the yucca and yucca moth. From Wayne's Word.

Study Questions

1. Seed dormancy is particularly common in the desert. a) Why might seed dormancy be particularly advantageous in the desert? b) Describe two dormancy mechanisms used by desert plants. Include how dormancy is broken and how the dormancy enhances fitness.   

2. Pake and Venable studied seed banks in the Sonoran Desert and in their discussion state "Risk (of seed mortality) can be lowered either by having large seed size, and thereby a lower variance in reproductive success of germinating seeds, or by having a large seed bank (of small seeds) and thereby buffering against high variance in per-capita reproductive success of germinating seeds." Explain this statement including why one of these strategies is more common than the other in desert environments.

3. Consider the reproduction of saguaro. Link the following ideas together: fruit eating birds; safe sites; and nurse trees. Include in your answer the definition of safe sites and nurse trees.

4. Compare and contrast the growth and survival strategies of desert annuals and herbaceous perennials.

5. On the surface it would seem that semelparous perennials would be at a disadvantage in the desert yet they do occur alongside their iteroparous competitors. Explain how it is that the semelparous strategy might persist in the desert.

6. Compare and contrast the floral characteristics of wind-pollinated and animal-pollinated flowers. Speculate why it is that animal pollination is more common in the desert.

7. Flowering in the unpredictable desert environment can be risky. Describe the options plants have to help ensure at least some success even when disaster strikes.

8. Reynolds measured plant reproduction in plots where rodents were excluded as well as in control plots where rodents were present. The effect of rodents on the reproductive success of perennial plants was different in dry versus wet years (see table below). Explain these results.