Chapter 3 Plant Life Histories: Of Birds and Bees
Seed Germination and Seedling Establishment
Annuals and Perennials
Seed dispersers as seed predators
Self-pollination and apomixis
Vegetative (clonal) reproduction
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.
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.
|Reproductive success (number of seedlings established) of perennial plants|
|Dry years||Moist years|
|Rodents present||very low||very high|