Dispersal enhances reproductive fitness in several ways.

With the evolution of the multicellular sporophyte generation, land plants were able to make many spores and disperse them across large distances on land. Dispersal is one of the most important stages in a plant’s life cycle. To understand why, imagine what would happen if a plant’s spores (or seeds) simply dropped straight down onto the ground below the parent plant. All the plant’s offspring would then attempt to grow in a very small space that might contain enough nutrients and light for only a few to establish themselves. In contrast, offspring dispersed by wind or other means are more likely to settle in a spot where they will not be forced to compete with closely related individuals for resources.

In addition, dispersal allows offspring to avoid pathogens and parasites. Viruses and bacteria travel easily from individual to individual in a densely packed population. An individual that settles away from the parent plant is less likely to encounter a pathogen. Finally, dispersal allows offspring to colonize new habitats. The evolution of new structures to enhance dispersal on land is a major theme in plant evolution.

Quick Check 1 In what ways are spores similar to gametes, and in what ways do spores and gametes differ?

Quick Check 1 Answer

Both spores and gametes are unicellular and haploid. Gametes are short-lived and require hydration; they are capable of fusing only with another gamete. In contrast, spores can be long-lived and can survive exposure to air because of the presence of sporopollenin, a tough, resistant covering that allows spores to withstand environmental stresses such as ultraviolet radiation and desiccation. A spore, once dispersed, can grow into a new individual.