Light

Light is the energy source plants use for photosynthesis, and photosynthesis is, ultimately, the only source of energy for the entire ecosystem, since it can occur only in the presence of sunlight. Many small forest-floor plants -- herbs and shrubs that are constantly overshadowed by taller trees -- have adapted to photosynthesise efficiently even under the very low light levels that reach the forest floor. For animals as well, diurnal and seasonal variation in light intensity and duration (the photoperiod) provides important cues for timing foraging, reproductive and migratory activity. Because …