D4.3.9 Phenology as research into the timing of biological events (HL) Notes

Phenology as Research into the Timing of Biological Events

1. Imagine walking through a forest in early spring.
2. The trees are bare, but tiny buds are beginning to swell.
3. Birds are returning from migration, and flowers are starting to bloom.
4. These events are not random they are carefully timed to align with environmental cues like day length and temperature.
5. This study of the timing of biological events is called phenology.

What is Phenology?

1. The study of the timing of seasonal biological events, such as flowering, migration, and leaf fall.
2. Phenology helps us understand how organisms interact with their environment and how these interactions are changing due to climate change.

Key Variables Influencing Biological Events

1. Photoperiod (Day Length)

1. Photoperiod refers to the length of day and night over the course of the year.
2. It is a key environmental cue for many organisms, helping them time their biological events, especially in temperate and boreal regions.

Effect on Flowering in Deciduous Trees

1. Deciduous trees use changes in photoperiod to time events like flowering and budburst.
2. As the days lengthen in spring, trees "sense" the longer photoperiods and begin the processes needed to break dormancy, including flowering.
3. In fruit trees like apples and cherries, a longer photoperiod can trigger flowering, ensuring that the flowers are produced at a time when conditions are optimal for pollination.

Effect on Bird Migration and Nesting

1. Many bird species, such as the Eastern European Swallow, rely on photoperiod to time their migration.
2. As the photoperiod shortens in the fall, birds instinctively prepare for migration to warmer climates.
3. The lengthening of days in spring triggers the birds to return to their breeding grounds and initiate nesting.
4. If photoperiod cues are disrupted, it could lead to mistimed migration and breeding, with potentially negative impacts on reproductive success.

2. Temperature Patterns

1. Temperature is another crucial variable in phenology.
2. The timing of temperature fluctuations can influence everything from the blooming of flowers to the hatching of eggs in birds.

Effect on Flowering in Deciduous Trees

1. Temperature plays a critical role in budburst and flowering of deciduous trees.
2. In temperate regions, trees rely on a period of cold dormancy during winter (called vernalization) to prepare for spring growth.
3. Once temperatures rise above a certain threshold, buds begin to burst open, and flowers bloom.
4. Warmer temperatures due to climate change may cause these events to occur earlier in the spring, disrupting the synchrony between flowering and pollination.

Effect on Bird Nesting

1. Birds also use temperature patterns to time their nesting.
2. Warmer temperatures in spring can cause birds to start nesting earlier. However, if temperatures rise too early or too rapidly, it may lead to a mismatch between the timing of food availability (such as insects) and the needs of the chicks.
3. This mismatch can result in poor survival rates for offspring.