IB Biology D4.3 Notes

Phenology

Phenology is the study of seasonal changes in plants and animals and how they are influenced by seasonal cues. Many biological phenomena synchronise with day length (photoperiodism) or temperature change, such as:

1. Bud burst
2. Bud set
3. Flowering
4. Dormancy 

These events must align with other biotic and abiotic ecosystem occurrences to coincide with seasonal light and warmth for growth, pollination and seed dispersal. Additionally, the migration of animals and birds and bird nesting must also be carefully timed to coincide with availability of resources.

However, the timing of biological events is being changed due to global warming. As such timings are often interlinked between species, disruption to one species will influence another.

If for example, growth or budding of a particular species needs to occur at a specific time, when a particular breeding animal species relies on that food source, such disruption will impact that. Timed events can become unsynchronised when warmer temperatures bring one set of events in one species forward, but a second species uses photoperiods uninfluenced by climate change.

There are three particular examples to remember:

1. The great tit - this is a bird that feeds on caterpillars, a great energy source needed to raise their chicks. Climate change has pushed peak caterpillar growth and populations forward, mismatching the peak caterpillar supply as a food source for great tits and chick hatching. As a result, a higher rate of unsuccessful breeding is occurring, decreasing the population of the great tit. Models predict that a 24-day mismatch between peak caterpillar supply and chick hatching could lead to local extinction of the great tit.
2. In the northern tundra, reindeers migrate in late spring to their feeding grounds. Here they feed on herbs and local vegetation. The cue for this is day length and so this is consistent from year to year. However, their main food source, Arctic mouse-ear chickweed is temperature sensitive and thus when it becomes too warm, it dies and no longer appears when the reindeer arrives, creating a mismatch.
3. Spruce bark beetles have life cycles that span two years. They lay eggs in the tree bark in June. These hatch as larvae and within a month they start consuming the spruce. Soon after they pupate and re-emerge the following spring as adults. The cue for their emergence is an ambient temperature of 16°C. When summers are warmer, spruce bark beetles compress their life cycle from 2 years to 1 year. Ultimately climate change is increasing the damage done by such insects. The shortened life cycles of the beetles mean more beetles are reproducing, increasing population numbers. Normal predator–prey systems which afford the trees time to regenerate in between population bursts are being disrupted.