Climate Change: Phenology (HL) (HL IB Biology)

• The impact of climate change can be assessed by studying events that occur in nature
• One field of study that can allow this kind of research is that of phenology, which can be defined as

The study of the timing of biological events

• Examples of such biological events include
  • Migration
  • Egg laying
  • Flowering
  • Hibernation

Phenology: deciduous trees

• The effect of environmental factors on the timing of events such as bud setting, bud bursting, and flowering can be studied
  • Bud setting is the process of leaf and flower bud development
  • Bud bursting is the process by which buds unfold, and results in new leaves and flowers
  • A tree is said to be flowering when flower buds have burst
• The timing of the processes described above is crucial to the reproductive success of trees
  • Trees that rely on animal pollinators, such as insects, need to time flowering to coincide with the emergence of their pollinators
  • Trees that use other mechanisms, such as wind or water, may be reliant on the weather, tides, or river volume, which may also be seasonal

Phenology: bird migration & nesting

• Birds migrate to different parts of the world at different times of year; this ensures that temperatures are suitable, and that they have enough resources all year round; it is essential that birds carry out their migration journeys at the right time of year
  • The weather during the migration journey needs to allow birds to reach their new habitat
    • E.g. storms at certain times of year may blow birds off course
  • Birds that migrate too early may find that the environmental conditions are not suitable, or that resources are not yet available, when they reach their destination
  • Birds that migrate too late may find that nesting sites are all taken, or that there are no mates available
• Birds need to nest and lay their eggs at the right time of year so that chick hatching coincides with resource availability
  • Birds often rely on insect larvae, such as caterpillars, which in turn rely on leaf bud bursting for their food; all of these factors are connected, and contribute to functional food webs

CC BY-SA 3.0, via Wikimedia Commons

CC BY-SA 4.0, via Wikimedia Commons

Events such as bud bursting (left) and chick rearing (right) must happen at the right time of year in order for ecosystems to function

• Climate change can disrupt the timings of biological events
  • Environmental cues may no longer function as they should, e.g.
    • Temperature may be different to previous years
    • Day length, known as photoperiod, may not coincide with events that may have occurred in the past
• If events do not occur at the right time, species will be left without the resources that they need, and food chains will be disrupted
  • Trophic levels may be missing from the food chain
  • This is known as a trophic mismatch

Arctic mouse-ear chickweed & migrating reindeer

• Reindeer are migratory mammals, and they rely on day length as the environmental cue for seasonal migration
• Arctic mouse-ear chickweed is a plant that forms part of the diet of reindeer; its peak productivity is determined by temperature signals
• The reindeer migration is unaffected by climate change, but the availability of food that allows them to breed and raise young is affected by climate change; this mismatch between migration timing and resource availability can affect the ability of reindeer to breed successfully

Great tits & caterpillars

• Great tits are small birds that often feed on insects; they are especially dependent on caterpillars for feeding their young during breeding
  • The great tits need the greatest biomass of caterpillars around 9 days after their chicks hatch
• While both great tit egg hatching and caterpillar availability are determined by temperature cues, the disruptive effect of global warming on caterpillars appears to be stronger than that on great tits, with caterpillar biomass peaking around 2 weeks earlier and egg hatching peaking around 1 week earlier as a result of global warming
• This results in a temporal mismatch between peak need and peak food availability, reducing the breeding success of the great tits
  • Temporal = related to time

Phenology mismatch diagram

Data from the study of great tit and caterpillar populations shows that global warming has caused a temporal mismatch between peak caterpillar biomass and peak feeding needs of great tit chicks

Climate change and the spruce bark beetle

• Spruce bark beetles are insects that lay their eggs under the bark of spruce trees and other coniferous tree species; they occur in Europe and North America
• The beetles feed and mature under the bark of the trees, causing damage and sometimes killing the trees when high numbers of beetle larvae are present
  • Eggs hatch into larvae which feed from tree phloem and other tissues
  • Larvae pupate into adult beetles
  • Beetles emerge from the bark and the cycle repeats
• The life-cycle of the beetles can occur once or twice each year; this is determined by temperature
• Global warming has increased the number of life cycles completed each year; higher temperatures mean that two life cycles are more likely to occur
• This increases the size of the beetle population and means that trees are subject to the damaging larvae twice each year; this increases the chance of tree death

CC BY 3.0, via Wikimedia Commons

Spruce bark beetles can kill trees, partially or completely killing areas of coniferous forest; global warming makes tree death more likely