Life Cycles (HL) (DP IB Environmental Systems & Societies (ESS)) : Revision Note

Life Cycles of Different Species

• Every species has a life cycle that includes stages of growth, reproduction, and death

• Life cycles can vary greatly between species in terms of:

  • Reproductive behaviour

  • Lifespan

• Some species reproduce quickly with many offspring, while others invest heavily in fewer offspring to ensure their survival

r-strategists

• r-strategists are species that produce many offspring but provide little or no parental care

• These species tend to live in unstable or unpredictable environments

  • In these environments, the ability to reproduce quickly is an advantage

• For example, insects like flies or mosquitoes are r-strategists

  • They lay hundreds of eggs at once but do not care for them

• r-strategists are good at colonising new habitats or taking advantage of temporary resources

• They typically have short lifespans and their population size can fluctuate rapidly

• Rabbits are another example of an r-strategist

  • They reproduce quickly and in large numbers, making them well-suited to environments where food availability fluctuates

K-strategists

• K-strategists produce fewer offspring but invest more in their care to increase the survival rate

• These species tend to live in stable environments

  • In these environments, competition for resources is high

• For example, elephants are K-strategists

  • They produce one calf at a time and invest heavily in its care for years

• K-strategists generally have longer lifespans, stable populations, and thrive in mature ecosystems

• Oak trees are another example of K-strategists

  • They produce fewer seeds (acorns), but these seeds have a better chance of growing into mature trees due to the stable environment of a mature forest

  

Comparing r- and K-strategists

• r-strategists:

  • Many offspring

  • Little or no parental care

  • Short lifespan

  • Population size fluctuates

  • Adapted to unstable environments

  • Examples: bacteria, dandelions, some small mammals

• K-strategists:

  • Few offspring

  • High parental care

  • Long lifespan

  • Stable population size

  • Adapted to stable environments

  • Examples: humans, large mammals like whales and elephants

Succession and life cycles

• In early stages of succession, r-strategists tend to dominate because they can colonise quickly.

• As the environment stabilises and matures, K-strategists become more dominant due to their competitive advantage in resource-rich but stable environments

Human Impacts on Life Cycles

• Human activities, such as pollution, habitat destruction, and climate change, can have significant impacts on the life cycles of plants and animals

• Understanding a species' niche and its life cycle is important for identifying how humans affect these processes

Climate change and life cycles

• Climate change alters environmental conditions like temperature and rainfall patterns

  • This can affect species' life cycles

  • For example, warmer temperatures caused by climate change can lead to:

    • Earlier flowering in plants

    • Changes in migration patterns of birds

• Many species’ life cycles are synchronised with the seasons

  • For example, plants might flower in spring when pollinators like bees are most active

• If climate change causes this timing to shift, it can disrupt the relationship between species

  • For example, the pied flycatcher bird migrates to Europe in the spring to feed on caterpillars

    • If caterpillars emerge earlier due to warmer springs, the birds may arrive too late to find food, affecting their reproduction

  • Insects like butterflies rely on specific temperature ranges for development

    • Warmer temperatures can cause butterflies to emerge earlier in the season

    • This may lead to mismatches with the flowering of the plants they rely on for nectar

• The melting of Arctic sea ice due to global warming impacts the life cycles of polar bears

  • Polar bears rely on sea ice to hunt seals

  • With less ice, their hunting season shortens, reducing their fat reserves needed for reproduction and survival

Habitat destruction and life cycles

• Deforestation and urban expansion can disrupt the habitats that species rely on for parts of their life cycles, like breeding or feeding grounds

  • For example, sea turtles return to specific beaches to lay their eggs

    • However, these habitats are threatened by tourism and development, affecting their reproductive success

  • Destruction of wetlands impacts amphibians like frogs, which depend on these areas for breeding

Pollution and life cycles

• Pollution can directly affect the life cycles of species by damaging their health or the habitats they depend on

  • For example, pesticides used in agriculture can reduce insect populations

    • This impacts the life cycles of species that feed on them, like birds or bats

  • The use of neonicotinoid pesticides in agriculture affects the life cycles of bees

    • Exposure to these chemicals reduces their ability to forage and reproduce

    • This threatens populations of these pollinators that are crucial for many plant species, including crops for human consumption