Natural Disruptions to Ecosystems (College Board AP® Environmental Science): Study Guide

Natural disruptions to ecosystems include events such as:

• Floods

• Volcanic eruptions

• wildfires

• Droughts

• Hurricanes

• Earthquakes and tsunamis

These disruptions can have both short-term and long-term environmental consequences

• Short-term impacts:

  • Immediate destruction of habitats

  • Displacement of organisms

  • Loss of biodiversity

  • Changes in food webs

  • Water shortages

• Long-term impacts:

  • Changes in species composition

  • Shifts in ecosystem structure, e.g. desertification

  • Potential extinctions

Natural disruptions can sometimes have environmental consequences greater than human-made disruptions

• Example: A volcanic eruption can release massive amounts of ash, particulate matter and gases—this can lead to short-term global cooling by reflecting sunlight, as well as long-term ecosystem impacts

Earth system processes occur on varying time scales and can be classified as:

• Periodic

• Episodic

• Random

Periodic processes:

• Occur at regular, repeated intervals, such as seasons or tidal cycles

• Example: Seasonal changes affect plant growth, animal behavior, and migration patterns

Episodic processes:

• Occur occasionally and irregularly but are still predictable, such as hurricanes or El Niño events

• Example: El Niño and La Niña occur every 2-7 years, affecting ocean temperatures and disrupting weather patterns globally

Random processes:

• Occur unpredictably, such as meteor impacts or unexpected volcanic eruptions

• Example: A meteor impact can cause mass extinction events, as seen with the Cretaceous-Paleogene extinction

Earth’s climate has experienced significant changes over geological time due to natural factors, including:

• Changes in solar radiation and Earth’s orbit (Milankovitch cycles)

• Volcanic activity releasing greenhouse gases and aerosols

• Natural variations in atmospheric composition, e.g. varying concentrations of atmospheric CO₂

• Changes in ocean circulation patterns

• Plate tectonics (continents drifting to different latitudes)

For example, the Ice Ages were periods of significant cooling caused by variations in Earth’s orbit and axis tilt

These natural changes have driven evolutionary adaptations and shifts in ecosystems over millions of years

Sea levels have fluctuated over geological time due to changes in:

• The shape and volume of the ocean basins

• The amount and volume of available water

• The amount of glacial ice on Earth

• Thermal expansion (as the oceans warm due to climate change, seawater expands)

• Coastal land subsidence (sinking)

During Ice Ages, sea levels were lower as water was locked in glaciers and sea ice

• In warmer periods, melting ice caused sea levels to rise

• Example: The last glacial maximum (about 20,000 years ago) saw sea levels approximately 120 meters lower than today

  • This exposes continental shelves and greatly altered habitats

The main reason for changes in sea level today is glacier and sea ice melts caused by global warming

• Rising and falling sea levels impact coastal ecosystems, altering habitat availability for species like mangroves and coral reefs

Major environmental upheavals, such as tectonic activity, climate change, or asteroid impacts, can cause widespread habitat changes

• Forests may transition into grasslands or deserts due to changes in temperature or precipitation

• Aquatic ecosystems may shift due to changes in salinity, water levels, or nutrient availability

Habitat changes force species to adapt, migrate, or face extinction

Organisms migrate for both short- and long-term reasons

• These migration often occur in response to natural disruptions

Short-term migrations:

• Triggered by seasonal changes

  • Example: Birds migrating to warmer regions during winter to find food, breeding partners and suitable habitats

• Triggered by immediate environmental factors (e.g. natural disasters)

  • Organisms escaping natural disasters and the effects of these events on their habitats

• Triggered by food or water shortages

Long-term migrations:

• Driven by gradual habitat changes over time, such as desertification or sea level rise

• Example: Polar bears moving farther inland in search of food as Arctic ice melts due to climate change

  • This shift leads them to develop new hunting strategies instead of their traditional reliance on seals

  • As their natural habitat diminishes, polar bears increasingly encroach on human settlements, scavenging for food in garbage dumps and posing challenges to local communities

Migration plays a critical role in species survival by allowing organisms to:

• Find new resources

• Avoid unfavorable conditions