APES Notes 2.5 - Natural Disruptions to Ecosystems

Scientific concepts / discoveries / nature phenomena

Natural disturbance (definition)

A natural disturbance is a natural event that:

• Disrupts an ecosystem’s structure and/or function
• Can interrupt energy and matter cycling
• Can displace organisms and reshape or destroy ecosystems/habitats

Examples of natural disturbances

• Tornadoes
• Hurricanes
• Wildfires
• Asteroid impacts
  • Example given: an impact about 65 million years ago, linked to dinosaur extinction

Relative scale vs. human disturbance

Natural disturbances can be more destructive than many human-caused disturbances. For example:

• Human impacts such as clear-cutting/farming may be localized or gradual
• Large-scale natural events (e.g., asteroid impacts) can be globally catastrophic

Time scales of natural disturbances

Natural disturbances occur on different temporal patterns:

• Periodic: regular, predictable cycles

  • Example: wet/rainy seasons alternating with dry seasons (e.g., savannah regions)

• Episodic: relatively frequent but not strictly regular/predictable

  • Examples: hurricanes, droughts, fires
  • Seasonal likelihood: more fires in California summer than winter

• Random: unpredictable timing even if the mechanism is known

  • Examples: earthquakes, asteroid impacts

Natural climate change mechanisms (long time scales)

Earth’s climate varies due to natural (non-human) factors, including:

• Changes in Earth’s orbital eccentricity (distance from the Sun)

  • Approximate periodicity mentioned: every 100,000–400,000 years

• Variation in Earth’s axial tilt

  • Affects how sunlight is received differently by hemispheres

These cycles drive regular temperature shifts, such as:

• Ice ages
• Warmer periods

Natural variations in atmospheric CO₂ over long periods are attributed to:

• Ocean warming → oceans release/allow more CO₂ to accumulate in the atmosphere
• Increased plant growth → plants take up CO₂

Context for current CO₂ levels

The video emphasizes that although CO₂ has varied naturally, current CO₂ changes exceed anything seen in human history, motivating scientific concern about climate change (without diminishing the role of human-caused climate change).

Sea level rise (natural changes over geologic time)

Sea level fluctuates due to changing global temperatures:

• Warmer periods → polar ice cap melting → more water enters oceans
• Thermal expansion: warmer water expands, increasing ocean volume

A positive feedback loop is described:

• Higher CO₂ → warmer atmosphere/ocean
• Warmer ocean holds less CO₂ → releases more CO₂
• More CO₂ → additional warming → more ice melt

Implications for habitats from environmental change

Major environmental disturbances can cause habitat destruction, alteration, or loss, including:

• Sea level rise impacts on estuaries/coastal wetlands

  • Coastal estuaries become flooded
  • Estuaries can lose their brackish characteristics (salt + freshwater mix)
  • Species that require land–water transition zones are affected

• Habitat shift/squeezing

  • Salt marshes and mangroves may lose extent
  • Deeper water offshore can prevent them from migrating outward
  • Remaining habitat must shift toward land (if possible), otherwise it is reduced/removed

• Plant community changes due to reduced sunlight

  • Increased water depth reduces sunlight reaching aquatic plants
  • Some species cannot survive if submerged too deeply

• Coastal flooding removes terrestrial-edge ecosystem functions

  • Flooding inland reduces habitat components that terrestrial-dependent organisms rely on

Migration as a response to environmental disturbance

Species may migrate to track conditions such as rainfall, temperature, or food timing:

• Predictable migration example: wildebeest following rainfall across the Serengeti
• Temperature-driven range shifts: ocean species moving poleward/northward as waters warm
• Climate-change timing mismatch example: birds shifting breeding/migration earlier because
  • Caterpillar hatching dates advance with earlier spring warming
  • Birds must synchronize egg laying/hatching with peak food demand

Data/trends practice concept (first leaf timing vs. latitude)

A described map/graph uses first leaf date as a function of latitude:

• Dark orange: ~8 days earlier
• Dark blue: ~8 days later

The FRQ connection is to explain how distance from the equator/latitude correlates with phenology (leaf-out timing).

Listed researchers or sources featured

• No specific researchers, authors, or external sources are named in the subtitles provided.
• The only named individual is the presenter: Mr. Smeeds.