Lecture Notes: Natural Disruptions to Ecosystems

Objective

• Explain how natural disruptions impact ecosystems and habitats (short-term and long-term).
• Practice the skill of describing trends and data.

Natural Disturbances

• Definition: Natural events disrupting the structure/function of ecosystems.
  • Interrupt energy and matter cycling.
  • May displace organisms.
  • Can reshape or destroy ecosystems or habitats.
• Examples: Tornadoes, hurricanes, fires, asteroid impacts.
• Natural disturbances can be more significant than human-caused disturbances (e.g., asteroid impact 65 million years ago).

Time Scales of Natural Disturbances

• Periodic Events: Occur with regular frequency (e.g., wet/dry seasons on savannahs).
• Episodic Events: Occur frequently but irregularly (e.g., hurricanes, droughts, fires).
• Random Events: Unpredictable timing (e.g., earthquakes, asteroid strikes).

Natural Climate Change

• Causes:
  • Slight changes in Earth's orbit and tilt—result in ice ages and warmer periods.
  • Natural variation in carbon dioxide levels.
• Temperature Variability:
  • Regular shifts in Earth's temperature.
  • Natural CO2 variations due to ocean warming or increased plant growth.
• Current Concerns: Human-driven climate change exceeds natural CO2 levels seen historically.

Sea Level Rise

• Variation over geologic time due to Earth's temperature changes.
• Causes:
  • Increased CO2 leads to warmer periods, melting polar ice caps, and thermal expansion of water.
  • Positive feedback loop: Warmer oceans release more CO2.
• Effects on Habitats:
  • Habitat destruction or alteration.
  • Loss of coastal estuaries due to flooding.
  • Change in water depth and salinity affects plant and animal communities.

Implications for Habitats

• Habitat Loss: Coastal estuaries flooded, leading to species migration or death.
• Changes in Plant Communities: Sunlight availability decreases for aquatic plants, altering species composition.

Migration

• Natural disturbances cause species migration.
• Examples:
  • Wildebeest migrations following rain patterns.
  • Ocean species moving northward due to warming.
  • Birds adjusting migration timing due to insect hatching changes.

Practice FRQ: Describing Trends in Data

• Analyze changes in first leaf date of honeysuckle plant in the US.
• Describe the relationship between latitude and change in first leaf date.
• Explain the cause of this relationship.

• Reminder: Think like a mountain, write like a scholar.