Global Ecology - 23

Global Ecology & The Biosphere

Learning Objectives

• Understand global climate patterns and how they shape ecosystems.
• Identify terrestrial and aquatic biomes.
• Explore how physical geography and human activity influence ecological communities.

Climate and the Biosphere

What is the Biosphere?

• The biosphere includes all living communities on Earth.
• Understanding its distribution requires studying global climate patterns.

Factors Affecting Solar Energy Distribution

1. Atmospheric Modification:
   • Atmosphere reflects/absorbs ~50% of solar energy.
   • Ozone layer absorbs harmful UV rays.
   • Re-radiated heat is trapped by greenhouse gases → Greenhouse Effect.
2. Earth’s Curvature
   • Angle of Incidence
3. Latitude:
   • Higher latitudes = sun’s rays spread over larger areas → cooler temps.
   • Equator receives direct sunlight → warmer/ Impacts seasonality
   • Impacts angle of incidence
4. Earth’s Tilt and Seasons:
   • Earth's tilt (23.5°) causes seasonal variation in solar input.
   • Seasons are more pronounced away from the equator.
   • Example: Northern Hemisphere has summer solstice when tilted toward the sun.

Relationship between the Earth and Sun

• Revolution around the sun: seasons
• Rotation (Earth spinning): Day and night

Global Air Circulation

Key Concepts:

• Hot air rises, cools as it rises, and holds more moisture.
• Equator: Warm, moist air rises → cools → heavy rainfall.
• 30° N/S: Dry air descends → deserts.
• 60° N/S: Some rising moist air → moderate precipitation.
• 90° N/S: Cold, dry air descends → polar deserts.

Wind Patterns

• Caused by surface air movements in 3 circulation cells per hemisphere.
• Coriolis Effect: Earth’s rotation curves wind direction.
• Winds are named by their origin direction.

Ocean Circulation

Surface Currents

• Driven by surface winds → form circular gyres.
• Influence regional climates (e.g., Gulf Stream warms Europe).

Upwelling

• Deep, nutrient-rich water rises to the surface.
• Supports high productivity (e.g., off California and Peru).

Regional and Local Climate Effects

Rain Shadow Effect

• Moist air rises over mountains → cools & rains on windward side.
• Dry, warm air descends on leeward side → forms deserts (e.g., Great Basin Desert).
• Directly related to air temperature

Elevation

• Temperature drops ~6°C per 1000m rise.
• Altitude changes mirror latitude shifts → changing biomes up mountains.

Terrestrial Biomes

Overview

1. Tropical Rain Forest
   • Near equator, year-round warmth & rain.
   • Highest biodiversity & net primary productivity (NPP).
   • Tall trees, epiphytes, nutrient-poor soil (fast nutrient cycling).
   • Aseasonal, High precipitation
   • The tropics receive more solar energy per unit area because sunlight strikes the Earth at a near perpendicular angle to the surface of the earth
2. Savanna
   • Between rain forests & deserts (10–20° N/S).
   • Seasonal rainfall, fire-adapted grasses, migratory herbivores.
   • Widely spaced trees and shrubs
3. Desert
   • Evaporation > precipitation, temps can be hot or cold.
   • Sparse vegetation, drought-adapted species (e.g., cactus).
   • High temp, low precipitation
4. Temperate Grassland (Prairie)
   • More rain than deserts but not enough for forests.
   • Hot summers, cold winters, fertile soil → agriculture.
   • Fire and grazing maintain grasses.
   • Herbaceous vegetation
5. Temperate Deciduous Forest
   • Cold winters, warm summers, ample rain.
   • Deciduous trees drop leaves → winter dormancy.
   • Rich biodiversity, layered vegetation.
6. Temperate Evergreen Forest
   • Coastal, mild temps, summer drought.
   • Dominated by conifers (e.g., redwoods, pines).
   • Large Trees
7. Taiga (Boreal Forest)
   • 50–65° N, long winters, short growing seasons.
   • Dominated by evergreen conifers, low plant diversity, home to large mammals.
   • Moderate precipitation
8. Tundra (Arctic & Alpine)
   • Treeless, cold, low precipitation, permafrost.
   • Dominated by mosses, lichens, small shrubs.
   • Alpine tundra found at high elevations with similar conditions.

Aquatic Biomes

Freshwater Ecosystems

• Watershed: the area of land that drains into a stream, river, lake, estuary, etc.
• Lakes & Ponds:
  • Lakes lack nitrogen and phosphorus
    • Oligotrophic Lakes: low nutrients, clear, low productivity, healthy, Hypolimnetic oxygen deficit rare or short-term, small phytoplankton, NPP limited (phosphorus).
    • Eutrophic Lakes: high nutrients, algal blooms, low oxygen, unhealthy, Hypolimnetic oxygen deficit common and prolonged, dense plant cover, high decomposition rates, high NPP.
  • Photic zone: sunlight supports photosynthesis.
  • Thermal stratification affects oxygen & temperature layers.
• Wetlands:
  • High NPP, filter pollutants, buffer storms.
• Oligotrophic Lakes: low nutrients, clear, low productivity.
• Eutrophic Lakes: high nutrients, algal blooms, low oxygen.

Human Impact: Eutrophication

• Caused by nutrient runoff (e.g., fertilizers).
• Can be reversed by stopping nutrient input.

Marine Ecosystems

Ocean Zones

1. Open Ocean: low NPP, limited nutrients.
2. Continental Shelf: nutrient-rich, includes coral reefs, estuaries.
3. Upwelling Zones: high productivity due to nutrient-rich water.
4. Deep Sea: cold, dark, high pressure, bioluminescent species.

El Niño-Southern Oscillation (ENSO)

• Periodic climate event caused by weakened trade winds.
• Reduces upwelling →warmer, low nutrients → ecosystem crash (e.g., Galapagos).
• Global impacts: SE US → wetter, Asia → drier, Chile → more vegetation.
• Westerly winds from western pacific.
• Shift in precipitation.
• La nina: more intense upwellings up the coast.

Biome Distribution Determining Factors

• Temperature + Precipitation = best predictors of biome type.
• Primary productivity correlates with these variables.

Climate-Biome Relationship

• Example: Tropical rain forests = warm + wet → high NPP.
• Some variations explained by soil type or disturbance history.