Ecology and the Biosphere

Ecology and the Biosphere

Introduction to Ecology

  • Ecology is the scientific study of the interactions between organisms and their environment.
  • Ecologists focus on the distribution and abundance of organisms.
  • The environment consists of biotic and abiotic factors.
    • Biotic factors: living components (organisms in the area).
    • Abiotic factors: nonliving components (temperature, energy, water, nutrients).
  • Habitat: the specific environment an organism lives in, including biotic and abiotic factors.
  • Ecological research involves:
    • Field research.
    • Laboratory experiments (controlled conditions).
    • Theoretical approach (mathematical and computer models).

Levels of Ecological Study

  • Organismal Ecology: Studies how an organism's physiology and behavior meet environmental challenges.
    • Example: Adaptations of the Himalayan blue poppy to freezing temperatures.
  • Population Ecology: Focuses on groups of individuals of the same species in a specific area.
    • Example: Factors affecting the size of a blue poppy population in an alpine meadow, such as nutrient availability or seed dispersal.
  • Community Ecology: Examines assemblages of populations living close enough for potential interaction.
    • Focuses on interspecies interactions.
    • Example: Competition between poppies and other plants for nutrients.
  • Ecosystem Ecology: Includes both biotic and abiotic components.
    • Focuses on chemical cycling and energy flow.
    • Example: How rapidly decaying plants release inorganic molecules in an alpine meadow.
  • Landscape Ecology: Studies arrays of ecosystems and the exchange of energy, materials, and organisms among them.
    • Landscapes are visible as distinctive patches.
    • Example: Himalayan alpine meadows within a mountain landscape that includes forests.
  • Biosphere: The entire portion of Earth inhabited by life, from the atmosphere to the depths of the oceans.

Human Impact on the Environment

  • Human activities have significantly altered landscapes through:
    • Overgrazing.
    • Deforestation.
    • Overcultivation.
    • Industrial and agricultural practices spreading pollutants.
    • Contamination of groundwater.
    • Depletion of groundwater.
    • Species extinction.
    • Potentially catastrophic changes in global climate.
  • The widespread use of DDT raised concerns about long-term effects, leading to:
    • Evolution of DDT resistance in insects.
    • Publication of "Silent Spring" by Rachel Carson, highlighting the dangers of pesticide use.
  • The 1970s saw legislative acts aimed at curbing pollution.
  • Solving environmental problems requires decisions based on values and ethics, not just ecological understanding.
    • Examples of questions to be addressed:
      • How should land use be regulated?
      • Should we try to save all species?
      • What alternatives to environmentally destructive practices can be developed?
      • How can we balance environmental impact with economic needs?

Abiotic Factors Influencing Life

  • Energy Sources: Solar energy (photosynthesis) powers most ecosystems, but some rely on chemical energy (e.g., hydrothermal vents).
    • Light is a limiting factor in aquatic environments due to absorption by water and particles.
  • Temperature: Affects metabolism.
    • Most organisms have an active metabolism between 0°C and 45°C.
    • Adaptations exist for extreme temperatures (e.g., archaeans in hot springs).
    • Mammals and birds can maintain internal temperature.
    • Amphibians and reptiles have a more limited distribution due to reliance on external heat.
  • Water: Essential for all life.
    • Terrestrial organisms face the risk of drying out.
    • Aquatic organisms deal with solute concentration challenges (freshwater vs. marine).
  • Inorganic Nutrients: Nitrogen and phosphorus are crucial for photosynthetic organisms.
    • Soil structure, pH, and nutrient content affect plant distribution.
  • Aquatic Factors: Oxygen availability, salinity, current, and tides are important.
    • Cold, fast-moving water has higher oxygen content.
  • Terrestrial Factors: Wind increases water loss.
    • Fire is a frequent disturbance in some ecosystems, leading to plant adaptations.

Distribution of Organisms

  • Species presence in a location can be due to:
    • Evolution from ancestors in that location.
    • Dispersal to and survival in that location.
  • Pronghorn Antelope (Antilocapra americana):
    • Descendant of North American ancestors.
    • Adaptations to arid, windswept environments with temperature fluctuations:
      • Thick coat with hollow hairs for insulation.
      • Ability to raise hair patches to release heat.
      • Teeth specialized for tough plant material.
      • Stomach with cellulose-digesting bacteria.
  • Evolutionary History and Predation:
    • The pronghorn's speed (up to 97 km/h97\text{ km/h}) is hypothesized to be due to selection pressure from the now-extinct American cheetah.
    • Protection from predators is also achieved through herd living, camouflage, and keen eyesight.
  • Environmental Change:
    • Significant environmental changes can make existing adaptations less advantageous.
    • Natural selection adapts populations to local conditions but may limit distribution.

Regional and Global Climate Patterns

  • Climate (temperature and precipitation) is crucial in determining the distribution of organisms.
  • Global climate patterns are influenced by solar energy and Earth's movement:
    • Uneven distribution of solar energy due to Earth's curvature.
    • Seasons result from the planet's tilt on its axis.
  • Tropics: Greatest annual solar input and least seasonal variation.
    • High temperatures lead to evaporation and rainfall.
    • Air masses cool and descend at 30∘30^\circ north and south, creating deserts.
    • Trade winds dominate the tropics.
  • Temperate Zones: Seasonal variations and moderate temperatures.
    • Moist conditions around 60∘60^\circ latitude lead to coniferous forests.
  • Prevailing Winds: Result from air mass movement and Earth's rotation.
    • Trade winds blow east to west, westerlies blow west to east.
  • Ocean Currents: Result from winds, planet's rotation, and unequal heating.
    • Gulf Stream warms the west coast of Great Britain.
  • Landforms: Mountains affect rainfall.
    • Air cools and drops moisture on the windward side, creating a rain shadow on the leeward side.
  • Biomes: Major ecological associations, determined primarily by temperature and precipitation for terrestrial biomes and salinity for aquatic biomes.
    • Marine biomes: Oceans, intertidal zones, coral reefs, estuaries.
    • Freshwater biomes: Lakes, streams, rivers, wetlands.

Aquatic Biomes

  • Marine ecosystems are diverse, varying by light penetration, distance from shore, and substrate.
  • Pelagic Realm: Open water.
  • Benthic Realm: Seafloor.
  • Photic Zone: Up to 200 m, where photosynthesis occurs.
  • Coral Reefs: Diverse biomes in warm tropical waters.
  • Aphotic Zone: Below the photic zone, with limited or no light.
  • Intertidal Zone: Where ocean meets land.
  • Estuary: Where freshwater merges with the ocean.
    • High productivity due to nutrient input from the river.
  • Wetlands: Transitional between aquatic and terrestrial ecosystems.

Freshwater Biomes

  • Include lakes, ponds, rivers, and streams.
  • Lakes and Ponds: Plant and animal communities vary with depth.
    • Photic and aphotic zones.
    • Temperature affects water layers.
    • Nutrient levels influence phytoplankton growth.
  • Rivers and Streams: Change from source to mouth.
    • Near source: cold, clear, fast-flowing.
    • Downstream: warmer, murkier, slower.
  • Wetlands: Marshes, swamps, and bogs.
    • High species diversity.
    • Reduce flooding and improve water quality.

Terrestrial Biomes

  • Grouped into nine major types, distinguished by dominant vegetation.
  • Geographic distribution depends on climate (temperature and precipitation).
  • Biomes may look alike due to convergent evolution.
  • Local disturbances create patchiness.
Tropical Forests
  • Occur in equatorial regions with warm temperatures and consistent day length.
  • Tropical rain forests have high rainfall and high species diversity.
  • Soils are typically poor due to rapid decomposition and nutrient uptake.
Savannas
  • Grasslands with scattered trees.
  • Warm year-round with seasonal rainfall.
  • Poor soils and frequent fires inhibit tree establishment.
Deserts
  • Driest terrestrial biomes with low and unpredictable rainfall.
  • Can be hot or cold.
  • Plants and animals adapted to drought and extreme temperatures.
Chaparral
  • Dominated by dense, spiny shrubs with tough evergreen leaves.
  • Mild, rainy winters and hot, dry summers.
  • Adapted to periodic fires.
Temperate Grasslands
  • Treeless, with cold winter temperatures.
  • Periodic droughts and fires.
  • Large grazing mammals.
Temperate Broadleaf Forests
  • Midlatitude regions with sufficient moisture for large trees.
  • Deciduous trees that drop their leaves seasonally.
  • Soils are rich in nutrients.
Coniferous Forests
  • Dominated by cone-bearing evergreen trees.
  • Taiga is the largest terrestrial biome.
  • Long, cold winters and short, wet summers.
  • Soils are thin and acidic.
Tundra
  • Expansive areas of the Arctic with permafrost.
  • Cold climate with little light in autumn and winter.
  • Vegetation includes dwarf shrubs, grasses, mosses, and lichens.
Polar Ice
  • Covers land at high latitudes.
  • Extremely cold year-round with low precipitation.
  • Limited vegetation.

The Global Water Cycle

  • Connects aquatic and terrestrial biomes.
  • Driven by solar energy.
  • Involves precipitation, evaporation, and transpiration.
  • Human activities affect the water cycle, such as deforestation and groundwater pumping.