Week 6: Succession, Climate, Biomes, and Ecosystems

Succession

  • The orderly replacement of populations of plants and animals in an area following a disturbance, until a stable community is established.

  • Climax Community: The stable community at the end of succession, determined by local climate, which has the largest population and species diversity.

  • Transition from r-selected to K-selected species indicates a shift from species that produce many offspring with less investment in each to those that produce fewer offspring but invest more resources in their care.

Reasons for Succession

  • Causes:

    • Succession is largely driven by the organisms themselves, modifying their environment to make it less favorable for current species and more suitable for others.

Consequences of Succession

  • Changes in community structure:

    • Increase in community diversity

    • Increase in abundance of species

    • Shift from r-selected to K-selected species

Types of Succession

  1. Primary Succession:

    • Occurs in an area with no soil (e.g., newly formed volcanic islands or glacial moraines).

    • Progression: autotrophic prokaryotes → lichens and mosses → grasses → shrubs → trees.

  2. Secondary Succession:

    • Begins in an area where soil remains after a disturbance (e.g., after a forest fire).

Role of Lichens

  • Pioneers: Lichens are vital in early stages on new rock and soil surfaces due to their ability to:

    • Break down rock through physical penetration and chemical attack.

    • Trap windblown soil.

    • Add nitrogen to soil, facilitating succession.

  • Indicator Species: Sensitivity to pollution means lichens can signal air quality issues.

Plant Life Succession

  • Succession on Bare Rock: The process from bare rock to climax community is driven by the changes induced by the vegetation itself.

  • Example in Alaska: After glacial retreat in Glacier Bay, pioneer species like alder are succeeded by Sitka spruce, western hemlock, and mountain hemlock.

Climate and Biomes

Climate Concepts

  1. Climate: Long-term prevailing weather conditions in a region that significantly influence the distribution of organisms.

  2. Determinants: The four major abiotic components are:

    • Temperature

    • Precipitation

    • Sunlight

    • Wind

Global Climate Patterns

  • Variations in heat and light from the sun affect climate zones; the tropics receive more direct sunlight than polar regions.

  • Seasonal changes in light and temperature correlate with Earth's tilt and orbit around the sun.

Latitudinal Influence

  • At the equator: warm temperatures and high precipitation

  • Deserts form at the Tropics of Cancer and Capricorn due to subsiding dry air.

Definition of Biome

  • Biomes: Major types of ecosystems occupying broad geographic areas, characterized primarily by vegetation type and climate.

Terrestrial Biomes

  • Grassland Biome: Dominated by grasses.

  • Temperate Deciduous Forest: Dominated by deciduous trees.

  • Biomes are named after the mature plant community prevalent in the area and include adaptations specific to local climates.

Aquatic Biomes

  • Classified by physical and chemical characteristics, not by dominant vegetation.

  • For freshwater: water movement, depth, temperature, and salinity are key features.

Examples of Major Biomes

  • Terrestrial:

    • Tropical rain forest

    • Coniferous forest

      • spans northern NA and Eurasia

    • Temperate deciduous forest

      • Spans eastern NA and Asia, Europe, eastern AU, NZ, and southern Chile

    • Temperate grassland

      • Spans Great Prairies and Central Asia/ Mongolia

    • Desert

    • Tundra

      • North Pole and neighbouring region

  • Aquatic:

    • Freshwater:

      • Oligotrophic lakes

        • nutrient-poor, oxygen-rich, deep, cold, low productivity (most lakes in Canada

      • Eutrophic lakes

        • nutrient-rich, oxygen-poor, shallow, warm, high productivity

      • Rivers

      • Wetlands

        • inundated by water for some time

    • Marine: Estuaries (transition area between river and sea, e.g. where the Fraser River empties), Intertidal zones, Coral reefs, Open ocean

Ecosystems, Nutrient Cycling, and Climate Change

Characteristics Limiting Production

Terrestrial Ecosystems

  • Major Factors:

    • Temperature: Influences both growth and metabolism.

    • Precipitation: Affects water availability for organisms.

  • Climograph

    • plots annual mean temperature and precipitation in a region

  • Ecotone

    • transition from one type of habitat/ ecosystem to another (e.g. grassland to forest)

Aquatic Ecosystems

  • Limiting Factors:

    • Light: Limits photosynthesis, especially at depths.

    • Nutrients: Essential for growth but can limit productivity.

Primary Production Dynamics

  • Gross Primary Productivity (GPP): Total primary production in an ecosystem.

  • Net Primary Productivity (NPP): GPP minus the energy used for respiration by primary producers (availability to consumers).

  • NPP measurements reveal variations in ecosystem productivity:

    • High NPP: Tropical rainforests, estuaries, and coral reefs.

    • Low NPP: Marine ecosystems are unproductive per unit area but contribute significantly due to their vast surface area.

Nutrient Limitation

  • Limiting Nutrients: Elements required for production that are found in short supply; nitrogen and phosphorus are commonly limiting in marine contexts.

  • Eutrophication: Occurs when excessive nutrients lead to algal blooms, causing significant ecological impacts (e.g. loss of most fish species)

Key Chemical Elements Required by Organisms

  • Carbon and Hydrogen: Found in carbohydrates, lipids, proteins, and nucleic acids.

  • Oxygen: Found in organic molecules, essential for cellular respiration, which produces ATP.

  • Nitrogen: Essential for amino acids and nucleic acids.

  • Phosphorus: Important for nucleic acids and ATP.

Nutrient Cycling

Water Cycle

  • Movement through evaporation, transpiration, condensation, precipitation, and through surface and groundwater driven by solar energy.

Carbon Cycle

  • Essential for organic molecules; involves processes like photosynthesis, respiration, and decomposition, with CO2 released from natural and anthropogenic sources.

Nitrogen Cycle

  • Nitrogen must be converted by bacteria to forms available to plants (NH4+ or NO3–); atmospheric nitrogen is the principal reservoir.

Phosphorus Cycle

  • Involves phosphate (PO4^3−) as the primary inorganic form; major reservoirs include marine sedimentary rocks and oceans

Human Impact on Nutrient Cycling

  • Activities disrupt ecosystems, affecting trophic structures and nutrient cycles.

  • Nutrient Enrichment: Includes the addition of fertilizers leading to environmental pollution and altered ecosystems.

    • e.g. DDT and CFC (chlorofluorocarbons)

  • Greenhouse Gas Effects: Rising CO2 levels due to human activities contribute to climate change, reflected by phenomena such as the Greenhouse Effect, which regulates Earth's temperature.

    • Greenhouse gases include

      • methane, water vapour, nitrous oxide, CFCs

Climate Change Implications

  • Effects include rising global temperatures, changing species distributions, and increased productivity in some plants, limited by nutrient availability.

  • Human-induced changes complicate existing ecological balances and biodiversity.