Copy of IB ESS SL Notes

2.1 Species and Populations

• Ecology: The study of living (biotic) and non-living (abiotic) components that interact within an ecosystem.

• Abiotic factors: Non-living factors influencing organisms/system.

  • Example: Sunlight affects temperature and evaporation rates.

• Levels of organization: Species → Population → Community → Ecosystem → Biome → Biosphere.

• Ecosystem: A community of interdependent organisms and their physical environment.

• Species: A group of organisms capable of reproducing and producing fertile offspring.

• Scientific Names: Used to identify species scientifically (Genus species); always italicized or underlined.

• Keystone Species: Crucial species for ecosystem maintenance, influencing structure and nature of ecosystems.

  • Example: Wolves in Yellowstone, beavers in rivers.

• Niche: Specific role of an organism encompassing where, when, what, and how it lives.

  • Associated with trophic levels in ecosystems.

  • Example: Plants as primary producers, tigers in herbivore population control.

• Niche Theory: No two species can occupy identical niches simultaneously to avoid competition.

  • Fundamental Niche: Range of conditions a species can live under.

  • Realized Niche: Actual conditions an organism lives under, often affected by competition.

  • Case Study: Joseph Connell's barnacles - comparing fundamental and realized niches.

• Intraspecific competition: Competition between the same species, stabilizing population size and influencing phases of growth.

Interactions Between Organisms

• Predation: The act of hunting.

• Herbivory: Consumption of plants.

  • Example: Rabbits eating grass.

• Parasitism: One organism relies on another for nutrition, often harming the host.

• Mutualism: Interaction where both species benefit.

• Competition: Struggle for resources; can be intra-specific or inter-specific.

• Amensalism: One species is harmed while another is unaffected.

  • Example: Cows and sheep in pasture; cows starve due to competition from sheep.

• Neutralism: No significant relationship exists between organisms.

• Competitive exclusion principle: No two species can occupy the same niche indefinitely in limiting resource conditions.

• American Alligator: A keystone species that creates gator holes for refuge of aquatic species during dry seasons.

Bioaccumulation vs Biomagnification

• Pesticides: Man-made pollutants including herbicides, fungicides, and bactericides, designed to manage pests.

• Bioaccumulation: Accumulation of substances (toxins) in an organism over time; organisms cannot eliminate them effectively.

  • Examples: DDT, Methyl Mercury; associated effects include cancer and birth defects.

• DDT:

  • Benefits: Low toxicity for humans, effective against insects, inexpensive to produce.

  • Problems: Long environmental activity, causes shell thinning in birds.

  • Status: Banned in North America since the 1970s but still used in the Third World.

• Biomagnification: Increasing concentration of toxins in organisms at higher trophic levels.

Ecological Pyramids

• Ecological Pyramids: Represent numerical relationships between trophic levels in a community.

  • Choice of pyramid depends on data type/quantity collected.

• The Second Law of Thermodynamics states energy decreases along food webs; thus, pyramids narrow as one ascends trophic levels.

  • Energy Loss: Approximately 90% lost at each level due to homeostasis, heat, and movement.

• Pyramid of Biomass: Represents standing stock of each trophic level.

• Pyramid of Productivity: Represents energy flow through trophic levels, always decreases as it ascends due to energy loss.

2.2 Communities and Ecosystems

• Solar Energy Fate: Measured in joules per second per square meter (J s -1 m-2).

• Solar Constant: The rate of solar energy reaching the top of Earth’s atmosphere.

• Productivity: Conversion of solar energy into biomass over time, measured per unit area.

2.3 Flows of Energy and Matter: Biomes

• Biomes: Collections of ecosystems sharing similar climatic conditions.

• Biosphere: Portions of Earth inhabited by living organisms.

  • Aquatic Biomes: Freshwater and Marine; include swamps, rivers, coral reefs, and deep oceans.

  • Deserts: Characterized by hot and cold variations.

  • Forests: Tropical, Temperate, Boreal (Taiga).

  • Grasslands: Tropical, Temperate, Savanna.

  • Tundra: Arctic and Alpine types.

• Climate: Major influencing factor regarding growth patterns, with geography also significant.

  • Factors: Temperature, precipitation, latitude, and altitude.

Biome Specific Characteristics

Tropical Rainforest

• Characteristics: Hot and wet, high biodiversity.

• Climate: Rainfall 2000-5000 mm/yr, average temperature 26-28 degrees Celsius.

• Productivity: High net productivity; continuous growing season.

Deserts

• Characteristics: Dry, high daily temperature variation.

• Climate: Less than 250 mm/yr precipitation.

• Adaptations: Drought-resistant plants, small mammals.

Temperate Grasslands

• Characteristics: Dominated by grasses, ideal for agriculture.

• Climate Factors: Precipitation equals evaporation.

• Biodiversity: Low compared to forests.

Temperate Forests

• Characteristics: Mild climate, often deciduous.

• Climate Factors: Rainfall 500-1500 mm/yr.

Arctic Tundra

• Characteristics: Cold, low biodiversity, thin soil.

• Climate Factors: Low precipitation, permafrost present.

Deep Ocean

• Characteristics: Covers 65% of Earth's surface, diverse environments from shallow to deep.

• Light Limitation: Nutrient levels are low, leading to low primary productivity.

Succession and Zonation

• Succession: Ecosystem evolution over time.

• Zonation: Ecosystem changes along gradients (e.g., altitude).

• Primary Succession: Colonization of barren land; starts with pioneer species.

  • Stages: Colonization, Establishment, Competition, Stabilization.

• Secondary Succession: Recovery of complex ecosystems after disturbance.

K and R Strategists’ Reproductive Strategies

• K-Strategists: Stable environments; longer-lived, fewer offspring.

• R-Strategists: Unstable environments; short life cycles, rapid reproduction.

• Survivorship Curves: Illustrates lifespan and mortality at various life stages.