Ecology


Food Web / Food Chain

  • Producer (PP): Autotrophs that produce their own organic food using sunlight (photosynthesis) or chemical energy (chemosynthesis).

  • Consumer (CC): Heterotrophs that rely on consuming other organisms for nutrients and energy.

    • Primary Consumers (PC): Herbivores that eat producers.

    • Secondary Consumers (SC): Carnivores or omnivores that eat primary consumers.

    • Tertiary Consumers (TC): Apex predators or carnivores that eat secondary consumers.

  • Decomposer (D): Organisms (such as bacteria and fungi) that break down dead organic material and return nutrients to the soil.

  • Food Chain (FC): A single linear sequence showing the direct flow of energy from one organism to another.

  • Food Web (FW): A complex network of interconnected food chains reflecting real ecosystem energy flows.

  • Energy Flow: P→PC→SC→TCP→PC→SC→TC

Biotic vs. Abiotic Factors

  • Biotic Factors: Living or once-living components of an ecosystem.

    • Examples: Plants, animals, fungi, bacteria, leaf litter, decaying organic matter.

  • Abiotic Factors: Nonliving chemical and physical features of an environment.

    • Examples: Water, sunlight, temperature, soil composition, rocks, air, pH levels.

Population Size

  • Population Increases (↑↑):

    • Births (BB): Addition of individuals through reproduction.

    • Immigration (II): Movement of individuals into a population from another area.

  • Population Decreases (↓↓):

    • Deaths (D): Loss of individuals due to mortality.

    • Emigration (E): Movement of individuals out of a population to another area.

Growth Rate

  • Formula: Growth Rate=(B+I)−(D+E)Growth Rate=(B+I)−(D+E)

  • Positive Growth Rate (++): Population is increasing (↑↑).

  • Negative Growth Rate (−−): Population is decreasing (↓↓).

  • Zero Growth Rate (00): Population size remains stable (→→).

Exponential vs. Logistic Growth

  • Exponential Growth:

    • Shape: J-shaped curve.

    • Characteristics: Rapid, unrestricted population growth occurring when resources are unlimited and environmental resistance is minimal.

    • Relationship: Birth rate significantly exceeds death rate (B>DB>D).

  • Logistic Growth:

    • Shape: S-shaped curve.

    • Characteristics: Growth starts exponentially, slows down as resources become limited, and levels off.

    • Relationship: Population levels off when it reaches the carrying capacity (KK).

Carrying Capacity

  • Carrying Capacity (CC): The maximum population size that a specific environment can sustainably support over time.

  • Limiting Factors:

    • Density-Dependent Factors: Competition, food availability, disease, predation, and space.

    • Density-Independent Factors: Natural disasters, severe climate events, and temperature extremes.

Age Structure Diagrams

  • Pre-Reproductive (Pre-R): Young individuals not yet capable of reproducing.

  • Reproductive (R): Sexually mature individuals capable of producing offspring.

  • Post-Reproductive (Post-R): Older individuals past reproductive age.

  • Wide Base: High proportion of young individuals (Pre-R), indicating rapid population growth (↑↑).

  • Narrow Base: Lower proportion of young individuals compared to older tiers, indicating population decline (↓↓).

  • Uniform / Straight Sides: Stable population growth rate.

Survivorship Curves

  • Type I: High survival rate throughout early and middle life; high mortality rate in old age (e.g., humans, large mammals).

  • Type II: Constant mortality rate throughout the organism's entire lifespan regardless of age (e.g., birds, rodents, reptiles).

  • Type III: Extremely high mortality rate early in life, but individuals that survive to adulthood live relatively long lives (e.g., marine fish, plants, invertebrates).

Reading Population Models

  • X-axis: Typically represents time, age group, or generations.

  • Y-axis: Represents population size, number of survivors, or growth rate.

  • Symbols & Trends:

    • ↑↑ = Increasing trend

    • ↓↓ = Decreasing trend

    • →→ = Stable/constant trend

    • JJ = Exponential growth trajectory

    • SS = Logistic growth trajectory

Species Interactions

  • Competition (-$ / -): Both species are negatively affected as they compete for limited resources (e.g., food, light, territory).

  • Predation (++ / −−)**: One organism (predator) hunts, kills, and consumes another organism (prey).\n- Mutualism (+//+): Both species benefit from the interaction (e.g., bees and flowering plants).\n- Commensalism (+//0): One species benefits while the other is neither harmed nor helped (e.g., barnacles on whales).\n- **Parasitism (+//-)): One organism (parasite) lives on or inside another organism (host), deriving nutrients at the host's expense.

The 3 Biogeochemical Cycles

  • Water Cycle:

    • Evaporation (E): Water turns from liquid to vapor and rises into the atmosphere.

    • Condensation (C): Water vapor cools and turns into liquid water droplets, forming clouds.

    • Precipitation P): Moisture falls from clouds as rain, snow, sleet, or hail.

    • Collection (C) / Runoff: Water gathers in lakes, rivers, oceans, and groundwater reservoirs.

    • Transpiration: Evaporation of water from plant leaves into the atmosphere.

  • Carbon Cycle:

    • Photosynthesis (PS): Autotrophs absorb atmospheric CO2CO2​ to synthesize organic sugars.

    • Cellular Respiration (CR): Organisms break down glucose, releasing CO2CO2​ back into the atmosphere.

    • Decomposition: Microorganisms break down organic matter, releasing carbon into soil and atmosphere.

    • Combustion: Burning fossil fuels and biomass releases stored carbon as CO2.

  • Nitrogen Cycle:

    • Nitrogen Fixation (NF): Conversion of inert atmospheric N2N2​ into usable ammonia (NH3NH3​) by specialized bacteria or lightning.

    • Nitrification: Ammonia is converted into nitrites (NO2−NO2−​) and nitrates (NO3−NO3−​).

    • Assimilation: Plants absorb nitrates from soil to build proteins and nucleic acids.

    • Decomposition / Ammonification: Decomposers convert organic nitrogen back into ammonia.

    • Denitrification: Soil bacteria convert nitrates back into atmospheric N2N2​ gas.

Energy Pyramid & Trophic Levels

  • Energy Transfer Rule: Only approximately 10%10% of energy is passed from one trophic level to the next higher level.

  • Energy Loss: The remaining 90%90% of energy is lost as heat through metabolic processes or unconsumed biomass.

  • Trophic Levels (TL):

    • 1st Trophic Level: Producers (PP) - highest energy level.

    • 2nd Trophic Level: Primary Consumers (PCPC) - herbivores.

    • 3rd Trophic Level: Secondary Consumers (SCSC) - carnivores eating herbivores.

    • 4th Trophic Level: Tertiary Consumers (TCTC) - top apex predators.

Photosynthesis vs. Cellular Respiration

  • Photosynthesis (PS):

    • Inputs (Reactants): 6CO2+6H2O+sunlight6CO2​+6H2​O+sunlight

    • Outputs (Products): C6H12O6+6O2C6​H12​O6​+6O2​

    • Location: Chloroplasts (specifically thylakoids and stroma).

    • Purpose: Converts solar energy into chemical energy stored in glucose molecules.

  • Cellular Respiration (CR):

    • Inputs (Reactants): C6H12O6+6O2C6​H12​O6​+6O2​

    • Outputs (Products): 6CO2+6H2O+ATP6CO2​+6H2​O+ATP

    • Location: Mitochondria (cytoplasm for glycolysis, matrix and inner membrane for Krebs cycle and ETC).

    • Purpose: Breaks down chemical energy in glucose to generate usable cellular energy (ATP).

  • Summary Comparison:

    • Photosynthesis stores energy: 6CO2+6H2O+light energy→C6H12O6+6O26CO2​+6H2​O+light energy→C6​H12​O6​+6O2​

    • Cellular Respiration releases energy: C6H12O6+6O2→6CO2+6H2O+ATPC6​H12​O6​+6O2​→6CO2​+6H2​O+ATP

Scientific Method

  1. Question (Q): Identify a clear problem or phenomenon to investigate.

  2. Research (R): Gather existing background knowledge and observations.

  3. Hypothesis (H): Formulate a testable prediction (often an "If… then…" statement).

  4. Experiment (E): Design and conduct a controlled procedure to test the hypothesis.

  5. Data Collection (D): Record qualitative observations and quantitative measurements.

  6. Analyze (A): Interpret data using graphs, statistics, and calculations.

  7. Conclusion (C): Accept or reject the hypothesis based on data analysis and share findings.

Experimental Variables

  • Independent Variable (IV): The single factor intentionally manipulated or changed by the experimenter.

  • Dependent Variable (DV): The factor measured or observed to see how it responds to changes in the IV (data collected).

  • Controlled Variable (CV): Factors kept constant across all test groups to ensure a fair test.

  • Control Group (CG): A baseline group left untreated or kept under natural conditions for direct comparison.

Laboratory Safety

  • Wear safety goggles and personal protective equipment (PPE) at all times.

  • Strictly no eating, drinking, or chewing gum in the laboratory environment.

  • Read and follow all written and verbal instructions carefully.

  • Do not perform unauthorized or unapproved experiments.

  • Immediately report all chemical spills, broken glassware, or injuries to the teacher/lab supervisor.

  • Tie back long hair, roll up loose sleeves, and secure dangling jewelry.

  • Never directly inhale chemical fumes; use the wafting technique if instructed.

  • Know the locations and proper operation of safety equipment (eyewash station, safety shower, fire extinguisher, fire blanket).

  • Dispose of chemical waste, biological waste, and sharp objects in designated specialized waste containers.