Unit 8: Ecology, Cycling of Matter, and Human Impact

Earth's Origin and the Early History of Life

• Timeline of Earth and Life

  • Earth's Origin: Approximately $4.6 \times 10^9$ years ago (4.6 billion years ago). During this period, the Earth formed, the first oceans appeared, and the atmosphere underwent gradual development.
  • Appearance of Organisms: Approximately $2.4 \times 10^9$ years ago (2.4 billion years ago).
  • Evolutionary Progression: Early life forms were unicellular organisms known as prokaryotes. Over time, more complex multicellular organisms evolved.

• Classifying Organisms by Energy Acquisition

  • Autotrophs: Organisms that produce their own food (e.g., plants, algae, phytoplankton, and some bacteria).
  • Heterotrophs: Organisms that do not make their own food and must consume other organisms (e.g., animals, fungi, most protozoa, and most bacteria).

Fundamental Principles of Ecology

• Definition of Ecology: The branch of biology that studies the relationships between organisms and their environment. It focuses on how living things interact with one another and with non-living components such as air, water, soil, and climate.

• Levels of Ecological Organization (Smallest to Largest)

  1. Individual: A single organism, such as an individual plant or animal.
  2. Population: A group of interacting individuals of the same species that occupy the same area at the same time and are capable of interbreeding.
  3. Community: All the different populations of different species interacting and occupying the same place.
  4. Ecosystem: A community of living organisms (biotic factors) interacting with their non-living (abiotic) environment.
  5. Biome: A large region of the world characterized by a specific climate and specific types of plants and animals adapted to that environment (e.g., deserts, rainforests, tundra, grasslands, and coral reefs).
  6. Biosphere: All parts of the Earth where life exists, including land, water, and the atmosphere.

• Key Ecological Concepts

  • Biotic Factors: Living components of an ecosystem.
  • Abiotic Factors: Non-living components of an ecosystem (e.g., sunlight, temperature, water, soil).
  • Habitat: The specific place where a population lives.
  • Niche: The specific role an organism plays in its environment, including what it eats, where it lives, its predators, and its place in the food chain.

Interactions and Energy Flow in Ecosystems

• Symbiotic Relationships

  • Mutualism: An interaction where both species benefit ($+ / +$). Example: Sea anemone and clownfish.
  • Commensalism: An interaction where one species benefits and the other is unaffected ($+ / 0$). Example: Whale and barnacle.
  • Parasitism: An interaction where one species benefits (the parasite) and the other is harmed (the host) ($+ / -$). Example: Dog and tick.
  • Competition: An interaction where species compete for the same limited resources (e.g., food, water, space) ($- / -$).

• Food Chains and Trophic Levels

  • Producers (Autotrophs): Occupy the first trophic level; they make their own organic nutrients using photosynthesis.
  • Consumers (Heterotrophs): Cannot make their own food; they obtain energy by eating other organisms.
    • Primary Consumers ($1^\circ$): Feed directly on producers (Herbivores).
    • Secondary Consumers ($2^\circ$): Feed on primary consumers (Carnivores/Omnivores).
    • Tertiary Consumers ($3^\circ$): Feed on secondary consumers.
  • Decomposers: Organisms like fungi and bacteria that break down dead plants, animals, and organic waste, recycling nutrients back into the ecosystem.

• Energy Pyramids and the $10\%$ Rule

  • The Rule: Only approximately $10\%$ of the energy available at one trophic level is transferred to the next higher trophic level. The remaining $90\%$ is lost, primarily as heat through metabolic processes.
  • Energy Distribution Example:
    • Producers (Trophic Level 1): $10,000\,Kcal$
    • Primary Consumers (Trophic Level 2): $1,000\,Kcal$
    • Secondary Consumers (Trophic Level 3): $100\,Kcal$
    • Tertiary Consumers (Trophic Level 4): $10\,Kcal$

• Food Webs: A complex network of multiple interacting food chains that demonstrates biodiversity and shows that nothing in nature stands alone.

Biological Concentration of Toxins

• Bioaccumulation: The accumulation and buildup of toxins within a single organism over the course of its lifetime.
• Biomagnification: The increase in toxin concentration levels as you move higher up the food chain.
  • Case Study: Mercury in Tuna: Mercury is taken up by plankton in trace amounts. As it moves up the chain (Animal plankton $\rightarrow$ Small fish $\rightarrow$ Large fish $\rightarrow$ Tuna), each predator accumulates the mercury present in all the prey it consumes, leading to high concentrations in top predators like tuna.

Biogeochemical Cycles

• Elemental Composition of the Human Body

  • Water: $62\%$
  • Protein: $16\%$
  • Fat: $16\%$
  • Minerals: $6\%$
  • Carbohydrates: $1\%$
  • Key Elements: Oxygen ($65\%$), Carbon ($18\%$), Hydrogen ($9.5\%$), Nitrogen ($3.2\%$), Calcium ($1.5\%$), Phosphorus ($1.2\%$), Potassium ($0.4\%$), Sulfur ($0.2\%$), Sodium ($0.2\%$), Chlorine ($0.2\%$), and Magnesium ($0.1\%$).

• The Phosphorus Cycle

  • Importance: Essential for building DNA, RNA, ATP, cell membranes, and bones.
  • Process:
    1. Weathering of phosphate rocks releases phosphorus into soil and water.
    2. Plants take up phosphorus from the soil.
    3. Phosphorus passes through food webs as consumers eat plants and other animals.
    4. Decomposition and waste return phosphorus to sediments.
    5. Geological processes eventually form new phosphate rock over long timescales.

• The Nitrogen Cycle

  • Importance: Required for amino acids, proteins, and nucleic acids. Atmospheric nitrogen ($N_2$) makes up $78\%$ of the atmosphere but is unusable by most organisms in its gaseous form.
  • Steps:
    1. Nitrogen in Atmosphere: Present as $N_2$ gas.
    2. Nitrogen Fixation: Bacteria (often in legume root nodules) or lightning convert $N_2 \rightarrow NH_3$ (Ammonia).
    3. Nitrification: Nitrifying bacteria convert Ammonia ($NH_3$) into Nitrites ($NO_2^-$) and then Nitrates ($NO_3^-$), which plants can absorb.
    4. Animal Absorption: Animals eat plants to obtain nitrogen.
    5. Decomposition: Waste and dead organisms return nitrogen to the soil.
    6. Denitrification: Denitrifying bacteria convert Nitrates ($NO_3^-$) back into $N_2$ gas.

• The Carbon Cycle

  • Photosynthesis: Plants take in $CO_2$ and water, using sunlight to produce Glucose ($C_6H_12O_6$) and Oxygen ($O_2$).
  • Cellular Respiration: Animals and plants use oxygen to break down glucose, releasing energy (ATP), water, and $CO_2$ back into the atmosphere.
  • Human Disruption: The cycle is currently unbalanced due to the burning of fossil fuels and deforestation, emitting carbon faster than it can be absorbed.

Human Impact and Global Climate Change

• The Greenhouse Effect: A natural process where greenhouse gases (e.g., $CO_2$, $CH_4$, $H_2O$, $N_2O$) trap heat to keep Earth livable.

  • Runaway Greenhouse Effect: Caused by excess human emissions, leading to global warming, melting ice, rising sea levels, and extreme weather.
  • Algal Blooms: Caused by excess nitrogen and phosphorus (often from fertilizers) entering water systems, leading to rapid algae overgrowth that depletes oxygen and kills aquatic life.

• Environmental Degradation Issues

  • Overfishing: Global fish consumption reached $20.2\,kg$ (45 lb) per capita in 2020. Marine populations have crashed by $50\%$ in the last 4 decades.
  • Deforestation: Removal of trees destroys habitats and increases atmospheric $CO_2$.
  • Acid Rain: Atmospheric pollution reactions resulting in rain that harms plant life.
  • Urbanization: Leads to habitat destruction and increased water/air pollution.
  • Invasive Species: Non-native species that outcompete native species for resources.
  • Waste Lagoons: Specifically in North Carolina, hog farm waste can contaminate groundwater and streams.

• Conservation Solutions

  • No-Fish Zones: Example: Papah\u0101naumoku\u0101kea Marine National Monument. Research shows a "spillover benefit" where fish populations recover and move into nearby fishing areas, increasing catch rates for Yellowfin tuna ($+54\%$) and Bigeye tuna ($+12\%$).
  • Individual Actions: Recycling, avoiding single-use plastics, using energy-efficient appliances, planting trees, and increasing awareness.

Population Ecology

• Population Characteristics

  • Density: The number of individuals per unit area or volume.
  • Dispersion: How individuals are spaced.
    • Clumped: Groups (e.g., schools of fish, herds).
    • Uniform: Evenly spaced (e.g., nesting penguins, territorial bushes).
    • Random: Unpredictable spacing (e.g., wind-blown seeds).
  • Demographics: The statistical study of traits like age, sex ratio, birth rates, and death rates.

• Population Regulation

  • Density-Dependent Factors: Effects intensify as density increases (e.g., competition, disease, predation, parasitism).
  • Density-Independent Factors: Effects occur regardless of density (e.g., weather events, natural disasters, climate change, human disturbances).

• Growth Models

  • Exponential Growth ($J$-curve): Unlimited growth occurring when resources are abundant and birth/death rates are constant.
  • Logistic Growth ($S$-curve): Growth that levels off at the Carrying Capacity ($K$), which is the maximum number of individuals the environment can support given available resources.

• Human Population Context

  • The human population reached 8 billion in 2022.
  • Since 1900, growth has been exponential due to better sanitation, improved medicine, and agricultural advancements.
  • Age Structure Pyramids:
    • Increasing population: Large base of young people (e.g., India).
    • Stable population: Similar numbers across age groups (e.g., France).
    • Decreasing population: Few young people compared to older generations.