AS

Ecology Notes

Ecology & Population Ecology

Ecology

  • Ecology is the study of living (biotic) and non-living (abiotic) components of the environment and their interactions.

Biotic Components

  1. Producers (Autotrophs): Organisms that make their own food (self-feeders).
    • Examples: Plants, Protists, Bacteria
  2. Consumers (Heterotrophs): Organisms that consume other organisms (other feeders).
    • Examples: Animals, Protists, Fungi, Bacteria
  3. Decomposers: Break down dead plants and animals.
    • Examples: Fungi, Bacteria

Types of Producers

  1. Autotrophs: Use sunlight to make food (e.g., plants using sunlight to make glucose).
  2. Chemotrophs: Use chemicals to make food (e.g., bacteria using hydrogen sulfide around volcanic vents).

Types of Consumers

  1. Scavengers: Feed on dead organisms (detritivores; e.g., vultures, hyenas).
  2. Herbivores: Eat only plants (e.g., deer, rabbits, some insects).
  3. Carnivores: Eat only meat (e.g., lions, tigers, sharks).
  4. Omnivores: Eat both plants and animals (e.g., humans, bears).
  5. Decomposers: Absorb and break down dead material into simple nutrients (e.g., fungi, microorganisms).

Interactions

  • Community: The producers, consumers, and decomposers in an area (e.g., trees, bacteria, fungi, foxes, rabbits, birds in a forest).
  • Trophic Level: Each step in the transfer of energy (producer, consumer, decomposer).

Food Chain

  • A food chain illustrates what eats what and the transfer of energy from one organism to another.
  • It is simple, direct, and involves only one organism at each trophic level.
  • Example:
    • Producer: Plant
    • Primary Consumer: Rabbit (herbivore)
    • Secondary Consumer: Fox (omnivore/carnivore)
    • Tertiary Consumer/Decomposer: Fungus

Food Web

  • Food chains connected in a community.

  • More complex than food chains, involving multiple organisms at each trophic level.

  • Organisms can be at different trophic levels based on what they eat.

  • Example:

    • Producers: Plants
    • Primary Consumers: Rabbits, insects, deer
    • Secondary Consumers: Fox, birds, humans
    • Tertiary Consumers/Decomposers: Bacteria, fungi

  • Food chains and webs maintain balance; decomposers break down dead organisms for plant nutrients.

  • If the rabbit population decreases, the fox population will decrease and the plant population will increase.

Biomass

  • Total mass of organic matter at each trophic level.
  • Potential energy to be eaten and used.
  • Transfer of biomass is inefficient; only 10% of energy is transferred to the next level (10% law).

Ecological Pyramids

  • Show trophic relationships between consumers and producers at different trophic levels.
  • Indicate the amount of biomass at each level.
  • Kilocalories (kcal) are units of measurement for energy and biomass.
  • Trophic Level Examples:
    • Producers: 1,900 kcal
    • Primary Consumers: 190 kcal
    • Secondary Consumers: 19 kcal
    • Tertiary Consumers:. 1.9 kcal

Biomagnification & Invasive Species

  • Humans can significantly alter ecosystems and food webs.
  • Invasive Species: Non-native species that take over an ecosystem (e.g., nutrias, bamboo).
  • Biomagnification: The increase in concentration of substances (e.g., pesticides like DDT) in organisms at higher trophic levels.
    • DDT example: DDT sprayed on marshes contaminated zooplankton, then small fish, then large fish, and finally fish-eating birds.
    • Larger organisms contain more DDT because they consume more prey.

Populations

  • A population is a group of organisms of the same species in a particular area (e.g., students in a classroom).
  • Population growth rate depends on:
    1. Mortality: Decrease due to deaths.
    2. Natality: Increase due to births.
    3. Immigration: Organisms moving into a population.
    4. Emigration: Organisms leaving a population.

Limiting Factors

  • Any condition that limits the size of a population.
  • Can be biotic (living) or abiotic (non-living).

Main Limiting Factors

  1. Competition: Organisms compete for food, water, space, and sunlight (biotic).
  2. Predation: One organism hunts and eats another (biotic).
  3. Parasitism and Disease: Parasites feed off hosts, and diseases spread easily in high-density populations (biotic).
  4. Pollution: Contaminates food, water, and habitat (abiotic).
  5. Climate: Weather and storms can destroy habitats (abiotic).

Types of Limiting Factors

  1. Density-Dependent: Limit population when it reaches a certain density (e.g., parasitism, disease, competition, predation).
  2. Density-Independent: Affect population regardless of density (e.g., climate, pollution).

Predation Curve

  • Shows the relationship between a predator and its prey.
  • There are usually more prey than predators.
  • If there were more predators, all prey would die, collapsing the ecosystem.

Growth Curves

Exponential Growth

  • Rate of growth increases with each new generation, due to high natality and immigration, and low mortality.
  • Also known as J-shaped growth.
  • Examples: Bacteria and humans.

Logistic Growth

  • Population growth slows or stops after exponential growth.
  • Also known as S-shaped growth.
  • Carrying Capacity: The number of organisms that can be supported by environmental resources.
    • At carrying capacity, births and immigrations equal deaths and emigrations.

Boom and Bust Curve

  • Represents exponential growth followed by a sudden collapse.
  • Can show growth rate over a year or many years (e.g., reindeer graph).

Estimating Population Size

Mark and Recapture Method

  • Ecologists catch, mark (tag), and release a sample of organisms.
  • Later, they recapture another sample and count how many are previously marked.
  • Equation to estimate population size (N): N = \frac{nM}{R} Where:
    • N = Estimated population size
    • n = Number of organisms in the second capture
    • M = Number of marked organisms from the first capture
    • R = Number of recaptures (marked organisms in the second capture)
  • Example:
    • 20 mice captured and marked initially (M = 20)
    • 30 mice captured later (n = 30)
    • 10 of the 30 were tagged (R = 10)
    • N = \frac{30 \times 20}{10} = 60

Age-Structure Diagrams

  • Graphs the number of people in different age groups in a population.
  • Helps predict future population size and indicates socio-economic conditions.
  • Characteristics:
    • Broad base and narrow top: Rapid growth (e.g., Kenya).
    • Equal distribution: Slow growth (e.g., United States).
    • Narrow base and broad top: Zero growth or decrease (e.g., Italy).

Population Interactions

Types of Interactions

  • Competition: Organisms use the same resources (e.g., plants competing for water and sunlight).
  • Predation: One organism (predator) consumes another (prey) (e.g., lion and zebra).
  • Parasitism: One organism (parasite) feeds on another (host), usually causing harm (e.g., tapeworm and dog).
  • Mutualism (Symbiosis): Each organism benefits from the interaction (e.g., birds picking leeches out of alligators' teeth).
  • Commensalism: One organism benefits while the other is unharmed (e.g., barnacle and whale).

Succession

  • When a community re-establishes itself after a disturbance (e.g., fire, human clearing).
  • Primary Succession: First stage of regrowth with pioneer species (e.g., annuals and perennials).
  • Climax Community: Established community, often with hardwood trees.

Aquatic Succession

  • Example: Decomposition of a whale carcass on the ocean floor.
  • Scavengers and decomposers consume the tissue.
  • Decomposition enriches the ocean floor with nutrients, supporting marine worms.
  • Heterotrophs break down the skeleton into chemical compounds for chemosynthetic bacteria.

Climate & Biomes

  • Climate consists of the temperature and precipitation of an area.

Climate Zones

  1. Tropical: 30°-0° (Extremely warm, little temperature variation).
  2. Temperate: 60°-30° (Temperature varies between cold and hot).
  3. Arctic/Polar: 90°-60° (Extremely cold, little temperature variation).

Biomes

  • Consist of biotic and abiotic factors and their interactions.

Major Biomes

  • Tropical Rain Forest: Hot and wet; high rainfall (e.g., sloths in Brazil, Costa Rica).
  • Tropical Dry Forest: Hot with dry and wet seasons (e.g., elephants in India).
  • Savanna: Hot with seasonal rainfall (e.g., lions, zebras, gazelles in Kenya).
  • Desert: Hot and dry; low rainfall (e.g., cactus, jack rabbits in Arizona, USA).
  • Grasslands: Moderate temperature with some rainfall year-round (e.g., bison, prairie dogs in Midwest (Texas), USA).
  • Tundra: Cold and dry; low rainfall (e.g., polar bears, reindeer in Alaska, USA).
  • Boreal Forest (Taiga): Cold with seasonal rainfall (e.g., coniferous forest, moose, wolves, beavers in Russia and Canada).
  • Woodland & Shrubland (Chaparral): Moderate temperature; evergreen shrubs, seasonal rainfall (e.g., coyotes, fox, deer, rabbit in California, USA).
  • Deciduous Forest: Moderate temperature; deciduous trees with cold winters and warm summers; year-round precipitation and fertile soil (e.g., deer, squirrels, raccoons, skunks, songbirds, shrubs, conifers, deciduous trees in Virginia, USA.)
  • Freshwater: Found in ALL climate regions
  • Aquatic
  • Marine
  • Estuaries

Virginia's Biome Profile

  • Virginia is a deciduous forest biome with cold to moderate winters and warm summers.
  • Year-round precipitation and fertile soil.
  • Both terrestrial and aquatic ecosystems.

Terrestrial Ecosystem

  • Dominant plants and wildlife: deer, squirrels, raccoons, skunks, songbirds, shrubs, conifers, and deciduous trees (oak and maple).

Aquatic Ecosystem

  1. Freshwater: Standing and flowing water in the James River.
  2. Estuaries: Where rivers meet the sea, mixing salt and freshwater in the Chesapeake Bay.
  3. Marine: Coastal oceans with saltwater in the Atlantic Ocean.