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.