Ecology & Population Ecology Notes

Ecology

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

Biotic Components

The living species are categorized into three main groups:

1. Producers (Autotrophs): Organisms that produce their own food (self-feeders).

   • Examples: Plants, Protists, Bacteria

2. Consumers (Heterotrophs): Organisms that cannot produce their own food and must consume other organisms (other feeders).

   • Examples: Animals, Protists, Fungi, Bacteria

3. Decomposers: Consumers that break down dead plants and animals.

   • Examples: Fungi, Bacteria

Types of Producers

• Autotrophs: Use sunlight to create food (e.g., plants).

• Chemotrophs: Use chemicals to create food, especially in environments lacking sunlight (e.g., bacteria around volcanic vents using hydrogen sulfide).

Types of Consumers

Consumers are further divided into five groups:

1. Scavengers: Feed on dead tissues (detritivores) (e.g., vultures, hyenas).

2. Herbivores: Consume only plants (e.g., deer, rabbits, some insects).

3. Carnivores: Consume only meat (e.g., lions, tigers, sharks).

4. Omnivores: Consume 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 combination of producers, consumers, and decomposers in a specific area (e.g., trees, bacteria, fungi, foxes, rabbits, birds in a forest).

• Trophic Level: Each step in the transfer of energy through an ecosystem involving producers, consumers, and decomposers.

• Food Chain: A simple, direct sequence that shows what eats what and the transfer of energy from one organism to another, involving only one organism at each trophic level.

Food Chain Example

• Food Web: Interconnected food chains in a community, which are more complex than food chains and involve multiple organisms at each trophic level.

Food Web Example

Producers (plants) are consumed by primary consumers (rabbits, insects, deer), which are then consumed by secondary consumers (fox, birds, humans), and eventually, decomposers (bacteria, fungi) break down dead organisms.

Note: Organisms can occupy different trophic levels in a food web depending on their diet.

Food chains and food webs maintain balance within an ecosystem. Decomposers are essential for breaking down dead organisms into plant nutrients.

Impact of Population Changes

• If the rabbit population decreases, the fox population would likely decrease as well, while the plant population would increase.

Biomass and Energy Transfer

• Biomass: The total mass of organic matter at each trophic level, representing potential energy.

• 10% Law: Only about $10\%$ of the energy from one trophic level is transferred to the next level. This inefficiency limits the number of trophic levels in an ecosystem.

• Ecological Pyramids: Visual representations showing the trophic relationships and biomass at each level. Kilocalories (kcal) are units of measurement for energy and biomass.

Human Impact

Biomagnification & Invasive Species

*Humans can significantly alter ecosystems.

• Invasive Species: Non-native species that can dominate an ecosystem (e.g., nutria and bamboo in Virginia).

• Pesticides & Pollution: Pesticides like DDT can contaminate groundwater, enter streams, and accumulate in organisms through biomagnification.

• Biomagnification: The concentration of toxins, such as DDT, increases as it moves up the food chain because larger organisms consume more contaminated prey.

DDT Example and Biomagnification

Microscopic water animals were contaminated by DDT, and consumers of these zooplankton became contaminated. As the food chain progressed, larger consumers contained more DDT.

Populations

• Population: A group of organisms of the same species living in a particular area (e.g., students in a classroom).

• Population Growth Rate: Depends on four main factors:

  1. Mortality: Decrease in population due to deaths.

  2. Natality: Increase in population due to births.

  3. Immigration: Organisms moving into a population; increases population size.

  4. Emigration: Organisms leaving a population; decreases population size.

Limiting Factors

• Limiting Factor: Any condition that restricts the size of a population.

• Limiting factors can be biotic (living components like predators, prey) or abiotic (non-living components like temperature, precipitation, storms).

Main Limiting Factors

1. Competition: Organisms compete for resources like food, water, space, and sunlight.

2. Predation: One organism (predator) hunts and eats another (prey); affects both populations.

3. Parasitism and Disease: Parasites feed off a host, and diseases spread easily in dense populations.

4. Pollution: Contamination of habitat, reducing available resources.

5. Climate: Weather conditions can destroy habitats.

Types of Limiting Factors

1. Density-Dependent Factors: Limit population growth as population density increases (e.g., parasitism, disease, competition, predation).

2. Density-Independent Factors: Affect a population regardless of its density (e.g., climate, pollution).

Predation Curves

A predation curve illustrates the relationship between predator and prey populations. Typically, there are more prey than predators.
If there were more predators than prey, all the prey would die off, leading to the collapse of the ecosystem.

Population Growth Curves

Exponential Growth

Occurs when the growth rate in each new generation is a multiple of the previous generation, characterized by high immigration and natality and very low mortality. This is also known as a J-curve. Examples include bacteria.

Logistic Growth

Occurs when population growth slows or stops after a period of exponential growth, resulting in an S-shaped curve. A key concept in logistic growth is the carrying capacity.

• Carrying Capacity: The maximum number of organisms an ecosystem can support with its available resources. At carrying capacity, births and immigration equal deaths and emigration.

Boom and Bust Curve

A boom and bust curve represents exponential growth followed by a sudden population collapse, influenced by factors like resource availability.

Population Estimation

Mark and Recapture Method

Ecologists use this method to estimate population size. Organisms are captured, tagged, and released. A second sample is captured, and the number of recaptured tagged individuals is used to estimate the total population size.

• Equation: $N = \frac{nM}{R}$

  • $N$ = Estimated population size

  • $n$ = Number of organisms in the second capture

  • $M$ = Number of marked organisms from the first capture

  • $R$ = Number of recaptured (marked) organisms in the second capture

• Example: If 20 mice are captured and tagged initially ($M = 20$), and later 30 mice are captured with 10 being tagged ($n = 30$, $R = 10$), then $N = \frac{30 \times 20}{10} = 60$ mice.

Age-Structure Diagrams

An age-structure diagram graphs the number of people in different age groups within a population. These diagrams help predict future population sizes and indicate socioeconomic trends.

• A broad base and narrow top indicate a growing population.

• A narrow base and broad top indicate a declining or stable population.

Population Interactions

There are several ways populations of organisms interact:

Succession

*When an area is destroyed by a fire or cleared by humans, succession is the process by which a community tries to reestablish itself.

• There are two types of succession:

  • Primary Succession: The first stage of regrowth, involving pioneer species like annuals, mosses, lichens, and perennials. These species help break down the substrate and create soil. This occurs in areas where no soil previously existed, such as after a volcanic eruption or glacial retreat.

  • Secondary Succession: Occurs in areas where soil is already present but the existing community has been disturbed or removed (e.g., after a fire, flood, or human activity). It starts with fast-growing plants like grasses, then shrubs, followed by pinewood trees. Because soil is present, secondary succession tends to be faster than primary succession.

• Climax Community: The final, stable community, often consisting of hardwood trees.

Aquatic Succession with whale carcass

In aquatic environments, succession involves the decomposition of a whale carcass. Scavengers and decomposers consume the tissue, enriching the ocean floor with nutrients. Heterotrophic bacteria break down the skeleton into compounds that chemosynthetic bacteria use.

Climate & Biomes

• Climate: The average 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 seasons).

3. Arctic/Polar: 90°-60° (Extremely cold, little temperature variation).

• Biome: A large geographic area characterized by specific climate conditions, animal populations, and plant species that interact with each other.

Major Biomes

Virginia Biome Profile

• Climate: Cold to moderate winters and warm summers with year-round precipitation.

• Deciduous forest biome with terrestrial and aquatic ecosystems.

Terrestrial Ecosystem

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

Aquatic Ecosystem

Composed of:

1. Freshwater: Standing and flowing water (e.g., James River).

2. Estuaries: Where rivers meet the sea, mixing salt and freshwater (e.g., Chesapeake).

3. Marine: Coastal oceans with saltwater (e.g., Atlantic Ocean).