Ecology and Population Dynamics: Study Notes for General Biology

Ecology and Population Dynamics

Discovering Ecology

Ecology is the scientific study of interactions among organisms and their environment. Ecologists investigate how living things interact with each other and with nonliving components of their surroundings.

• Features Studied by Ecologists: Ecologists focus on distribution (where organisms live) and abundance (how many organisms are present).

Earth's Climate Influences the Distribution of Terrestrial Biomes

Biomes are large ecological areas on Earth's surface, with distinct climate, flora, and fauna. Climate is a major factor in determining the distribution of biomes.

• Biotic and Abiotic Components: Biotic components are living things (plants, animals, microbes). Abiotic components are nonliving factors (temperature, water, sunlight, soil).

• Major Abiotic Factors: Temperature, precipitation, sunlight, and wind are key abiotic factors shaping climate and biome distribution.

• Biome Location: Biomes are located based on climate patterns, which are influenced by latitude, altitude, and proximity to water bodies.

Aquatic Biomes are Diverse and Dynamic Systems that Cover Most of Earth

Aquatic biomes include freshwater and marine environments, each with unique physical and chemical properties.

• Diversity of Aquatic Biomes: Aquatic biomes are classified by salinity, depth, and water movement (e.g., lakes, rivers, oceans, estuaries).

• Distribution Factors: Abiotic factors such as light penetration, temperature, and nutrient availability determine the distribution of aquatic biomes.

Interactions Between Organisms and the Environment Limit the Distribution of Species

The distribution of species is limited by both biotic and abiotic factors. Ecologists ask questions to understand these limitations.

• Types of Questions: Ecologists may ask about physical barriers, resource availability, competition, predation, and climate.

• Examples of Limiting Factors: Abiotic: temperature, water, soil pH. Biotic: predation, competition, disease.

Biotic and Abiotic Factors Affect Population Density, Dispersion, and Demographics

Population ecology studies how populations change over time and space, focusing on density, dispersion, and demographic patterns.

• Density vs. Dispersion: Density is the number of individuals per unit area. Dispersion describes how individuals are spaced (clumped, uniform, random).

• Methods for Estimating Density: Sampling, mark-recapture, and direct counts are common methods.

• Dispersion Patterns: Clumped (most common, due to resource availability), Uniform (territoriality), Random (least common).

• Population Characteristics: Populations are described by survivorship curves: Type I (high survival early, low later), Type II (constant death rate), Type III (high death rate early, survivors live long).

The Exponential and Logistic Models Describe the Growth of Populations

Population growth can be modeled mathematically. The two main models are exponential and logistic growth.

• Exponential Growth: Population increases rapidly under ideal conditions, without limiting factors.

• Logistic Growth: Population growth slows as it approaches carrying capacity (K), due to limited resources.

• Carrying Capacity (K): The maximum population size an environment can sustain.

• Equations:

Exponential Growth Equation:

$\frac{dN}{dt} = rN$

Logistic Growth Equation:

$\frac{dN}{dt} = rN \left( \frac{K-N}{K} \right)$

• Terms in Logistic Model:

  • r: Intrinsic rate of increase

  • K: Carrying capacity

  • N: Population size

Population Dynamics are Influenced Strongly by Life History Traits and Population Density

Population growth is affected by life history traits (e.g., age at reproduction, number of offspring) and density-dependent or density-independent factors.

• Life History Traits: Strategies organisms use to maximize survival and reproduction (e.g., r-selected vs. K-selected species).

• Density-Dependent Factors: Effects increase with population density (e.g., competition, disease).

• Density-Independent Factors: Effects are unrelated to population density (e.g., weather, natural disasters).

• Examples:

  • Density-Dependent: Food shortage, predation, disease spread.

  • Density-Independent: Floods, droughts, temperature extremes.

Survivorship Curves: Types and Characteristics

Survivorship curves graphically represent the number of individuals surviving at each age.

Type	Description	Example Organisms
Type I	High survival in early/middle life, increased mortality in old age	Humans, large mammals
Type II	Constant mortality rate throughout life	Birds, rodents
Type III	High mortality early in life, few survivors live long	Fish, marine invertebrates

Test Your Understanding

• Factual Statement: Practice writing out questions as factual statements to reinforce learning.

• Hypothesis Formation: Develop hypotheses based on observations and scientific reasoning.

Additional info: Academic context and definitions have been expanded for clarity and completeness.