Populations

Population Studies Overview

  • Levels of Biological Organization

    • Organism

    • Population

    • Community

    • Ecosystem

    • Biosphere

Population Characteristics

  • Groups of Species

  • Density Variability

    • Dispersion Patterns:

    • Clumped

    • Random

    • Uniform

    • Variations:

    • Size

    • Age

    • Genetic Composition

Mortality Rates of Various Species

  • Fish (Tuna): 6,000 per year

  • Frog: 200 per year

  • Hare: 12 per year

  • Large Cat (Puma): 2 per year

  • Chimpanzee: 1 every 5 years

r-selected vs. K-selected Species

  • r-selected Species:

    • Example: Species that produce many offspring quickly; high mortality rates during early life stages.

  • K-selected Species:

    • Example: Species that produce fewer offspring but invest more time and resources into nurturing; typically characterized by lower mortality rates.

Survivorship Curves

  • General Description:

    • Graph showing the number of individuals surviving at each age for a given species.

  • Types of Survivorship Curves:

    • Type I (Convex curve)

    • Characteristic: Late loss; high survivorship throughout life.

    • Examples: Humans, Elephants, annual plants.

    • Typical of: K-selected species.

    • Type II (Diagonal curve)

    • Characteristic: Constant loss; independent of age.

    • Examples: Birds, rodents, Hydra, perennial plants.

    • Type III (Concave curve)

    • Characteristic: Early loss; low mortality after maturity.

    • Examples: Small fish.

    • Typical of: r-selected species.

Population Change Calculation

  • Population growth equation:

    • Growth = (Births - Deaths) + (Immigration - Emigration)

    • Understanding Factors:

    • Births and immigration add individuals to a population.

    • Deaths and emigration remove individuals from a population.

Immigration and Emigration Defined

  • Immigration:

    • Movement of individuals into a population.

  • Emigration:

    • Movement of individuals out of a population.

Population Density

  • Definition:

    • Population Density = Population / Area of Land

Population Growth Dynamics

  • Exponential Growth:

    • Defined as an “unlimited” rate of growth where the birth rate exceeds the death rate.

    • Initial slow growth when population is small, followed by a rapid increase as it enlarges.

Logistic Growth

  • Definition:

    • Growth that is limited by certain limiting factors.

    • Characterized by an initial period of exponential growth followed by stabilization as the population approaches its carrying capacity.

Carrying Capacity

  • Definition:

    • The largest population that an environment can support at any given time.

Factors Affecting Carrying Capacity

  • Examples of Limiting Factors:

    • Disease / Parasites

    • Accidents

    • Starvation

    • Hunting

    • Natural disasters (e.g., fires, floods)

    • Predation

Density-Dependent vs. Density-Independent Limiting Factors

  • Density-Dependent Factors:

    • Starvation

    • Disease transmission

    • Resource competition

  • Density-Independent Factors:

    • Tornadoes

    • Droughts

    • Freezing weather

Population Pyramids

  • Types of Population Growth:

    • Expanding rapidly

    • Expanding slowly

    • Stable

    • Declining

  • Population age groups typically categorized as:

    • Ages 45+

    • Ages 15-44

    • Under 15