Population Ecology Review

Definition of Population

  • A population is a group of individuals of the same species living in a specific area.

Population Ecology

  • Population ecology focuses on studying populations and analyzing factors that affect population size and their changes over time.
  • Math in Population Ecology:
  • Math concepts are included but are less emphasized in exams.
  • Key to understand how to use and apply equations provided on exams.

Understanding Density

  • Density is the number of individuals per unit area.
  • Determining density can rely on:
  • Counting individuals: Effective in small areas.
  • Sampling techniques: Count in small areas and extrapolate to estimate total population size.
  • Knowing population density provides insight into:
  • Availability of resources for growth and sustainability.
  • Relationships between population sizes and resource use.

Body Size and Population Density

  • Larger species tend to have lower population densities because they require more resources for sustenance compared to smaller species.

Dispersion Patterns

  • The dispersion of individuals within a population can be:
  • Clumped: Individuals are gathered in patches.
  • Uniform: Evenly spaced individuals, often due to territoriality or resource limitation.
  • Random: Unpredictable spacing with no clear pattern.

Population Dynamics

  • Population sizes are dynamic, influenced by births, deaths, immigration, emigration, and external factors like disease and disasters.
  • Demography: The study of vital population statistics and changes over time.

Life Tables and Survivorship Curves

  • Life tables summarize survival patterns across different ages.
  • Survivorship Curves Types:
  • Type 1: Low death rates early in life; high rates later (e.g., humans).
  • Type 2: Constant death rate across lifespan (e.g., many birds).
  • Type 3: High death rates early on with lower rates for survivors (e.g., many trees).

Population Growth Models

  • Exponential Growth Model:
  • Populations grow under ideal conditions with unlimited resources, leading to a J-shaped growth curve.
  • Formula:
    • ( \frac{dn}{dt} = r_{max} \cdot n )
  • Logistic Growth Model:
  • Population growth slows as it approaches carrying capacity, leading to an S-shaped curve when resources become limited.
  • Formula:
    • ( \frac{dn}{dt} = r_{max} \cdot n \cdot \frac{K - n}{K} )
  • Where K is the carrying capacity.

Life History and Selection

  • Life History: Traits that influence an organism's reproductive and survival schedules; influenced by:
  • Timing of reproduction.
  • Frequency of reproduction.
  • Number of offspring produced.
  • K-selection: Traits sensitive to population density in high-density populations (density-dependent).
  • r-selection: Traits that maximize reproductive success in low-density environments (density-independent).

Density-Dependent vs. Density-Independent Factors

  • Density-Dependent Factors:
  • Affect population growth based on density, e.g., competition, disease.
  • Lead to changes in birth and death rates.
  • Density-Independent Factors:
  • Impact populations regardless of density, e.g., natural disasters.
  • Do not change birth or death rates directly.

Practice Problems

  • Exercises included in the packet for calculating growth rates and understanding models based on real-world scenarios.