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.