8.3 - 8.4 - Population Ecology

Definition and Importance

• Population: A group of individuals of the same species that interact with each other and their environment.

• Population Ecology: Analyzes factors that affect population size and how and why it changes over time.

Key Concepts

1. Density:

   • Definition: The number of individuals per unit area.

   • Influences: Determined by resource availability in the environment (e.g., food, space, light).

2. Population Growth:

   • Per Capita Rate of Increase: Calculated using the formula dN/dt = B - D

     • dN: Change in population size.

     • dt: Change in time.

     • B: Birth Rate.

     • D: Death Rate.

Models of Population Growth

1. Exponential Growth Model:

   • Description: Describes a population living under ideal conditions with abundant resources and freedom to reproduce.

   • Growth Pattern: Population grows rapidly at a constant rate, forming a J-shaped curve.

   • Formula: dN/dt=rmax*N

     • dN: Change in population size.

     • dt: Change in time.

     • rmax​: Maximum per capita growth
       rate of the population.

     • N: Population size.

Visual Representation

• Exponential Growth: Typically depicted as a J-shaped curve on a graph where the y-axis represents population size and the x-axis represents time.

Logistic Growth Model

Description: The logistic growth model describes population growth that slows as the population size nears its carrying capacity. This model is more realistic for populations in natural environments.

Formula: dN/dt=rmax*N((K−N)/K)

• dN: Change in population size

• dt: Change in time

• rmax​: Maximum per capita
  growth rate of the population

• N: Population size

• K: Carrying capacity