
Population ecology is concerned with:
 Changes in population size
 Factors that regulate population over time
 Essentially, how and why populations change

Population
 A group of individuals of a single species that occupy the same general area
 Described by the number and distribution of individuals

Individuals in a population:
 Rely on the same resources
 Are influenced by the same environmental factors
 Are likely to interact and breed with one another

Population ecology
The study of how and why populations change

Cause of variation in population sizes
 A population increases through birth and immigration
 Death and emigration out of an area decrease the population

Population dynamics
The interactions between biotic and abiotic factors

Population density
 The number of individuals of a species per unit area or volume
 Ecologists use a variety of sampling techniques to estimate population densities

Examples of population density:
 The number of oak trees per square kilometer in a forest
 The number of earthworms per cubic meter in forest soil

Important population variables
Density and dispersion patterns

Dispersion pattern of a population
Refers to the way individuals are spaced within their area

Dispersion patterns can be:

Clumped pattern
Individuals are grouped in patches

Uniform pattern
Individuals are equally spaced in the environment

Random pattern
The individuals in a population are spaced in an unpredictable way

Life tables
Track survivorship over the life span of individuals in a population

Survivorship curves
 Plot the proportion of individuals alive at each age
 Type 1, Type 2, and Type 3

Exponential growth model
 The rate of population increases under ideal conditions
 Calculated using the equation G=rN; G is the growth rate, N is the population size, r is the per capita rate of increase

Logistic growth model
 This growth model takes into account limiting factors
 Limiting factors are environmental factors that restrict population growth

Boomandbust cycles
 Food shortages
 Predatorprey interactions

Age structure diagram
Reveals a population's growth trends

US Census Bureau projection
 8 billion people within the next 20 years
 9.5 billion by the mid21st century

Ecological footprint
Helps understand resource availability and usage


