Population Ecology

How biotic and abiotic factors influence size, distribution, density, and composition of populations

Population Ecology

What is population?

A group of individuals of a single species living in the same area at the same time

Define Density

Number of individuals per unit area or volume

Define Distribution

What are the three Patterns of Dispersion?

1. Clump Distribution

2. Random Distribution

3. Uniform Distribution

Individuals that are found in groups or patches within their particular habitat. The presence of other individuals increases their fitness. Usually prey, few predators (wolves) This is known as…

Clump Distributions

When does Random Distribution usually occur?

When there is an absence of strong attractions or repulsion’s from among individuals

Define Random Distribution

Individuals are spread out in the environment irregularly; the position of one individual is independent of another.

What results from direct negative interaction between individuals?

Uniform Distribution & Territoriality

Uniform Distribution is…

a distribution pattern where individuals are evenly spaced in an environment due to competition or territorial behavior.

-Rare in nature

-Presence of one hinders another

-Distance between individuals is maximized

Territoriality

a behavior exhibited by individuals to defend and maintain exclusive use of a specific area, often to secure resources such as food, mates, or nesting sites. Boundaries are created

How to calculate population size?

1.Census

2.Survey

What does the Census do?

Counts every individual in the population

*The MOST accurate but usually not feasible/practical

What does a Survey do?

Estimates population size by sampling a subset of individuals instead of counting them all, then extrapolating to the geographic range.

*Can be modified based on pop size, geographic range THOUGH some info about the population is needed beforehand, usually feasible/practical

Survey is most effective when

Uniform Distributed or Random Distribution is occuring

Survey NOT effective when…

Clump Distribution is occurring

Examples of Survey Types

1.Area/Volume based survey

2.Line Survey (transect), counting as you move along a line - used when organism that are large (birds or large mammals), not effective if geographic range is large

3.Mark and Recapture survey - VERY effective for birds and large mammals

How to calculate Mark and Recapture Density?

Example of how to calculate density

N = (S*n)/x

N = (328)(200)/64

N = ~1025 individuals

True or False

Immigration

Influx of new indi

Define Demography

study of the vital statistics of a population and how they change over time

*Often done using life table

What are Life Tables and what do they do?

It summarizes the mortality and survival rates of a population, showing how these factors affect demographic changes over time.

-Developed in the 1950s for insurance companies

Types of Life Tables

1. Cohort Table - follows groups of same aged individuals from birth until they all die

2. Static Life tables - made from data collected at all ages at one time

Static Life Table

A type of life table that summarizes the mortality and survival rates of a population from data collected at one specific point in time.

• Static/stationary (vertical)

• A specific point in time (snapshot) of all individuals regardless of age

Cohort Table

• Dynamic (horizontal)

• Much harder to do

• Takes more time and money

• Takes into account birth until death

The first column (x) specifies the age class while the second column (N_x) is the number of individuals at start of each age class

As (x) increases, (N_x) is equal to or less than the previous (N_x) value

Demographic types

1. Semelparity

2. Iteroparity

Semelparity

Have only ONE reproductive event in their lifetime

Iteroparity

Capable of multiple reproductive events

45,617 divided by 2187 = each has an average of 20.86 kids

If R₀ = less than 1; population is declining

If R₀ = 1; population is replacing itself

If R₀ = greater than 1; population is growing

What does T represent and how is it calculated 

T represents the generation time

In this case T = 7 months

What is r and how is it calculated?

Per capita rate of increase

What is R

Net reproductive rate