PopulationsPopulationsEcology Unit

Newark Academy Summer Session 2014

PopulationPopulation

A group of organisms all of the same species living within a particular place at the same time

Population SizePopulation Size

Population size is the number of individuals it contains.

Size is a fundamental and important property of a population but it can be difficult to measure directly.

Population DensityPopulation Density

Population density is the number of individuals per unit area or volume.

Population density helps to measure how crowded a population is.

Population Dispersion – describes Population Dispersion – describes the spatial distribution of the spatial distribution of individuals within a population.individuals within a population.

Population DynamicsPopulation Dynamics

All populations are dynamic – they change in size and composition over time.

Birth rate: number of births occurring in a period of time.

Death Rate: (mortality rate) number of deaths in a period of time.

How do these terms relate to population growth?

Age Structure : The distribution of Age Structure : The distribution of individuals among different ages individuals among different ages in a population.in a population.

Patterns of Mortality – Patterns of Mortality – Survivorship CurvesSurvivorship Curves

Survivorship CurvesSurvivorship Curves

Population Growth RatePopulation Growth Rate

The amount by which a population’s size changes in a given time.

Influenced by four factors:◦Birth rate◦Death rate (mortality rate)◦Immigration◦Emigration

Calculating ChangeCalculating Change

Per capita = Per individualBirth rate / 1,000 individualsDeath rate / 1, 000 individuals

Birth rate – death rate = growth rate / capita

What if it is a negative number?What if it is a positive number?

Calculating ChangeCalculating Change

Suppose there are 38 births / 1,000 people (birth rate = 0.38)

There are 89 deaths / 1,000 people (death rate = 0.89)

Calculating change (growth rate or N):

0.38 – 0.89 = -0.51 What is happening to the population?Assuming the current population is 200,000

people, what will be expected population the following year?

Population Growth - Population Growth - ExponentialExponential

Limiting FactorLimiting Factor

A factor that restrains the growth of a population is known as a limiting factor.

Examples of limiting factors include (but not limited to) ◦Food◦Space◦Ability to eliminate waste◦Dissolved oxygen

Logistic Model of Population Logistic Model of Population GrowthGrowth

The Logistic Model of population growth builds on the exponential model but takes into consideration limiting factors.

The logistic model takes into consideration the carrying capacity of the environment.

Carrying capacity (K) = the number of individuals an environment cam support over a long period of time.

Logistic ModelLogistic Model

Exponential vs. LogisticExponential vs. Logistic