Chapter 8: Understanding Populations Section 1: How Populations Change in Size Part 1

Properties or Populations

Population Properties  Population  A set of individuals within a species living in the same place at the same time.  Properties of Populations  Population Size  Population Density  Population Dispersion

Population Properties  Population Size  Total # of individuals  EX: Population = 800  Population Density  # of individuals per unit of area.  EX: 800/km 2

Population Properties  Population Dispersion  Arrangement of the population’s individuals  Can be:  Even  Clumped  Random.

How Does a Population Grow?

Growth Rate  Growth Rate = Birth Rate – Death Rate  Positive (+) G.R. = More births than deaths  Zero (0) G.R. = same births as deaths  Negative (-) G.R. = less births than deaths

Reproductive Potential  Reproductive Potential  Maximum number of offspring that each member of the population can produce.  Organisms have high R.P. when:  Low age of reproduction  Can reproduce many times  Have greater than 1 offspring at a time.

Reproductive Potential  Example of Low R.P.  Elephants  Begin mating around 20 years of age.  Gestation period is 22 months.  Females usually have 4-6 calves over a 60 year lifetime.  Example of High R.P.  Rabbits  Sexually mature around 6 months of age.  Gestations period is about 30 days  Average litter is 4-12 offspring

What Limits Population Growth?

Carrying Capacity  Natural conditions are neither ideal or perfect.  Populations can not grow at their reproductive potential forever.  Carrying Capacity  Maximum population that an ecosystem can support  Pop size where births and deaths are equal.

Carrying Capacity  A population may increase beyond its’ carrying capacity, but not for long.  Resources get used up quickly and the population will soon decrease.

Carrying Capacity  A species reaches carrying capacity when it uses a resource at the same rate that natural replenishes the resource.  Limiting Resource  Resource that determines the growth of the species.