POPULATION STUDIES

Growth of populations

FACTORS INCREASING POPULATION

FACTORS DECREASING POPULATION

• BIRTH• IMMIGRATION

• DEATH• EMIGRATION

CALCULATING GROWTH RATE OF A POPULATION

• Growth rate = (birth rate + immigration rate) – (death rate + emigration rate)

For example

When the growth rate is >0 the population is increasingWhen the growth rate is <0 the population is decreasing

Quantifying risk

Which population is at a more significant risk of displaying a significant decline in population numbers? Why?

Distribution

Measuring Distribution

• A line transect is the best method to use when measuring changes along a land surface. Gradual changes in environment are referred to as environmental gradients

Measuring Abundance

• There are 3 methods of measuring abundance

1. Direct observation

2. Quadrat

3. Capture – mark - recapture

Direct observation

• Time consuming

• Involves monitoring a particular area either by being present on capturing an entire area by photograph and counting the individuals present

Quadrat• Used to measure density of organisms that do not move very much (e.g. plants,

some insects, etc) a quadrat is an effective method used to make predictions on population numbers.

• Quadrat’s involve the marking out of a square area for observation(usually 1m X 1m)

The following is observed- The number of individuals of each species is counted or the relative number of each species is estimated using a scale from abundant (3) to absent (0)- The percentage of cover is estimated - The totals of the quadrat are averaged- The use of a simple mathematic calculation can give the total number or % cover for each species

AVERAGE DENSITY OF MEMBER SPECIES = TOTAL NUMBER OF INDIVIDUALS COUNTED ÷ AREA OF EACH QUADRAT x NUMBER OF QUADRATS

This will give you an average of the number of individuals found per square meter

Capture – mark - recapture

• Commonly used to measure abundance of mobile species.

• Step 1: Capture: Animals are caught randomly

Step 2: Mark: Each captured animal is marked then returned to its habitat

Step 3: Recapture: Later a random sample is taken and the number of marked animals is compared to the number or unmarked animals captured. From this information a total population can be estimates

MARK CAPTURE REMARK

Carrying Capacity

The Carrying capacity of an ecosystem refers to the levels of life sustaining resources an environment contains.

It has been estimated that 100km2 of moist tall eucalypt forest is the minimum area possible to support 10 000 sugar gliders as a viable population.

POPULATION REGULATION

POPULATION REGULATION

OVERVIEW OF POPULATION

RESTORING / CONTROLLING POPULATIONS

• Student task

Pg 331, 331 of Nelson Biology units 1&2

Write a summary of current methods used to control and restore population numbers