14.1 Characteristics of PopulationsEwen Lee and Adriena Wong

Special Key Terms

habitat – the place where an organism or species normally lives

species – organisms that resemble one another in appearance, behaviour, chemistry, and genetic makeup, and that interbreed, or have the ability to interbreed, with each other under natural conditions to produce fertile offspring

Population Size and Density

To study populations, scientists measure certain characteristics: Population size Population density (D) Population dispersion

Population Density (D)

The number of individuals of the same species that occur per unit area or volume

D = N/SN = total number counted

S = amount of space

Example

What is the population density of 480 elephants living in a 600 hectare (ha) region?

D = N/S

D= 480 elephants/600 ha

D=0.8 elephants/ha

Population Density

Population density can be deceiving because of the unusable space within a habitat

Ecologists need to distinguish between:

1. Crude Density

2. Ecological Density

Population Dispersion

1. Clumped dispersion

2. Uniform dispersion

3. Random dispersion

Measuring Population Characteristics

Biologists use different techniques to measure population because it is usually unreasonable to count the exact number of organism

This may include: Using a quadrat The mark-recapture method

Mark-Recapture Method

Used for fish species and large animals

Animals are first captured and tranquillized (if necessary)

They are then marked with tags or bands or dye and released

After enough time as passed for the marked animals to mix with the non-marked ones, a second sample is captured

Mark-Recapture Method

M/N = m/nM = total # marked

N = total population

m = # of recaptures

n = size of second sample

Example

Using the mark-recapture method, scientists mark 80 seals were marked and then released. Two weeks later, 110 seals were captured. 12 of them were marked. What is the total size seal population of the area?

N = Mn/m

N = (80)(110)/12

N= 733.33

Technological Tracking

Instead of marking the animals with dye or bands, biologists may also attach radio collars, satellite-linked devices or other equipment to the animals

This helps researchers track animals over a large geographic range.

Patterns can be mapped in geographic information systems (GIS)

Ethics of Studying Wild Populations

People are concerned with the the effects of these techniques:

1. What are the effects on animals being pursued, captured and marked?

2. What are the long-term effects of repeated tranquillizing of large animals?

3. Are marking techniques humane?

4. Can the collars and tags harm the animals?

CCAC

CCAC – the Canadian Council of Animal Care

Is developing ethical guidelines for wildlife research:

1. Researchers must reduce their use of animals

2. Researchers must refine techniques to minimize stress and pain

3. Researchers must replace the trapping of animals with other techniques when possible

THANK YOU