Populations are dynamic.What influences them?

How do we measure them?Why is measuring them useful?

Why do different organisms have different reproductive rates?

Core PopulationsOutline how population size is affected by natality, immigration, mortality and emigration. (2)Draw and label a graph showing aExplain the reasons for the exponential growth phase, the plateau phase, and the transitional phase betweenthese two phases. (2)List three factors that set limits to population increase. (1)Σpopulation growth curve. (1)   Describe one method of random sampling, based on quadrat methods that is used to compare the population sizeof two plant or two animal species. (2)Outline the use of a transect to correlate the distribution of plant or animal species with an abiotic variable.(2)

Population ecology Option G   http://sciencevideos.wordpress.com/bis-ib-diploma-programme-biology/05-ecology-evolution-and-conservation/03-populations/    Distiguish between r-strategies and K-strategies. (2)Discuss the environmental conditions that favour either r-strategies or K-strategies. (3)Describe one technique used to estimate the population size of an animal species based on a capture-mark-release-recapture method. (2)Describe the methods used to estimate the size of commercial fish stocks. (2)Outline the concept of maximum sustainable yield in the conservation of fish stocks. (2)Discuss international measures that would promote the conservation of fish. (3)

If the first graph shows a growing population, can you draw 3 similar images for 1. a population in decline and 2. a population that is stable.

In reality most populations exhibit signs of all three at some point.

The Phases

What are the limiting factors to population growth?

Where is the human population right now?

Our growth phase

Population:

• A group of individuals…• … of the same species…• … living in a certain defined area.

Question: How do you measure the size of a population?

Plants and sedentary animals are easy to count…

1

23

4

12

34

1Large animals which are present in small numbers are also easy to count…

• Small animals which move about a lot are more difficult to count…

•… especially if there are large numbers of them!

• Scientists have to find a way of estimating the size of the population.

The Lincoln Index•Since it is impossible to count every single individual in a large population, a method of marking the animals is used.

• We call this a Mark-Release-Recapture method: • Animals are captured, marked and released, then…• A second sample of animals is captured, and the marked animals recorded.•We can estimate the size of the population from the number of recaptured (marked) animals

The Practicalities

1. Capture a large number of animals

The method of capture should not cause the animals any undue stress which might make them more vulnerable…

Example 1:

Shoot them…

… with a tranquilliser dart

Example 2:

Pitfall traps

Example 3:

For aquatic animals…

… netting

…or make it more obvious to predators

2. Mark the animals

e.g. with non-toxic paint

It is important that the manner of the marking does not affect the behaviour of the animal…

3. Release the animals back into their environment

Animals go about their daily business…

…and generally mix with other animals

4. A couple of days later…

… capture a new sample

5. Estimate the population size using the Lincoln index

LincolnIndex

=Number marked in second sample

Total caught in second sample=

Total marked in whole population

Size of whole population

Remember: Total marked in whole population is the same as the size of the first sample!

Working out population size, x

x =Size of First sample Size of Second sample×

Number marked in second sample

For our example…

Size of first sample = 8

Size of second sample = 9

Number marked in second sample = 3

Size of Second samplex =

Size of First sample ×

Number marked in second sample

=8 × 9

3= 24

How accurate is our estimate?

Estimates are more accurate if:

1. there is enough time between samples to allow animals to mix with rest

2. no animals migrate into or out of the population

PERU

3. the procedure is repeated several times

(For each repeat, animals should be marked with a different colour or on different parts of their bodies)

What about real populations that are endanger?

Solutions?