Lesson 3.1

• Biologie
• Middelbare school
• vwo
• Leerjaar 4

Populations

What is a population?

With reference to the following statements about a woodland ecosystem. Which statement describes a population?

1. All the oak trees
2. All the plants
3. All the plants and animals

Population size

immigration

emigration

death

birth

Population growth

Involves:

1. Biotic potential: max reproduction rate given all the resources the population needs
2. Environmental resistance: all factors that may limit growth. (scarcity of resources, predation, climate conditions etc)
3. Carrying capacity: max population size that can be supported by a particular environment

Population curves

• J-curve: often seen in fast reproducing organisms that colonise a new environment. Exponential growth followed by hitting a limiting factor and often the population crashes
• S-curve: Exponential growth until population hits environmental resistance and stabilises around the carrying capacity

Carrying capacity

Environmental resistance

Few reproducing individuals

Exponential growth

What is population density?

Environmental resistance

Can be:

• Density indepent: these factors influence all organism in a population irrespective of population density. Can be biotic of abiotic
• Density dependent: the influence of these factors on population size depend on the density of the population. Usually the higher the density the bigger the impact of these factors. Always biotic

Density independent

Density dependent

Light

parasitism

earthquake

competition

disease

Measuring population

Size and density

Why?

• Knowing if population is increasing or decreasing
  - Useful for predicting future developments 
  - Understanding if conservation is working

How?

• Ideally exact numbers, but total count is often not possible
• Therefor, estimates of size
• Method used for estimates mainly depends on the type of organism
• Plants/ not very mobile animals: quadrat or transect (first video)
• Mobile animals: mark-recapture (second video)

What is a square called that we use to sample populations?

1. grid
2. quadrat
3. cube
4. quarter

These four 1m2 squared quadrats were place in a 8m2 garden. Estimate the total population of flowers in the whole garden.

1. 16
2. 8
3. 40
4. 20

Which one of these is a correct assumption you need to make about a population between samplings?

1. It is a closed population
2. It won't rain between samplings
3. There are lots of deaths
4. There are lots of births

If 50 crabs were captured and marked and then released and then a few days later 25 were caught and of those 5 were marked. What would the estimate of the population be?

1. 500
2. 250
3. 75
4. 200

Homework

• Read pages 440-441, 450-451
• Complete this lessonup
• Complete worksheet population size on Classroom