5.3 POPULATION DYNAMICS

Population: A group of individual of the same species living in a defined area that have the potential to interbreed and produce fertile offspring.

IB 5.3 Assessment Statements5.3.1 Outline how population size is affected by natality, immigration, mortality, and emigration.

5.3.2 Draw and label a graph showing a sigmoid (S-shaped) population growth curve.

5.3.3 Explain the reasons for the exponential growth phase, the plateau phase, and the transitional phase between these two phases.

5.3.4 List three factors that set limits to population increase.

5.3.1 Outline how population size is affected by natality, immigration, mortality and emigrationOutline: give a brief account or summary.

In ecosystems, population sizes fluctuate (change) over time for a variety of reasons:

1. Natality: Birth Rate

2. Mortality: Death Rate

3. Immigration: Members arriving from other places.

4. Emigration: Members leave the population.

Side Note: Density Independent vs. Dependent Variables

Density independent and Density dependent variables can affect population sizes in addition to the aforementioned factors.

What’s the difference?Density Independent Factors: factors like drought, fire, intense

weather, hurricanes, etc. that will reduce population size independent of population density.

Density Dependent Factors: factors like competition, disease, predation, and parasitism that tend to increase with increasing populations numbers.

Mount Saint Helens Eruption – 1980

Then & Now

5.3.2 Draw and label a graph showing a sigmoid (S-shaped) population growth curve

• Draw and label: represent by means of pencil lines and/or add labels to a diagram.

S-Shaped Growth Curve – 5.3.3(Defined & Explained)

1. The Exponential or Logarithmic Growth Phase: The number of individuals increases at a faster and faster rate. Causes:• Abundant food, space, or light.• Little or no competition for resources.• Favorable abiotic factors like temperature or dissolved oxygen levels.• Little or no predation or disease.

2. The Transitional Phase: The growth rate slows down considerably—the population is still increasing but at a slower and slower rate. Causes:• More individuals means more competition for resources, limited space, faster spread of

disease.• More individuals means more predators.

3. The Plateau or Stationary Phase: The number of individuals has stabilized—there is no more growth. Causes:• Predators and disease increase mortality.• Food supply is limited so organisms have fewer offspring.• The number of births + immigrations is balanced with the number of deaths + number of

emigrations.

Bacterial Growth(An example of Logistic Growth)

Brain TeaserAn illustration of the power of exponential growth

Exponential Growth

Human Population Calculator & (What’s Your Number?)

Carrying Capacity (K)Populations cannot continue to grow and grow forever.

Population numbers will eventually stabilize.

Carrying Capacity (K): The maximum number of individuals that a particular habitat can support.

5.3.4 List three factors that set limits to population increase/ size• List: give a sequence of names or other brief answers with no explanation.Limiting Factors: Those factors in an environment/ ecosystem that set limits to population growth.

Examples of limiting factors for ANIMAL populations• Food availability• Availability of mating partners• Presence of parasites and/or disease• Predation and competition• Available space (nesting, breeding, feeding, etc.)

Examples of limiting factors for PLANT populations• Light Intensity• Temperature• Carbon dioxide levels• Nutrient availability • Predation

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Australia(Introduced/Invasive Species)