PopulationsPopulations

IB HL3IB HL3

Today’s Standards Today’s Standards 5.3.1- Outline how population size is 5.3.1- Outline how population size is

affected by natality, immigration, mortality, affected by natality, immigration, mortality, and emigration.and emigration.

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

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

5.3.4- List three factors that set limits on the 5.3.4- List three factors that set limits on the growth of populations.growth of populations.

Today’s storyToday’s story For populations we are For populations we are

going to discuss going to discuss volcanic activity in the volcanic activity in the Pacific Northwest and Pacific Northwest and more specifically the more specifically the eruption of Mount eruption of Mount Saint Helens in1980.Saint Helens in1980.

To the left we have a To the left we have a picture of Mt. Rainer a picture of Mt. Rainer a great example of an great example of an alpine ecosystem.alpine ecosystem.

This is how Mount This is how Mount Saint Helens began.Saint Helens began.

The storyThe story

On a calm morning a seemingly lazy On a calm morning a seemingly lazy mountain began to shake things up. mountain began to shake things up. Literally!Literally!

By nine a.m. the mountain had By nine a.m. the mountain had erupted and forever changed the erupted and forever changed the Washington scenery.Washington scenery.

The massive trees were knocked over The massive trees were knocked over like mere sticks, while the pristine like mere sticks, while the pristine rivers were filled with toxic gases and rivers were filled with toxic gases and ash.ash.

http://gallery.usgs.gov/videos/234http://gallery.usgs.gov/videos/234

A seismograph fromMount Saint Helens

How does this affect How does this affect populations?populations?

The eruption The eruption that day that day affected more affected more lives than just lives than just the people the people who died.who died.

Entire Entire populations of populations of organisms organisms were as well. were as well. How so?How so?

But life will prevailBut life will prevail

The species that The species that had died or moved had died or moved began to return. began to return.

Ash is one of the Ash is one of the most fertile soils most fertile soils plants can grow in plants can grow in and through seeds and through seeds being dispersed being dispersed and deposited life and deposited life has slowly has slowly returned.returned.

Population FactorsPopulation Factors

Natality- number of organisms being born.Natality- number of organisms being born. Immigration- members moving into an Immigration- members moving into an

area.area. Mortality- number of organisms dying.Mortality- number of organisms dying. Emigration- members moving out of an Emigration- members moving out of an

area.area. How would each of these factors apply to How would each of these factors apply to

the event of the Mount Saint Helens the event of the Mount Saint Helens eruption?eruption?

Population Growth CurvePopulation Growth Curve

This is the sigmoid This is the sigmoid growth curve (s-growth curve (s-curve).curve).

It has 3 major It has 3 major stages which you stages which you must be able to must be able to identify and identify and represent on your represent on your own graphs in the own graphs in the future. future.

Please Draw :)Please Draw :)

The stagesThe stages

1. Exponential growth- this is sometimes 1. Exponential growth- this is sometimes known as the logarithmic phase, in which known as the logarithmic phase, in which the number of organisms increases at a the number of organisms increases at a faster and faster rate.faster and faster rate.

2. Transitional phase- the growth slows 2. Transitional phase- the growth slows down considerably. The population is still down considerably. The population is still growing, but at a slower and slower rate.growing, but at a slower and slower rate.

3. Plateau phase- also called the stationary 3. Plateau phase- also called the stationary phase. This is where the population phase. This is where the population stabilizes and there is no more growth.stabilizes and there is no more growth.

Causes of each phaseCauses of each phase

Exponential:Exponential:– In a perfect world a population will basically In a perfect world a population will basically

double on a regular basis. double on a regular basis. Ex. Most bacteria colonies will double their Ex. Most bacteria colonies will double their

population every hour.population every hour.

Plentiful resources such as food, Plentiful resources such as food, habitat, etc.habitat, etc.Little or no competitionLittle or no competitionFavorable abiotic factorsFavorable abiotic factorsLittle or no predation or disease.Little or no predation or disease.

Causes of the phasesCauses of the phases

Transitional:Transitional:– Eventually the factors in exponential Eventually the factors in exponential

growth will disappear or run out. This growth will disappear or run out. This leads to the transitional phase.leads to the transitional phase. Increasing competition for resourcesIncreasing competition for resources Predators begin moving into the areaPredators begin moving into the area Large numbers of organisms in a small Large numbers of organisms in a small

space means that opportunities for disease space means that opportunities for disease are presented.are presented.

Causes of the phasesCauses of the phases Plateau:Plateau:

– Think about the plants taking advantage of the Think about the plants taking advantage of the fertile volcanic ash. As the plants’ seeds are fertile volcanic ash. As the plants’ seeds are deposited over time, there is less and less deposited over time, there is less and less available space fro new seeds to germinate and available space fro new seeds to germinate and grow.grow.

– As plants grow larger and larger herbivores As plants grow larger and larger herbivores enter the area the food supply will be limited enter the area the food supply will be limited and therefore there will be smaller numbers of and therefore there will be smaller numbers of offspring.offspring.

– Predators and disease increase.Predators and disease increase.– Usually by now the number of births will equal Usually by now the number of births will equal

the number of deaths in the area.the number of deaths in the area.

Carrying CapacityCarrying Capacity

As we know populations cannot As we know populations cannot continue to grow forever and they continue to grow forever and they will meet their carrying capacity.will meet their carrying capacity.

Carrying capacity (K) is the Carrying capacity (K) is the maximum number of organisms an maximum number of organisms an area can support.area can support.

Examples?Examples?

Limiting FactorsLimiting Factors

Anything that defines the carrying Anything that defines the carrying capacity.capacity.

The limiting factors can change The limiting factors can change based specifically on the population based specifically on the population and its needs.and its needs.– Ex. Ex.

Availability of resourcesAvailability of resources -Predation-Predation

Waste build upWaste build up -Disease-Disease