Populations IB HL3

Today’s Standards Outline how population size is affected by natality, immigration, mortality, and emigration Outline how population size is affected by natality, immigration, mortality, and emigration Draw and label a graph showing a sigmoid (s-shaped) population growth curve Draw and label a graph showing a sigmoid (s-shaped) population growth curve Explain the reasons for the exponential growth phase, the plateau phase, and the transitional phase between these two phases Explain the reasons for the exponential growth phase, the plateau phase, and the transitional phase between these two phases List three factors that set limits on the growth of populations List three factors that set limits on the growth of populations.

Today’s story For populations we are going to discuss volcanic activity in the Pacific Northwest and more specifically the eruption of Mount Saint Helens in1980. For populations we are going to discuss volcanic activity in the Pacific Northwest and more specifically the eruption of Mount Saint Helens in1980. To the left we have a picture of Mt. Rainer a great example of an alpine ecosystem. To the left we have a picture of Mt. Rainer a great example of an alpine ecosystem. This is how Mount Saint Helens began. This is how Mount Saint Helens began.

The story On a calm morning a seemingly lazy mountain began to shake things up. Literally! On a calm morning a seemingly lazy mountain began to shake things up. Literally! By nine a.m. the mountain had erupted and forever changed the Washington scenery. By nine a.m. the mountain had erupted and forever changed the Washington scenery. The massive trees were knocked over like mere sticks, while the pristine rivers were filled with toxic gases and ash. The massive trees were knocked over like mere sticks, while the pristine rivers were filled with toxic gases and ash A seismograph from Mount Saint Helens

How does this affect populations? The eruption that day affected more lives than just the people who died. The eruption that day affected more lives than just the people who died. Entire populations of organisms were as well. How so? Entire populations of organisms were as well. How so?

But life will prevail The species that had died or moved began to return. The species that had died or moved began to return. Ash is one of the most fertile soils plants can grow in and through seeds being dispersed and deposited life has slowly returned. Ash is one of the most fertile soils plants can grow in and through seeds being dispersed and deposited life has slowly returned.

Population Factors Natality- number of organisms being born. Natality- number of organisms being born. Immigration- members moving into an area. Immigration- members moving into an area. Mortality- number of organisms dying. Mortality- number of organisms dying. Emigration- members moving out of an area. Emigration- members moving out of an area. How would each of these factors apply to the event of the Mount Saint Helens eruption? How would each of these factors apply to the event of the Mount Saint Helens eruption?

Population Growth Curve This is the sigmoid growth curve (s- curve). This is the sigmoid growth curve (s- curve). It has 3 major stages which you must be able to identify and represent on your own graphs in the future. It has 3 major stages which you must be able to identify and represent on your own graphs in the future. Please Draw :) Please Draw :)

The stages 1. Exponential growth- this is sometimes known as the logarithmic phase, in which the number of organisms increases at a faster and faster rate. 1. Exponential growth- this is sometimes known as the logarithmic phase, in which the number of organisms increases at a faster and faster rate. 2. Transitional phase- the growth slows down considerably. The population is still growing, but at a slower and slower rate. 2. Transitional phase- the growth slows down considerably. The population is still growing, but at a slower and slower rate. 3. Plateau phase- also called the stationary phase. This is where the population stabilizes and there is no more growth. 3. Plateau phase- also called the stationary phase. This is where the population stabilizes and there is no more growth.

Causes of each phase Exponential: Exponential: –In a perfect world a population will basically double on a regular basis. Ex. Most bacteria colonies will double their population every hour. Plentiful resources such as food, habitat, etc. Little or no competition Favorable abiotic factors Little or no predation or disease.

Causes of the phases Transitional: Transitional: –Eventually the factors in exponential growth will disappear or run out. This leads to the transitional phase.  Increasing competition for resources  Predators begin moving into the area  Large numbers of organisms in a small space means that opportunities for disease are presented.

Causes of the phases Plateau: Plateau: –Think about the plants taking advantage of the fertile volcanic ash. As the plants’ seeds are deposited over time, there is less and less available space fro new seeds to germinate and grow. –As plants grow larger and larger herbivores enter the area the food supply will be limited and therefore there will be smaller numbers of offspring. –Predators and disease increase. –Usually by now the number of births will equal the number of deaths in the area.

Carrying Capacity As we know populations cannot continue to grow forever and they will meet their carrying capacity. As we know populations cannot continue to grow forever and they will meet their carrying capacity. Carrying capacity (K) is the maximum number of organisms an area can support. Carrying capacity (K) is the maximum number of organisms an area can support. Examples? Examples?

Limiting Factors Anything that defines the carrying capacity. Anything that defines the carrying capacity. The limiting factors can change based specifically on the population and its needs. The limiting factors can change based specifically on the population and its needs. –Ex. Availability of resources-Predation Waste build up-Disease