Population Growth

Population group of individuals of the same species living in the same area, potentially interacting

Population Growth Four factors can affect population size: Birthrate – number of births Death rate – number of deaths Emigration – number of individuals moving away from a population Immigration – number of individuals moving into a population

A population can grow when its birthrate is greater than its death rate.

Understanding Exponentials Put your pens down for a minute & think about this: An employer offers you two equal jobs for one hour each day for fourteen days. The first pays $10 an hour. The second pays only 1 cent a day, but the rate doubles each day. Which job will you accept? 5

Understanding Exponentials Now, how much would your employer owe you if you stayed at this job for another 2 weeks? Job 2 lags for a long time before exponential growth kicks in! What would happen if this type of growth took place within a population?

Exponential Growth Under ideal conditions with unlimited resources, a population will grow exponentially. Exponential growth occurs when the individuals in a population reproduce at a constant rate.

Exponential Growth

Logistic Growth As resources become less available, the growth of a population slows or stops. Logistic growth occurs when a population's growth slows or stops following a period of exponential growth.

Logistic growth is characterized by an S-shaped curve.

Carrying Capacity (K) The largest number of individuals of a population that a given environment can support is called its carrying capacity. When a population reaches the carrying capacity of its environment, its growth levels off. The average growth rate is zero.

What factors limit population growth? A limiting factor that depends on population size is called a density-dependent limiting factor. Density-dependent limiting factors include: Competition (for food, water space, sunlight and other essentials) Predation (predator- prey relationships) parasitism disease

What factors limit population growth? Density-independent limiting factors affect all populations in similar ways, regardless of the population size. Examples of density-independent limiting factors include: unusual weather natural disasters seasonal cycles certain human activities—such as damming rivers and clear-cutting forests

Focus Question Monday, October 6th What are the interactions that occur within communities?

Community Interactions Community interactions, such as competition, predation, and various forms of symbiosis can powerfully affect an ecosystem.

Population – group of individuals of the same species living in the same area, potentially interacting. Community – group of populations of different species living in the same area, potentially interacting. What are some ecological interactions?

Fitness – how well an organism fits in its environment.

Why are ecological interactions important? Interactions can affect distribution and abundance. Interactions can influence evolution.

Types of ecological interactions competition predation parasitism mutualism commensalism symbiosis

Competition – two species share a requirement for a limited resource  reduces survival of one or both species

Predation – one species feeds on another  enhances fitness of predator but reduces survival of prey herbivory is a form of predation

Parasitism – one species feeds on another  enhances survival of parasite but reduces fitness of host.

Mutualism – two species provide resources or services to each other  enhances survival of both species. http://www.youtube.com/watch?v=Xm2qdxVVRm4

Commensalism – one species receives a benefit from another species  enhances survival of one species; no effect on fitness of the other species. http://www.youtube.com/watch?v=fkzUziLiiDM

Symbiosis – two species live together  can include parasitism, mutualism, and commensalism.

Isle Royale near Lake Superior

Organizing ecological interactions effect on species 1 + 0 - predation herbivory parasitism mutualism + - commensalism effect on species 2 competition

Choose an organism and describe the type of community interactions that affect the success of that organism. List the limiting factors of the carrying capacity of the habitat

How would you describe the trends seen within this graph? Bunny Fox Grass Time (Months)

Focus Question Wednesday, October 9th What types of human activities can disturb an ecosystem and cause succession?

Monday October 10th Write down your answer on a separate piece of paper: What is the difference between an organism’s habitat and niche?