Do Now 3/15/16Why do you think populations do not grow infinitely?

Teaching Point

SWBAT:

1) Differentiate logistic and exponential growth2) Identify what factors affect population growth and the

carrying capacity

PopulationsA population is a group of organisms of a single species that lives in a given area. The area inhabited by a population is called its geographic range. A population’s range can vary enormously in size, depending on the species. Population density refers to the number of individuals per unit area. Individuals in a population are either spaced out randomly, uniformly, or clumped.

PopulationsA population’s growth rate determines whether the size of the population increases, decreases, or stays the same. Populations also have an age structure, or the number of males and females of each age a population contains.

Population GrowthA population may grow if individuals move into its range from elsewhere, which is called immigration. The opposite of immigration is emigration, where a population decreases in size when individuals move out of the population’s range.

When there is unlimited resources, a population will grow exponentially. This exponential growth means that the larger a population gets, the faster it grows. This growth is shaped like a “J” on a graph.

Population Growth

When there is not unlimited resources, logistic growth happens. Logistic growth is shaped liked a “S” on a graph. Logistic growth happens when:1. A population grows rapidly2. Growth slows3. The growth stops

Population Growth

The growth will stop at a certain population size. This population size is called the carrying capacity. The carrying capacity is the maximum number of individuals of a particular species that a particular environment can support.

Population Growth

Populations show logistic growth (“S” shape) because of limiting factors exist in the environment. Limiting factors are factors that control the growth of a population. There are several kinds of limiting factors that are depending on how big the population is; such as competition, predation, parasitism, and disease.

So Why Does Logistic Growth Happen

Others, like natural disasters and unusual weather, do not depend on how big the population is. Acting separately or together, limiting factors determine the carrying capacity of a population.

So Why Does Logistic Growth Happen

Density-dependent limiting factors happen when the population density, or the number of organisms in a certain space, reaches a certain level. These factors do not affect small populations. Examples of density-dependent limiting factors are competition, predation, herbivory, parasitism, and disease.

Density-Dependent Limiting Factors

Competition depends on the size of a population because the more individuals living in an area, the sooner they use up the available resources.

The size of the predator and prey populations can affect the size of each other. The populations of predators and prey can cycle up and down at times. Herbivores and plants follow the same pattern.

Density-Dependent Limiting Factors

Parasitism and disease depends on population size because the larger the host population, the more easily parasites and disease can spread from one host to another.

Density-Dependent Limiting Factors

Density-Independent Limiting Factors affect all populations in similar ways, regardless of population size and density. Unusual weather such as hurricanes, droughts, or floods, as well natural disasters like wildfires can act as density-independent limiting factors.

Density-Dependent Limiting Factors

Let’s review the Population Distribution Worksheet:

Questions:

4

10

14

16

17

What Now1) Work on the Guided Practice individually or with a partner2) When finished, let a teacher check your work and stamp

the paper3) If not finished by the end of class, it is homework4) If you finish before class, complete any missing work

ClosureUnderneath your teaching points:

What is the difference between density-dependent and density-independent limiting factors?