Populations

Populations

Lesson Goals

• Students will be able to explain how changes in an ecosystem affect populations in that system.

Standards

• 6.LS.4 Investigate and use data to explain how changes in biotic and abiotic components in a given habitat can be beneficial or detrimental to native plants and animals.

• 6.LS.3 Describe specific relationships (predator/prey, consumer/producer, parasite/host) and symbiotic relationships between organisms. Construct an explanation that predicts why patterns of interactions develop between organisms in an ecosystem.

Populations

• A population is a group of individuals of the same species in the same place at the same time

• The amount of individuals making up a population is called the population size.

• The human population of Muncie is 68,750. The world human population is 7.674 billion

Populations

• Population size can describe all species, not just humans.

• The squirrel population in my neighborhood might be 236

• The black walnut tree population in Muncie might be 670

Open Ended

What is the population of humans in your house?

Open Ended

What is the approximate population of dogs on your block?

Population Density

• Population density is the number of individuals of a population in a specific area

• You can calculate population density (D) of squirrels in your yard by dividing the number of individuals (n) by the area that they inhabit  $\left(D=n\div area\right)$  

Population Density

• For example, if there were 140 earthworms (n) in a  $4m^2$  area of your yard, the density (D) of earthworms would be 140 divided by  $4m^2$ .

•  $D=n\div area$  

•  $D=140\ earthworms\div4m^2$  

•  $D=35\ earthworms\ per\ m^2$  

Multiple Choice

What is the population density of a population of 80 squirrels in a  $5\ km^2$  park?

•  $20\ squirrels\ per\ km^2$  

• 16 squirrels per sq km

• 12 squirrels per sq mi

• 10 squirrels per sq mi

Population Growth

• With all of this info ecologists can predict how populations will change .

• If a population could grow without anything stopping it, it would have exponential growth. The graph shows what an exponential growth curve looks like.

Exponential Growth

• If a bacteria began at noon dividing every hour, by one there would be two of them.

• By 2:00 there would be four. At 3:00 there would be 8 bacteria.

• Every hour the number would double.

• By noon the next day there would be 16,777,216 bacteria (now that's an infection!)

Population Limits

• Exponential growth is rare in nature for many reasons.

• Predators, space, available food, all of these factors limit the growth of populations

• The greatest population a particular environment can support is called the carrying capacity

Graphing Population Data

• A graph of data showing the carrying capacity of a population is different than an exponential growth graph curve.

• This graph shows the carrying capacity of a population. The population will grow until it reaches the carrying capacity, then it will level off.

Population Size in Nature

• In nature all sorts of factors impact population sizes - forest fires, hunting, drought.

• As a result, population growth rarely is a smooth curve.

• How would different factors impact different populations?

Population Growth Data

• The population of Seals in Alaska grew over the past century due to limits on seal hunting.

• Early in the century the population was low because of hunting. With the limits in place the population has grown.

Multiple Choice

Does this graph show a population undergoing exponential growth or one that has reached its carrying capacity?

• Exponential growth

• Carrying Capacity

Exceeding Carrying Capacity

Read this comic about The Reindeer of St. Matthew Island:

https://www.stuartmcmillen.com/comic/st-matthew-island/#page-1

Poll

What was the cause of the death of the Reindeer on St, Matthew Island?

• poison

• climate

• population growth

• predators

Population Cycles

• In normal natural ecosystems populations go through cycles

• When conditions are good, populations grow, often these times are followed by population decrease.

• In the chart, when the population of wolves was down the moose population increased, when the wolf population went up, the moose population went down.

Communities and Ecosystems

• All of the interacting populations in an area make up a community

• For example, a city park community may be made up of grasses, and weeds, trees and bushes, birds, squirrels, racoons, hawks and maybe even cayotes.

• A community and its abiotic (nonliving) environment make up an ecosystem.

Earth's Biomes

• Scientists group all of the ecosystems of the Earth into large groups called biomes.

• A biome is a very big ecosystem characterized by it's dominant plants, animals and features.

• There are two major types of biomes: aquatic and land biomes.

Aquatic Biomes

• The major aquatic biomes are shown in this picture.

• The organisms that live in each biome are determined by the amount of saltiness, the movement, and the depth of the water.

Land Biomes

• Land biomes are categorized as tropical forest, savanna, desert, polar and high-mountain ice, chaparral, temperate grassland, temperate deciduous forest, coniferous forest, and tundra. 

• Temperature and rainfall are the main abiotic factors that determine the kinds of organisms that live in each land biome.

Multiple Choice

What is an ecological system called that consists of all of its biotic and abiotic factors?

• community

• ecosystem

• habitat

• pure culture

Multiple Choice

Which factor is a biotic factor of an ecosystem?

• the bacteria that live in the intestine of a rabbit

• the amount of water vapor present in a rain forest

• the temperature of water in a stream

• the rocks that provide cover for a rattlesnake

Multiple Choice

What is true of the population shown in this graph?

• The population is not changing much over time.

• The population is growing unchecked.

• There are many factors at work to control the population.

• The population has increased until it reached its carrying capacity.

Poll

You got this?

• Yes

• No

Poll

What parts do you fully understand

• Population growth

• Biomes

• Communities

• Population