1What is Population Ecology?

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Ecology is...

the study of interactions among organisms with each other and with their environment

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Ecology studies these interactions at different levels, called levels of organization.

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Level of Organizati

on

Definition Example

Species individuals that can breed with one another

Population all the individuals of the same species in an area

Community

all the different species in an area

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Level of Organizati

on

Definition Example

Ecosystem the community plus the physical factors in an area

Biome large area that has a particular climate and particular species of plants and animals

Biosphere the part of the earth that supports life

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So....Population Ecology is

the study of how the population sizes of species living together in groups change over time and space

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Population Characteristics

There are three characteristics that all populations have:

1) population density,

2) spatial distribution,

3) and growth rate.

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1. Population Density

Refers to the number of individuals in relation to the space

Population Density =

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1. Population Density

Example: What is the density of a rabbit population of 200 living in a 5 km2 range?

Solution: Population Density =

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1. Population Density

Example: What is the density of a rabbit population of 200 living in a 5 km2 range?

Solution: Population Density =

Population Density =

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1. Population Density

Example: What is the density of a rabbit population of 200 living in a 5 km2 range?

Solution: Population Density =

Population Density =

Population Density = 40 rabbits / km2

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1. Population Density

Density – dependent factors – factors that can affect a population growth because of its density. E.g. Food supply, competition for mates, spread of disease.

Density- independent factors – factors that can affect a population growth regardless of its density. E.g. Forest fires, Flood, Habitat destruction, Pollution

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2. Spatial Distribution

Refers to the pattern of spacing of a population within an area

3 types: clumped, uniformly spaced, and random

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2. Spatial Distribution

Results from dispersion – the spreading of organisms from one area to another

Three types of barriers prevent dispersal: Physical barriers (e.g. mountains, oceans) Ecological barriers (e.g. grassland animals do

not move into forests) Behavioural barriers (e.g. birds that prefer

tall trees over short trees will not disperse into short trees)

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3. Growth Rate

Refers to how fast a population grows

4 factors determine how a population changes:

Natality (birth rate) Mortality (death rate) Immigration (individuals moving into a

population) Emigration (individuals moving out of a

population)

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3. Growth Rate

Population change can be calculated as:

Birth rate – death rate + immigration - emigration

 

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3. Growth Rate

Example: In a given year, a pack of timber wolves experiences the birth of 3 pups and the death of a lone wolf. No animals moved into the pack but 1 wolf did leave.

Solution:

Birth rate – death rate + immigration - emigration

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3. Growth Rate

Example: In a given year, a pack of timber wolves experiences the birth of 3 pups and the death of a lone wolf. No animals moved into the pack but 1 wolf did leave.

Solution:

Birth rate – death rate + immigration - emigration

= 3 – 1 + 0 – 1

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3. Growth Rate

Example: In a given year, a pack of timber wolves experiences the birth of 3 pups and the death of a lone wolf. No animals moved into the pack but 1 wolf did leave.

Solution:

Birth rate – death rate + immigration - emigration = 3 – 1 + 0 – 1 = 1 Meaning that in this year, the wolf pack experienced

a growth of 1 wolf. 

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How do know how many organisms make up a population?

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Yes, we count them!

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But what about…?

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Population Sampling Methods

When the number of organisms in a population is hard to count, scientists estimate the total population size

They do this by first sampling the population and then calculating a population size based on the data

There are 3 methods: Mark-Recapture, Quadrat, and Random Sampling

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1. Mark-Recapture Sampling

Also called ‘tagging’

A sample of organisms is captured and marked and then returned unharmed to their environment

Over time, the organisms are recaptured and data is collected on how many are captured with marks

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1. Mark-Recapture Sampling

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1. Mark-Recapture Sampling

Example: In order to estimate the population of sturgeon fish in the river, biologists marked 10 sturgeon fish and released them back into the river. The next year, 15 sturgeon were trapped and 3 were found to have marks.

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1. Mark-Recapture Sampling

Example: In order to estimate the population of sturgeon fish in the river, biologists marked 10 sturgeon fish and released them back into the river. The next year, 15 sturgeon were trapped and 3 were found to have marks.

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1. Mark-Recapture Sampling

Example: In order to estimate the population of sturgeon fish in the river, biologists marked 10 sturgeon fish and released them back into the river. The next year, 15 sturgeon were trapped and 3 were found to have marks.

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1. Mark-Recapture Sampling

Example: In order to estimate the population of sturgeon fish in the river, biologists marked 10 sturgeon fish and released them back into the river. The next year, 15 sturgeon were trapped and 3 were found to have marks.

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1. Mark-Recapture Sampling

Best for mobile populations, such as fish and birds

Problems occur when no marked organisms are captured

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2. Quadrat Sampling

A sampling frame (quadrat, usually 1m2) is used to count the individuals in a mathematical area

Population size is then estimated based on the data from the quadrat

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2. Quadrat Sampling

Example: A biologist counts 13 mushrooms in a 1m x 1m quadrat. The area of study is 12m2.

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2. Quadrat Sampling

Example: A biologist counts 13 mushrooms in a 1m x 1m quadrat. The area of study is 12m2.

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2. Quadrat Sampling

Example: A biologist counts 13 mushrooms in a 1m x 1m quadrat. The area of study is 12m2.

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2. Quadrat Sampling

Example: A biologist counts 13 mushrooms in a 1m x 1m quadrat. The area of study is 12m2.

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Quadrat Sampling

Best for small stationary populations, such as plants & mushrooms

Problems occur when the quadrats are placed in ‘abnormal’ locations

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3. Random Sampling

The number of organisms within a small area (plot) is counted.

The plots are often placed randomly throughout the sampling area

Population size and density are then estimated based on the plot representation.

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3. Random Sampling

1. Find the average # of individuals in the areas you sampled.

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3. Random Sampling

1. Find the average # of individuals in the areas you sampled.

2. Multiply the average by the # of plots to find the population estimate

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3. Random Sampling

Example: A sample was taken to count the number of silver maple trees in the forest. The number of trees counted in the grid is shown below.

             5 3

4 4

1

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3. Random Sampling

Example: A sample was taken to count the number of silver maple trees in the forest. The number of trees counted in the grid is shown below.

1.

5 3

4 4

1

per plot

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3. Random Sampling

Example: A sample was taken to count the number of silver maple trees in the forest. The number of trees counted in the grid is shown below.

1.

5 3

4 4

1

per plot

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3. Random Sampling

Example: A sample was taken to count the number of silver maple trees in the forest. The number of trees counted in the grid is shown below.

1.

5 3

4 4

1

per plot

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3. Random Sampling

Example: A sample was taken to count the number of silver maple trees in the forest. The number of trees counted in the grid is shown below.

2.5 3

4 4

1

per plot

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3. Random Sampling

Example: A sample was taken to count the number of silver maple trees in the forest. The number of trees counted in the grid is shown below.

2.5 3

4 4

1

per plot

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3. Random Sampling

Example: A sample was taken to count the number of silver maple trees in the forest. The number of trees counted in the grid is shown below.

2.5 3

4 4

1

per plot

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3. Random Sampling

Best for large stationary populations, such as trees or coral

Problems occur when random sampling is not followed

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Now it’s your turn…