1 What 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 Sampling1. 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 SamplingExample: 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 SamplingExample: 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 SamplingExample: 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 SamplingExample: 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 SamplingExample: 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 SamplingExample: 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 SamplingExample: 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…