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Week 4 - Sampling, Bio-invasion and Predation, and Succession

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Date: Thursday, 18 September 2025, 3:24 PM

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Week 4 - Sampling, Bio-invasion and Predation, and Succession

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LESSON 3.1: Investigating the Distribution of Living Things in the Environment
ACTIVITY A: Sampling the Distribution of Living Things









Required Readings

Science in Action 7
pages 50-54
or
Science Focus 7
pages 68-78



Watch the movie "CAPTURER
Measuring populations is important work. By studying the habitats, populations, and ranges of different species, we can learn how species interact, where they tend to migrate, and the number of individuals in a species in that area. We can also understand how a species is distributed. Scientists who want to monitor the population trends of different species in the community would find it very difficult to go into a community and try to count or observe every living organism. Scientists have therefore had to develop techniques to help them estimate population sizes and track the range of different organisms. These methods involve counting a small sample that represents the larger population. These accurate counts are then multiplied to give an estimate over the entire area being sampled

There are a number of methods employed by scientists doing population sampling:

Mark-Recapture Method

What about those animals that are not as visible such as the mice in a field or the Bull Trout in Alberta's rivers and streams. How do you measure these populations?

To perform the mark-recapture method, you must first capture the organisms and mark them with some form of identification within a set period of time and a set area. If it is a mouse, you could mark it with a dot of paint. If it is a large mammal, it could be an ear tag. After you have completed the capture and mark step, you will need to record the number caught and marked, and then release your catch back in the area they were captured. After a period of time you will need to return to the sample area and re-capture the organisms.

When you re-capture the organisms you will record how many organisms have the original mark and how many are unmarked. From this you will be able to estimate what the population of this species is in this area.

After you view the video and you are having trouble understanding this method, go to the Internet and the web search engine called "Google". Now type in "mark and recapture method" then type "Enter" to view the results of your search. Now read the possible contents of the various results until you decide which one is most likely to have the information related to this lesson in it. Then you can learn how the process works by checking out a couple of web sites.

  • Mark-Recapture Method
  • Photograph or Video Analysis Method
  • Radio Tracking Method
  • Quadrat Sampling
  • Line Transect
Photograph or Video Analysis Method

Population counting gets a little more interesting when you try to study animals in the wild. Unlike plants, most animals have the tendency to flee or fight at any sign of danger. Neither of these instincts are good when you are a curious scientist. To get accurate estimates of animal populations you must be more creative.

One technique which allows you to keep your distance and gather information about groups of animals is the photograph or video analysis method. This is ideal for birds flying in groups overhead or herds of large animals such as caribou. If a herd can be photographed from an aircraft, it can be analysed later on the ground. If a group is spread over a wide area, numerous photographs may need to be taken.

To simplify the counting task, you can lay a grid over the picture and count the amount of organisms in each grid square. Record each number and add up all the numbers to get a total for the picture. When using video, the ability to analyze the film frame by frame makes counting the specimens a realistic task.

Radio Tracking Method

To better understand a species' range, the radio tracking method is employed to monitor the day to day movements of a species.

In Canada's western Rockies and grassland areas, the grizzly bear population is being carefully studied. Ecologists are worried about the decline in the population of the Grizzly bear in these areas. At one time, the grizzly population was around 6000 bears in Alberta. Today, there are approximately 800 remaining. Management and conservation of the bears needs to be based on a thorough knowledge of the species. To study the bears habitat, a few of the bears have been trapped, fitted with radio collars and released.

Scientists now track the bears with radio receivers from the ground and air. This provides scientists with a clear profile of the complete habitat and movements of the grizzly without disturbing their natural movements.

If human development is proposed for areas that overlap with the grizzlies' range, efforts can then be made to allow the bears' habitat to remain undisturbed.

ACTIVITY B: Quadrant and Line Sampling

Required Readings

Science in Action 7
pages 50-54
or
Science Focus 7
pages 68-78

Watch the movie "QUADRAT"
If you need to estimate the population for small organisms, quadrat sampling is the best method to use.

Quadrant Sampling


In the spring, when dandelions go through their first flowering cycle, you observe that there may be many flowers all over your lawn. Your parents decide to hire someone to spray the lawn to make the grass grow and to remove the dandelions. You decide to do a study to see how effective the lawn spray will be in removing the dandelions. Before the lawn is sprayed you decide to count the dandelions, but as there appears to be thousands of flowers on the lawn, it would be too time consuming to count them all. So you use quadrat sampling.

You pick a one metre square area of the lawn that appears to represent the general dandelion population. Here you take four short pegs and place one of them in each corner of your sample square meter. You tie a string around the four pegs to distinguish the area you would like to sample. Then you count the dandelion plants that grow in that area. After you have counted the area inside your square meter, you calculate the total area of your lawn to come up with an estimated number of dandelions on the lawn.

Example:

1. Dandelions counted in area sampled: 143 dandelions per metre square
2. Size of lawn: 12 m long by 7 m wide
3. Calcuate the area of the lawn: 12m x 7 m= 84 m2
4. Estimate the number of dandelions on the lawn: 143 dandelions x 84 m2 lawn= 12 012 dandelions on my 84m2 lawn.
5. Answer in a complete sentence: It is estimated that there are 12 012 dandelions growing on my lawn that measures 84 m2.
If you were to do this experiment in the fall after the lawn had been sprayed you could then tell if the spraying had an effect on the numbers of dandelions.

Line Transect

When estimating low growing plants, quadrat sampling is the best method to use. But it is not an appropriate method when larger objects need to be measured. The line transect method allows the scientist to estimate which species are most common to an area.

To do a line transect study, you would need a few poles and a string approximately 10 meters in length . Along your string, mark or tie something at even intervals of approximately 50 centimetres. Tie the ends of the string to two poles that can be held in a vertical position by fellow scientists. While they are holding the poles against the ground the string that runs between the two poles should be straight and taut. Now you need to count and record all those things touching or growing directly above or below each interval along the string.

Exercise 3.1: Quadrant Sampling

Lesson 2


LESSON 3.2: Interactions and Changes occur in Ecosystems
ACTIVITY A: Bioinvasion and Predation
Required Readings

Science in Action 7
pages 55-61
or
Science Focus 7
pages 52-54

Living things interact with abiotic and biotic factors within their niche. The factors can be symbiotic in nature such as a bee and a flower. The bee obtains the nectar while the flower is pollinated by the pollen from another flower.

Bioinvasion

Relationships within this ecosystem can be challenged or changed as new species are introduced. The zebra mussel was introduced into the Great Lakes resulting in the extermination of the shellfish industry. At the time the zebra mussel had no enemies in the lakes. Visit this link and read about the affect that these creatures have had.




Predation

Imagine you want to do an experiment on population growth. You find a deserted island in the middle of the South Pacific Ocean. The island is lush with vegetation and there happens to be no predators or rabbits on this island. So you drop off two male and two female rabbits on the island and you leave.

In one year, you come back to the island. To your delight, your rabbits are doing well. They have reproduced and now the number of rabbits is at 55. They all appear to be healthy and there is lots of food on the island, so you leave.

When you return in another year, you are astounded to find the rabbits have been breeding rapidly. During this visit you counted 967 rabbits on the island, but you start to wonder if the food supply will be able to sustain this population growth of rabbits. It is possible for a population to increase so rapidly that it will grow beyond the carrying capacity of the environment. If this happens, the population usually experiences a crash, with large numbers of individuals dying in a short period of time. Such a rapid increase in the population might cause a long term decrease in the carrying capacity of the island. Such a large population might be so desperate for food that it might strip the plants bare, delaying their ability to regrow. This could reduce the carrying capacity of the environment below its former level and limit for many years the number of individuals that could live in the environment. You are now worried about the effect your experiment may be having on the environment. But it is too difficult to round up all the rabbits, so you let nature play its course.
When you return at the end of the third year, you find the population of rabbits has decreased to 450 rabbits. As expected, the carrying capacity of the island was reached and large numbers of rabbits died off over the last year. There appears to be much less grass on the island. At this point you realize, the island has a limit to the number of rabbits it can feed. Some of the rabbits have starved, others have died from disease.

To continue with the study you come back to the island the next year. There are now 500 rabbits living on the island. Again you find the population to be at approximately the same numbers as the year before. You concluded the population has now stablized, the number of deaths due to starvation and disease is approximately the same as the amount of births. Since there are no predators on the island, the key factors for limiting the population is the food supply. It determines the island's carrying capacity.

In the fifth year of the experiment, you return to the island and observe that once again the rabbit population is at 425 rabbits. A fairly stable population. Now that your rabbit population has stabilized, you want to expand your experiment and add a predator to the island that consumes rabbits as its primary food source. A male and female coyote are brought to the island.

Consider what will happen to the coyote and rabbit populations on the island in the sixth, seventh, eight, ninth, and tenth years of the experiment.
Exercise 3.2: Bioinvasion and Predation

Lesson 3


LESSON 3.3: Succession
ACTIVITY A:Succession
Required Readings

Science in Action 7
pages 62-65
or
Science Focus 7
pages 56-59
The types of living organisms found in a particular area changes over time. Some changes can be man-made such as fire, agriculture and logging of forest products, others may be caused by avalanches, volcanoes and floods and some are simply an orderly change of species in a community. Succession is a natural occurrence in the aging of an ecosystem.

A very young ecosystem is the bare rock of a mountain or a sand dune that forms along the edge of a large lake. At first little life survives in these areas. Lichens, mosses and algae begin to cling to the rocks, slowly breaking down the surface of the rock causing a small amount of soil to form. Falling into the cracks of the rocks, the soil provided a place for seeds of small plants and hardy bushes to grow and small insects to live. These species form pioneer communities which continue to break down the rock even further allowing more plants to grow.

Cedar and birch trees are common pioneer trees. Areas that contain these trees tend to be early in their cycle of succession. As leaves and dead plant material from the pioneer species fall to the ground, they help to form humus. Slowly more soil is built up on the rock, and worms, birds, mice and other small rodents populate the area. As the soil becomes deep, other trees such as Maple and Oak begin to grow, forming soil even faster as more plant matter falls to the forest floor.


succession_big.jpg (37671 bytes)


Large animals make their home in the forest where the huge stands of decidious trees begin to darken the underbrush of the forest and keep the moisture in. This provides shelter and nutrients for many species, but the pioneering community can not compete with the larger trees for sunlight and slowly die out. This final stage is called the climax stage in the cycle that changes bare rock to a mature decidious forest. A maple forest is considered to be a climax This process of succession can take thousands of years.

Exercise 3.3: Succession

Section 3 Notes

You will have two opportunities to write this section quiz. This quiz consists of 10 questions. Use the results from your 1st attempt to help you prepare for your second attempt. Your best score will be taken as your assessment mark. You have 10 minutes to complete this multiple choice quiz. Remember to do this quiz under testing conditions without texts, aids, or help.

Click the icon to go to the quiz.