Module 9S2 Changes in Populations

Module 9S2 -Changes in Populations

Introduction

Module 9: Section 2 has four lessons dealing with population changes. You will learn to use formulas for population size, density, growth rate, and per capita growth rate. These can be used to help make informed decisions as wildlife managers, developers, politicians, academics, and concerned citizens. You will see how comparing collected data with the normal patterns of growth observed in different species assists in decision making.

You will learn that different species have evolved two distinct strategies of growth to maximize their reproductive potential and survivability (r and K selection). A given set of species characteristics indicates each strategy. You will learn that you can predict the course of a given population by matching it with those characteristics.

You will learn that there is debate and controversy about how human growth differs from the growth patterns of other species. You will consider how well human populations can be characterized by the same parameters as other species. You will also study how human populations tend to differ from others due to our tendency to change our own environments using technology.

In This Module

Section 2: Lesson 1—Factors Influencing Growth

This lesson will explore the factors that influence the growth of a population and determine whether or not the population size increases, decreases, or remains stable.

The focusing questions being addressed in this lesson are:

• What are the factors that influence populations?
• How do these factors influence population change?

Section 2: Lesson 2—Measuring Growth

In this lesson you will explore the type of data that can be collected about population sizes, how it can be interpreted and how the results of these studies can be applied.

The focusing questions being addressed in this lesson are:

• How can data be analyzed to study population dynamics?
• What terms describe these population changes?

Section 2: Lesson 3—Growth Patterns

There are many different growth patterns for natural populations. You will examine these, and compare them to the unique pattern of human population growth.

The focusing questions being addressed in this lesson are:

• What are the types of population growth patterns?
• How do growth patterns illustrate the types of changes over time?

Section 2: Lesson 4—r and K Selected Growth Patterns

In this lesson you will examine the characteristics and reproductive strategies of two categories of population types.

The focusing question being addressed in this lesson is:

• What are the characteristics and reproductive strategies of r and k selected organisms?

Big Picture

 As a biologist employed by National Parks Canada, you might be required to collect data on population changes of different species within the park. Why? What are the applications of this kind of information? Ecological communities are so complex – often there are several species at the same trophic level, or some species occupying two levels in intricate food webs. Every level of the food chain controls the populations of those levels above and below it, limiting the prey available to levels above it, and limiting the amount of predation on levels below it. The result is a complex interdependence that is difficult for us to comprehend. This is why communities are so fragile and easily disrupted – often unintentionally – by human activities. One seemingly isolated human action has a domino-like effect throughout the community. 

To prevent disruption, or perhaps to determine the effect of a disruption, we need to quantify populations – the size of them, and the factors that lead to changes in them. We can use this information to predict the consequences that our actions hold for other species. We need to be able to use simple mathematical formulas to describe the quantitative changes taking place.  Similarly we need to know the normal growth patterns of different populations in order to know whether something abnormal is going on. Different species have evolved different strategies of growth rates to maximize their survivability and reproductive success. Understanding these strategies is key to managing populations. Lastly, we need to view our own species as a population and quantitatively describe the patterns of human growth and how these patterns are likely to affect other members of the community.

Essential Question

• How do you measure, interpret, and analyze the changes in a population over time?

Lesson 4.9.1S2

Lesson 1—Factors Influencing Growth

Get Focused

Elk Island Bison: Natality, Mortality, Immigration, and Emigration

At any given time, you can access information about populations of many species in our national parks. When we read about the numbers of individuals in a given population, we might have the impression that numbers are static. In fact, in an open environment numbers are constantly changing – a population count signifies just a moment in time.

By the end of this lesson, you should be able to answer the following focusing questions:

• What are the factors that influence population size?
• How do these factors influence population change?

Module 9: Section 2—Lesson 1 Assignment

In addition to your lesson work as listed below, any summary notes, diagrams, charts or tables should be stored in the course folder for your teacher’s feedback and study as you prepare for exams.

Once you have completed all of the learning activities in this lesson, you can complete the online assignment.

Bio30 4.9.1S2 online assignment

You should also watch the tutorial video for this lesson and submit a summary.  Bio30 tut# 4.9.1S2 Human Populations

The other questions in this lesson are not marked by the teacher; however, you should still answer these questions. The Self-Check and Try This questions are placed in this lesson to help you review important information and build key concepts that may be applied in future lessons.

After a discussion with your teacher, you must decide what to do with the questions that are not part of your assignment. For example, you may decide to submit to your teacher the responses to Try This questions that are not marked. You should record the answers to all of the questions in this lesson and place those answers in your course folder.

4.9.1S2 page 2

Explore

Crash Course - Population

The size of a population is the result of four population determining factors at work. These factors can increase, decrease, or work together to maintain population size. They are natality, mortality, immigration, and emigration.

Read

Read pages 707–708 in the textbook. Attempt to derive a formula that expresses the effect of natality, mortality, immigration, and emigration on change in population numbers. Then read pages 708-712.

Self-Check

To see if your formula works, try the following questions and check your work.

1. A case study of Swans in Grande Prairie
   
   A breeding flock of trumpeter swans near Grande Prairie is made up of 50 pairs. This year there were 165 live hatchlings, no new birds joined the flock, 5 animals were shot, and 8 did not return this spring from their migration.
   
   How has the population of trumpeter swans changed?

Try This

1. Complete the "4.11 Population Size" drag-and-drop activity.

Self-Check

SC 1.

Human Population Change

Answer the following questions. You may wish to score your response. (4 marks)

1. The Canadian population is growing significantly yet birth rates are dropping. Use the dN formula to suggest three different explanations.
2. Population numbers have much to do with the lifespan of the organism. Why would women of Japanese ethnicity have a longer life expectancy when they live in Japan than when they live in North America? Suggest three possible reasons and explain your answers.

Discuss

Native aboriginal Albertans are in many cases given different legal hunting bag limits than non-natives. Research the reasons for this difference and post a response to the question of whether the difference in bag limits is justified. Discuss your work with your instructor and other students.

Self-Check

SC 2.
How might a drought that decreased grass populations affect herbivore population numbers? Referring to the formula for ∆N, suggest four different ways.

4.9.1S2 page 3

Lesson Summary

The four determining factors of population size are natality, mortality, immigration, and emigration. Natality and immigration increase population size; mortality and emigration decrease population size. Population size is represented as N.

Change in a population is symbolized as delta N (∆N). The formula for change in population size is ∆N = (natality + immigration) – (mortality + emigration)

Lesson 4.9.2S2

Lesson 2—Measuring Growth

Get Focused

White-tailed deer are browsers—they love the tender buds of shrubs and young trees that make up the transition area between fields and forest. Increasing deforestation due to urban sprawl and agriculture has opened up much more of this transitional habitat. In addition, natural predators of deer such as coyotes have been forced out of these areas by the same human activities. Hunting, which has been a traditional method of keeping white tail deer populations down, has fallen out of favor in modern times, with the taste for venison (deer meat) being met by domestic ‘deer farms’. With high food supply, and without predators, the size of white-tailed deer populations is large enough that in many areas of North America they are considered pests. In the state of Pennsylvania, more deer are killed by cars on the highway than die as a result of hunting.  An increasingly popular product is a device that sends out a high pitched sound from cars traveling rural roads, deterring deer from crossing roads, preventing vehicle/deer collisions. (Does this have an effect on gene flow?) Without competition and predation to weed out the sick and poorly adapted, the gene pool of white-tailed deer is becoming weaker, with a greater incidence of parasitism and contagious disease. With natality greater than mortality, the rate of growth continues to increase. With little selection of superior alleles, the gene pool is increasingly inferior to its previous state.

By the end of this lesson you should be able to answer the following focusing questions:

• How can data be analyzed to study population dynamics?
• What terms describe these population changes?

Module 9: Section 2—Lesson 2 Assignment

One you have completed all of the learning activities for this lesson, you can complete the online assignment.

Bio30 4.9.2S2 online assignment

You should also watch the tutorial video for this lesson and submit a summary.  Bio30 tut#4.9.2S2 Pop Density

In addition to your lesson work as listed below, any summary notes, sample problems, diagrams, charts or tables should be stored in the course folder for your teacher’s feedback and study as you prepare for exams.

You must decide what to do with the questions that are not marked by the teacher.

Remember that these questions provide you with the practice and feedback that you need to successfully complete this course. You should record the answers to all of the questions and place those answers in your course folder.

4.9.2S2 page 2

Explore

How do field biologists count organisms? One of the biggest problems that field biologists face is how to get accurate population counts. Remember that organisms that swim, run, hide, burrow, fly, are dangerous, or are very small - are of these making them difficult to count, so estimation methods have to be used. In this lesson, you will learn some of the sampling methods used and how to do some of the calculations that give the population numbers meaning to those (like wildlife managers) who analyze the data.

Read

Read pages 704–705 and 708–709 in the textbook for information on determining the rates of population growth.

Pay close attention to the concept of density, growth rate, and per capita growth rate as ways of indicating how much the population has changed. Create a clear and easily accessible table in your course folder for the formulas and their definitions. Remember that in the Diploma exam you will encounter many of these problem-solving situations. Whenever possible, practice solving problems from the text or from this lesson. If you are having any difficulty, consult with your instructor.

Read

Read pages 705 and 707 on "Distribution Patterns: Random, Clumped, Uniform."

Make notes on the significance of each distribution pattern and what conditions lead to each pattern. Diagrams are also a good way to store this information in your course folder.

Self-Check

1. The population size of microscopic Paramecia in a 1 L hay infusion needed to be determined. By using a depression slide (a microscope slide with a well in the center) at medium power, and averaging the results of 3 1mL samples, it was found that there were on average 4 Paramecia/mL of hay infusion. What was the population (N) in the entire 1 L infusion?
2. Refer back to Get Focused. Will the lack of competition and natural selection in white-tailed deer populations increase or decrease the genetic diversity of the gene pool? Explain your answer.  
3. There is a lovely white daisy with fern-like leaves that adds brightness and cheer to the roadside ditches of rural Alberta. Unfortunately, it is an inadvertently introduced species and is very invasive, competing vigorously with indigenous wild species. Your job is to provide data on the spread of the species, beginning with a population count in a 1 km2 parcel of land.
   1. How would you count them? (Refer to samples on page 704-5)
   2. Would you do one sampling or several? Why?
   3. Would it be more informative to express the count as N (population size) or as density (Dp =   #    ) Why or why not?

4.9.2S2 page 3

Discuss

On the discussion board, brainstorm with other students and/or your instructor as to what technologies might assist field biologists in their counts of dangerous animals, highly mobile species (insects, migratory organisms), aquatic organisms, and very small species. List several technologies in your course notes.

Self-Check

It is very important in this module to practice problem solving. Similar questions will be part of your Diploma exam.

SC 1. Do questions 5, 6, and 7 on page 709 of your text.

SC 2. Your job is to determine N for black spruce in a 100 km2 parcel of land. In the chart below are the numbers of black spruce found in 5 randomly chosen quadrats of 1km2 each.

Reflect on the Big Picture

Finally, we have the key to the previous lessons which are all based on data about the numbers of individuals with certain phenotypes or alleles. Without the work of field biologists who actually get out and reliably count the organisms, all of our analysis and application to the concept of genetic change and evolution cannot be carried out. You should see now that accurate counts are essential to the process. Why?

Self-Check

To review the concepts of this lesson and prepare for your assessment, complete the procedure questions from Thought Lab 20.1: Distribution patterns and population size estimates, on p. 706.

You are now ready to apply your understanding to the following assignments. Submit your work to your instructor.

4.9.2S2 page 4

Lesson Summary

All population calculations are based on accurate counts of numbers of organisms and their phenotypes/genotypes. Formulas and methods that allow us to consistently and accurately count and analyze population counts are essential.

• Most organisms can be counted by extrapolation from an average of small density samples.
• Density is determined by Dp = N or Dp = N
                                           A            V
• Change in population is calculated by Nfinal – Ninitial
• Growth rate gives information about how fast the population is changing:
  
              gr = delta N                                     gr can be positive or negative.
                     Delta t
• Per capita growth rate gives information about how much of the change each initial individual is responsible for:
  
              cgr = delta N   or  Nfinal – Ninitial          cgr can also be positive or negative         
                         N               Ninitial
• Populations can be distributed randomly where there is low competition, organisms can be clumped in the presence of significant competition, and organisms can be distributed uniformly if there is territoriality, or if the population is artificial (e.g. agriculture)

Lesson Glossary

density: the number of individuals in a given unit of area (land) or volume (air or water) 

• Dp = N or Dp = N    
         A            V

growth rate (gr): the change in the number of individuals in a unit of time

• gr = delta N = final population – initial population  
         delta t                 change in time
  
• Gr will be positive if the population size is increasing, and negative if it is decreasing.

per capita growth rate (cpr): the rate of change per individual

• cgr = delta N   or  Nfinal – Ninitial         
             N                Ninitial               
• Cgr can also be positive or negative depending on whether the initial N is.

clumped distribution: organisms grouped together; occurs in highly competitive environments

random distribution: no pattern exists in organism distribution; occurs in environments with little competition

uniform distribution: organisms are equally spaced apart; occurs in artificial environments (e.g.agriculture)

Lesson 4.9.3S2

Lesson 3—Growth Patterns

Get Focused

How many offspring is a woman capable of having in her lifetime? A woman is capable of ovulating from puberty to menopause - let’s say 30 years. There are approximately 12 opportunities a year to produce an egg, so that’s 30 × 12 = 360 opportunities. However, it takes 9 months of gestation to make an offspring, and if the mother is nursing, she may not ovulate for a few months after the birth – so let’s say she’s capable of having 1 child each year for those 30 years. Therefore, each woman has the potential to produce 30 offspring in her 80 year lifespan. This number doesn’t take many factors into consideration: multiple births, miscarriages, missed ovulations, malnutrition, maternal/child mortality, sterility, etc. However, it is still a very impressive figure. With over 7 billion people on the planet and approximately half female, you can see how human population could get right out of hand if conditions were favorable! A glance at the human population graph may convince you it has. Humans however do not typically produce 30 offspring, and they reproduce at a much slower rate than their biology might permit them to.

As impressive as the biotic potential of humans is, it pales in comparison to a typical female field mouse, which at 1 month is capable of breeding and having a litter of 10 young after a gestation period of 20 days. She is capable of breeding again 24 hours after her litter is delivered. Even though she may only live 5 months in the wild due to predation, the reproductive potential of a wild mouse is staggering: 4 months (120 days) of breeding with one litter of 10 pups every 20 days = a potential to produce 60 offspring in her 5 month lifespan, and achieving this potential is common. (A startling reminder of how necessary predators like coyote, fox, the domestic cat, and possibly poisons like Warfarin (p.691) are to controlling mouse populations.

By the end of this lesson you should be able to answer the following focusing questions:

• What are the different types of population growth patterns?
• How do growth patterns illustrate these types of changes over time?

Module 9: Section 2—Lesson 3 Assignment

After you have completed all of the learning activities for this lesson you can complete the online lesson.

Bio30 4.9.3S2 online assignment

You should also watch the tutorial video for this lesson and submit a summary.  Bio30 tut# 4.9.3S2 Population Types

In addition to your lesson work as listed below, any summary notes, sample problems, diagrams, charts or tables should be stored in the course folder for your teacher’s feedback and study as you prepare for exams.

You must decide what to do with the questions that are not marked by the teacher.

Remember that these questions provide you with the practice and feedback that you need to successfully complete this course. You should record the answers to all of the questions and place those answers in your course folder.

4.9.3S2 page 2

Explore

What factors determine the biotic potential (r) of a species? If you compare the biotic potentials of the mouse and the human reproductive stories above, you should be able to find at least four differences between them that account for the differences in biotic potential. Differences in biotic potential are partly responsible for how fast population numbers change.

Read

Do all populations grow in the same way? It would not seem so from the information given about humans and mice!

Read p. 709 and 711 on exponential and logistic growth patterns. It is very important to make notes on the characteristics of species that typify these patterns. Draw graphs that show the characteristic shapes of both kinds of growth. Label the 2 graphs with the phases of growth. Save these notes in your course folder. You will note that interpreting graphs is an important skill in biology 30. If you use The Key to prepare for the diploma exam, you will have the opportunity to see many types of questions based on graphs, or you can go to the Government of Alberta Education website to view samples of Diploma exam questions.

 How much growth can an environment sustain without depletion of already scarce resources? In other words, what is the carrying capacity (K) of the environment?

Read

Read pages 711–712 and make notes on how the concept of carrying capacity applies to exponential and logistic growth patterns. What are the consequences of growth beyond carrying capacity?

In one habitat the carrying capacity for white-tailed deer may be very high, and in another, very low. What factors determine how high the carrying capacity of a given environment may be? As populations increase, environmental resistance slows growth rates. Environmental resistance may be due to density independent factors such as climate and natural disasters, but is more likely due to the density dependent effects of population growth, such as lack of food and/or water, high predation, high parasitism, and lack of space.

Read

Read page 712 and look at "Figure 20.5" to make a list of both density dependent factors and density independent factors that cause environmental resistance.

Try This

This Population Density Factors activity wll help you sort density-dependent and density-independent factors.

Is it possible for a habitat to not have a carrying capacity? Is there a species that is capable of changing its habitat to continually increase the carrying capacity? Is there an upper limit to this carrying capacity? Before you form an answer, check out "Figure 20.22" on page 733 that illustrates the human population curve. Then do the following Try This activity.

Try This

1. Assume species A was introduced into a new environment. Population counts produced the following data:
   
   

   Generation	Population (N)
   1	2
   2	3
   3	4
   4	8
   5	15
   6	31
   7	32
   8	33
   9	33

   
   Graph the data on the table. Use the graph to answer the following questions?
   
   
   1. Is the population above growing in a logistic or exponential pattern? Support your answer. What is the shape of the curve?
   2. What is K (carrying capacity) in this population?
   3. List 4 density dependent factors that could have contributed to environmental resistance.
   4. Provide 2 density independent factors that could affect K in this population. State whether each factor would increase or decrease K.
2. Regarding "Figure 20.2" on p. 733 of your text:
   
   
   1. At approximately what year did the human population enter the exponential growth phase?
   2. Prior to that time, what was the approximate carrying capacity of Earth?
   3. State 4 significant developments that began to increase the carrying capacity from that time.
   4. Provide 2 pieces of evidence that demonstrate how density-dependent factors are contributing to environmental resistance in human populations?

4.9.3S2 page 3

Watch and Listen

To review these concepts and understand graphing, watch the following video. You may choose to make notes as you view the presentation:

r and K selection

Self-Check

SC 1.

In this unit, practice problems and graphing are essential. The following self-check is an opportunity to practice your skills.

Caribou: Exponential or Logistic?

1. 

   © Clément Billet #2296248/Fotolia LLC

   Caribou live in the arctic and subarctic tundra, feeding on lichens in the winter and willows, grasses and sedges in the summer. Their most important predator is the wolf. The winter migration takes them from the open tundra to the protection of the boreal forests; in spring they return to the calving grounds of the tundra. During the fall ‘rut’ (breeding period) the most dominant male breeds with up to 15-20 females, with one calf born to each mother in the spring. The following data describes caribou reindeer population changes on St. Paul Island, Alaska from 1910 to 1950.
   

   Year	Population (N)
   1910	30
   1920	300
   1930	350
   1940	1200
   1950	0

   
   
   1. Graph the data from the table above. Label axes and provide a title and units.
   2. Considering the information you were given regarding reindeer reproductive habits and predation, would you predict that the population growth curve would be logistic or exponential?
   3. Analyze the graph. In a statement, describe the growth pattern that existed from 1910 to 1950.
   4. Does the data support your prediction from B?
   5. Consider all the information you have been given about caribou populations. Hypothesize as to 2 reasons for the observed growth pattern. Indicate whether each reason is density dependent or density independent.

Bacterial Growth
Answer the following questions and store your answers in your course folder. Remember how important these problem solving and graphing skills are in this unit.

In suitable abiotic conditions, and with adequate food, E. coli bacteria (part of your normal intestinal flora) undergo binary fission every 20 minutes. Thus, with each generation, populations double and each generation is only 20 minutes long. Typically, bacteria introduced onto a medium will go through the following phases

• Lag phase: slow growth

• Exponential growth: doubling with each generation

• Death phase: population crashes due to competition for food and accumulation of toxins.

1. Using your calculator (using 2n as a function):
   
   

   • fill out the following table

   • graph the results (it is only necessary to plot every second generation)

   Exponential Population Growth in E.coli Bacteria
   generation #	population (N)
   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   13
   14
   15
   16
   17
   18
   19
   20

   
   Assume the environment (the Petri dish containing the nutrient medium) can only support 1 million bacterial cells.

   
   
   1. At what generation has the population outstripped its environment and will begin to crash? If generation 1 was time 0, at what time did the population crash?
   2. Draw a graph showing the growth curve. Label axes correctly and provide a title. Label the graph with lag phase, exponential phase, and death phase.
   3. With each successive generation, what happens to the difference between N of the previous population and N of the current population?
   4. A population of lilies is growing exponentially with a generation time of 3 days. The water lilies threaten the species living below the surface by cutting off sunlight. At this point in time, the lilies cover half the pond. How long before the whole pond is covered?

Discuss

Develop, present, and defend a position on Earth’s carrying capacity of Homo sapiens on the discussion board. Work with other students and your instructor in developing more ideas. File you work in your course folder.

Self-Check

1. Which of the following would not be an example of environmental resistance?
   
   
   1. drought
   2. increase in predators
   3. disease due to waste accumulation
   4. lack of food
   5. lack of nesting sites
      
      
2. Exponential growth is found only in
   
   
   1. organisms with a high biotic potential
   2. organisms with a low biotic potential
   3. organisms reproducing at their biotic potential
   4. organisms that have many offspring at a time
3. Match birth rates (b) and death rates (d) to the phases of the logistic growth curve:
   
   
   1. stationary phase: high b, low d
   2. lag phase: low b, high d
   3. exponential phase: high b, low d
   4. lag phase: b and d are equal
4. Which of the following is paired correctly?
   
   
   1. exponential growth – population crash
   2. logistic growth – J curve
   3. exponential growth – carrying capacity
   4. exponential growth – S curve
      
      
5. Look at the graph on page 722 of your text.
   
   What conclusion can you draw from the graph?
   
   
   1. density of hares was highest in the control group
   2. removing predators doubled the population density
   3. when population density rises, environmental resistance offered by lack of food and increased predators are equally important in controlling density
   4. the combined effect of removing both food and predators was greater than the sum of both effects.

4.9.3S2 page 4

Reflect and Connect

Apply your skills and understanding of this lesson by completing the following assessment and submitting it to your instructor.

Module 9: Section 2—Lesson 3 Assignment

Zebra Mussels

Zebra mussels were introduced into the Great Lakes inadvertently from ballast from a European freighter. Since then zebra mussel populations have increased rapidly and become a major ecological problem.

Retrieve your copy of Module 9: Section 2—Lesson 3 Assignment that you saved to your computer earlier in this lesson. Complete the assignment. Save your completed assignment in your course folder. Submit your completed Module 9: Section 2—Lesson 3 Assignment to your teacher for assessment.

Lesson Summary

• Biotic factors that are affected by population density are called density dependent factors. Examples are food, water, oxygen, space, parasitism, and predator populations.
• Abiotic factors that affect population density are called density independent factors. Examples are climate, temperature, storms, drought, frost, wind, precipitation.
• Given unlimited resources the highest rate of reproduction is called biotic potential, symbolized by r.
• Populations growing at biotic potential form a J curve and have exponential growth rates.
• Populations growing in environments with limited resources will not exceed a population size known as the carrying capacity, symbolized by K.
• Populations growing in environments with limited resources will display and S-shaped or logistic growth curve.

Lesson Glossary

biotic potential (r): highest per capita growth rate possible

carrying capacity (K): the theoretical maximum population size that the environment can sustain over an extended period of time; may change as the quality of the habitat changes

The population is at carrying capacity when it levels off during logistic growth.

density dependent factors: biotic factors that limit a habitat’s carrying capacity (e.g. parasites, disease, increase in predators, lack of water/food/territory); the impact increases with the density of the population

density independent factors: abiotic factors that limit a habitat’s carrying capacity (e.g. fire, flood, frost)

The impact is not affected by the density of the population.

environmental resistance: rhe combined effects of factors that limit population growth; prevents a population from growing at its biotic potential; determines the carrying capacity of the environment

exponential growth pattern: exhibited by a population that doubles with each generation; results in a J-shaped curve; begins with a lag phase, followed by a steep rise

The term ‘exponential phase’ refers to a section of the logistic growth curve (S) where births exceed deaths. This phase occurs after the lag phase and before the stationary phase.

logistic growth: a population increase resulting in an S-shaped curve

Begins with slow growth, steepens to exponential growth, and then levels to a carrying capacity due to competition because of environmental resistance.

Lesson 4.9.4S2

Lesson 4—r and K Selected Life Strategies

Get Focused

Consider the dandelion: a lovely yellow flower with a bad reputation. Dandelions can be seen bursting through lawns in the spring, creating color and cheer. Unfortunately, our culture considers them a weedand uses herbicides in an attempt to get rid of them before they out-compete the grass species that form our lawns. Many cultures look forward to dandelion season to harvest the dents du lion (lion’s teeth) leaves as one of the first edible species of spring, bringing vitamins and minerals after a long winter. Wind pollination occurs almost immediately after flowering, and the seed heads which look like balls of fluff, are carried away by the wind, increasing their dispersal. The entire life cycle is completed in 3 weeks ensuring reproduction is completed before frost, drought, heat, or flooding is able to prevent it. Unstable conditions require a strategy that produces as many offspring as possible, as quickly as possible, with no other investment of energy.

The beaver (Castor canadensis) only becomes fertile after 3 years. Generally only 2 young are born, and they stay with their mother for 2 years, watching and learning the skills needed to harvest trees, make dams, build lodges, and avoid predators. Though there are few young, they are highly skilled by the time they leave her and therefore have a higher chance of survival. What kind of environmental conditions would favor such a long-term investment of energy?

By the end of this lesson you should be able to answer the following focusing question: 

• What are the characteristics and reproductive strategies of r-selected and K-selected organisms?

Module 9: Section 2—Lesson 4 Assignment

 After you have completed all learning activities for this lesson you can complete the online assignment.

Bio 30 4.9.4S2 online assignment

In addition to your lesson work as listed below, any summary notes, sample problems, diagrams, charts or tables should be stored in the course folder for your teacher’s feedback and study as you prepare for exams.

You must decide what to do with the questions that are not marked by the teacher. Remember that these questions provide you with the practice and feedback that you need to successfully complete this course. You should record the answers to all of the questions and place those answers in your course folder.

4.9.4S2 page 2

Explore

The Amazing Race

If you have a good imagination you might be able to visualize a competition being held in which all species of the planet are lined up and given the following two tasks to complete in order to win the competition:

• Make as many offspring as possible. The offspring must survive long enough to reproduce.
• Spread yourselves as far and wide over the planet as possible.

Each entrant is given $1000 in ATP energy currency which they can use to complete the tasks. How they spend the money is entirely up to them, but each body system employed in the quest requires more energy. If you were one of these species, what strategy would you use?

• Would the kind of environment you’re in make a difference to your strategy? (stable vs. unstable)
• Is it better to reproduce at biotic potential (r) or just enough to remain at carrying capacity (K)?
• Should you attempt to improve your offspring’s survival by nurturing them, or just concentrate on producing more offspring?
• Should you begin reproducing as soon as possible or wait until later?
• Is it better to reproduce only once a year when conditions are good, or continually?

Of course we know that the strategies used by organisms to survive are not chosen, but is rather the result of random mutations being acted upon by the organism’s environment; resulting in the selection of successful genotypes/phenotypes. However, 2 major life strategies have emerged: r selected strategy and K selected strategy.

To learn about these strategies, do the following readings and assignment:

Read

Read pages 711-713 and pages 733, 735, and 736 in the textbook.

Self-Check

Characteristics of r and K selected species

Complete the following table in your course folder using your reading assignment of p. 712-3.

4.9.4S2 page 3

Lesson 4: Lab

Population Growth Rates in Different Countries

This is a data analysis lab that allows you to compare human population growth rates in different countries using demographic data gathered in 2001.

Problem (Purpose)
How do population growth rates differ by country?

Materials

• You will require a calculator.

Procedure

Refer to Thought Lab 20.5 on page 734 of the textbook.

Analyze the demographic information given in the data table according to the instructions in the analysis, conclusions, and real world applications sections.

Analysis

1. Calculate annual population growth rate for each country and place on the chart.
    
         gr = delta N = b-d
                    y        y
                                                                                             (2.5)
2. Calculate per capita growth rate for each country and place on the chart.
   
         Cgr = delta N
                       N
                                                                                       (2.5)
3. Why is the cgr negative for some populations? Describe the growth curve for a population with negative annual cgr. (2)
4. If the populations of the above country were graphed over 10 years, which of the above countries would you expect to show the steepest growth curve? Why? (2)
5. Is the initial size of the population more important than the per capita growth rate in determining the steepness of the growth curve? Why or why not? (2)
6. Does there appear to be a correlation between how developed the country is and its cgr? Justify your answer. (1)
7. Compare gr and cgr for the different countries. Which gives a better indicator of how fast the population will increase? Why?

Conclusions

What conclusions can you make from this exercise? Extract at least 3 sepearate conclusions from the data. Refer back to the problem statement. (3)

Real World Applications

Although the rate of population growth for the entire human species is nearly exponential, you’ve seen in the analysis above that the human species is made up of many sub-populations that have strikingly different growth patterns.

You are aware of all the factors that cause population numbers to change.

Apply your conclusions to the problem of human population control by devising a strategy that could be implemented to control human population growth rates. The strategy should have a specific goal, a target group, and state specific components of the plan or steps of implementation. Consider whether you would apply the same strategy to all human populations. You may assume that the political and economic limitations are the same as those that exist now. (5)

4.9.4S2 page 4

Going Beyond

Discuss the ramifications of your conclusions. How can we apply this information in the real world, where human population growth is a pressing issue?

Self-Check 1

Life Strategies and Population Change

Where on the population growth curve does natural selection begin to favor those with superior alleles? There are no winners without a competition. Competition only begins when scarcity of resources, waste accumulation, contagious disease, high predation and other density dependent factors become a daily fact of life. The organism’s physical, chemical, and behavioral traits combine to keep it alive and reproducing when those around it are not.

Using the following graph illustrating exponential and logistic growth, answer the questions and file your work in your course folder.

Logistic (S) versus Exponential (J) growth curves

SC 1. Label the region on the logistic curve where you would expect there to be the greatest competition and therefore selection of favorable alleles. Support your answer.

SC 2. Label the region on the logistic graph where you would expect to see the highest concentration of ‘winners’ (those with the most favorable alleles). Support your answer.

Sc 3. Where on this graph would you expect to see the predator-prey cycles that we discussed in a previous lesson occurring? Support your answer.

SC 4. What would you expect to happen to the J curve if it were extended? Why?

Self-Check

Application of Growth Curves to Different Species

For wildlife managers, deviations from expected growth patterns indicate a problem.

SC 5. In lesson 3, Try This, you graphed the data from a population of caribou from 1910 to 1950 that showed an extended period of exponential growth followed by a crash. Considering what you know now about the characteristics of K-selected species, was the graph typical? Why or why not?

SC 6. According to the table you created in Assignment #1 above, are Homo sapiens r or K selected? View figure 20.22 on page 733. Does the population growth curve support your decision? Why or why not?

SC 7. Read p.733 and 735 and view the Age Pyramids in Figure 20.23 to see age-pyramid representations of growth rates in the Congo, Sweden, and Germany. Which of the countries shows exponential growth? Negative growth? Stationary or carrying capacity growth?

SC 8. Compare Fig. 20.22 and 20.24. Both show human growth rates. Why does figure 20.24 appear to have a much flatter slope?

4.9.4S2 page 5

Lesson Summary

• A population can be described as r selected (J curve) or K selected (S curve). The terms are used in comparison to each other.
• K selected species live close to carrying capacity, have long life spans, are generally small in mass, reproduce later in life, and have small numbers of offspring, which they nurture.
• r selected species are growing close to their biotic potential, have short life spans, early reproductive ages, are generally small in mass, and have large numbers of offspring with large die-off.
• K and r selection are 2 extremes of a continuum – most species fit in between.
• Phenomena influenced by human activity such as climate change, over-harvesting, pollution, and introduction of invasive species into foreign environments can greatly affect populations.
• Age pyramids are useful tools for predicting future populations.
• Human populations were at carrying capacity for most of history. Technology has increased life expectancies and decreased infant mortality, causing the carrying capacity and population growth rates to increase exponentially.
• Due to reduced birth rates, most human populations are no longer growing exponentially, though a few are.
• The human carrying capacity will be influenced by growth rates, age structures, the state of the environment, and technological developments, but will likely be approximately 9 billion. 

Lesson Glossary

K-selected strategy: takes advantage of stable conditions; characterized by few offspring with much investment and nurturing to increase offspring survival

r-selected strategy: takes advantage of favorable conditions; characterized by early reproduction and high reproductive rate with little investment in offspring survival

Module Summary and Assessment

Module Summary—Section 2

To quantitatively describe changes in populations we need several tools. Formulas for population size, density, growth rate, and per capita growth rate allow us to collect the appropriate information needed to make informed decisions as wildlife managers, developers, politicians, academics, and concerned citizens. By itself, this data is not useful, unless we compare it to the normal patterns of growth observed in different species.

Different species have evolved two distinct strategies of growth to maximize their reproductive potential and survivability (r and K selection). These patterns are indicated by specific growth curves (logistic K and exponential J). A given set of species characteristics indicates each strategy, and we can predict the course of a given population by matching it with those characteristics.

Observed changes from the normal patterns are considered flags that indicate disruption, either from human activities, density independent factors, or density dependent factors. Human populations can be characterized by these same parameters, however human populations tend to differ from others due to our tendency to change our own environments using technology. Debate and controversy about how human growth differs from the growth patterns of other species has led to differing predictions about future human population trends.

Module Assessment—Section 2

In addition to submitting summaries for the tutorial videos in this module, you should have also submitted the assignments listed below.

Bio30 4.9.1S2 online assignment

Bio30 4.9.2S2 online assignment

Bio30 4.9.3S2 online assignment

Bio30 4.9.4S2 online assignment

Unit Summary and Assessment

In your study of Unit D you worked at

• explaining how populations can change over time
• describing the ways that members of a population interact with each other and with members of other populations
• analyzing quantitatively how populations change over time
• analyzing the technologies used by society in controlling and managing populations

In Module 8 you explored the genetics of populations and how we can quantitatively measure the way populations change. You also investigated how many factors can interact to cause populations to evolve or remain stable.

In Module 9: Section 1 you described the relationships that exist between organisms, the mechanisms that organisms use to protect themselves from each other, and how the species make-up of communities changes over time in the process of succession.

In Module 9: Section 2 you looked at how population size and changes can be measured, interpreted, and the results of the studies applied to the control of population growth.

Together these modules help you to understand how both an individual’s contributions to the gene pool and the interactions within communities result in change over time.

Unit Assessment

The unit assessment for this unit is as follows.

Unit 4 quiz

Unit 4 exam or Unit 4 examIPP

Your key parent/contact or we-connect coordinator will need to obtain the passwords for the quiz and the exam

Course Summary and Assessment

Course Conclusion

Congratulations, you have completed Biology 30!

Don't forget to complete the course exit survey to obtain a 10% bonus on a quiz mark.

Course Survey

If you have submitted all course work you can complete the practice final (link below) and replace your lowest unit exam mark.

Practice final or Practice final IPP

Good luck !