1. Population Size FOSS Populations & Ecosystems

2. Introduce “Population” Write in your notebook a definition of a population. You have four minutes to write. Population: All the individuals of a species that are living in an area at one time.

3. Introduce “Reproductive Potential” Every population has the potential to increase in size. Some populations have the potential for slow, steady growth; others have the potential to increase rapidly. If you have the proper info at hand, you can calculate the potential for population growth for any organism. 1 of 3

4. Introduce “Reproductive Potential” Please write the following definition in your notebook. The theoretical unlimited growth of a population over time is its reproductive potential. 2 of 3

5. Introduce “Reproductive Potential” Write ‘Reproductive potential’ as your sub-heading. Under that, you have 2 minutes to answer ‘what info would you need in order to predict the size of the population in the future?’ I will call on some of you for pieces of suggestions. 3 of 3

6. Milkweed-Bug Reproductive Potential sheet Please take 3 minutes to read the introductory material. When you are done, please look up at the screen. Entomologists have discovered some general info about the lives of milkweed bugs living in the wild. That info is written on your sheet in the question and answer chart. Based on the info at hand, you should be able to figure out how many bugs will be in the population after a month, 2 months, or a year, if nothing limits population growth. 1 of 9

7. Milkweed-Bug Reproductive Potential sheet Guess how many milkweed bugs will be in the population if you start with just one adult male and one adult female bug, and the population reproduces without limitation for a year. Write your guess on the sheet now. 2 of 9

8. Milkweed-Bug Reproductive Potential sheet Start working on the sheet. Goal: Calculate the population after each successive 2-month interval. The sheet will help you and your partner organize both your thinking as you progress. 3 of 9

9. Milkweed-Bug Reproductive Potential sheet The first part of your sheet should look like this. Notice the Parents & Offspring add together to get the Total Population of 102. 4 of 9

10. Milkweed-Bug Reproductive Potential sheet The second part of your sheet should look like this. Notice the Offspring column has 2500 males and 2500 females. Why is that? According to your table, each female can lay 100 eggs. Since there are 50 females, 50 x 100 = 5000. Furthermore, the male to female ratio is 50/50, you have to divide the 5000 in half, hence 2500. 5 of 9

11. Milkweed-Bug Reproductive Potential sheet What should the next part look like? Remember, your previous total population’s number has to be correct, if your next population is also going to be correct. The next part should look like this. 6 of 9

12. Milkweed-Bug Reproductive Potential sheet After 8 months… 7 of 9

13. Milkweed-Bug Reproductive Potential sheet After 10 months… 8 of 9

14. Milkweed-Bug Reproductive Potential sheet After 12 months… 9 of 9

15. Discussing Milkweed-Bug Reproductive Potential sheet Without any limitation on population growth, every egg produces a new individual in the population, and every individuals lives out its natural life, 4 months. 1 of 3

16. Discussing Milkweed-Bug Reproductive Potential sheet Only females produce eggs. Half the population is female. Both male and female bugs are 2 months old when they reach maturity and mate, and the females produce 100 eggs. (That's the same as 50 eggs for every bug.) 2 of 3

17. Discussing Milkweed-Bug Reproductive Potential sheet When a generation reaches maturity at 2 months, its parents are 4 months old, and they die. Dead bugs, must be subtracted from the population. The population at any time is the number of immature milkweed bugs plus their parents, minus their grandparents. 3 of 3

18. Putting the population in context. As a consensus, a pair of milkweed bugs has the potential to produce a population of almost 32 billion bugs in 1 year. That number of milkweed bugs, would: Circle Earth eight times if they stood in a line, nose to tail. Cover about eight football fields if they all crowded together, but didn't crawl on top of one another. Have a mass equal to about 600 Randolph Middle Schools. Fill about 12 typical middle school classrooms from floor to ceiling.

19. Discuss implications Clearly the population of milkweed bugs does not increase in the real world at the rate WE calculated. Write ‘Population implications’ in your notebook. Under that, answer ‘what prevents the population of milkweed bugs from covering the planet?’ Write with your neighbor for 3 minutes to come up with reasons why the population is limited in the real world.

20. New VOCAB: Limiting Factor Populations are always subjected to limiting factors in the natural world. A LIMITING FACTOR is any biotic or abiotic factor that acts in some way to limit the number of individuals that survive and reproduce in a population.

21. Biotic and Abiotic limiting factors What are some biotic and abiotic factors that might limit the growth of milkweed bugs in nature? 1 of 2

22. Biotic and Abiotic limiting factors Humans Primates Disease on environment Fishes Avians Pathogens Human-made objects Floods Tornados Ice storms Tsunami Food source BioticAbiotic 2 of 2

23. Unlimited Population Growth We looked at the results of a theoretical population of milkweed bugs that reached maturity in 2 months, produced 100 eggs per female, had 100% hatch, produced equal numbers of males and females, and lived a total of 4 months. We found that after a year the population was about 32 billion individuals. 1 of 2

24. Unlimited Population Growth But what would happen to the population if one of the variables changed? What would happen if, for instance, females laid 150 eggs? 2 of 2

25. The Multimedia Computers are great tools for doing calculations. We can use the computer to calculate the reproductive potential of milkweed- bug populations with different characteristics than the one we investigated. 1 of 2

26. The Multimedia Go to www.fossweb.comwww.fossweb.com Username: randolphmssci Password: zPv6721 Go to the milkweed-bug simulations. Open ‘Milkweed Bugs, Unlimited’. Run it with the default population, which has the same characteristics as the population that students calculated. 2 of 2

27. The Milkweed-Bug Hatching Investigation sheet. One critical factor in the milkweed-bug reproductive cycle is the successful hatching of the eggs. If the eggs don't hatch, the population will not grow. Some students conducted a set of experiments to look into egg hatching. We have a record of the experimental procedure they used and the data they collected. 1 of 2

28. The Milkweed-Bug Hatching Investigation sheet. Review the purpose and design of the experiments on page 31 to learn what the investigators were interested in finding out. Study the data on page 32 to see what effect each variable had on egg hatching. Summarize the results of the experiments and write up your conclusions on page 33. 2 of 2

29. Analyzing the Milkweed-Bug Hatching Investigation sheet. Good inferences are: Humidity and light do not seem to limit milkweed-bug hatching. Temperature can be a limiting factor. Temperatures below 10 o C and over 40 o C seem to prevent hatching. Temperatures around 10 o C reduce hatching. Eggs at 20-40 o C hatch in large numbers; cooler temps can extend the time. 1 of 3

30. Analyzing the Milkweed-Bug Hatching Investigation sheet. Ecologists use many different methods to get info about ecosystems. One technique is to conduct lab experiments. By bringing a little bit of the natural world into the lab, the scientist can focus on one isolated aspect of the system. 2 of 3

31. Analyzing the Milkweed-Bug Hatching Investigation sheet. In the lab the variables can be carefully controlled in order to determine cause- and-effect relationships. The milkweed- bug hatching experiment is an example of just such a lab investigation. Other methods used by ecologists to better understand ecosystems include field observations and computer models, similar to the one we used. 3 of 3

32. Algae & Brine Shrimp Populations The field ecologists who study the Mono Lake ecosystem observe that the populations vary a lot over the course of a year. Sometimes, for instance, there are almost no brine shrimp in the lake, and at other times there are trillions. 1 of 3

33. Algae & Brine Shrimp Populations They reasoned that there must be some limiting factors that result in small populations sometimes and huge populations at other times. The scientists know that the survival of the whole Mono Lake ecosystem depends on the algae. 2 of 3

34. Algae & Brine Shrimp Populations If the algae population (the producers) is large, the ecosystem will have the capacity to support large populations of primary consumers. The scientists wanted to understand the factors that limit the populations of two important organisms in Mono Lake, the planktonic algae and the brine shrimp. They set up a yearlong laboratory experiment. 3 of 3

35. Algae & Brine Shrimp Experiments sheet Please look at Algae and Brine Shrimp Experiments. Please take 5 minutes to read the experimental setup & procedure described on page 34 & 35. The following slide tells what you should’ve understood. 1 of 2

36. Algae & Brine Shrimp Experiments sheet Eight experimental aquariums were set up & maintained as described on page 34. Each aquarium had only one variable that changed over the course of the experiment. The populations were sampled every month for 1 whole year. The data the scientists collected are recorded on page 36. Please start working on this sheet for the next 30 minutes. 2 of 2

37. Analysis of Algae & Brine Shrimp Experiments sheet Some questions to guide you if you’re lost: Which experiments were maintained at a consistently cold temperature all year? Which were maintained at a consistently warm temperature? Which experimental aquariums were maintained at the same temp as Mono Lake throughout the year? What would a graph of time versus temp look like for the aquariums maintained at the same temp as Mono Lake throughout the year? 1 of 1

38. Discussion of Algae & Brine Shrimp Experiments sheet To start this discussion, what is a limiting factor? Keeping this definition in mind, I would like one spokesperson to share their group’s conclusions about the effects of light & temp on the two Mono Lake organisms, planktonic algae, and brine shrimp. 1 of 4

39. Discussion of Algae & Brine Shrimp Experiments sheet Overall, here were the main ideas: Within the light & temp ranges that were investigated, algae were not significantly limited. Population increase was slightly slower in the low-light situation, but at the end of the year the population of algae was the same in all four aquariums. Brine shrimp were not limited by light intensity, but were significantly limited by temp. 2 of 4

40. Discussion of Algae & Brine Shrimp Experiments sheet In the low-temperature situation none of the eggs hatched. In the variable-light situation the population growth and decline were directly related to water temp. The greatest population increase was in the warm water. In Mono Lake the populations would potentially be subjected to other limiting factors. 3 of 4

41. Discussion of Algae & Brine Shrimp Experiments sheet For the algae, abiotic factors would include CO 2, nutrients, and space; biotic factors would include predation by primary consumers & diseases. For the brine shrimp, abiotic factors would include O 2 and space; biotic factors would include food, predation by secondary consumers and diseases. 4 of 4

42. Population Dynamics  Up to this point we have been looking at theoretical population growth, which we called reproductive potential, and laboratory data obtained from experiments conducted away from the natural ecosystem.  Now we are going to look at some real data collected from the field by ecologists working at Mono Lake. 1 of 2

43. Population Dynamics  Study the two graphs located on the left.  Based on what you know about the populations of planktonic algae & brine shrimp, and the light and temp conditions at Mono Lake…  how big do you think the populations of those two organisms will be over the course of a year? 2 of 2

44. Comparing Predictions to Data  Please look at your Mono Lake Data sheet.  The light and temp graphs are on page 38, and the population graphs for planktonic algae, brine shrimp, and another organism, the brine fly, are on page 39. 1 of 2

45. Comparing Predictions to Data  Please study the graph for details for 2 minutes.  Here are two questions:  Were your predictions for the algae & brine shrimp populations accurate?  How can the drop in algae population during the warmest part of the year be explained? 2 of 2

46. New VOCAB: biotic limiting factors  Sometimes a population’s size is limited by other organisms. These are called biotic limiting factors.  What are some of the ways populations might be limited by other organisms?

47. Other biotic relationships  When one organism eats another, the population of those being eaten is reduced.  Answer the following questions in your notebook:  What happens to the population of oak trees when squirrels gather the acorns for food?  What happens to the population of trout when the fish are diseased by a fungus? 1 of 2

48. Other biotic relationships  So, using your answers from the two previous questions, here’s the main question:  What are some ways organisms limit the populations of others without eating them?  In any case, a population is limited by reduction of the potential for new members to enter the population or…  Decrease any chance for new members, you decrease the population. 2 of 2

49. Analysis of Mono Lake Data sheet  Ecosystems are dynamic.  That means they are always changing. The Mono Lake graphs show how some of the populations of organisms change and how the abiotic conditions change throughout the year.  Please look at the Analysis of Mono Lake Data sheet. Using the info in the graphs to support your ideas.  You will have 20 minutes to work.

50. Revisit abiotic factors  Here are some “big picture” questions:  Mono Lake population are affected by abiotic factors. What abiotic factors did you look at?  How does temperature affect the populations in the lake?  What other abiotic factors could affect the populations in the lake?

51. Revisit biotic factors  Here are some “big picture” questions:  Mono Lake populations are affected by biotic factors. What biotic factors did you look at?  Brine shrimp eat planktonic algae. Describe how algae act as a biotic limiting factor on the population of brine shrimp.  Describe how brine shrimp act as a limiting factor on the algae population.  What causes the bird populations to increase and decrease so rapidly in the Mono Lake ecosystem?

52. Summarizing the ecosystem  Mono Lake is a dynamic ecosystem. The populations of organisms living there fluctuate dramatically during the year. This is a normal and healthy situation at Mono Lake.  During the cold of winter, Mono Lake looks like a wasteland. No birds swim on its surface, and no brine flies or brine shrimp are active. The lake is turning a healthy dull green color, however, as the planktonic algae experience an explosive phase of population growth. 1 of 5

53. Summarizing the ecosystem  The algae population increases rapidly because for awhile there are no limits on its growth. Light, nutrients, and CO 2 are plentiful. The algae are not limited by the near-freezing temp of the water, and most of the predators are dormant.  As spring arrives, the increased solar energy warms the water. Brine shrimp & brine flies hatch and start eating the algae. The hungry predators eat the algae faster than the algae can reproduce, so the algae population starts to decline. 2 of 5

54. Summarizing the ecosystem  As summer approaches, the first birds, the gulls, arrive. They feast on the brine shrimp. The gulls slow the population growth of the brine shrimp, but don’t reverse it.  It is not until July, when all the migratory birds are present, that the brine shrimp begin to decline. They decline because they are reaching the limit of their food supply on one side, and 100’s and 1000’s of birds are eating them on the other side.  The brine shrimp population declines rapidly. 3 of 5

55. Summarizing the ecosystem  By October the nutrients in the water have been depleted, and predation has taken its toll on the algae population. It falls to its lowest level.  The cooling water causes the eggs laid by the remaining brine shrimp and the pupae of the brine flies to fall into dormancy, and the brine shrimp and brine fly populations drop to zero. 4 of 5

56. Summarizing the ecosystem  When the surface water approaches freezing, it is so dense that it plunges to the bottom of the lake, stirring up the nutrient-rich sediments, making them available to the algae.  The algae begin, once again, to reproduce rapidly, turning the lake green.  The producers have set the stage for a repeat of the age-old surge of life in the Mono Lake ecosystem. 5 of 5

57. New CONCEPT: interdependence  After the Mono Lake ecosystem explanation, we have an important point that is counterintuitive:  Since growth seems like a good indicator of health,  however, populations all have the potential to grow way beyond the ability of the environment to support them,  therefore, decreasing a population can save the population. 1 of 3

58. New CONCEPT: interdependence  Think about it…  It’s clear the brine shrimp depend on a source of algae for their well-being.  But the brine shrimp depend on the migratory bird predators to keep their numbers in check so they don’t exhaust or damage their algae food source.  And the algae need limits so they don’t extract all the nutrients from the water. 2 of 3

59. New CONCEPT: interdependence  Out of the previous slide, the new concept is INTERDEPENDENCE.  In your notebook, based on what you learned from the last couple of days, write what you think ‘interdependence’ means?  Interdependence: A healthy population has limits imposed on it. Those limits are abiotic and biotic limiting factors. 3 of 3

60. Ecosystems and balance  You probably heard the term balanced used to describe an ecosystem that is functioning well.  In your notebooks, for six minutes, answer the following question:  What do you think is meant by the term “balanced ecosystem”? 1 of 2

61. A better term…  Here’s a better term than balanced.  A better term to describe a fully functioning ecosystem - healthy.  A healthy ecosystem can absorb stress and fluctuation without falling into disarray. A healthy ecosystem is flexible and durable. 2 of 2

62. Mono Lake in the Spotlight reading  Please discuss with your pair the following question:  Why did the gull population experience a decline in 1982?  Two factors converged to stress the gull population.  1. Water diversion caused a drop in the lake level so that a land bridge formed. Predators, like coyotes, were able to walk to the nesting area on the small island. The nesting was disrupted. 1 of 2

63. Mono Lake in the Spotlight reading  2. More devastating to the gull population was the failure of the brine shrimp. Water diversion resulted in increased salinity of the water.  The increased salinity apparently suppressed the population growth of the 1st generation of brine shrimp that year. Only 15% of the expected shrimp hatched. That year 25,000 baby gulls starved. 2 of 2

64. Summarizing the effect of abiotic factors  Abiotic factors can have enormous influence on the activities in an ecosystem. We have seen how water temperature influences population size - some populations decrease when the temp declines, and others increase.  What might happen if the temp stayed warm all year?  What might happen to the Mono Lake ecosystem if water diversion were allowed to continue? 2 of 2