Lab 5 – Understanding Population growth

11 Jun Lab 5 – Understanding Population growth

Question
Lab #5 – Understanding Population growth –from an ecological perspective first.

Background: We are going to start a series of lab activities that will explore the issue of population growth.. We will first look at population growth from a purely ecological perspective (chapters 2 and 3), then we will look at population growth from a direct human perspective (chapter 4) then we will look at population growth from a more indirect human perspective.

1. Population growth: ecological perspective

2. Population growth: direct human perspective

3. Population growth: indirect human perspective

When we talk about a natural population we are often interested in what will happen to the population in the future: will it increase, will it decrease or will it remain the same. The population size for an organism is determined as follows:

Population size = (births + immigration) – (deaths + emigration)

To accomplish this lab (#1 above) we will employ a simulation activity (you will not need to go outside). A simulation is an activity that attempts to model a relationship in nature that one is likely not to encounter without great effort being expended. The key to any good simulation is to base the model on reality (what really happens in nature). So we are going to look at what happens to natural populations in nature as per the predator/prey relationship (since in fact every animal is likely a predator to something else as well as a prey to something else (think food chain):

The predator prey relationship we are going to consider is that between the field mouse (prey)

and the weasel (predator)

(Photo credit: NYS DEC).

The simulation activity we are doing is a classic simulation activity used by many to represent this predator/prey relationship.

Predator-Prey Simulation

Assumptions: As noted above we must base our simulation on the reality of nature so we make some assumptions based on natural observations as noted below-

Mouse population assumptions

1. The surviving number of mice (dried beans) always double their numbers at the end of each generation.

2. The most mice (dried beans) that may ever be in the meadow (bowl) is 100…. In other words the carrying capacity for mice in the meadow (bowl) is 100…you can never have more than 100 mice in your meadow (you can never have more than 100 beans in the bowl).

3. You must start each generation with at least 10 mice…for example let’s say at the end of a generation there are 4 mice left….those 4 mice double to become 8…. But then 2 additional mice are added to make 10 before you start the next generation…. So in other words 2 mice move into the meadow by immigration.

Weasel population assumptions

1. Each generation must start with at least one weasel….so if all the weasels die during a generation, a new weasel immigrates into the meadow at the start of the next generation,.

2. For a weasel (spoon) to survive it must capture at least 5 mice (beans).

3. For every 5 mice captured the weasel produces 1 offspring…so a weasel (spoon) that captures 5,6,7,8,or 9 mice (beads) produces 1 offspring…a weasel (spoon) that captures 10-14 mice (beads) produces 2 offspring… a weasel (spoon) that captures 15-19 mice (beads) produces 3 offspring… and so on

Materials:

-a 5” bowl from the kitchen

-a spoon (teaspoon size) from the kitchen

-100 dried beans or shelled peanuts from the kitchen pantry or small beads from somewhere else

Procedure:

1. The dried beans represent the field mice(prey), the bowl represents a meadow (habitat), the spoon the weasel (predator).

2. Place 10 “field mice” in the bowl. This is the initial population for the meadow and is the minimum population (the lowest number) that may begin each generation!

3. Place the plastic bowl on a flat surface and without looking run the spoon through the bowl, this will represent the weasel hunting for the field mice in one generation.

4. Count the number of field mice (beans) caught and record in the data table (see below). Subtract the number caught from the number that you started with in the bowl and record that number as the surviving prey. Double the numbers of surviving prey and place that number of mice in the bowl. This will be the initial field mouse population for the next generation. For example if there are 7 mice left after the weasel has hunted, those 7 mice double (add 7 to the dish), and so on. This number of field mice is the initial prey for the next generation. Remember you must always have the minimum population number of 10 when you start the next generation….. though you may have more than 10

5. The weasel must catch five field mice to survive, if less than five are caught the weasel dies or emigrates (leaves) the meadow. Note: A new weasel will migrate into the meadow at the beginning of the next generation if there are no weasels remaining at the end of a generation., If a weasel catches 5 mice then she survives and she reproduces one weasel for every five caught. (see above)

6. If there are two weasels then you must scoop the spoon two times through the bowl and record the total number captured. You scoop through the dish as many times as you have weasels. Subtract the total numbered captured from the initial population to get your surviving prey number to double for the next generation. The number of field mice in the meadow (bowl) can never exceed the carrying capacity of 100.

7. Complete 20 generations of weasel predation and record the data in the table provided.

8. Graph the initial population of predator (weasel) and prey(field mice) for each generation (use excel if able to).

9. Answer the following questions:

A) From your graph describe the relationship between the population size of the mice and the population size of the weasel…be specific. Do you think this is an accurate representation of this relationship, why or why not? Who controls who… do the mice control the weasels or do the weasels control the mice?

B) Go to http://isleroyalewolf.org/ and you will go to a most interesting website dealing with Isle Royale…. click on the “Technical” drop down menu and then click on ” data and interpretation”… under #1 Five Decades of Wolf – Moose Dynamics click on the “Click here” button at the end of the paragraph… a graph of moose/wolf predator prey interaction from Isle Royale will appear. Look at the graph and click the “next” button and read the description of what has happened with this real-world predator/prey relationship. Does this graph from the real world correspond to the simulated graph you produced? How is it similar, how is it different? Who controls who in the case of the wolf and the moose?

Email to me your completed lab answers by 10.28.16

Generation Initial

field mouse (prey)

population (a) Number

field mice

caught

(b) Surviving

field mice

(a-b) Initial

weasel(predator)

population Number of

initial

weasels that survived

Number of

weasel

offspring

1 10 1

2

3

4

5

6

Continue for 20 generations….

Sample data sheet: What follows is an example of what may happen (a sort of play-by-play) and a completed sample data table so you can see how you might fill in the data table.

Generation 1) You start with 10 beans in the dish….. you scoop through the bowl once and capture 4 beans (placing the beans in a container other than the bowl where you are storing your beans)…leaving 6 surviving field mice (beans)…. The initial weasel does not survive…and no offspring is produced. Look at the chart below to see how to complete the first generation.

Generation 2) You start with 12 beans (the 6 that survived in generation 1 have doubled) in the dish…. you scoop through the bowl once (as a new weasel comes in to the meadow since none survived in the first generation) and capture 6 beans (placing the beans in a container other than the bowl where you are storing your beans)…leaving 4 surviving field mice…. The initial weasel does survive…and produces one offspring. Look at the chart below to see how to complete the second generation.

Generation 3) You start with 10 beans in the dish (the four surviving field mice double to make 8 and 2 new mice come in to the meadow by immigration- recall you must always have 10 as a minimum to start each generation)…. you scoop through the bowl twice (as the weasel in generation 2 survived and produced an offspring) and the first scoop captures 0 mice and the second scoop captures 2 mice for a total of 2)…leaving 8 surviving field mice in the meadow (bow)l…. The initial weasel does not survive nor does the second weasel (the offspring from the previous generation).Look at the chart below to see how to complete the third generation.

Generation 4) You start with 16 beans (the 8 from the preceding generation double)in the dish…. you scoop through the bowl once (as a new weasel comes to the meadow since none survived in the third generation) and capture 4 beans (placing the beans in a container other than the bowl where you are storing your beans)…leaving 12 surviving field mice…. The initial weasel does not survive…and produces no offspring.Look at the chart below to see how to complete the fourth generation.

Generation 5) You start with 24 beans in the dish (12 surviving from generation 4 have doubled)…. you scoop through the bowl once (as a new weasel comes to the meadow since none survived in the fourth generation) and capture 5 beans (placing the beans in a container other than the bowl where you are storing your beans)…leaving 19 surviving field mice…. The initial weasel does survive…and produces one offspring.Look at the chart below to see how to complete the fifth generation.

Generation 6) You start with 38 beans in the dish (the 19 surviving field mice double to make 38 you scoop through the bowl twice (as the weasel in generation 5 survived and produced an offspring) and the first scoop captures 5 mice and the second scoop captures 2 mice for a total of 7 )…leaving 31 surviving field mice…. The initial weasel does survive but the second weasel (the offspring from the previous generation) does not….. if this were to continue you would be starting with 62 mice in generation 7 with two weasels…. Continue through 20 generations.. Look at the chart below to see how to complete the sixth generation.

Generation Initial

fieldmouse (prey)

population (a) Number

fieldmice

caught

(b) Surviving

fieldmice

(a-b) Initial

weasel(predator)

population Number of

initial

weasels that survived (must catch five mice to survive)

Number of

weasel

offspring (one offspring for every 5 mice captured)

1 10 4 6 1 0 0

2 12 6 4 1 1 1

3 10 2 8 2 0 0

4 16 4 12 1 0 0

5 24 5 19 1 1 1

6 38 7 31 2 1 1