Teacher Resources—Animal Arms Races Learning Outcomes Time

252 POGIL

Life Science Activities | Designed to Support the NGSS

Activity 11

Teacher Resources—Animal Arms Races

Learning Outcomes

1. I can

distinguish between nondefensible and defensible resources.

2. By analyzing and interpreting evidence about types of competition strategies, the

defensibility of resources and the competition for mates, I can predict which animals are likely

to develop extreme weapons.

3. I can explain how extreme weapons affect the probability of successful reproduction.

Time Estimate

90 minutes (longer for middle school students)

Designed Specically to Support ese NGSS* Standards:

MS-LS4-4

Construct an explanation based on evidence that describes how genetic variations of traits in

a population increase some individuals’ probability of surviving and reproducing in a specic

environment. [Clarication Statement: Emphasis is on using simple probability statements and

proportional reasoning to construct explanations.]

MS-LS1-4

Use argument based on empirical evidence and scientic reasoning to support an explanation

for how characteristic animal behaviors and specialized plant structures aect the probability of

successful reproduction of animals and plants respectively.

HS-LS4-2

Construct an explanation based on evidence that the process of evolution primarily results from

four factors: (1) the potential for a species to increase in number, (2) the heritable genetic variation

of individuals in a species due to mutation and sexual reproduction, (3) competition for limited

resources, and (4) the proliferation of those organisms that are better able to survive and reproduce

in the environment. [Clarication Statement: Emphasis is on using evidence to explain the inuence

each of the four factors has on number of organisms, behaviors, morphology, or physiology in terms

of ability to compete for limited resources and subsequent survival of individuals and adaptation of

species.]

* NGSS and Next Generation Science Standards are registered trademarks of Achieve. Neither Achieve nor the lead states and partners that developed

the Next Generation Science Standards were involved in the production of, and do not endorse, this product.

Prerequisites

1. Students can locate relevant information from complex diagrams and data tables.

2. Students can compare and contrast multiple drawings of similar objects in order to identify

subtle dierences.

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Life Science Activities | Designed to Support the NGSS 253

Activity 11

3. Students can explain that if an organism reproduces, it passes its genetic material to the next

generation.

4. Students can explain that the population of organisms may change if only some of the members

if the original population reproduce successfully.

To Prepare Before Facilitating:

Make copies of pages 264–269 (double sided/stapled).

It may be helpful to hand out the activity as three separate tasks: pages 264–265, page 266, and

pages 267–269.

Make copies of pages 270-271 to hand out as enrichment to teams that nish early.

Additional Resources

Many videos are available to introduce your students to dung beetles. Here is one:

https://www.youtube.com/watch?v=Cz8zVQ0XTR8

Here is a “Bozeman Science” video that summarizes Natural Selection. It would be great for students

to watch AFTER completing this activity.

http://www.bozemanscience.com/001-natural-selection

YouTube video: “Animal Structures and What ey Mean”

https://www.youtube.com/watch?v=iwGgc73Dv0o&feature=youtu.be

Short video about stalk eyed ies

https://www.youtube.com/watch?v=bGX7zZk0Eo4

For students who are particularly interested in extreme animal weapons, here are interviews with

Doug Emlen, the author of the book, Animal Weapons:

Interview 1: https://www.youtube.com/watch?v=No6mB6V1wL4

Interview 2: https://www.youtube.com/watch?v=CyidhY2dc5I

Much of the information in this activity is based on unpublished data from 2015 and 2016

interviews of researchers at the Lavine Lab at Washington State University, Pullman WA and the

Emlen Lab at University of Montana, Missoula MT. e work was funded through the National

Science Foundation Animal Behavior Award NSF IOS 1456731 to the WSU and UM Departments

of Entomology.

254 POGIL

Life Science Activities | Designed to Support the NGSS

Activity 11

Assessment Questions

1. Circle the defensible resources.

2. Circle the one statement in the nal column that is correct.

Type of Animal

Do males

compete for

females?

Do males have

a defensible

resource?

Do males

engage in one-

on-one duels?

Your prediction:

Will males have an

extreme weapon?

Termites Yes Yes Yes Yes No

Crows Yes No No Yes No

Wolf Yes Yes No Yes No

Rhinoceros

Beetles Yes Yes Yes Yes No

3. Write one or two sentences that explain how extreme weapons aect the probability of

reproductive success. Base your answer on the situation shown in the following drawing.

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Life Science Activities | Designed to Support the NGSS 255

Activity 11

Animal Arms Races

Why? Answer Key (Suggested Answers)

You’ve heard about human arms races where one country builds a fast ghter jet, a destructive nuclear

bomb, a very accurate gun. Soon another country responds by building faster jets, more destructive

bombs, more accurate guns. is spiral of competition leads to the evolution of faster, more powerful,

more accurate weapons. All this eort is invested to defend a country’s resources. In nature we nd a

variety of animals with oversized body parts that act as weapons, such as moose with huge antlers and

walruses with gigantic tusks. Yet there are similar animals without these weapons, such as horses and seals.

Why do some animals have these large weapons while other similar animals do not? ere are even very

closely related animals where some species have large weapons and others do not, such as dung beetles. In

this activity, we will explore the conditions and behaviors required for species to evolve oversized weapons,

and we will investigate a species that seems to defy evolutionary theory.

Use the information from Model 1 to answer Questions 1–5.

Reach an agreement with your team before writing down your consensus answer.

1. List the three column headings in Model 1 (see page 256).

Defensible Resources, Nondefensible Resources, Dierence

2. Circle the items in the following list that are classied as resources in Model 1.

mates food trees fence homes

people dung bridge fruit

3. If you had the job of guarding these resources in Model 1, which column would you prefer to

defend? Explain your reasoning.

Defensible resources because there is some type of barrier or restricted access point that is

easy to guard. is makes it easier to keep resources away from competitors.

4. Complete the “Dierence” column in Model 1.

a. Identify the dierence between each pair of examples.

b. Underline this dierence.

c. Explain how that dierence allows the same resource to be protected in one situation but

not in the other situation.

Check with your teacher before you continue.

5. In your own words, write one complete sentence that denes the term defensible resource.

It is any resource that the animal (or person) can easily protect from others.

Model 1—What is a Defensible Resource?

Defensible Resources Nondefensible Resources Dierence

Middle Ages Walled

Village

Resources: Food, Water,

Homes, Animals,

People

Middle Ages Village

Resources: Food, Water,

Homes, Animals, People

A wall: e villagers can close the gate

and keep animals and other people

away from their food, water, homes

and families

Fenced Fruit Tree

Orchard

Resource: Ripe Fruit

Unfenced Fruit Tree

Orchard

Resource: Ripe Fruit

Fences: The owner can keep animals

and people away from trees when the

fruit is ripe, so the owner gets all the

fruit. The restricted access makes the

resource easier to guard.

Tunneling Dung

Beetle

Resource: Mate (in

tunnel)

Non-Tunneling Dung

Beetle

Resource: Mate with food

(dung)

Tunnel: e male dung-rolling beetle

must keep other males away from the

female. ere is only one way to get

into the tunnel where the female is

located, and it can be guarded.

Stalk-Eyed Flies

Resource: Small roots to

stand on while mating

House Flies

Resource: Any surface to

stand on while mating

Small root to stand on: e male

y can guard his female mates from

other males. ere is only one way to

get to small root where the females are

located, and it can be guarded.

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Activity 11

Model 2—Dierent Competition Strategies for Defending a

Resource

Competition Strategies

Examples

Agility

(speed,

quick changes

in direction)

Scramble

(competitors

approaching from

many directions)

One-on-One

Duel

(matched test

of strength)

Fighter Pilots X X

Jousting Knights

Elk X

Football Players

Piling on the Ball

Carrier

Dragon Flies X

Ball-Rolling

Dung Beetle

Use the information from Model 2 to answer Questions 6–9.

Reach an agreement with your team before writing down your consensus answer.

6. Discuss how each example of competition should be classied best: agility, a scramble or a one-

on-one duel. Draw an X in the one box to show your team consensus answer.

Check with your teacher before you continue.

7. Circle the pictures of examples in Model 2 that have oversized weapons.

8. Circle the type of competition strategy that is always associated with the presence of

oversized weapons

9. Predict which of the following species seem most likely to use one-on-one duels as their

competition strategy. Circle your answer(s).

Some students might circle only the crab. at is okay.

agility scramble one-on-one duels

Model 1—What is a Defensible Resource?

Defensible Resources Nondefensible Resources Dierence

Middle Ages Walled

Village

Resources: Food, Water,

Homes, Animals,

People

Middle Ages Village

Resources: Food, Water,

Homes, Animals, People

A wall: e villagers can close the gate

and keep animals and other people

away from their food, water, homes

and families

Fenced Fruit Tree

Orchard

Resource: Ripe Fruit

Unfenced Fruit Tree

Orchard

Resource: Ripe Fruit

Fences: The owner can keep animals

and people away from trees when the

fruit is ripe, so the owner gets all the

fruit. The restricted access makes the

resource easier to guard.

Tunneling Dung

Beetle

Resource: Mate (in

tunnel)

Non-Tunneling Dung

Beetle

Resource: Mate with food

(dung)

Tunnel: e male dung-rolling beetle

must keep other males away from the

female. ere is only one way to get

into the tunnel where the female is

located, and it can be guarded.

Stalk-Eyed Flies

Resource: Small roots to

stand on while mating

House Flies

Resource: Any surface to

stand on while mating

Small root to stand on: e male

y can guard his female mates from

other males. ere is only one way to

get to small root where the females are

located, and it can be guarded.

258 POGIL

Life Science Activities | Designed to Support the NGSS

Activity 11

Model 3—To Have or Not to Have Extreme Weapons

Type of Animal

Drawing of

Male

Do males

compete for

females?

Do males have

a defensible

resource?

Do males

engage in one-

on-one duels?

Do males have

an extreme

weapon?

Elk Yes

Yes

Herd of females

Yes Yes

Sea Star

Releases sperm/eggs

into the water

Yes

Food (sections of

shellsh beds)

Yes No

Stalk-eyed Fly Yes Yes Yes

House Fly Yes No No No

Tunneling

Dung Beetles

Yes

Tunnel with

dung (food) and

female in it

Yes Yes

Ball-Rolling

Dung Beetles

Yes

Ball of dung

in the open

No No

Wolves Yes

Yes

Cave for females

Not physically,

but by dominant

personality

Rhinoceros

Beetle

Yes

Sap (food) oozing

from tree

Yes Yes

Use the information from Model 3 to answer Questions 10–16.

Reach an agreement with your team before writing down your consensus answer.

10. Which gender(s) of each species are included in the drawings in Model 3?

Males

Yes

Roots

to stand

on while

mating

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Activity 11

11. Compare the column headings in Model 1, Model 2 and Model 3.

Circle the phrases that are found in more than one of these models.

Defensible resources Nondefensible resources Agility

Scramble One-on-One duel Extreme weapons

12. Based on the drawings in Model 3, complete the last column of the Model 3 data table.

13. Write Yes or No to answer each of the following questions.

For all of the eight species shown in Model 3, do all of the males…

a. compete for female mates? No b. have a defensible resource? No

c. engage in one-on-one duels? No d. have an extreme weapon? No

Check with your teacher before you continue.

14. List the names of the species with males that develop extreme weapons. Circle the extreme

weapon on the drawings of each of your listed species.

Elk, Stalk-eyed y, Tunneling dung beetle, Rhinoceros beetle

15. Carefully review Model 3 to determine the situation and the behaviors documented in the

species you have circled. In 1–2 complete sentences, clearly summarize the behaviors and

situations that are similar in all of the species that develop extreme weapons.

All of the animals that develop extreme weapons have these behaviors in common: they

compete for females and they engage in one-on-one duels. e situation that these animals

all have in common is that they have a defensible resource.

16. Consider the following data on three species we have not analyzed. Based on your understanding

of the behaviors and situations that lead to the evolution of extreme weapons, ll in the table.

Type of

Animal

Do males

compete for

females?

Do males

have a

defensible

resource?

Do males

engage in

one-on-one

duels?

Do you predict that males will

have an extreme weapon?

Explain your answer

clearly and completely.

Fiddle Crab Yes

Yes

Burrow with

females in it

Yes

Yes, the ddler crab engages in the

same behaviors and has the same

situations as described in the answer

to Question 15.

Mouse Yes

Yes

Burrow with

females in it

No, the mouse shows only two of the

three behaviors/situations that seem

to be required to develop extreme

weapons.

Termite Yes

Yes

Fortress with

limited entrance

Yes

Yes, the termite engages in the

same behaviors and has the same

situations as described in the answer

to Question 15.

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Life Science Activities | Designed to Support the NGSS

Activity 11

What I Still Wonder…

17. Write one additional question you have about animal weapons or about changes over

time in animal species.

Answers will vary.

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Activity 11

Extension Questions

Read is!

When evolutionary biologists began investigating the evolution of extreme weapons in dung

beetles, they encountered a very confusing problem. From observations of horned male dung

beetles defending the entrances to their tunnels, it seemed that only the beetles with the

longest horns would ever have access to females. us their male ospring should develop

longer horns, too. Evolutionary theory would have predicted that over time all of the

male beetles would develop longer and longer horns. Surprisingly, no matter how many

generations of beetles the researchers bred, there were always some hornless male beetles

in every generation. In Model 4, you will analyze data from underground observations of

these beetles to generate an explanation for why hornless male beetles never completely

disappeared from the population.

Model 4—e Mystery of the Tunneling Dung Beetle

Type of

Animal Drawing

Do Males

Compete for

Females

Do Males have

a Defensible

Resource?

Do males

Engage in One-

on-one Duels?

Do Males have

an Extreme

Weapon?

Tunneling

dung beetle

male

(Horned)

Yes

Females in a Burrow?

Yes Yes

Tunneling

dung beetle

male

(Hornless)

No No No No

Tunneling

dung beetle

female

(Hornless)

--- --- ---

A B

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Activity 11

18. In Box A of Model 4, all the male beetles have horns.

a. How many male beetles are present?

Four

b. How many female beetles are present?

Two

19. Compare the male beetles in Box A. e male beetle with the largest horns usually wins one-on-

one duels over access to the tunnel. is beetle is the only one that can mate with the female and

produce ospring. Circle the beetle in Box A that is most likely to produce ospring.

20. e horn length of male beetles is most closely related to their father’s horn length.

Predict the type of male beetle ospring that the winner in Box A will produce:

Hornless Short horns Medium horns Long horns

Explain your answer:

e male beetle with the longest horns is most likely to win access to the female. His male

ospring will also have long horns, similar to his own.

21. Compare the male beetles in Box B. Based on the drawing, describe what the sneaky hornless

male beetle has done to gain access to mate with the female.

e sneaky hornless male dug a side tunnel to reach the female. is way he didn’t need to

ght the long-horned male to gain entrance to the female’s tunnel!

22. Describe how being hornless might make it easier to sneak into a tunnel unnoticed and mate

with a female. Include your ideas about the diculty of sneaking in to build a side tunnel if you

have larger or smaller horns.

e sneaky hornless males might be able to dig a tunnel more easily than a male with horns.

At the least, the tunnel could be smaller than if a horned male beetle tried to dig a tunnel.

is way he could get to the female quickly. Also maybe the long-horned male might think

the hornless male is a female since they look the same.

23. Write 3–4 sentences that justify the following claim. Include evidence from Model 4 and your

answers to Questions 17–21.

“As long as tunneling dung beetles continue to behave in the same manner as they did during

research observations, there will always be at least some hornless males in the population.”

e processes of evolution should favor more and more long-horned male beetles in the

population as time passes since these beetles will be able to mate more frequently and pass

on their long-horn genes to their male ospring. Eventually, if all male beetles had to ght

to gain access to females, the hornless males would mate so rarely that they would eventually

die out and no longer be present in the population. However, if the “sneaky male” behavior

continues, at least a few hornless males will be able to mate with females and pass along

their hornless gene to their ospring. is means there will probably always be at least a few

hornless males in each generation.

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Life Science Activities | Designed to Support the NGSS 263

Activity 11

Assessment Questions

1. Circle the defensible resources.

Students may or may not include the castle, depending on their assumption of resources held

within its walls.

2. Circle the one statement in the nal column that is correct.

Type of Animal

Do males

compete for

females?

Do males have

a defensible

resource?

Do males

engage in one-

on-one duels?

Your prediction:

Will males have an

extreme weapon?

Termites Yes Yes Yes Yes No

Crows Yes No No Yes No

Wolf Yes Yes No Yes No

Rhinoceros

Beetles Yes Yes Yes Yes No

3. Write one or two sentences that explain how extreme weapons aect the probability of

reproductive success. Base your answer on the situation shown in the following drawing.

In the situation shown, male

beetles are ghting for the

females. Because the male

with the longest horns win

ghts with other males, the

long-horned male can defend

the entry to the tunnel where

the females are located. He

will be the only male that

mates and produces ospring,

so he is more likely to have

reproductive success than the

males without the extreme

weapon (horns).

264 POGIL

Life Science Activities | Designed to Support the NGSS

Student Activity 11

Animal Arms Races

Why?

You’ve heard about human arms races: one country builds a fast ghter jet, a destructive nuclear bomb, a

very accurate gun. Soon another country responds by building faster jets, more destructive bombs, more

accurate guns. is spiral of competition leads to the evolution of faster, more powerful, more accurate

weapons. All this eort is invested to defend a country’s resources.

In nature we nd a variety of animals with oversized body parts that act as weapons, such as moose with

huge antlers and walruses with gigantic tusks. Yet there are similar animals without these weapons, such

as horses and seals. Why do some animals have these large weapons while other similar animals do not?

ere are even very closely related animals where some species have large weapons and others do not, such

as dung beetles.

In this activity, we will explore the conditions and behaviors required for species to evolve oversized

weapons, and we will investigate a species that seems to defy evolutionary theory.

Use the information from Model 1 to answer Questions 1–5.

Reach an agreement with your team before writing down your consensus answer.

1. List the three column headings in Model 1 (see page 256).

2. Circle the items in the following list that are classified as resources in Model 1.

mates

food trees fence

homes

people dung bridge fruit

3. If you had the job of guarding these resources in Model 1, which column would you prefer to

defend? Explain your reasoning.

4. Complete the “Dierence” column in Model 1.

a. Identify the dierence between each pair of examples.

b. Underline this dierence.

c. Explain how that dierence allows the same resource to be protected in one situation but

not in the other situation.

Check with your teacher before you continue.

5. In your own words, write one complete sentence that denes the term defensible resource.

Model 1—What is a Defensible Resource?

Defensible Resources Nondefensible Resources Dierence

Middle Ages Walled

Village

Resources: Food, Water,

Homes, Animals,

People

Middle Ages Village

Resources: Food, Water,

Homes, Animals, People

Fenced Fruit Tree

Orchard

Resource: Ripe Fruit

Unfenced Fruit Tree

Orchard

Resource: Ripe Fruit

Fences: The owner can keep animals

and people away from trees when the

fruit is ripe, so the owner gets all the

fruit. The restricted access makes the

resource easier to guard.

Tunneling Dung

Beetle

Resource: Mate (in

tunnel)

Non-Tunneling Dung

Beetle

Resource: Mate with food

(dung)

Stalk-Eyed Flies

Resource: Small roots to

stand on while mating

House Flies

Resource: Any surface to

stand on while mating

266 POGIL

Life Science Activities | Designed to Support the NGSS

Student Activity 11

Competition Strategies

Examples

Agility

(speed,

quick changes

in direction)

Scramble

(competitors

approaching from

many directions)

One-on-One

Duel

(matched test

of strength)

Fighter Pilots

Jousting Knights

Elk

Football Players

Piling on the Ball

Carrier

Dragon Flies

Ball-Rolling

Dung Beetle

Use the information from Model 2 to answer Questions 6–9.

Reach an agreement with your team before writing down your consensus answer.

6. Discuss how each example of competition should be classied best: agility, a scramble or a one-

on-one duel. Draw an X in the one box to show your team consensus answer.

Check with your teacher before you continue.

7. Circle the pictures of examples in Model 2 that have oversized weapons.

8. Circle the type of competition strategy that is always associated with the presence of

oversized weapons

9. Predict which of the following species seem most likely to use one-on-one duels as their

competition strategy. Circle your answer(s).

Model 2—Dierent Competition Strategies for Defending

a Resource

agility scramble one-on-one duels

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Student Activity 11

Model 3—To Have or Not to Have Extreme Weapons

Type of Animal

Drawing of

Male

Do males

compete for

females?

Do males have

a defensible

resource?

Do males

engage in one-

on-one duels?

Do males have

an extreme

weapon?

Elk Yes

Yes

Herd of females

Yes

Sea Star

Releases sperm/eggs

into the water

Yes

Food (sections of

shellsh beds)

Yes

Stalk-eyed Fly Yes Yes Yes

House Fly Yes No No No

Tunneling

Dung Beetles

Yes

Tunnel with

dung (food) and

female in it

Yes Yes

Ball-Rolling

Dung Beetles

Yes

Ball of dung

in the open

Wolves Yes

Yes

Cave for females

Not physically,

but by dominant

personality

Rhinoceros

Beetle

Yes

Sap (food) oozing

from tree

Yes

Use the information from Model 3 to answer Questions 10–16.

Reach an agreement with your team before writing down your consensus answer.

10. Which gender(s) of each species are included in the drawings in Model 3?

Yes

Roots

to stand

on while

mating

268 POGIL

Life Science Activities | Designed to Support the NGSS

Student Activity 11

11. Compare the column headings in Model 1, Model 2 and Model 3.

Circle the phrases that are found in more than one of these models.

Defensible resources Nondefensible resources Agility

Scramble One-on-One duel Extreme weapons

12. Based on the drawings in Model 3, complete the last column of the Model 3 data table.

13. Write Yes or No to answer each of the following questions.

For all of the eight species shown in Model 3, do all of the males…

a. compete for female mates? b. have a defensible resource?

c. engage in one-on-one duels? d. have an extreme weapon?

Check with your teacher before you continue.

14. List the names of the species with males that develop extreme weapons. Circle the extreme

weapon on the drawings of each of your listed species.

15. Carefully review Model 3 to determine the situation and the behaviors documented in the

species you have circled. In 1–2 complete sentences, clearly summarize the behaviors and

situations that are similar in all of the species that develop extreme weapons.

16. Consider the following data on three species we have not analyzed. Based on your understanding

of the behaviors and situations that lead to the evolution of extreme weapons, ll in the table.

Type of

Animal

Do males

compete for

females?

Do males

have a

defensible

resource?

Do males

engage in

one-on-one

duels?

Do you predict that males will

have an extreme weapon?

Explain your answer

clearly and completely.

Fiddle Crab Yes

Yes

Burrow with

females in it

Yes

Mouse Yes

Yes

Burrow with

females in it

Termite Yes

Yes

Fortress with

limited entrance

Yes

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Life Science Activities | Designed to Support the NGSS 269

Student Activity 11

What I Still Wonder…

17. Write one additional question you have about animal weapons or about changes over

time in animal species.

270 POGIL