Question
Understanding Beavers as Ecosystem 1.12
Engineers
1 It is hard to view a human-made dam without
noticing the remarkable feat of engineering
and design required to create one. The Hoover
Dam, the largest dam in the world at the time of
its completion in 1935, stores enough water in
Lake Mead to irrigate 2 million acres. Humanmade dams, such as the Hoover Dam, generally
serve to retain water. The large body of water
that forms from the retained river behind the
dam is known as the reservoir. By retaining the
river and creating a reservoir, dams transform
a fast-moving river ecosystem into a relatively
still lake ecosystem. Humans are not the only
animal on the planet capable of this type of
ecosystem engineering. According to National
Geographic, “beavers are second only to humans
in their ability to manipulate and change their
environment.”
2 Ecologists refer to the beaver as an ecosystem
engineer because, other than humans, beavers
are the only known animal to be able to create
a wetland habitat. They have the ability to
drastically alter an aquatic ecosystem’s biotic and
abiotic characteristics as they gnaw down trees
to build dams and dig tunnels in order to access
their lodges (see the figure on the next page).
Much like the area behind human-made dams,
the area behind the beaver-made dam becomes
flooded and forms a new body of water with
ecological characteristics different from that of the
river area. This new body of water is known as a
beaver pond.
MY NOTES
BIO_U1_SR.indd 65 25/03/20 11:15 PM
Unit 1: Ecological Systems
Student Resource
© 2021 College Board
Pre-AP Biology 66
MY NOTES
Lesson 1.12: Understanding Beavers as Ecosystem Engineers
HANDOUT
1.12
3 The building of the beaver’s unique habitat is no
simple task. The common phrase “eager beaver”
offers a vivid description of the effort and energy
the beaver must put in to gnawing down large
and small trees to supply the logs it needs. In fact,
MIT, a top engineering university, adopted the
beaver as its official mascot in the early 1900s due
to the beaver’s masterful display of engineering
when constructing its dam and lodge.
Diagram of beaver habitat
4 The North American beaver (Castor canadensis)
is well suited to be nature’s engineer. It is the
largest rodent in the U.S., measuring between
2 and 3 feet in length and weighing up to
60 pounds when fully grown. Beavers have
many anatomical characteristics that support
their aquatic life. They have strong hind legs
with webbed feet that aid in swimming. They
also have the ability to secrete oils from scent
glands near their tails that are used to condition
their fur so that it has waterproof-like qualities.
Like many aquatic organisms, beavers have a
thick layer of fat that helps them float and stay
warm in their aquatic home. They even have a
specialized membrane that covers their eyes while
swimming—a function similar to swimmers’
goggles.
BIO_U1_SR.indd 66 25/03/20 11:16 PM
Unit 1: Ecological Systems
Student Resource
© 2021 College Board
67 Pre-AP Biology
Lesson 1.12: Understanding Beavers as Ecosystem Engineers
HANDOUT
1.12
Beaver skull and teeth
MY NOTES
5 What might be most impressive about beavers
are their inch-long upper and lower incisors (see
the figure above). These teeth continue to grow
throughout beavers’ entire lives. That may seem
quite frightening to some animals nearby; however,
the only organisms that should cringe with fear
are plants. Beavers use those impressive incisors
to cut down trees that line riverbanks in order
to construct their dams and homes, which are
called lodges. Also, as an herbivore, a beaver’s diet
consists of leaves, bark, twigs, and aquatic plants—
not other animals. While beavers are not predators,
they do have to protect themselves from predators.
Scientists have evidence to suggest that beavers
build dams in order to prevent their primary
predators, such as coyotes, from accessing their
lodges by surrounding the entrance with water.
6 While the methods and reasons for beavers
constructing their dams and lodges are varied,
scientists are more concerned with the changes that
take place in the river or stream ecosystem once the
dam is built. The beaver pond, a wetland habitat
that forms behind the dam, will have different
characteristics from the river or stream it is now
separated from. The diversity of the flora and fauna
in this newly engineered wetland is described in
the following excerpt from a wetland ecologist’s
BIO_U1_SR.indd 67 25/03/20 11:16 PM
Unit 1: Ecological Systems
Student Resource
© 2021 College Board
Pre-AP Biology 68
Lesson 1.12: Understanding Beavers as Ecosystem Engineers
research journal, which captures her first trip to
scout out potential beaver pond sites for research
along a portion of the Red River in Texas, a
tributary river that feeds the Mississippi River.
7 As we hike along the river, the unrelenting Texas
heat is made somewhat bearable by the shade of
the towering eastern cottonwood and black willow
trees. The beavers have made good use of these trees
along the river, as both a dam and dome-like lodge
are visible bookends to a small pond in the middle.
As we approach the edge of the pond, several
frogs leap to safety in the water. It’s not surprising
they are there since we notice plenty of swarming
invertebrates such as stone flies and damselflies. A
decent amount of emergent plants, such as cattails,
and submerged plants, like elodea, are visible in the
pond. The numerous gizzard shad fish present lead
me to believe there must be a healthy population of
zooplanktons since that is their primary food source.
It was a real treat to see a pair of blue-winged teal
ducks bobbing for submerged vegetation. This seems
like a viable site for our future research.
8 Many organisms, like those described by the
researcher, are not adapted to live in the quickmoving waters of the river, and so they make
the beaver pond their home. But this newly
engineered ecosystem does not last forever.
Beaver lodges are abandoned as colonies die off
or move on to another part of the river. Over time
the dam will breach, meaning water will rise up
and over the top of the dam, and the pond will
drain back into the river, restoring the river or
stream ecosystem that was originally there.
Reference:
Wright, J., Jones, C., Flecker, A. (2002). An ecosystem
engineer, the beaver, increases species richness at the
landscape scale. Ecosystems Ecology. 132: 96–101.
MY NOTES
HANDOUT
1.12
BIO_U1_SR.indd 68 25/03/20 11:16 PM
Unit 1: Ecological Systems
Student Resource
© 2021 College Board
69 Pre-AP Biology
HANDOUT
1.12
Lesson 1.12: Understanding Beavers as Ecosystem Engineers
Stating Key Ideas
After reading the passage, use the sentence frames provided below to state some key
ideas from the text.
happens as a result of
I know that are because
I predict would change
if occurs.
and are similar
because
and are different
because
Based on , I can infer that
is because
.
.
.
.
.
BIO_U1_SR.indd 69 25/03/20 11:16 PM
Unit 1: Ecological Systems
Student Resource
© 2021 College Board
Pre-AP Biology 70
Lesson 1.12: Understanding Beavers as Ecosystem Engineers
Using Evidence from the Text
Build on the key concepts you recorded in the previous section to respond to the
following prompts.
1. For each claim below, decide to either support (agree with) or refute (disagree
with) it. List at least 2–3 examples of evidence from the text to support your view.
Claim 1: Both humans and beavers are skilled ecosystem engineers.
Do you support or refute this claim?
Evidence:
Evidence:
Evidence:
Claim 2: Beavers are not well adapted to living in aquatic ecosystems.
Do you support or refute this claim?
Evidence:
Evidence:
Evidence:
HANDOUT
1.12
BIO_U1_SR.indd 70 25/03/20 11:16 PM
Unit 1: Ecological Systems
Student Resource
© 2021 College Board
71 Pre-AP Biology
HANDOUT
1.12
2. Using observational data from the researcher’s journal notes, write out or sketch
a hypothetical food web for the beaver pond on Red River. Then, predict how
this food web might change once the beaver dam is gone (breached) and the
ecosystem returns to a river
Engineers
1 It is hard to view a human-made dam without
noticing the remarkable feat of engineering
and design required to create one. The Hoover
Dam, the largest dam in the world at the time of
its completion in 1935, stores enough water in
Lake Mead to irrigate 2 million acres. Humanmade dams, such as the Hoover Dam, generally
serve to retain water. The large body of water
that forms from the retained river behind the
dam is known as the reservoir. By retaining the
river and creating a reservoir, dams transform
a fast-moving river ecosystem into a relatively
still lake ecosystem. Humans are not the only
animal on the planet capable of this type of
ecosystem engineering. According to National
Geographic, “beavers are second only to humans
in their ability to manipulate and change their
environment.”
2 Ecologists refer to the beaver as an ecosystem
engineer because, other than humans, beavers
are the only known animal to be able to create
a wetland habitat. They have the ability to
drastically alter an aquatic ecosystem’s biotic and
abiotic characteristics as they gnaw down trees
to build dams and dig tunnels in order to access
their lodges (see the figure on the next page).
Much like the area behind human-made dams,
the area behind the beaver-made dam becomes
flooded and forms a new body of water with
ecological characteristics different from that of the
river area. This new body of water is known as a
beaver pond.
MY NOTES
BIO_U1_SR.indd 65 25/03/20 11:15 PM
Unit 1: Ecological Systems
Student Resource
© 2021 College Board
Pre-AP Biology 66
MY NOTES
Lesson 1.12: Understanding Beavers as Ecosystem Engineers
HANDOUT
1.12
3 The building of the beaver’s unique habitat is no
simple task. The common phrase “eager beaver”
offers a vivid description of the effort and energy
the beaver must put in to gnawing down large
and small trees to supply the logs it needs. In fact,
MIT, a top engineering university, adopted the
beaver as its official mascot in the early 1900s due
to the beaver’s masterful display of engineering
when constructing its dam and lodge.
Diagram of beaver habitat
4 The North American beaver (Castor canadensis)
is well suited to be nature’s engineer. It is the
largest rodent in the U.S., measuring between
2 and 3 feet in length and weighing up to
60 pounds when fully grown. Beavers have
many anatomical characteristics that support
their aquatic life. They have strong hind legs
with webbed feet that aid in swimming. They
also have the ability to secrete oils from scent
glands near their tails that are used to condition
their fur so that it has waterproof-like qualities.
Like many aquatic organisms, beavers have a
thick layer of fat that helps them float and stay
warm in their aquatic home. They even have a
specialized membrane that covers their eyes while
swimming—a function similar to swimmers’
goggles.
BIO_U1_SR.indd 66 25/03/20 11:16 PM
Unit 1: Ecological Systems
Student Resource
© 2021 College Board
67 Pre-AP Biology
Lesson 1.12: Understanding Beavers as Ecosystem Engineers
HANDOUT
1.12
Beaver skull and teeth
MY NOTES
5 What might be most impressive about beavers
are their inch-long upper and lower incisors (see
the figure above). These teeth continue to grow
throughout beavers’ entire lives. That may seem
quite frightening to some animals nearby; however,
the only organisms that should cringe with fear
are plants. Beavers use those impressive incisors
to cut down trees that line riverbanks in order
to construct their dams and homes, which are
called lodges. Also, as an herbivore, a beaver’s diet
consists of leaves, bark, twigs, and aquatic plants—
not other animals. While beavers are not predators,
they do have to protect themselves from predators.
Scientists have evidence to suggest that beavers
build dams in order to prevent their primary
predators, such as coyotes, from accessing their
lodges by surrounding the entrance with water.
6 While the methods and reasons for beavers
constructing their dams and lodges are varied,
scientists are more concerned with the changes that
take place in the river or stream ecosystem once the
dam is built. The beaver pond, a wetland habitat
that forms behind the dam, will have different
characteristics from the river or stream it is now
separated from. The diversity of the flora and fauna
in this newly engineered wetland is described in
the following excerpt from a wetland ecologist’s
BIO_U1_SR.indd 67 25/03/20 11:16 PM
Unit 1: Ecological Systems
Student Resource
© 2021 College Board
Pre-AP Biology 68
Lesson 1.12: Understanding Beavers as Ecosystem Engineers
research journal, which captures her first trip to
scout out potential beaver pond sites for research
along a portion of the Red River in Texas, a
tributary river that feeds the Mississippi River.
7 As we hike along the river, the unrelenting Texas
heat is made somewhat bearable by the shade of
the towering eastern cottonwood and black willow
trees. The beavers have made good use of these trees
along the river, as both a dam and dome-like lodge
are visible bookends to a small pond in the middle.
As we approach the edge of the pond, several
frogs leap to safety in the water. It’s not surprising
they are there since we notice plenty of swarming
invertebrates such as stone flies and damselflies. A
decent amount of emergent plants, such as cattails,
and submerged plants, like elodea, are visible in the
pond. The numerous gizzard shad fish present lead
me to believe there must be a healthy population of
zooplanktons since that is their primary food source.
It was a real treat to see a pair of blue-winged teal
ducks bobbing for submerged vegetation. This seems
like a viable site for our future research.
8 Many organisms, like those described by the
researcher, are not adapted to live in the quickmoving waters of the river, and so they make
the beaver pond their home. But this newly
engineered ecosystem does not last forever.
Beaver lodges are abandoned as colonies die off
or move on to another part of the river. Over time
the dam will breach, meaning water will rise up
and over the top of the dam, and the pond will
drain back into the river, restoring the river or
stream ecosystem that was originally there.
Reference:
Wright, J., Jones, C., Flecker, A. (2002). An ecosystem
engineer, the beaver, increases species richness at the
landscape scale. Ecosystems Ecology. 132: 96–101.
MY NOTES
HANDOUT
1.12
BIO_U1_SR.indd 68 25/03/20 11:16 PM
Unit 1: Ecological Systems
Student Resource
© 2021 College Board
69 Pre-AP Biology
HANDOUT
1.12
Lesson 1.12: Understanding Beavers as Ecosystem Engineers
Stating Key Ideas
After reading the passage, use the sentence frames provided below to state some key
ideas from the text.
happens as a result of
I know that are because
I predict would change
if occurs.
and are similar
because
and are different
because
Based on , I can infer that
is because
.
.
.
.
.
BIO_U1_SR.indd 69 25/03/20 11:16 PM
Unit 1: Ecological Systems
Student Resource
© 2021 College Board
Pre-AP Biology 70
Lesson 1.12: Understanding Beavers as Ecosystem Engineers
Using Evidence from the Text
Build on the key concepts you recorded in the previous section to respond to the
following prompts.
1. For each claim below, decide to either support (agree with) or refute (disagree
with) it. List at least 2–3 examples of evidence from the text to support your view.
Claim 1: Both humans and beavers are skilled ecosystem engineers.
Do you support or refute this claim?
Evidence:
Evidence:
Evidence:
Claim 2: Beavers are not well adapted to living in aquatic ecosystems.
Do you support or refute this claim?
Evidence:
Evidence:
Evidence:
HANDOUT
1.12
BIO_U1_SR.indd 70 25/03/20 11:16 PM
Unit 1: Ecological Systems
Student Resource
© 2021 College Board
71 Pre-AP Biology
HANDOUT
1.12
2. Using observational data from the researcher’s journal notes, write out or sketch
a hypothetical food web for the beaver pond on Red River. Then, predict how
this food web might change once the beaver dam is gone (breached) and the
ecosystem returns to a river
Answers
GPT-4o mini
### Stating Key Ideas
1. **___ happens as a result of ___:** A beaver pond forms as a result of the beaver constructing a dam across a river.
2. **I know that ___ are ___ because __:** I know that beavers are ecosystem engineers because they create wetland habitats and change the ecological characteristics of their environment.
3. **I predict ___ would change ___ if ___ occurs:** I predict that the biodiversity of the area would change significantly if the beaver dam is breached and the pond drains, returning the ecosystem to its original river form.
4. **___ and ___ are similar because ___:** Beavers and humans are similar because both are capable of substantially altering their environments to create new ecosystems.
5. **___ and ___ are different because ___:** Beaver ponds and natural rivers are different because beaver ponds are still water ecosystems with different flora and fauna, while rivers are fast-moving and support entirely different types of organisms.
6. **Based on __, I can infer that ___ is ___ because ___:** Based on the description of the beaver’s adaptations in the text, I can infer that the beaver is well-suited to its aquatic habitat because it has webbed feet for swimming and waterproof fur.
---
### Using Evidence from the Text
**Claim 1: Both humans and beavers are skilled ecosystem engineers.**
**Do you support or refute this claim?**
**Support**
- **Evidence:** The text states, "According to National Geographic, 'beavers are second only to humans in their ability to manipulate and change their environment.'" This indicates that beavers are recognized as skilled engineers.
- **Evidence:** The passage describes how beavers alter their environment by "gnawing down trees to build dams and dig tunnels." This shows their capability to engineer ecosystems similar to human-made structures.
- **Evidence:** The creation of the beaver pond, which “drastically alter[s] an aquatic ecosystem’s biotic and abiotic characteristics,” is another point supporting the claim that beavers are skilled engineers.
---
**Claim 2: Beavers are not well adapted to living in aquatic ecosystems.**
**Do you support or refute this claim?**
**Refute**
- **Evidence:** The passage explains that beavers have “strong hind legs with webbed feet that aid in swimming,” which demonstrates their adaptations for aquatic life.
- **Evidence:** It is mentioned that beavers have a “thick layer of fat that helps them float and stay warm in their aquatic home.” This shows they are well-suited to an aquatic environment.
- **Evidence:** The text notes that beavers have a specialized membrane that covers their eyes while swimming, similar to swimmers’ goggles, indicating further adaptation to their aquatic life.
---
### Food Web for the Beaver Pond on Red River
**Hypothetical Food Web:**
1. **Producers:**
- Cattails
- Elodea (submerged plants)
- Aquatic algae
2. **Primary Consumers:**
- Herbivorous insects (e.g., damselflies in their larval stage)
- Frogs (eating algae and small plants)
- Zooplankton (feeding on algae)
3. **Secondary Consumers:**
- Gizzard shad fish (eating zooplankton)
- Blue-winged teal ducks (feeding on submerged vegetation and small aquatic organisms)
4. **Tertiary Consumers:**
- Predatory insects (e.g., larger dragonflies)
- Other birds of prey that can feed on fish or frogs
**Predicted Changes After the Beaver Dam is Breached:**
- Once the beaver dam is gone, the pond will drain, turning the area back into a river ecosystem. This will significantly reduce the diversity of the aquatic plants, as many species that thrive in still water will be replaced by those that prefer faster-moving water.
- Birds and aquatic species that rely on still waters such as frogs, blue-winged teal ducks, and soft-bodied aquatic invertebrates may decline significantly, whereas fish species more suited to flowing water may become more abundant.
- The food web will likely shift towards more rapid-moving water species, including certain aquatic insects, fish, and possibly bank-dwelling plants and animals.
---
This exercise integrates your understanding of the ecological roles of beavers as ecosystem engineers and invites advanced thinking about food webs and ecological changes over time.
1. **___ happens as a result of ___:** A beaver pond forms as a result of the beaver constructing a dam across a river.
2. **I know that ___ are ___ because __:** I know that beavers are ecosystem engineers because they create wetland habitats and change the ecological characteristics of their environment.
3. **I predict ___ would change ___ if ___ occurs:** I predict that the biodiversity of the area would change significantly if the beaver dam is breached and the pond drains, returning the ecosystem to its original river form.
4. **___ and ___ are similar because ___:** Beavers and humans are similar because both are capable of substantially altering their environments to create new ecosystems.
5. **___ and ___ are different because ___:** Beaver ponds and natural rivers are different because beaver ponds are still water ecosystems with different flora and fauna, while rivers are fast-moving and support entirely different types of organisms.
6. **Based on __, I can infer that ___ is ___ because ___:** Based on the description of the beaver’s adaptations in the text, I can infer that the beaver is well-suited to its aquatic habitat because it has webbed feet for swimming and waterproof fur.
---
### Using Evidence from the Text
**Claim 1: Both humans and beavers are skilled ecosystem engineers.**
**Do you support or refute this claim?**
**Support**
- **Evidence:** The text states, "According to National Geographic, 'beavers are second only to humans in their ability to manipulate and change their environment.'" This indicates that beavers are recognized as skilled engineers.
- **Evidence:** The passage describes how beavers alter their environment by "gnawing down trees to build dams and dig tunnels." This shows their capability to engineer ecosystems similar to human-made structures.
- **Evidence:** The creation of the beaver pond, which “drastically alter[s] an aquatic ecosystem’s biotic and abiotic characteristics,” is another point supporting the claim that beavers are skilled engineers.
---
**Claim 2: Beavers are not well adapted to living in aquatic ecosystems.**
**Do you support or refute this claim?**
**Refute**
- **Evidence:** The passage explains that beavers have “strong hind legs with webbed feet that aid in swimming,” which demonstrates their adaptations for aquatic life.
- **Evidence:** It is mentioned that beavers have a “thick layer of fat that helps them float and stay warm in their aquatic home.” This shows they are well-suited to an aquatic environment.
- **Evidence:** The text notes that beavers have a specialized membrane that covers their eyes while swimming, similar to swimmers’ goggles, indicating further adaptation to their aquatic life.
---
### Food Web for the Beaver Pond on Red River
**Hypothetical Food Web:**
1. **Producers:**
- Cattails
- Elodea (submerged plants)
- Aquatic algae
2. **Primary Consumers:**
- Herbivorous insects (e.g., damselflies in their larval stage)
- Frogs (eating algae and small plants)
- Zooplankton (feeding on algae)
3. **Secondary Consumers:**
- Gizzard shad fish (eating zooplankton)
- Blue-winged teal ducks (feeding on submerged vegetation and small aquatic organisms)
4. **Tertiary Consumers:**
- Predatory insects (e.g., larger dragonflies)
- Other birds of prey that can feed on fish or frogs
**Predicted Changes After the Beaver Dam is Breached:**
- Once the beaver dam is gone, the pond will drain, turning the area back into a river ecosystem. This will significantly reduce the diversity of the aquatic plants, as many species that thrive in still water will be replaced by those that prefer faster-moving water.
- Birds and aquatic species that rely on still waters such as frogs, blue-winged teal ducks, and soft-bodied aquatic invertebrates may decline significantly, whereas fish species more suited to flowing water may become more abundant.
- The food web will likely shift towards more rapid-moving water species, including certain aquatic insects, fish, and possibly bank-dwelling plants and animals.
---
This exercise integrates your understanding of the ecological roles of beavers as ecosystem engineers and invites advanced thinking about food webs and ecological changes over time.