Unit A Lesson A8 Ecosystem Invaders
Completion requirements
Lesson A8: Ecosystem Invaders
Video Lesson
Often and for various reasons, a species can arrive in an ecosystem new to it, but sometimes this change is due to the actions of humans. The result is huge effects on the ecosystem. Watch the video lesson to learn about some of these ecosystem invaders.
Lesson A8: Ecosystem Invaders
Invasion of the Earthworms!
Few people know that our seemingly harmless garden helpers are not from here. North America’s native earthworms were wiped out during the last ice age 10 000 years ago. The worms we find in our gardens originate from Europe. They hitched rides across the ocean with the agricultural materials early settlers brought with them. With almost no native worms as competition, these worms multiplied very quickly.
If you dig into any garden, probably you will find an earthworm or two wriggling in the soil as part of healthy garden ecosystems. Earthworms break down dead plant matter into soil. In the process, they release nutrients back into the ecosystem.
Few people know that our seemingly harmless garden helpers are not from here. North America’s native earthworms were wiped out during the last ice age 10 000 years ago. The worms we find in our gardens originate from Europe. They hitched rides across the ocean with the agricultural materials early settlers brought with them. With almost no native worms as competition, these worms multiplied very quickly.
If you dig into any garden, probably you will find an earthworm or two wriggling in the soil as part of healthy garden ecosystems. Earthworms break down dead plant matter into soil. In the process, they release nutrients back into the ecosystem.
Reading and Materials for This Lesson
Science in Action 7
Materials:
Science in Action 7
Reading: Pages 55–56
Materials:
No other materials are needed for this lesson.
Figure A.3.8.1 – A wild maple forest usually has a thick leafy understory of saplings, herbs, and shrubs.
Figure A.3.8.2 – What happened to the understory in this maple forest?
Earthworms on Vacation
Few people know that our seemingly harmless garden helpers are not from here. North America’s native earthworms were wiped out during the last ice age 10 000 years ago. The worms we find in our gardens originate from Europe. They hitched rides across the ocean with the agricultural materials early settlers brought with them. With almost no native worms as competition, these worms multiplied very quickly.
If you dig into any garden, probably you will find an earthworm or two wriggling in the soil as part of healthy garden ecosystems. Earthworms break down dead plant matter into soil. In the process, they release nutrients back into the ecosystem.
Few people know that our seemingly harmless garden helpers are not from here. North America’s native earthworms were wiped out during the last ice age 10 000 years ago. The worms we find in our gardens originate from Europe. They hitched rides across the ocean with the agricultural materials early settlers brought with them. With almost no native worms as competition, these worms multiplied very quickly.
If you dig into any garden, probably you will find an earthworm or two wriggling in the soil as part of healthy garden ecosystems. Earthworms break down dead plant matter into soil. In the process, they release nutrients back into the ecosystem.
Today’s earthworms are bioinvaders. Bioinvasion is a powerful word. We think of bioinvader organisms as quickly forming large colonies that ruin everything in their paths. Many do that. However, sometimes the effects of invasive organisms can be subtle
at first. Then, eventually, in their new ecosystem they can cause significant problems. To determine how far-reaching those effects can be.might be difficult.
In some hardwood forests, earthworms are doing more damage than good. Hardwood forests, such as the maple forests in Quebec, are being transformed by the common earthworm. The earthworm may be putting them at risk.
Worms recycle nutrients in soil. That is a good thing. The problem is that Canadian and American hardwood forests evolved without earthworms. Trees such as maples drop their leaves every autumn. Over the years, this produces a thick layer of leaf litter in which new tree seedlings sprout. The seedlings absorb nutrients from the litter as it decays.
In some hardwood forests, earthworms are doing more damage than good. Hardwood forests, such as the maple forests in Quebec, are being transformed by the common earthworm. The earthworm may be putting them at risk.
Worms recycle nutrients in soil. That is a good thing. The problem is that Canadian and American hardwood forests evolved without earthworms. Trees such as maples drop their leaves every autumn. Over the years, this produces a thick layer of leaf litter in which new tree seedlings sprout. The seedlings absorb nutrients from the litter as it decays.
Figure A.3.8.3 – What’s this!? I can’t believe earthworms are invaders!
Figure A.3.8.4 – Almost every garden contains earthworms, but they are an invasive species in North America.
When earthworms entered this ecosystem, they made quick work of all those leaves. By spring every year, almost all traces of leaf litter are gone. The nutrients in the leaves are churned deep into the soil. The delicate shallow roots of the seedlings
of native trees, herbs, shrubs, and wildflowers did not evolve to push their way down into dense soil. Now, these seedlings sprout and then soon die. The earthworms have two effects. First, the forest cannot regenerate. Second, the forest begins to
lose its thick multilayered understory of seedlings, herbs, shrubs, and wildflowers. In many hardwood forests with earthworms, only grass and short groundcovering plants grow. The tall old trees stand starkly alone.
The biodiversity of the hardwood forest is reduced severely. Understory plants provide a rich habitat for many animals -- wonderful food and shelter. Many songbirds, for example, used to live in the maple forests. Now, they are disappearing.
Where did the Ovenbird go?
The biodiversity of the hardwood forest is reduced severely. Understory plants provide a rich habitat for many animals -- wonderful food and shelter. Many songbirds, for example, used to live in the maple forests. Now, they are disappearing.
Where did the Ovenbird go?
Figure A.3.8.5 – The ovenbird is one of many songbirds native to maple forests.
Scientists that monitor ovenbirds are discovering that their numbers are declining in earthworm-invaded hardwood forests. Ovenbirds are especially vulnerable to the loss of the forest understory. They build their nests near to or on the ground. The understory
conceals the nests from predators such as chipmunks. In addition, It provides the birds with abundant insects, snails, and spiders to eat. It is a suitable habitat for both the ovenbird and its prey animals. Without the understory, the forest is a
poor habitat for this species.
Bioinvaders are NOT Invaders in their Natural Habitat
In their native home in Europe, earthworms fit the ecosystem without harming it. There, trees and other organisms evolved along with the earthworm to develop a balanced ecosystem. Ecosystems consist of complex interconnections between species. When the earthworms were introduced to North America, they unbalanced their new ecosystem. The invasion of just one species can have far-reaching effects.
Bioinvaders are NOT Invaders in their Natural Habitat
In their native home in Europe, earthworms fit the ecosystem without harming it. There, trees and other organisms evolved along with the earthworm to develop a balanced ecosystem. Ecosystems consist of complex interconnections between species. When the earthworms were introduced to North America, they unbalanced their new ecosystem. The invasion of just one species can have far-reaching effects.
Figure A.3.8.6 – The ovenbird is in decline in hardwood forests.
The earthworm invasion eventually could lead to the extinction of some native hardwood tree species. It could lead to the extinction of some animals that live these forests. However, the general picture is unclear.
Earthworms have by now invaded soils all over North America. They are now present in most towns and cities in Alberta. They have lived in the foothills of Alberta since the 1980s. So far, only hardwood forests seem to be affected. Coniferous forests such as the boreal forest appear to be unaffected.
Luckily, the ovenbird, although in decline in hardwood forests, is doing well in the remainder of North America. The fate of other hardwood dwellers, and the forests themselves, is less clear. Scientists who monitor the forest ecosystem do not yet know what its future will be.
Earthworms have by now invaded soils all over North America. They are now present in most towns and cities in Alberta. They have lived in the foothills of Alberta since the 1980s. So far, only hardwood forests seem to be affected. Coniferous forests such as the boreal forest appear to be unaffected.
Luckily, the ovenbird, although in decline in hardwood forests, is doing well in the remainder of North America. The fate of other hardwood dwellers, and the forests themselves, is less clear. Scientists who monitor the forest ecosystem do not yet know what its future will be.
Watch More
The Ovenbird
Watch this video to hear what a male ovenbird song sounds like.
Watch this video to hear what a male ovenbird song sounds like.
Think • Interpret • Decide
Invasion of the Earthworms!
Instructions:
The following questions require your careful thought about the earthworm invasion of North America. If you do not understand any of the questions, you should return to the beginning of this lesson and re-read all the sections.
These questions are about the earthworm’s North American invasion. Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Instructions:
The following questions require your careful thought about the earthworm invasion of North America. If you do not understand any of the questions, you should return to the beginning of this lesson and re-read all the sections.
These questions are about the earthworm’s North American invasion. Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Think: What’s the point? Do you understand why the earthworm is considered to be an invasive species? If not, go through the lesson again.
Interpret: How did earthworms spread all over most of North America? After all, they don’t move very fast.
Decide: Does the earthworm story mean that all species that move into new ecosystems are bad?
Even though we think of earthworms as helpful creatures living in the soil, the earthworms in North America are not originally from this continent. North American earthworms became extinct thousands of years ago. The forests here adapted to not having
earthworms. Then European earthworms arrived on this continent suddenly. Our forests have been affected ever since.
Humans introduced earthworms to North America, and they provide transport options for them now that they are here. On their own, the worms travel only about 5 metres per year. However, fishermen use the invasive earthworms as bait. By dumping leftover
worms into ponds and lakes, they help them spread into new areas. Earthworms travel in soil tracked onto vehicles. Earthworms and their egg cases can wash down streams and rivers after rainstorms. By digging up a garden plant to give to your
friend, you may be offering earthworms a free ride.
The earthworm story does not mean all invasions are harmful. In nature, species move into new ecosystems all the time. Natural movement of species into new ecosystems usually does not cause harm, but when that movement is human-assisted, the movement
is usually much faster and usually harmful.
Some Bioinvaders do not Damage Ecosystems
Northern cardinals are birds once native only to the southern United States. Now, most of eastern Canada has populations of them. They have been coming to bird feeders around Edmonton since 2008.
Northern cardinals are birds once native only to the southern United States. Now, most of eastern Canada has populations of them. They have been coming to bird feeders around Edmonton since 2008.
These birds are able to increase their range because winters are becoming milder with climate change. They can move into new human communities where feeders are plentiful. Scientists have not found evidence that these birds are harming the native birds already in residence. Natural changes in the range of a species usually occur slowly and gradually, giving ecosystems time to adapt to the new species. On the other hand, human-assisted species invasions tend to be rapid, and they tend to cause ecosystem chaos.
Making Things Worse: Trying to Solve Bioinvasion with Bioinvaders
The introduction of a predator to get rid of an invasive species has had disastrous results in the past. An example is the introduction of the small Asian mongoose to Hawaii. Because rats were destroying sugar cane crops in Hawaii, people introduced the mongoose, hoping that mongooses would reduce the rat population by preying on them.
Figure A.3.8.7 – Northern Cardinals especially enjoy black sunflower seeds in backyard feeders.
The mongooses, who eat many kinds of prey, did eat some rats. However, mongooses hunt during the day and rats are active mostly at night. This minimized the predation on rats. A larger problem was the mongoose’s appetite for bird eggs. The rats were already
harming the native birds by eating eggs. The mongooses were even better at eating bird eggs. Hawaii’s native bird populations dropped greatly as a result. The mongooses are prolific breeders and they have no natural predators in Hawaii. Their widespread
invasion has had a disastrous effect on the island ecosystems.
Interestingly, both the mongoose and the rat are invasive species introduced to Hawaii by humans. The rats were introduced accidentally. They often infest cargo ships. The mongoose was a deliberate introduction. Predicting how invasive species will behave in their new non-native habitats is difficult, but caution is advised! At least, check their hunting times!
Interestingly, both the mongoose and the rat are invasive species introduced to Hawaii by humans. The rats were introduced accidentally. They often infest cargo ships. The mongoose was a deliberate introduction. Predicting how invasive species will behave in their new non-native habitats is difficult, but caution is advised! At least, check their hunting times!
Figure A.3.8.8 – The small Asian mongoose has no natural predators in Hawaii.
Watch More
Protecting Hardwood Forests
Some hardwood forests have not been invaded by earthworms yet. How can we protect them? Watch this video to see how the worms damage the forest and learn about things people can do to help prevent their spread.
Some hardwood forests have not been invaded by earthworms yet. How can we protect them? Watch this video to see how the worms damage the forest and learn about things people can do to help prevent their spread.
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.
Unit A Lesson 8 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps – if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
- DOWNLOAD the self-check quiz by clicking here.
- ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
- COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
-
REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
- SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
- CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Self-Check Time!
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Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.
An invasive species is any organism (plant, animal, fungus, or bacteria) that is not native and has a negative effect on its new ecosystem. Not all introduced species are invasive species. Some introduced species cause no harm and others die
out in the new ecosystem. There are many examples of introduced (non-native) species that do not harm the ecosystem. One example is the common bleeding heart garden plant.
The bleeding heart plant grows well in Alberta and it is not invasive. This was introduced from China in the 1800s. It grows well but does not escape gardens into the natural ecosystem. Sweet corn, a common crop in Taber, Alberta, is another non-invasive non-native plant. The earthworm qualifies as an invasive species because it harms the hardwood forest ecosystem.
The bleeding heart plant grows well in Alberta and it is not invasive. This was introduced from China in the 1800s. It grows well but does not escape gardens into the natural ecosystem. Sweet corn, a common crop in Taber, Alberta, is another non-invasive non-native plant. The earthworm qualifies as an invasive species because it harms the hardwood forest ecosystem.
Invasive species cause ecosystem damage by taking over and competing with native species. The invasive species pushes others from their habitats. An invasive plant might grow more vigorously than the native plants do, so it spreads at their
expense. An invasive animal might be a better predator than native animals are in the same ecological role. Therefore, native animals starve and die. Or, the invasive animal might not have any predators in the new ecosystem. Without any predation,
the population of the invade continues to grow, and native species can become extinct.
Every species is native to at least one ecosystem. In its native habitat, it is an important part of the food web. It helps balance the ecosystem. An example is the house sparrow.
In North America, the house sparrow is an invasive species introduced from Britain. Here, the house sparrow population exploded. The birds tend to live near humans where they find plenty of food and nesting sites. They eat whatever food is available, from seeds to table scraps to insects. They outcompete many native birds. In addition, the sparrows take over other bird’s nests before those birds return in spring. In them, they raise two or three clutches of eggs while many native birds raise just one.
In Great Britain, the house sparrow is native. Historically it was part of a healthy ecosystem. Today, those sparrows have all but disappeared. The reasons are not yet clear. In Great Britain, the house sparrow is considered an endangered species.
In North America, the house sparrow is an invasive species introduced from Britain. Here, the house sparrow population exploded. The birds tend to live near humans where they find plenty of food and nesting sites. They eat whatever food is available, from seeds to table scraps to insects. They outcompete many native birds. In addition, the sparrows take over other bird’s nests before those birds return in spring. In them, they raise two or three clutches of eggs while many native birds raise just one.
In Great Britain, the house sparrow is native. Historically it was part of a healthy ecosystem. Today, those sparrows have all but disappeared. The reasons are not yet clear. In Great Britain, the house sparrow is considered an endangered species.
Invasive species enter new ecosystems in many ways. Most invasions result from human activities. Introductions of species are often intentional. For example, agricultural and ornamental plants are introduced to new areas. Sometimes, they escape
their cultivation and become invasive in the natural ecosystem. Accidental introductions to new areas are often the result of organisms hitchhiking with freight as it is transported across land and oceans.
The best way to combat invasive species is to avoid their introduction in the first place. Remember that invasive species do too well in their new ecosystems. They are often very difficult to remove after they settle in. The best way to prevent
invasive species from spreading is to learn which species are invasive in your area. If you find one, report it to your local government office. Inform and educate others about invasive species.
ff. The collars can be recovered and reused. The caribou do not have to be recaptured.
ff. The collars can be recovered and reused. The caribou do not have to be recaptured.