The Huntington Library, Art Collections, and Botanical Gardens
Quiet Invaders: Looking at Invasive Species in Our Midst
Elements adapted from
Bureau of Land Management website: http://www.blm.gov/education/weed/explode.html
Krasny, Marianne. Invasion Ecology. Arlington, VA: National Science Teachers Association Press. 2003.
Overview
A series of three lessons explores important biological concepts surrounding Southern
California’s invasive plant species and their ecological effects. Lesson One focuses on plant
adaptations as a foundation for understanding how invasive species get to be so effective at
survival and reproduction that they out-compete natives. Lesson Two deals with learning to
identify common invasive species in Southern California, leading to a discussion about control
and prevention of the spread of invasives. Finally, Lesson Three is the protocol for conducting a
site survey to assess the composition of plant species in a local area, followed by a report on a
worldwide environmental concern involving invasive/introduced species.
Introduction
Invasive species are a threat to biodiversity. Invasives out compete native species for
resources by a variety of mechanisms. In plants this may mean shading out native flora by
having more rapid growth. With animals, an example may be the increased fecundity of an
invasive leading to the depletion of native species’ food supplies. When one organism declines in
this way, it is likely that other native species that were dependent on the organisms decline in
population as well. As a result, as the population of native species declines and a monoculture of
the invasive takes over, the effect ripples through the ecosystem resulting in an overall loss in
biodiversity.
As a way to encourage students to explore the effects of invasive and introduced species
worldwide, it is good to start by leading them through an examination of invasive species at
home. Here in Los Angeles, some of the more infamous introduced species—ones found to be
heavily affecting our ecosystem for the worse—are plants. The following is a list of some of the
plants causing the most concern, with associated websites for detailed reading:
Arundo donax or Giant Reed. See
http://tncweeds.ucdavis.edu/esadocs/documnts/arundon.html
Euphorbia esula or Leafy Spurge. See www.cdfa.ca.gov/phpps/ipc/weedinfo/euphorbiaesula.htm
Spartium junceum or Spanish Broom. See
www.cdfa.ca.gov/phpps/ipc/weedinfo/spartium-junceum.htm
Motivation
Have the students name a movie or television show in which aliens from space invade
Earth. In each case, ask why the aliens ultimately invade (not just to kill off the humans, but
most times they are, in one way or another, using the earth for its resources). Ask what would
happen if the hero of the movie didn’t “save the day”. What might happen to the levels of the
human population? Why? Challenge the students to name a real-life example of alien invasion.
Objectives
Upon completion of the 3-lesson unit, students should be able to
1. List characteristics that make native plants suited to the Southern California climate.
2. List characteristics that make plants invasive to Southern California so successful in this area.
3. Design a plant that would be a potential invasive species in Southern California.
4. Identify at least 5 common invasive plants in Southern California.
5. List common controls used to counteract or prevent damage from invasive plants.
6. List at least 4 reasons that invasive plants can be detrimental to an ecosystem.
7. List the species and concerns surrounding introduced/invasive organisms in another
ecosystem.
8. Use plot sampling technique to characterize the extent of an invasive species in a designated
site.
9. Use GPS technology and map skills to study a local region and mark outbreaks of invasive
plant specie(s).
Materials
Potted plant from an arid environment,
i.e., small cactus, euphorbia, or other
succulent
Potted plant from a tropical environment.
Many houseplants are tropical, like
zebrina, pothos or Philodendron, or
Dracaena
Sample of an area invasive/weedy plant
such as nasturtium, black mustard,
cheeseweed, dill, mint, Equisetum,
pampas grass, castor bean, iceplant, or
eucalyptus
Internet access or plant identification
books
Heavy paper for making flash cards
Scissors or paper cutter if card stock is not
cut
Printer to print out pictures of invasive
plants, or photocopies of pictures of
invasive plants
Optional: laminator or lamination sheets
for students to laminate their flash cards.
Site maps of the area you will survey
(available through local libraries or county
websites)
Early detection survey forms
GPS system (optional, but a great addition
to any surveying)
Tape measures and field markers (such as
ribbon and/or garden stakes)
Field trip forms and transportation
Associated California Biology Standards
6a. Students know biodiversity is the sum total of different kinds of organisms and is affected by
alterations of habitats.
6b. Students know how to analyze changes in an ecosystem resulting from changes in climate,
human activity, introduction of non-native species, or changes in population size.
6e. Students know a vital part of an ecosystem is the stability of its producers and decomposers.
6g. Students know how to distinguish between accommodation of an individual organism to its
environment and the gradual adaptation of a lineage of organisms through genetic change.
7a. Students know why natural selection acts on the phenotype rather than the genotype of an
organism.
7d. Students know variation within a species increases the likelihood that at least some members
of a species will survive under changed conditions.
8a. Students know how natural selection determines the differential survival of groups of
organisms.
Procedure
Lesson One
1. Review with the class a plant’s basic needs for survival: light, air, water, and nutrients
(L.A.W.N.).
2. Ask the class to then list some of the traits of a desert environment. Make a list on the board.
Based on what we know about what plants need to survive (LAWN), what might be the
limiting factors for growth and survival to a plant in this environment?
3. Present a plant from an arid environment to the class. Ask the student first to simply describe
what they see. Then tease out some of the key responses (light color, leaf shape, succulence,
small stature, green stem, hairs, etc.) and ask how these characteristic traits could possibly
have been selected for when living in an arid environment. You can use this time to
review/highlight the mechanisms of natural selection (What are factors of natural selection?
How is it defined? Etc.).
4. For each plant trait, you may then ask how an opposite characteristic might fare in the same
environment. For example, if light color helps reflect high light, what would happen to a
dark-colored plant? An example plant characteristics and their associated environmental
traits are: light color to reflect high light; hair or scales to shade and/or keep leaves and stems
more humid; rosette shapes to reduce surface area exposed to high light and funnel water to
roots; reduced leaves to limit surface area exposed to light; short stature to reduce area
exposed to light/heat; waxy covering and succulence/water storage to deal with low rainfall.
5. This is a good opportunity to highlight/review the fact that the class is focusing on the
physical traits apparent in each plant. The traits being discussed are examples of phenotypes.
Can the class discussion tell us anything about the genes involved in making these traits, the
genotype? (Only that they are changing, resulting in different phenotypes). Which are
selected against by environmental factors, genotypes or phenotypes? (In a narrow sense, the
genotype defines the phenotype. However, selection acts on phenotypes because differential
reproduction and survivorship depend on phenotype. If the phenotype affecting reproduction
or survivorship is genetically based, then selection can winnow out genotypes indirectly by
winnowing out phenotypes.)
6. Ask the class to next list the traits of a rain forest environment. Make a list on the board.
Based on what we know about what plants need to survive (LAWN), what might be the
limiting factors for growth and survival to a plant in this environment?
7. Present a plant from a tropical environment to the class. Ask the students to describe the
characteristics of the plant. How might each trait relate to survival in a tropical environment?
For example: dark colored, big leaves can catch more of the low light available on a forest
floor; leaf “drip tips” funnel water off of the leaf surface, preventing molds and diseases from
growing; climbing habit (like a vine) allows for access to limiting sunlight. Why are so many
houseplants native to the tropics?
8. Ask the class to list the characteristics of the Southern California climate and environment.
The class may have to consider what the area is like outside of the city. Make a list on the
board and isolate some of the limiting factors for plant growth. What do native plants in
Southern California look like? What traits do they have that allow for survival in our
environment? Make a list. This list should include, among other things, periodic fires, low
rainfall, hot temperatures, and high sunlight.
9. Now show the class an invasive plant from the area. As with the other plants, ask first what
characteristics they notice about the plant and then see if some of the traits can be tied to
survival here due to negation of the limiting factors. There may be some obvious traits that
reveal part of the “success” as an invasive, such as succulence in the iceplant, but many
invasives have “hidden” strategies. For instance, many native plants require fire to germinate
seeds, while many invasive plants do not. If the class does not see obvious examples of how
the plant can be come invasive, ask the class to brainstorm ideas about what a plant might
need to become invasive--to out compete native plants adapted to this environment.
10. Help guide the class discussion/brainstorm. Some less-visible reasons why plants become
invasive are:
a. Poison, bad taste, or other defenses that prevent them from being eaten, allowing
them to proliferate when natives are consumed by herbivores.
b. The invasive species may lack predators because the natural predators were “left
behind” in the home environment. How does altering the producers and consumers in
a habitat affect an ecosystem?
c. The ability to asexually reproduce. Some plants may spread by underground runners
or propagate from roots when aerial parts are broken up or eaten.
d. Vigorous growth that shades out competition.
e. Production of a large number of seeds, often ones that can survive a long time before
germination.
f. A growing season longer than that of natives, which means faster growth to maturity.
11. Show pictures or examples of invasive species that, because they have one or more of the
characteristics the class generated, have become a threat to native habitats.
12. Discuss the effects of invasive organisms on biodiversity and how alteration of habitats plays
into this effect. Why are certain areas or habitats higher risk? (Areas that have been disturbed
such as roadways are ripe for invasive plants to move in). Highlight areas and organisms
outside of California that are subject to invasives species, animal or plant.
The next step of the procedure can also be used as an Assessment for Lesson One.
13. Next, instruct students in groups of two to design and present a fictional invasive plant (for
an environment of your choosing) based upon the classroom discussion about adaptations,
plant needs, characteristics of invasiveness, and environmental limiting factors. Students
should include the scientific and common name, detailed description, habitat in which it is
most invasive, and country of origin. A variety of options are available for students to
express their understanding creatively. One example would be for students to design a
“wanted” poster with an associated press release. Students could also create a skit of a local
news report.
Lesson Two
1. For some or all of the following invasive or weedy plants in Southern California, students
should make a flash card for use in the field.
a. Bermuda buttercup (Oxalis pes-caprae)
b. Dandelion (Taraxacum officinale)
c. Shepherd’s purse (Capsella bursa-pastoris)
d. Henbit (Lamium amplexicaule)
e. Purple deadnettle (Lamium purpureum)
f. Broadleaf plantain (Plantago major)
g. Curly dock (Rumex crispus)
h. Black mustard (Brassica nigra)
i. Cheeseweed (Malva parviflora)
j. Spanish broom (Spartium junceum)
k. Leafy spurge (Euphorbia esula)
l. Alligatorweed (Alternathera philoxeroides)
m. Halogeton (Halogeton glomeratus)
n. Spotted knapweed (Centaurea maculosa)
o. Carnation spurge (Euphorbia terricina)
p. Giant reed (Arundo donax)
q. Castor bean (Ricinus communis)
r. Perennial pepperweed (Lepidium latifolium)
s. Yellow starthistle (Centaurea solstitalis)
2. Have the students decide on the format that they will use for their flash cards. The cards will
be used to help with easy and quick identification of invasives. Given that, the class should
brainstorm a list of information that should be included on the card. You may wish to
separate the list into “necessary information” and “helpful information”. The cards should at
minimum include both a photograph and text description of the plant and the habitat it likes
to invade. It is easier to remember particular invasives with inclusion of interesting facts
about the plant, where the invasive originated from, and how it was introduced into the area.
3. Students should then construct a set of flashcards using the materials available and including
the criteria decided upon in the class discussion.
Lesson Three
1. Familiarize yourself with the invasive species of concern in your area.
2. Contact local environmental organizations (e.g., local weed management board, park ranger
site, land trusts, The Nature Conservancy). These organizations can help you identify
invasive species in your area and help identify sites that might be useful for your study.
3. Make the final selection for both the invasive species and the area you will be surveying.
Locate maps of this area. Keep in mind that the invasive species you decide to survey will
have a natural habitat that it favors and this may help dictate an area to survey. Conversely, if
you have a particular site you are interested in surveying, try to determine if there is an
invasive species in that habitat.
4. Prepare students to learn how to identify the species that you will be surveying (see Lesson
Two). You can find descriptions and pictures on the internet. Make sure that students can
identify your plant at the time of year you will be surveying.
5. Divide the chosen survey area equally among groups. Students should measure off their own
subset area and clearly identify it with temporary markers.
6. Next, students should walk through and study their individual site and record information
about the target species. Use Early Detection Survey Data Form 1.
7. Students next estimate the size of the population (number of stems, or area covered) occupied
by your target species in each area, as directed in Form 1.
8. After student have thoroughly surveyed their area, they should synthesize and summarize
their results by completing Early Detection Survey Data Forms 2 and 3.
9. Before moving to any new areas, try to wipe off any plant material you and your students
may have on your clothing and wipe down your boots. This will help curb the relocation of
any seed or mater that could lead to a new outbreak.
10. Record on the map each location you visit. If you have a GPS system available, mark the
locations of the infestations.
11. Back in the classroom combine the class data. This will give your class an idea of the
distribution of your species in the area.
12. Name each area where there was an invasive patch with a unique number.
13. Using their answers from Form 3, lead the class in a discussion of possible plans for
eradication or minimization of effects of the invasive species. This can be continued by
working with the Extension Activities listed below.
Evaluation
The following questions are listed under the Analysis section of the student handout and may be
used as part of a report, class discussion, or assessment.
1. What are some of the traits that would help make a non-native plant invasive in this area?
2. What is an invasive plant?
3. List at least three visible phenotypes that you have seen in invasive plants in this area. List
three non-visible phenotypes you have learned about.
4. List 6 common invasive plants in Southern California and the conditions in which they are
most likely found.
5. How are invasive plants a threat to biodiversity?
6. How have the invasive plants you studied change the local ecosystem?
7. List at least 3 ways that humans contribute to the spread of invasive species.
8. If a non-native invasive species did not evolve in this area, how can it be so well-adapted to
conditions here that it is able to out-compete natives?
Extension Activities
1. Follow the same steps in the Lesson One procedure, but adapt it to a discussion of invasive
animal species. What are the common invaders? What traits make them invasive? What
problems do they cause? What traits do they share with invasive plants?
2. Have the students plan community outreach in their neighborhoods to educate and remove
invasive plants.
3. Have the students plan a fundraiser to raise money to plant native plants in place of invasive
or other non-native plants at their school.
4. Invite a guest speaker from a local environmental organization to speak to the class about
invasive eradication and/or native plantings. The class may want to plan a second field trip to
work with the organization in a conservation effort, such as a tree planting or invasive
removal day. Possible Southern California organizations include TreePeople, California
Invasive Plant Council, Rancho Santa Ana Botanic Gardens, California Native Plants
Society, the County Agricultural Commissioner/Weights and Measures (which included the
LA County Weed Management Area), The Nature Conservancy, and Environment
California. The class might also use these organizations to help in a study that compares two
sites, one in which no attempts have been made to control invasive species and the second in
which eradication methods have been performed.
5. With permission from the study site, return to the study site to conduct an invasivesmitigation effort based upon the class plan.
6. Prepare a quiz for the students with pictures of the plants that they have studied and questions
on habitat and place of origin.
7. Have the students break into groups and use pictures of the invasive species to play a game
of concentration. To play the game: Click on a card to turn it over, revealing a picture of one
of the invasive plants. Try to find the second card that matches the first. If the second card
does not match, both cards return to a face down position. If they do match, the cards turn to
reveal part of the background picture.
8. As homework, have students research and report on the environmental problems caused by
invasive species, or a specific species, in Southern California. It may be plant or animal.
Students should include the following information in their report:
What is the scientific name of the plant or animal?
Where is it from? (i.e., its native range)
Where is it invasive?
What effects has it had on the ecosystems in areas where invasion has
occurred?
What social and economic effects has the invasion of this species caused?
What is currently being done to eradicate the invasive species?
How easy is it for a person to acquire the species unknowingly or knowingly?
How did the invasion of the species start (where and when)?
How does the species spread?
9. Have the students determine the number of seeds an invasive can produce in an area by
completing the spotted knapweed scenario (separate handout).
Test Preparation
1. The factor that is the greatest threat to the success of a species is
(A)
Environmental pollution.
(B)
Loss of habitat.
(C)
Introduction of new predators into the natural habitat.
(D)
Competition.
2. Which statement about the rates of evolution for different species is in agreement with the
theory of evolution?
(A)
They are identical, since the species live on the same planet.
(B)
They are identical, since each species is at risk of becoming extinct.
(C)
They are different, since each species has different adaptations that function
within a changing environment.
(D)
They are different, since each species has access to unlimited resources.
3. Which of the following best explains why an organism introduced to an environment can be
readily-adapted to the conditions there?
(A)
Founder effect
(B)
Succession
(C)
Adaptive radiation
(D)
Coevolution
Student Sheets: Quiet Invaders
Name:______________________________
Procedure
1. After a class discussion about the nature and mechanisms surrounding invasive plants
species, your class will generate lists of traits for some invasive species in the area in which
you live.
2. Next, you will need to prepare to identify these species in the field. To do that, you will be
making flash cards for a series of common invasive plants. As a class, you will decide what
information will be most helpful in identifying invasive plants. You will include that
information on each flash card.
3. Using the knowledge you gained in your in-class discussions, you will now head out to the
field to conduct a census of invasive species in a given area.
4. Walk through and study the site and record information about the target species. Use the
Early Detection Survey Data Form 1.
5. Next, estimate the size of the population (number of stems, or area covered) occupied by
your target species in each area, as directed in Form 1.
6. After you have thoroughly surveyed the area and completed the above forms, you should
synthesize and summarize your results by completing Early Detection Survey Data Forms 2
and 3.
7. Before moving to any new areas, try to wipe off any plant material you may have on your
clothing and wipe down your boots. This will help curb the relocation of any seed or mater
that could lead to a new outbreak.
8. Back in class, you will combine data with your classmates. This should give you a bigger
picture about the state of the site you visited. How would you categorize the nature of alien
species invasion in this area?
Analysis
On a separate sheet of paper please complete the following:
1. What are some of the traits that would help make a non-native plant invasive in this area?
2. What is an invasive plant?
3. List at least three visible phenotypes that you have seen in invasive plants in this area. List
three non-visible phenotypes you have learned about.
4. List 6 common invasive plants in Southern California and the conditions in which they are
most likely found.
5. How are invasive plants a threat to biodiversity?
6. How have the invasive plants you studied change the local ecosystem?
7. List at least 3 ways that humans contribute to the spread of invasive species.
8. If a non-native invasive species did not evolve in this area, how can it be so well-adapted to
conditions here that it is able to out-compete natives?
Early Detection Survey Data Form 1: Field Results
(Taken from Invasion Ecology, NSTA press)
Fill out this form for each species for each site you survey (e.g. trail, wetland).
Name(s) _________________________________________________________
Date _________________________________
Species name_____________________________
Study area
Type of site surveyed
Brief description of site
Estimated number of stems of species
0
 1- 10 stems  10-100 stems
Estimated size of patch
 0 m2  <1 m2  1-4 m2
 >100 stems
 4-100 m2
 >100 m2
Mark the location of your site on the map of the study area and record GPS locations of
patches
Early Detection Survey Data Form 2: Summary Description
(Taken from Invasion Ecology, NSTA press)
Name _____________________________________ Date______________
Species surveyed ___________________________
Description of study site habitat and location:
Location
(number of
patch on map)
Site surveyed
Description of
site
Estimated
number of
stems
Estimated size
of patch
Early Detection Survey Data Form 3: Summary Questions
(Taken from Invasion Ecology, NSTA press)
Answer the following questions each species you surveyed. Use complete sentences.
1. Is the species you surveyed widespread or limited to just a few locations?
2. Describe the areas or habitats where the species is likely to be found (e.g., near wash basin).
3. What might have contributed to the proliferation of the invasive species in your area?
4. Are populations of the species relatively large or small? Justify your answer.
5. Do you notice any patterns in the abundance and distribution of species? What factors, or
processes, may account for these patterns? (E.g., resources such as water and light, seed
dispersal, reproductive rates.)
6. Does your map show sites that you surveyed where you did not find the species in addition to
sites where you did find the species? If you only showed sites where you found the species,
how might that affect your results?
7. Can you suggest a management strategy for this species? Use the results of the survey, what
you know about the species, and what you know about large and small patches to answer this
question.
8. What additional information might you need to better plan a control strategy? How might
you get this information?
9. If you found sites where your species was not present, were there any differences between
those sites and the sites where the species was present? Describe.
10. If you were going to repeat this survey, what would you do differently? How might you
improve the methods to get more reliable results?
11. Cite or document the references you used to find information about the species you surveyed.
Which references do you think are most reliable? Why?