Download Towards a Deeper Understanding of Native and Introduced Species

Towards a Deeper Understanding
of Native and Introduced Species
Photos: Merry Lea Environmental Learning Center of Goshen College
Introducing ecological complexity to your lesson plan helps dispel harmful myths
about the impact of invasive species
By Lisa Zinn, Jonathon Schramm and
Laura S. Meitzner Yoder
T
HE ISSUE OF INVASIVE SPECIES has arisen as
an important theme in environmental conservation
and environmental education. When teaching youth
about native, introduced, and invasive species, it is tempting
for educators to convey this simple message: Native = good;
non-native = invasive and bad. Although simplifications are
often important for educators to convey complex messages to
students, this particular message poses special risks for environmental educators. Learners may inadvertently demonize
individual species, without any awareness of the underlying
ecological principles—disturbance, niche, and competition—that contribute to species dominance in an ecosystem.
After a day of removing invasive plants, students may take
home a view that methods of control are relatively straightforward, and that control is urgently needed, while lacking
understanding of the possibility for prevention. Further, a
focus on invasive plants in natural ecosystems may not help
students to link this phenomenon to our food system, which
relies heavily on introduced species. This deepens the mental
divide that many people have in their thinking about natural
and managed ecosystems. In other words, valuable opportunities for deeper ecological understanding among students
are being lost in favor of a specific focus on removal of only
a few key invasive species in our ecosystems.
Is there a problem?
After experiences we had teaching about invasive species
at an informal environmental education center, we began to
rethink the language we used to teach about invasive species.
It became clear to us that terms such as alien, invasive, and
non-native had different connotations for the recent immigrants to our region than they have for long-term residents.
This prompted us to revisit our approach, with the intent of
developing more ecologically meaningful ways of talking
about issues related to species invasion.
We hope to encourage teachers to examine the ways they
are teaching invasive species to include more of the ecological complexity that is often lost as we try to motivate students
TEACHING ABOUT INVASIVE SPECIES – PERSPECTIVES
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to action. By grappling more fully with ecological realities,
we believe students will be better positioned to transfer their
understanding to new situations and species they will encounter
later. Invasive species education should be more aligned with
the broader goals of education for sustainability, interpreting
ecological complexity in ways that people can understand and
use. The challenge with invasive species is to “illustrate such
complexity, without overwhelming or confusing the learner” 1.
In our field-based teaching, one of our goals is to introduce students to ecological principles that affect changing
populations of native and introduced species.
We will focus on three of the most common misrepresentations of introduced—and particularly of invasive—species
that we have heard educators use (and used ourselves). This
particular example concerns an invasive plant called garlic
mustard (Alliaria petiolata), which was introduced to North
America in the mid-1800s and is now considered invasive
over much of the continent2. As environmental educators
many of us have found ourselves explaining this plant to students in something like the following manner:
“Not only does garlic mustard produce a huge number of seeds each year but it also emits chemicals into
the soil around it that kills other plants or keeps them
from growing. This allows the garlic mustard to completely dominate the area so none of our native plants
and flowers can grow there. This creates a monoculture
on the forest floor, which means only one species can
grow here, where originally there was a huge diversity
of native herbs and flowers. This is a problem!”
This explanation provides a quick way to introduce a
group of students to the invasive species they are encountering on the trail. However, explaining invasive species
in this manner can easily lead students to believe several
myths about invasive species: “The Myth of the Villainous
Invasive,” “The Myth of Black and White Distinctions” and
“The Myth of Static Ecosystems.” These myths are easy to
convey when we are teaching on the trail, but can be damaging to students’ perceptions of non-native species.
The Myth of the Villainous Invasive
When we teach this myth, we teach the false idea that invasive species somehow intend to dominate ecosystems and
exclude others more than other species do. After hearing
the explanation above about garlic mustard, students might
come away with the idea that garlic mustard is a dastardly
plant that does not play fair. It is a bully that comes in and
takes over by using sneaky tactics against our well-behaved
native species. Its intention is to come in and dominate the
landscape, leaving no room for pretty wildflowers.
In addition to anthropomorphizing the garlic mustard,
this myth also gives students the impression that the solution
to this lack of biodiversity on our forest floor is as simple
as getting rid of the garlic mustard. While this is part of the
solution, we also want to help students understand that it
will take more thinking. We have to consider soil nutrients,
canopy disturbance, excessive herbivore pressure, and other
factors that are influencing the “evil” garlic mustard’s rapid
growth, the relative scarcity of many native herbs, and also
our solutions to the problem.
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A better approach may be to talk about specific mechanisms the garlic mustard has that have allowed it to thrive so
well in both its original and new environments. You could
begin by asking students to brainstorm about challenges that
plants have to their survival (access to sunlight, competition
for water and nutrients, getting seeds to a location where
they can grow, predators, diseases, etc.) and then explain
that all plants have adaptations or survival strategies to deal
with these challenges:
“All plants have adaptations to help them survive
within their niche, or specific habitat. One of these
adaptations is that garlic mustard produces lots of
seeds at a time. Why do you think this might make it
good at surviving in this forest? Garlic mustard also
produces chemicals that are released into the soil to
keep other plants from growing. There are native
plants that use this chemical strategy also, like the
black walnut tree. Why would this help the garlic
mustard survive in a place where it is competing with
other plants for sun, nutrients, and water? These
adaptations helped it survive in its native landscape,
and these same features help garlic mustard spread
rapidly when humans move it to a new location. In the
new location, there are fewer predators and diseases
to attack it, and plenty of areas of disturbed land for
it to grow.
Not all plants and animals that are moved around
the world to new locations take over like garlic mustard. This usually happens when a species gets to a
new place, where it happens to grow really well: places
where farming, grazing and logging have opened up
many niches for growth are especially easy places for
an invasive to thrive. In a habitat like this, it will be
able to spread rapidly and out-compete the native species growing there for years before it came.
Why do you think this could be a problem for the
health of an ecosystem? It can decrease the ecosystem’s diversity and threaten some native species populations. Can you think of any ways we could work
toward stopping the spread of invasive species? What
would we have to consider?”
We suggest that if we focus on these characteristics of
introduced plants as things that are common to species
around the world, rather than their exotic origin and aggressive growth, we can help students to gain an appreciation
of ecological constraints that affect all species’ abundance
and distribution3,4. This in turn can help them to develop a
stronger understanding of how our management efforts can
effect underlying mechanisms, rather than only removing
the offending species.
The Myth of Black and White
Distinctions
When we teach this myth, we imply that all plants from
outside our region are “invasive,” and all native plants from
inside our region are “not invasive.” This is problematic for
a few reasons. For one, students may not realize that only
a minority of species introduced to a habitat will spread
on their own (naturalize), and only a minority of those will
TEACHING ABOUT INVASIVE SPECIES – PERSPECTIVES
spread enough to be called invasive. Those introduced plants
that do not become invasive are what we call “non-native” or
“introduced,” but are not necessarily “invasive.” Also, this
myth doesn’t work for a species that may be harmless and
native to one region but can wreak ecological havoc when
they become invasive in another part of the globe. This
means the native plants from our backyard might become
invasive when taken to another continent.
Most importantly, this simplified distinction neglects
the role of human activity in spreading species around the
globe. This is especially true of our agricultural species, or
others that we have an economic interest in promoting. We
rarely think of wheat or tomatoes or cassava as invasive, but
all do reach unnaturally high abundances, at least where we
cultivate them. Likewise, seeds that often accompany our
crop plants, e.g. weedy species from fields, often are accidentally introduced in high densities.
Although it is very easy for educators to slip into this
shorthand way of discussing invasive species, it is crucial
that we help students understand the ecological realities.
Species—invasive or otherwise—rely on certain conditions for survival that they can find in different places if
they are moved around by people or other natural forces.
This can reinforce that it is not simply the origin of a species that determines whether it is invasive or non-invasive,
but instead the interaction between species’ traits and the
community of which it is a part5. Continuing with the garlic
mustard example:
“Have you ever wondered why garlic mustard got
to North America from Europe in the first place? It
didn’t get here on its own; instead it was intentionally
planted by settlers from Europe who liked to use this
plant both for food and also for medicine. Naturally,
they thought it was a great idea to bring this important plant with them, so they planted it very widely
across the eastern United States. It slowly began to
spread into natural parts of the landscape, such as our
forests. They had no idea it would become invasive
at that time, but now we are having to deal with the
consequences. Can you think of any North American
species that might have been introduced to other parts
of the globe? In fact, many species of plants and animals have been moved around the world, both accidentally and intentionally by people, everything from
tomatoes to Canada goldenrod to beavers and mink.”
Emphasizing the unique histories of each species can
help students to remember to think ecologically about them,
to consider their survival needs and interactions with habitats old and new.
The Myth of Static Ecosystems
When we teach this myth, our students learn that ecosystems have one set way they should be and that any changes
that happen due to “evil” invasive species are harming the
system. In the example above, students could also take away
TEACHING ABOUT INVASIVE SPECIES – PERSPECTIVES
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we will share our ideas and I want you to explain why
you think any of these changes will occur.”
A rich follow-up discussion in the classroom could
involve having the students investigate other invasive species
in their area with a range of population trajectories: some
that have fallen from initially high numbers into lower but
stable sizes (like the multiflora rose), some that have been
successfully (or unsuccessfully) managed or controlled by
humans (like purple loosestrife), and some that have populations that are still increasing with an unknown ecosystem
response in the long-term (like garlic mustard).
Teaching about invasive species can be a difficult task:
the high level of ecological complexity can be difficult to
communicate to students. As environmental educators, it
is easy to fall back on catchy phrases and sound bites that
help us communicate the main ideas simply but often inaccurately. We hope the ideas presented above will help us as
educators capture a broader range of ecological principles
in their complexity. We encourage both formal and informal
educators to consider how teaching invasive species might
be strengthened so that important ecological concepts are
conveyed, but also so that students find these issues interesting and accessible. Informal educators can help by trying to
avoid these myths when taking students on the trail at nature
centers. Formal educators can help by following up on field
trips with discussions about the complex issues of native
species. Instead of teaching the oversimplified message that
“invasive species are bad!” how about: “Invasive species can
teach us important lessons about how we use the earth.”
the idea that the forest has always been rich in diversity and
that only changed since the garlic mustard invaded. Ecologists and environmental educators can fall prey to this
myth too, as human lifetimes are so short that we forget how
dynamic ecosystems are and that many of the landscapes
where we study and teach have a history of dramatic human
and natural disturbances e.g. fires, glaciation, flooding, etc.
Explaining the complex dynamics and changes that ecosystems go through over time can be a difficult concept to
communicate, especially to young students who don’t have
a lot of personal experience with changing landscapes. One
potential activity is to have students spend some time thinking about how a landscape might have looked in the past.
Using our garlic mustard example you could do a simple
trail activity using writing or drawing:
“As you look at this area do you see any clues to
what this landscape might have looked like 50 years
ago? What about 100 years ago? How big are the
trees? Does it look like they would have been here?
This landscape has changed a lot over time. Do you
think some plants are new here? Do you think some
plants are gone? Yes, ecosystems are changing. Scientists often use the word dynamic to mean that they
are always shifting and changing. Take a minute and
write (or draw) a description of what you think this
area will look like 100 years from now. Will these
trees still be here? Will garlic mustard still be the
dominant plant on the forest floor? When we are done
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Lisa Zinn teaches in the Sustainability and Environmental
Education Department (SEED) at the Merry Lea Environmental Learning Center of Goshen College in Goshen,
Indiana. Jonathon Schramm also teaches in SEED at
Merry Lea, working with graduate students on environmental
education curriculum design. Laura S. Meitzner Yoder
directs the Human Needs and Global Resources program
at Wheaton College, in Wheaton, Illinois. She works with
undergraduates who undertake cross-cultural experiential
learning on justice, poverty, and transformation.
Notes
1. McKeown, Rosalyn. Education for Sustainable Development Toolkit. Knoxville, TN: University of Tennessee, Energy, Environment and Resource Center.
2002.
2. Meekins, J.Forrest and Brian C. McCarthy. “Competitive ability of Alliaria
petiolata (Garlic Mustard, Brassicaceae), an invasive, nonindigenous forest herb.”
International Journal of Plant Sciences 160.4 (1999): 743-752.
3. MacDougall, Andrew S. and Roy Turkington. “Are invasive species the drivers
or passengers of change in degraded ecosystems?” Ecology 86 (2005): 42-55.
4. Mack, Richard N., Daniel Simberloff, W. Mark Lonsdale, Harry Evans,
Michael Clout and Fakhri A. Bazzaz. “Biotic invasions: causes, epidemiology,
global consequences and control.” Ecological Applications 10 (2000): 689-710.
5. Shea, Katriona and Peter Chesson. “Community ecology theory as a framework for biological invasions.” Trends in Ecology and Evolution 17 (2002): 170176.
TEACHING ABOUT INVASIVE SPECIES – PERSPECTIVES