Introduction to Invasive Species

Preparation: Print game cards from “Invasive Species Game Cards” (below) single-sided, 4 per page, going from left to right, top to bottom. Cut and fold each species’ card, so that the front has the name and picture of the species, and the back its ecological characteristics. Laminate them if you plan to use the game again. Print “Event Spinner & Stage Cards.” Create the spinner: Glue the printed Event Spinner page onto cardboard; cut a thin wedge out of cardstock (the spinner); punch a hole through the fat end of the wedge and the middle of the spinner board; attach spinner to board with a brad/paper fastener.

Engage: Show students slide #2 from the “Invasive Species Intro PowerPoint.” Have students discuss with a partner whether they think either of the animals shown is invasive. Why or why not? Show them slide #3 and have them discuss whether or not the shown species are invasive, and why they think that. After hearing several students’ thoughts about each of these pairs of images, use the information below to lead a class discussion about what it means to be ‘invasive.’ One common misconception students have is that any species in abundance is invasive, which is obviously not the case with migrations or dense native stands. This can lead to a good discussion on what it means for something to be ‘invasive.’

• Slide #3 shows mugwort and goldenrod. While both plants can grow to local abundance, mugwort is invasive, but goldenrod is not. Goldenrod is often found in diverse communities, only becoming locally abundant for a short time, while mugwort tends to out-compete goldenrod and most other native vegetation, establishing monocultures of itself that persist throughout the years.
• In slide #2, point out that while these animals are not invasive in one habitat, they are in others. For instance, with the photo of the goats, students may not realize that certain common species cause a lot of problems if they are in different habitat, such as goats on an island. Similarly, they may be so used to seeing earthworms, that they did not realize that they are invasive to New York’s deciduous forest; they cause the leaf litter layer to decompose so quickly that their presence dramatically changes forest nutrient cycles and soil profiles.

Explore:
 

Part 1: Explain the rules and play the invasive species game: “What makes a good invader?”

Go over species cards, [life] stages, and events. Describe how students will move backwards and forwards heel-to-toe and that the students who cross the finish line will be “in the community” and will have to describe to the class how they got there.

Take students outside or gather students them in a large, open room. Have students line up, shoulder to shoulder on the start line. Give each student a species card (you will not use whole set, but the ratio of invaders to natives should be about 1:2). Explain that students will move forward for stages (growth, seeds, reproduction) when the appropriate stage sign is held up. They will move backwards when an event is spun on the wheel (ex. fire, herbivory, human disturbance). Demonstrate how they will take steps (heel-to-toe).

Start the activity – 2 stages

i. Hold up a sign for one of the stages

ii. Students move forward the number of steps indicated on their card.

iii. Monitor students closely for too large/many steps. If students are caught not moving heel-toe steps or taking more steps than on their cards, they must move back 5 steps.

Continue the activity – 2 events

i. Spin the event spinner –Allow a student that has been paying attention and following directions to do this.

ii. Students move backward the number of steps indicated on their species card.

iii. Monitor students to make sure they are taking steps backwards.

Repeat 2 stages followed by 1 or 2 events until you have about 10 students across the finish line (these students are “in the community”) Have students in the community (the 10 or so that crossed the red line) line up along the finish line, with invasive and native species on opposite sides. Have students that did not make it into the community sit in front of the standing students. Have each student in the community read their species name, state whether they are invasive or native, and explain what helped them the most. How is it that they made it into the community? The students should remember which of the events hurt them the most or which stage allowed them to take the most steps. (This should be different depending on what species they are and what sorts of events were spun for this round). Ask some of the sitting students why they did not make it. Link the characteristics of the invasive species that made it into the community to some of the themes and invasive species examples brought up in the introduction.

You may repeat the activity as time allows (usually 2-3 rounds). Point out to students how the outcomes differ between rounds. What events caused the outcomes to change? Did certain things come up more often than others? What events led to a community consisting of mostly invasive species? Native?

Explain:

Definitions

Invasive species have been spread throughout the world, in effect mirroring the movements of humans as global trade has increased. A distinction should be made between non-native and invasive species. The exact definition of an ‘invasive species’ is so contested that shortly after the National Invasive Species Council came up with an official definition, they revised it and then issued an 11-page document to further explain what they meant by ‘invasive species’. In general, an invasive species is a non-native species which ‘invades’ a new region and through its competitive success causes ecological harm.

What makes an invasive species invasive?

The fact that non-native species did not evolve in a particular local environment most frequently results in their poor survival without human help (i.e. planted trees, crops, etc). However, when a non-native species turns out to be well suited for a particular local environment, it frequently has many competitive advantages over its native counterparts. For example, because the non-native species did not evolve in the local environment, it often ‘escapes’ from its enemies—fewer local predators recognize the foreign species as food and the local diseases don’t cause as much harm. It is important to note that this escape from predation has a two-fold negative effect on native species—not only does the non-native have the advantage of not being eaten, but because the seemingly inedible non-natives take up space in an area where predators forage, the native species get preyed upon yet more heavily.  This is called ‘apparent competition.’

While many non-native species experience this escape from their co-evolved predators, most do not become invasive. So what is it about certain species that makes them such successful competitors that they cause ecological damage? i.e. Why do some species become ‘invasive’ and others don’t? While scientists are still working to figure this out, the following characteristics tend to be common among invasive species:

• Generalists – they are able to succeed in a wide range of environmental conditions (particularly in human-disturbed areas)
• Good dispersers – they disperse themselves and/or their progeny across long distances
• High reproductive output – they make a lot of babies; for plants, this often means they make a lot of flowers and seeds
• Asexual reproduction – not needing to have sex can make reproduction in a new environment easier; there is no need to find a mate, and if one individual is already a good competitor, how much better a 1000 with the same genes?!
• Ability to directly harm your competitors – for plants, this often means secreting allelopathic chemicals; for animals, it may mean nest predation (e.g. starlings)

Human activities have been key in spreading invasive species

• Humans have intentionally introduced many invasive species, not knowing at the time that they would become invasive (e.g. starlings introduced, because Shakespeare mentions them in his works; garlic mustard, which is delicious but never became a successful commercial crop; on islands, released housecats have decimated bird and small mammal populations).
• Through increased globalization, we’ve also accidentally helped invasives move across continents and oceans (zebra mussels in ballast water; emerald ash borer in wood shipped from china; snakes and rats across oceans via stowing away on boats).
• Humans have severely fragmented landscapes—not only by building roads in the middle of forests, prairies, and wetlands, but by building houses with long driveways, ski slopes down what would be forested mountains, and stringing power lines through forests (and thus creating grassy areas good for predators of birds and small mammals to access what would otherwise be interior forest areas). Invasive plants and animals take advantage of these passageways by using them as highways for dispersal, safe access to otherwise unsafe areas, and by employing their ability to succeed in even such highly disturbed environments. We have essentially created a lot of edge habitat and nearly eliminated large contiguous habitats. In doing so, we have created favorable conditions for species which like edges and do well in disturbed areas and unfavorable conditions for species which require large contiguous habitat to forage for food and/or maintain protection from predators.

Why should we care?

Invasive species tend to disrupt healthy ecosystems and cause both economic and physical harm to our communities in many ways. One of the most significant ways they harm natural communities is in their ability to out-compete native species, frequently leading to a decrease in local and/or regional biodiversity. Ecosystems with high biodiversity are typically healthier and better able to sustain many of the ecological functions that humans depend upon for survival, such as clean water, clean air, soil fertility, and infectious disease control. Other ways they cause ecological harm include the following:

• Can increase soil erosion by forming monocultures of themselves. Diverse plant communities create more complex root systems better able to hold soil.
• Decrease habitat value for wildlife – provide food (and sometimes shelter) for fewer species of animals; sometimes directly harm native animals (e.g. black swallow wort/monarch butterflies); often changes soil chemistry to be less favorable for native plants; aquatic ones can severely alter fish habitats and thereby damage fishing industries
• Decrease recreational value for humans – particularly of aquatic systems. Zebra mussels, water chestnut, and eurasion milfoil are particular problems. These have strongly negative consequences for local economies.
• Decrease crop yields – resulting in hundreds of millions of dollars in loss annually in New York alone and often results in an increase of herbicide usage. (e.g. marmorated stink bug)

Other examples of invasive species in our area can be found with any quick Google search and in the websites listed in the Additional Resources section below.

What can we do about the invasive species problem?

• Minimize human disturbance
• Remove them
• Support legislation that bans the sale of invasive species or provides funding for invasive species detection and response
• Plant native plants both in our yards and in natural areas recovering from human disturbance
• Keep watch to detect ones new to the area at an early stage of the invasion and facilitate a rapid response
• Clean the mud off of your boots and your boats after you’ve passed through an area with lots of invasive plants; dump your boat’s ballast water prior to leaving any water body.
• Spread the word!

Extend: Use the PowerPoint presentation to introduce characteristics common to many invasive species and their impacts, with a focus on invasives in the Hudson Valley. It is also useful to have examples of invasive species such as dead zebra mussels, seeds of the water chestnut, and the native unionid mussel shells. At the conclusion of the PowerPoint, have students complete the Invasive Species Reading and Reading Questions alone and/or in groups, as you or they prefer.

Evaluate: Students should write a one-page response to the following question: How do invasive species change ecosystems?

Additional Resources:

NYIS homepage: http://nyis.info/

NYIS Aquatic Invasives: http://nyis.info/publications/

USDA Invasive Species: https://www.aphis.usda.gov/aphis/ourfocus/wildlifedamage/operational-ac…

DEC/Cornell Invasive Study: https://www.dec.ny.gov/press/121441.html

NY iMap: https://www.nyimapinvasives.org/