Music To most of us, these trees are beautiful.

But to a naturalist, this area is a mess.

When the community of living things developed in this area, this plant, called Brazilian pepper, wasn't here.

Now it's crowding out important plants like mangrove.

This is how nature works.

Theme Music Music About 150 years ago, gardeners brought Brazilian pepper from South America into Florida as an ornamental plant.

Because it wasn't here before, we call it an introduced plant.

Soon after Brazilian pepper arrived, its seeds were scattered beyond the garden fences.

The trees that grew from those seeds faced fewer competitors than in South America.

So they spread across the landscape like wildfire.

Most things that live in the habitat where they developed face conditions that curb their population.

A new organism that grows unchecked can overwhelm an established natural community.

The same thing can happen with other plants and with animals, fungi, and microbes.

In their native environment, they may be no problem, but in a new environment they can become pests.

Any group of organisms that are alive and can produce fertile offspring under natural conditions is called a species.

These birds are members of the same species because they naturally mate and produce babies that can grow up to make more birds of the same kind.

Species that live in the habitat where they originally developed are called native species.

Birch trees and moose are species native to North America.

Species living outside their native habitats are called exotic.

House cats are originally from Africa, so in North America they're an exotic species.

Exotic species that invade an area and overwhelm the native species are called invasive species.

Invasive species that overrun a habitat will compete for resources with native species, or upset relationships between predators and prey.

Exotic species get into habitats in lots of ways.

European colonists arrived in the New World with pigeons, cows, and chickens that they used for food.

They brought pheasants and brown trout to hunt and fish, and mute swans and starlings to remind them of home.

People sometimes purposely introduce a species that ends up becoming invasive.

Escaped cats, dogs, pigs, and horses can disrupt natural communities.

Escaped cats kill native birds, especially ground- nesting songbirds.

In Hawaii, some plants are endangered because introduced pigs are destroying them.

Invasive species like the zebra mussel are a real nuisance.

Zebra mussels arrived by accident in water from European seas and lakes.

Cargo ships dumped this water into the Great Lakes because no one thought the mussels would spread and multiply so quickly.

Now zebra mussels compete with native animals for food, and badly clog water intake pipes.

Another nuisance invader is the Africanized honeybee or killer bee.

In 1957, a few dozen colonies escaped from a research site in Brazil then mated with native bees.

The result was aggressive stinging bees that have spread steadily north.

Now they're in Texas, New Mexico, Arizona, and California.

We don't usually think of disease organisms as invasive species, but many of them are both exotic and invasive.

For example, viruses from one area are introduced to other areas by people who are infected, or even by animals that carry the virus without having the disease.

The flu and AIDS are spread this way.

Now that air travel and worldwide shipping have shrunk the world, we must be careful about moving living things from one place to another.

In many lakes around the country, milfoil is a big problem.

Let's go meet Dave and find out more about it.

Music So this is milfoil?

It doesn't look very harmful to our habitat.

Well, it is.

Actually, there's about ten species of milfoil that live in this region.

Only two of them are invasive.

The Eurasian milfoil and this one here, the varied milfoil.

And they aren’t dangerous in that they hurt anything really, like biting it or stinging it like an animal might, but they're just explosive in their growth.

It doesn't take long for them to take over a whole aquatic community.

So how did it get here?

Well, a lot of aquatic plants they get here just by accident.

Some were introduced, actually, we believe, when people have dumped aquariums with aquatic plants, it may have come from another part of the world into a water body.

Now, this water body probably got it from boats.

Now, it didn't come from the boats directly, but when boats were on another water body that had milfoil in it, it would get attached to the propellers, boat, or the trailer and then brought out.

And then when that boat was put into the lake, some of those little fragments that are on the plant probably got in the water, settle to the bottom, rooted, and then the stuff just took off in its growth.

So why did it become such a problem?

Mainly because it just is so competitive.

It just basically crowds out all the other plants that are growing there and not only does it grow from the bottom, but it grows all the way up to the top, and sometimes it grows in such thick mats it blocks out the sun, and then the plants that are underneath them can't get sunlight and they don't survive.

So what can people do to help?

Well, there's unfortunately not a lot we can do.

Invasive plants like milfoil are really difficult to control, let alone get rid of.

But one thing anybody can do, including anybody who takes a boat out on the lake with kids, can go around their boat and check to make sure there isn't any aquatic vegetation attached to the boat or the trailer.

Do you want to try it?

Yeah, let's do it.

Let's clean up this boat.

Music It seems to me that humans share some of the responsibility for the spread of invasive species.

We are responsible when you consider that three out of ten species of plants are invasive species in some parts of the world.

And it's not just plants.

In the animal world, too.

One animal that's an invasive species and affects the area that it lives in is the mute swan.

Music Mute swans are native to Europe and Asia and were brought to the US in the 1800s.

It's thought that they were first introduced as ornamental birds in the states along New York's Hudson River.

They were also introduced to ponds and parks across the country.

Mute swans have adapted and spread to wild habitats.

There are now thousands of them living in wetlands on the east coast and around the Great Lakes.

They have very long necks that let them feed on aquatic plants without diving under the water.

While they're swimming, they hold their neck in an S shape with their beak pointing down.

The mute swan is white with an orange bill, black markings around its eyes, and black feet.

They can weigh up to 40 pounds, and while they're very graceful on water, they're awkward on land.

Once in the air, they're graceful again and can fly at speeds up to 50 miles an hour.

Mute swans mate for life.

Females breed once a year and lay up to 8 eggs, in eggs laid every two days in nests made of plant materials and lined with feathers.

The female incubates the eggs and the male protects the nest.

The newly hatched chicks are called cygnets and have downy gray feathers.

Cygnets often rest on their parent's back while the parents swim.

This protects the cygnets from predators and keeps them warm and dry.

Cygnets fly when they're about three months old, but they stay with their parents until the next breeding season.

Mute swans live up to 50 years in captivity and 20 years in the wild.

Mute swans adapt well to the cold and won't migrate unless the water freezes and blocks access to food.

Mute swans are large, graceful birds.

Some people think they should be left alone because of their beauty.

Naturalist and wildlife biologist don't argue about their size and beauty, but they are concerned that the swans are a threat to the health of aquatic ecosystems because of their aggressive behavior towards other nesting waterfowl and the damage they do to aquatic plants.

Not only are our lakes and ponds impacted by invasive species, but so are our oceans.

Emily and Sam are going to visit with Professor Jim Morin and his researchers at the Shoals Marine Lab to talk about an invasive seaweed in the waters off their island.

Music Hi, Jim.

Hi, Sam.

Hi, Emily.

Where are we going to go today?

Well, first we're going to go out with Ben in the, in the Zodiac, and he's going to go diving and collect some codium, this introduced species that so common here, and some other animals for the lab.

Then you and I are going to go around to Bab's Cove here where there's a good intertidal, and we're going to go look at a bunch of other invasive species, as well as a lot of local species.

Sound like fun?

Yeah.

Let's go!

Music Ah!

Music So Ben has brought back a whole bunch of stuff, right?

And they're going to use that in some of their research.

And now we're going to go down and look at the intertidal.

And this is where you find things like, what's that?

Codium.

Codium.

That's right.

And it's an alga that originally came from Japan.

And it's been getting spread all over the world by humans.

Music How do all these species affect each other?

you mean, in terms of their interactions?

Well, a lot of things have no real direct effect.

Other things have some major impacts, especially when you get things overgrowing other things that start to sort of, smother them.

Like codium here, you know, this introduced species is really crowding out a lot of our kelps.

So it changes the whole complexion of the community.

One of the frightening things for biologists is that as things get distributed more and more around the world, that, and you have these kinds of major impacts on local communities, you'll cause, cause extinctions of many of the of the local species.

And so that, what we'll have is fewer and fewer species on a global scale.

Music Oh!

Ow!

A mussel.

What have we learned today?

Habitats have a natural balance of native plant and animal species.

When an invasive plant or animal species invades a habitat, it upsets the habitat’s natural balance.

Invasive species can cause damage to a habitat by competing for resources, damaging the habitat, or upsetting the balance of predator and prey.

Now you know how nature works!

Theme Music Major funding for Nature Works was provided by American Honda Foundation.

Additional funding was provided by Alice Freeman Muchnic, Alice J. Reen Charitable Trust, Cogswell Benevolent Trust, the Finisterre Fund, Greater Piscataqua Community Foundation, Morgridge Family Trust, the Natural Areas Wildlife Fund, Rawson L. Wood.

Support for this episode of Nature Works provided by Greater Piscataqua Community Foundation, Alice Freeman Muchnic, Laudholm Trust.

(animal sounds)