Music There are probably too many fish in this bowl, don't you think?

If it stayed this crowded, the fish wouldn't live very long.

There wouldn't be enough food, oxygen, shelter, water, or space for all of them.

Crowding like this happens in the wild.

Two living creatures sometimes have more babies than the environment can support.

When that happens, they start dying off.

This is how nature works!

Theme Music Music Each kind of organism is like a puzzle piece.

Without it, it doesn't get finished.

Nature's a little different from the puzzle, though.

There isn't just one perfect assembly of pieces.

Things change all the time.

Some years there's more deer in the woods than other years.

We call a whole group of one kind of animal, a population.

Most plant and animal populations are always going up and down.

For example, if deer have no predators, the population grows until they eat so many plants that the plants die back.

Then there's less to eat, so the deer population drops.

The fewer deer, plant populations grow and deer multiply again.

That change in balance is called dynamics.

It's an important way to look at how living things fit together.

We see population dynamics in our woods.

In some years, squirrels are everywhere and in other years, we hardly see any.

That's because the number of acorns an oak tree makes changes from year to year.

Our squirrel population changes, with the food supply.

Populations can also be shifted by weather.

A dry spring will shorten the life of temporary pools and puddles.

Frogs, toads and salamanders breed and lay eggs in these places, and when the pools dry up before tadpoles can develop, populations drop.

Conditions that mean life or death to an organism are the conditions that control its population.

The amount of available food, water, shelter, or living space determines how large a population grows.

In the desert, populations are small enough to share the limited water supply.

The number of birds that nest in holes in trees will drop if the tree holes aren't available.

Music Bad weather, disease, and predators also limit population size.

All these conditions limit populations, so they're called limiting factors.

Sometimes just bringing together a large number of one tiny living thing reduces its population, partly because disease spreads easily when many organisms are close together.

Predators help keep the populations of their prey in check.

When the number of predators in the area drops, the number of their prey can decline.

Sometimes the animal can become a pest just because too few predators are around to control its population.

In many areas of North America, white tailed deer are a problem because there aren't very many wolves, coyotes, or bobcats left.

Music Homes, highways, and shopping malls also change limiting factors for animal and plant populations.

We contaminate air, land, and water with chemicals and waste.

Changes in the populations of creatures in the wild tell us a lot about the connections between living things.

It's one important way to check on the health of the environment.

Music I'm done.

I know the natural world is a lot more complex than this puzzle.

Let's go ask Dave how limiting factors work.

Music So why is a porcupine a good example of population dynamics?

Well, any animal could be a good example, I guess.

But porcupines are interesting because their populations tend to be relatively stable.

Part of that comes from the fact that they have such great defense.

You know, those quills means they have relatively few predators.

And that means they can live to be fairly old for a small animal.

The other thing that makes it interesting is the fact they have a very slow reproductive rate, and they have just one baby a year.

That's so different from all the other rodents we talked about earlier that, that have just so many babies in a litter.

So combining the birth rate and the death rate, that's an important factor in population dynamics as well.

How does the porcupine affect the health of its community?

When they're feeding in coniferous trees like hemlocks around here, they'll chew on the branches and drop branches to the ground.

And when they do that, that benefits a whole number of, of wildlife, including things like, like deer that may be stressed in the wintertime.

The deer is a good example of an animal with, with a very dynamic population.

Music Whitetail deer are herbivores, or plant eaters.

If deer have enough food, water, and shelter, their population can grow very quickly.

The female deer, or doe, needs to be only one year old to give birth, and she can give birth to two fawns every year.

The lifespan of a deer in the wild can be as long as ten years, so over a doe's life, she may give birth to as many as 20 offspring.

If some limiting factors are missing, deer can over- populate an area quickly.

One of the reasons deer populations can grow too quickly is the lack of natural predators.

Gray wolves and mountain lions are predators of the whitetail deer.

Hunting and human development have reduced or eliminated gray wolf and mountain lion populations over much of their original range.

In these areas, there are no longer large natural predators.

of the white tailed deer.

Sometimes, a bobcat or a coyote will kill a young deer, but people and dogs are now the deer's main predators.

Music In rural areas, hunting helps control deer populations, but in suburban and urban areas, hunting is often not allowed, and deer populations can grow out of control.

Other limiting factors can change deer populations.

Parasites like lice, mites, and roundworms can weaken a deer and make it easier for disease and starvation to kill them.

Young and old deer often get sick and die, especially in the winter.

Deer and people are living closer together because both populations are growing larger.

When humans and deer share habitats, there can be problems for both of them.

People's gardens and shrubs are damaged when deer eat them.

Deer are often hit and killed by cars, damaging the car and sometimes killing the driver and passengers.

People can also be infected by Lyme disease, a disease carried by the deer tick.

Scientists are working to control deer populations, so humans and deer can safely share part of the same habitat.

There's a program at the University of New Hampshire that studies whitetail deer.

Daniel and Von are going to visit with Professor Peter Pekins and learn how he's helping to control their numbers.

Music There you go.

Have some.

Why does it appear to be so barren in this area?

Well, it's because we, we have more deer in the pen than should be here.

So the natural vegetation is eaten by the deer, besides the food that they're fed.

And surprisingly, there are some areas in the northeast, that don't look a whole lot different than this pen, because we have too many deer on the land.

Music So why do deer overpopulate?

Each situation is different.

And, each state has the responsibility of managing their deer herd.

So certain states may have overpopulation problems and other states may not, which created tremendous deer habitat throughout most of the country by breaking land up, cutting forests down, having lots of fields, agriculture.

How are states that are having trouble with their deer population trying to fix the problem?

The basic approach today still is trying to regulate herds through hunting.

But, to be fair or honest, I would say that we haven't been real successful yet, because we still have herds growing.

Is there any other way to control deer population, beside hunting it?

Winter in the northern ranges throughout the northeast.

Winter probably can control a deer herd.

Well, I should not say probably.

Absolutely it can.

And, in particular situations where deer are constrained into suburban and urban areas, contraception is a, is a technique that is receiving much attention today.

We are doing such work here at UNH, in conjunction with private organizations and state organizations, trying to get a handle on will contraception, does it work?

Can it be applied to free- ranging deer in such a way that you can control a deer herd?

How do you keep the deer so friendly?

I'm glad you asked, Von, because now we're going to go look at the fawns and you'll learn the rearing process that we use to try to keep these animals handleable and safe in captivity.

Music Von, that's apretty good job.

We do want them, we need these deer to imprint on humans.

Now, if you left these fawns with the tamest doe, you would never be able to handle the fawns, because they would only respond to another deer.

So these are hand-reared because of the special research we do here, where deer have to accept handling, confinement, and not be scared of people.

So it's actually very unique.

Very few people actually do research, raise deer in this manner anymore, but we would rather have deer that are not scared of us than deer that constantly have to be captured and drugged and so forth.

So.

Music What have we learned today?

Animal and plant populations are always rising and falling.

Usually populations balance themselves.

Limiting factors are the conditions that affect natural populations.

The availability of food, water, and shelter, weather conditions, and disease can all impact animal and plant populations.

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, Rawsen L. Wood.

(animal sounds)