food web centers
TRANSCRIPT
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WRITING CENTER
There are many organisms living in Jacksonville that are not native to Florida. Many were brought over on ships and some were pets that
have escaped or been let loose. On your Centers Worksheet, write a letter to Mayor Alvin Brown discussing how one of these species is
impacting other organisms. Be sure to include a small food web details the problems your species presents, including possible natives it
could kill off. (The organisms whose names are written in ITALICS should be part of your food web.)
Invasive Species #1:
Hydrilla
Hydrilla is an invasive species that was
introduced to Florida as an aquarium plant
in the 1950s. It grows up to an inch a day,
and forms thick mats of branches, like in
the picture above.
These thick mats block sunlight fromreaching native Florida water producers,
like Pondweed, Tapegrass, and Coontail.
Without sunlight, the native plants die.
Floridas freshwater sport fish, like the
Largemouth Bass and Bluegill Sunfish, have
spent their lives adapting to eat Insects that
feed on native plants. With Hydrilla
infestations, these fish are fewer in numberand usually grow to a smaller size.
Invasive Species #2:
Red-Eared Slider
R.E. Sliders are an invasive species that
were introduced to Florida as a pet. They
occur naturally in Mississippi River deltas.
The R.E. Slider is in competition with
Jacksonvilles native turtle, the Yellow-
Bellied Slider. Both are omnivores and eat
a variety of foods, including Fanwort,Waterweed, and Minnows
Invasive Species #3:
Brown Anole
The Brown Anole was first sighted in 1887.
It is native to Cuba and the Bahamas, but in
Jacksonville it is in direct competition with
our native Green Anole.
Brown Anoles and Green Anoles feed on
the same organisms, including Crickets,
Roaches, and Moths. Large male Brown
Anoles have also been known to eatsmaller Green Anoles.
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SCIENCE LITERATURE CENTER
Read the following two articles about food webs, and how the energy flow is shifting due to population change. When youve finished,
respond to the prompts on your Centers Worksheet.
Food Web WoesIf sharks disappeared from the ocean, rays might thrive, but shellfish would probably suffer.
Sharks are scaryno doubt about it. Just ask anyone whos seenJaws or other films that feature these sharp-toothed creatures.
But theres something that might be just as scary as meeting up with a sharkat least from an environmental perspective. Its the thought of what might happen
if sharks disappeared from the oceans. Thats because sharks are important players in delicate food webs, suggests a new study out of Canada.
Fishing companies have been killing large sharks for decades. Sometimes theyve done it on purpose, and sometimes theyve done it by mistake. Because of these
kills, the animals that sharks eat have boomed. And thats bad news for the creatures even lower on the food web.
Along the East Coast of the United States, only sharks that are at least 2 meters (6.6 feet) long are tough enough to eat a lot of the medium-size sharks, rays, and
skates living in those waters. Eleven large shark species in the region fit into that category.
Researchers led by Ransom Myers in Nova Scotia reviewed 17 surveys that counted big sharks and their prey during the past 35 years. They found that numbers of
all 11 species have dropped since 1972.
As the big sharks disappear, most of the smaller sharks, rays, and skates have increased in number. Surveys have shown increases in 12 of 14 species of these sea
creatures over the past 30 years. The populations of some of these species are 10 times as high as they were three decades ago.
Researcher Charles H. Peterson recently heard fishermen in North Carolina complaining that cownose rays were eating up all the regions bay scallops. He and his
colleagues at the University of North Carolinas Institute of Marine Sciences at Morehead City decided to test whether this was really happening.
To keep rays from eating scallops in certain areas, the scientists put a protective ring of poles around the scallops. Rays are wider than most sea creatures and
wont usually swim between poles that are spaced closely together. (The rays could turn sideways and fit through, but they dont usually do this.) Other animals,
however, swim easily through the gaps between poles.
In 2002 and 2003, at the beginning of the fall season, researchers found populations of bay scallops that were healthy and dense. But after rays migrated through,
the scallops nearly disappeared in areas that were not surrounded by poles. Within protected areas, only half of the scallops were gone. Its not even certain that
the missing ones got eaten, Peterson says, since they might just have swum away.
The study suggests that efforts to replace declining populations of shellfish, such as scallops and oysters, might require extra levels of protection against
predators.
The findings reinforce the message from a 1998 study of a food web in Alaska. In that area, killer whales can normally eat otters. Otters eat sea urchins.
And sea urchins eat kelp. When the whales ate more otters, the study found, sea urchins thrived, and the kelp suffered. In food webs, balance is key.E. Sohn
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Green InvadersNon-native plants put the squeeze on locals.
Green invaders are taking over America. Nope, not invaders from space. Plants. You might not think of plants as dangerous, but in this case they are threatening
nature's delicate food web.
The invaders are plants from other countries brought here to make gardens and yards look pretty. Ever since people started to arrive on America's shores, they've
carried along trees, flowers, and vegetables from other places.
Now there are so many of those plants, they are crowding out the native plants that have lived here since before human settlers arrived.
And that's a problem, says Dr. Doug Tallamy. He's an entomologist (an insect expert) at the University of Delaware. He explains that almost all the plant-eating
insects in the United States90% of themare specialized. That means they eat only certain plants.
Monarch butterfly caterpillars, for example, dine on milkweed. If people cut down milkweed and replace it with another plant, the butterflies will not have the
food source that they need to survive.
But the trouble doesn't stop there, it goes right across the food web. When insects can't get the right plants to eat and they die off, then the birds don't have
enough bugs for their meals. Tallamy points out that almost all migrating birds depend on insects to feed their young.
"We cannot let the plants and animals around us disappear," says Tallamy. "The way to preserve them is to give them food to eat. But when we plant non-native
plants, we are clobbering the food web, because then we don't have the insects the birds need to live."
Fewer of the right plants mean fewer bugs, and fewer bugs mean fewer birds. And that's bad for the Earth, because we need a variety of living things to keep the
planet healthy and beautiful.
The good news is, gardeners everywhere are working hard to protect native plants and get rid of the invaders. Many local garden centers sell native plants. "Just
Google 'native plants' and your location, and you can find out which plants really belong where you live," says Tallamy.
Planting the right things makes a real difference, and fast. He describes planting milkweed in a tiny city courtyard about the size of a living room one spring. By
summertime, that milkweed patch had produced 50 new monarch butterflies!
Tallamy encourages kids to go out and plant native plants. "Adopt a bird species in trouble and see if you can't plant some things that will attract the insects they
need," he suggests. "It will happeninsects move around a lot, and they will find the plants you put out there for them! C. Fox
Gaillardia, a native
Jacksonville flower.
Cownose Ray
eating oysters,
which are similar
to scallops.
Monarch caterpillar
eating the leaf
of a milkweed plant.
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DATA CENTER
Use the graphs below to analyze the Prairie Dogand Fox populations in the food webs.
Grass
Prairie
Dog
Black-footed Ferret
Fox