Polar Bears, Food Chains, Trophic Levels and Bioaccumulation and Biomagenification

1. Ask students what is the difference between a food chain and a food web?2. How do you organize organisms in a food chain? Who is on top and what is at the bottom?3. Have students cut out pictures and sort .4. Glue on sheet!5. Go through notes on energy flow through ecosystems.6. Show video on polar bears7. Read article with students regarding DDT and PCB’s – highlight with students/ summarize as go on side8. Students complete questions – refer to article and use internet….

Arctic Cod

Ringed Seal

Copepods

AlgaePolar Bear

Shrimp

Arctic Cod

Algae

Polar Bear

Copepods

Ringed Seal

Shrimp

What is an Ecosystem?

- Includes living things (biotic) in a specific area together with non-living factors (abiotic) and their interactions.o Biotic – ___________________________________________________________o Abiotic – ___________________________________________________________

Energy Flow through Ecosystems

Every organism needs to obtain energy in order to live. For example, plants get energy from the sun, some animals eat plants, and some animals eat other animals.

A food chain is the sequence of who eats whom in a biological community (an ecosystem) to obtain nutrition. A food chain starts with the primary energy source, usually the _______. The next link in the chain is an organism that makes its own food from the primary energy source -- an example is plants that make their own food from sunlight (using a process called photosynthesis). These are called autotrophs or _________________________________.

Next come organisms that eat the producers; these organisms are called herbivores or primary consumers -- an example is a __________________________________________

The next link in the chain is animals that eat herbivores - these are called secondary consumers -- an example is a __________________________________________

In turn, these animals are eaten by larger predators -- an example is _____________________________________

The tertiary consumers are are eaten by quaternary consumers -- an example is a hawk that eats owls. Each food chain end with a top predator, and animal with no natural enemies (like an alligator, hawk, or polar bear).

The arrows in a food chain show the flow of energy, from the sun to a top predator. As the energy flows from organism to organism, energy is ___________at each step. A network of many food chains is called a _______________.

Numbers of Organisms:In any food web, energy is lost each time one organism ________another. Because of this, there have to be many more ________ than there are plant-eaters. There are more producers than consumers, and more plant-eaters than meat-eaters. Although there is intense competition between animals, there is also an interdependence. When _______ ______________ goes extinct, it can affect an entire chain of other species and have unpredictable consequences.

Trophic Levels:The trophic level of an organism is the position it holds in a food chain.

1. Primary producers (organisms that make their own food from sunlight are the base of every food chain - these organisms are called autotrophs.

2. Primary consumers are animals that eat primary producers; they are also called herbivores (plant-eaters).3. Secondary consumers eat primary consumers. They are carnivores (meat-eaters) and omnivores (animals that

eat both animals and plants).4. Tertiary consumers eat secondary consumers.5. Quaternary consumers eat tertiary consumers.6. Food chains "end" with top predators, animals that have little or no natural enemies.

When any organism dies, it is eventually eaten by detrivores (like ___________________________________) and broken down by decomposers (mostly _________________________________), and the exchange of energy continues.

Task: Chose an endangered animal and create a food web including at least three food chains. Label the trophic levels and predator/prey relationships. Be sure to label producers and detrivoires/decomposers.

Some Possible choices:

Coastal Mountain Goat Sandhill Crane Raven blue whale (Balaenoptera musculus) ... sea otter (Enhydra lutris) ... snow leopard (Panthera uncia) ... Other: species at risk in Canada

What challenges does your chosen species have in terms of adapting to their environment, harm due to human impact,habitat loss, other biotic or abiotic factors?

Hook: http://www.pbslearningmedia.org/resource/lsps07.sci.life.eco.polarbear/polar-bears-and-climate-change/ - video discussing climate change and effect on polar bears

http://wildlife.org/ddt-pcbs-could-affect-polar-bear-hormones/

DDT, PCBs Could Affect Polar Bear Hormones

By Joshua Rapp Learn

Posted on April 13, 2015

Image Credit: Eric Regehr, USFWS

This image shows eight threats that will affect polar bear health in the next 20 years. Image Credit: Patyk et al.

Sitting at the top of the food chain as the world’s largest land carnivore has its benefits. You have your choice of food and few predators to confront.

But a series of new studies shows that being the top dog may be detrimental for polar bear (Ursus maritimus) development and fertility as contaminants like DDT and PCBs accumulate in their bodies.

“Hormone levels are actually affected, and this may cause effects on the metabolism of the animals,” said Bjorn Jenssen, a professor at the Norwegian University of Science and Technology and an author on two of the recent studies. “They may become more sluggish and slower. They may be less attentive. Maybe it could change their behavior.”

These chemicals, which originate from plastic pollution in the water and environmental contaminants, are swallowed up by smaller organisms and fish, which are in turn eaten by the seals that make up a large part of polar bear diet. As the chemicals move higher up this chain, they accumulate in higher quantities until they become “bio-magnified” in polar bears, according to Jenssen.

One of the studies, conducted in eastern Greenland, looked at the effects of the contaminants on thyroid hormones of polar bears. They found that these hormones — important for our memory and motor functions — had high levels of PCBs and DDT. “The levels of these contaminants are above these threshold levels for effects,” said Jenssen, the senior author for the study. He said the animals they tested with the highest levels of contaminants were likely affected by them.

The study was a unique opportunity offered through co-operation between the researchers and Inuit hunters legally allowed to kill the bears. But because of limited access, the researchers only tested blood and tissue samples from the kidney, liver, muscles and brains of seven different animals. “You can’t go out to shoot polar bears just to do research. You have to get samples from people who are allowed to hunt them for other reasons.” Jenssen is careful to point out that due to the small sample size of bears tested for hormonal contaminants, it was difficult to say for sure what the possible impacts could be.

Polar Bear Fertility

Jenssen, the senior author of the other study released this month in Environmental Research, and other researchers extracted blood samples from polar bears tranquilized from darts filed from helicopters in the remote Norwegian archipelago of Svalbard, which sits about halfway between that country and Greenland. They tested this blood to find that DDT and PCBs can have a negative impact on female polar bear sexual hormones.

“The regulation of sex hormones is disturbed. That is quite worrying,” Jenssen said. It could affect polar bear fertility, but this was difficult to prove as researchers would have to follow individual polar bears around and see if they were successful at giving birth.

But the study also tested four-month old polar bear cubs for contaminants and found high levels in their blood, likely because high levels of PCBs and DDT are transferred to the cubs through their mothers’ milk.

“The cubs are much more exposed to these compounds than the mothers are,” Jenssen said of the Svalbard bears, and worries about the particular effects they have on growing bears.

Although the bears tested in the two studies were different animals and no cubs were tested in the Greenland study, it’s likely the chemical contaminants are also affecting their thyroid hormones, which has implications for growth and development.

But there are signs that things are improving, likely due in part to bans on some of the agricultural pesticides containing these contaminants.

“We compared animals that were caught in 1998 with cubs that were caught in 2008, and actually we see that contaminant levels have decreased by around 50 percent,” Jenssen said. “That’s good news.”

Joshua Rapp Learn is a science writer at The Wildlife Society.

Refer to article and internet to respond to the following questions:

1. Polar bears are exposed to a number of toxic chemicals in their habitat despite being thousands of kilometres from the nearest towns. What are some of these toxic chemicals?

2. What effect do PCBs and DDT have on polar bears?

3. How did these toxic chemicals get into the blood of the polar bears?

4. Why have levels of PCBs gone down 50% in blood samples?

5. Define the following terms and give an example of each situation in naturea. Bioaccumulation

b. Biomagnification

6. Are the high levels of toxins in polar bear blood due to biomagnefication or bioaccumulation

Polar Bear Food Web

The above diagram illustrates _________________________________________________________________________

The Pyramid below shows how the polar bear fits at the top trophic level in the arctic ecosystem.

https://askabiologist.asu.edu/explore/frozen-life

__________________________________________________________________________________________________

http://news.nationalgeographic.com/2015/01/150130-polar-bear-penis-bone-pollution-baculum-climate-change/ - article on biomagnification and polar bear reproductive success (video as well)