Eating at a Lower Trophic Level PDF

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Professor Hanes...

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Name: ___Clarke Taylor Date: _____02/04/2020____

Eating at a Lower Trophic Level Purpose  

Calculate and compare human food needs at different trophic levels, using the data to construct a biomass pyramid Analyze the benefits and drawbacks of eating at lower trophic levels on a global scale

Background A trophic level, or feeding level, is made up of all the organisms whose energy source is the same number of consumption steps from the sun in a given ecosystem. The trophic level of plants (producers) is 1, while that of herbivores is 2 and that of animals that eat herbivores is 3. Higher trophic levels can exist for animals even higher on the food chain. In this exercise you will compute numerical values for human energy needs based on diets at different trophic levels. Problem The owner of a seaweed farm raises fish for food and insect control. Fish will eat shrimp and insect pests. The farmer allows the fish free range in his ponds. For purposes of the following exercise, you may make these assumptions:      

The farmer lives on 1 fish/day for a year 1 fish eats 25 shrimp/day 1,000 shrimp have a mass of 1 kg 1 shrimp requires about 30 g of seaweed/year 1 human requires about 600 shrimp/day Dry seaweed have about 3.3 cal/g

Show all your math using proper units 1. Calculate the number of shrimp a fish needs per year. a. 25 shrimp/day * 365 shrimp = 9,125 shrimp/year

2. How many shrimp are needed to supply the farmer with fish for a year? a. 9,125 shrimp/year for 1 fish * 365 fish/year = 3,330,625 shrimp/year 3. What is the total mass, in kilograms, of the shrimp that are needed to feed all the fish for the farmer in that year? a. 3,330,625 shrimp/year *1 kg/1000 shrimp = 3,330.625 kg/year 1

4. How many kilograms of seaweed are needed to feed all the shrimp (from #2) for one year? a. 3,330,625 shrimp/year * 30 g of seaweed/1 shrimp * 1 kg of seaweed / 1000 g of seaweed = 99,918.75 kg seaweed/year

5. Now suppose the farmer chose to eat shrimp instead of fish. How many people could the shrimp (from #2) feed for one year, compared to the one person that the fish fed? a. 3,330,625 shrimp/year * 1 year/365 days * 1 person day/600 shrimp = 15.2 people ~ 15 people

6. The farmer needs to consume 3,000 cal/day. If he ate only seaweed instead of fish or shrimp, how many people would his seaweed crop (from #4) feed for one year? a. 1 farmer day/3000 Cal/day * 1 year/365 days * 99,918.75 kg of seaweed/1 year * 3.3 Cal/1 g of seaweed * 1000 g of seaweed/1 kg of seaweed = 301 farmers

7. Draw an energy pyramid (without using actual numbers) of the trophic levels in this scenario. Farmer Fish 3,330.625 kg of shrimp 99,918.75 kg of seaweed 8. Why do most food chains not have a fourth and/or fifth trophic level? a. Due to the foods that are eaten. Most foods that are eaten are at the first trophic level (grains and foods that are plants), and some come from the second level (dairy). About 75% of the food comes from the first trophic level, and 25% comes from the second trophic level.

9. It seems, by a simple analysis, that the Earth could support many more people if we all ate at a lower trophic level. Should people generally eat at a lower trophic level? Outline three pros and three cons of such a practice. a. Pros: The planet could sustain more people. The planet is able to sustain more when the farmer ate more of the seaweed, than the fish. Eating producers could support 300 times the people than eating on the third trophic level. Eating vegetables is also just healthier than eating too much meat. 2

b. Cons: Eating lower on the food chain could result in broader areas used for monoculture, getting rid of the biodiversity. Without the higher trophic levels, that could reduce the lower trophic levels through the food chains. The shrimp population would have to stabilize, there would then need to be a higher seaweed production to support the higher trophic levels.

10. On average, cows produce 19 kg of protein/acre/year and soy produces 200 kg of protein/acre/year. How do these data help explain the fact that people in less-developed countries usually eat at lower trophic levels than those in developed countries? a. In less-developed countries with food scarcity, it makes more sense for the people to eat producers rather than consumers. Energy is lost between producers and cows, and the people as well. All nations would be able to support more people or have low environmental impact if people ate at lower trophic levels.

11. Comment on the success of omnivores, such as coyotes, rats, and humans. What relationship do you think exists between the success of these organisms and the fact that they can eat at many trophic levels? a. Omnivores can eat on multiple trophic levels. This allows for the ability to eat more when food is available, but less when meat is scarce. Eating both meat and vegetables increases food options.

12. Large predatory fish, which may be part of your diet at times, usually exist at the third or fourth trophic level. Explain why it may not be a good idea to eat these fish often, if at all. a. Bioaccumulation: Chemicals are not excreted by animals or plants. When a plant takes up that chemical, it is usually taken to the next trophic level. And so on and up the food chain that eventually when we eat that larger fish, that chemical becomes a part of us.

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