Name: ______
Ecosystems Lab
How many things can survive in that ecosystem?
In a food chain, energy is transferred from one organism to another. The food chain begins with plants, which capture energy from the sun and convert the energy to food through photosynthesis. The grasshoppers, bullfrogs, water snakes, and red-tailed hawks are consumers, which must eat other organisms to survive.
In ecology, the trophic level is the position that an organism occupies in a food chain – what it eats and what eats it. As you have learned, the greatest amount of energy in an ecosystem is found in trophic level one (producers) and decreases at each trophic level as you move up the food chain. The transfer of energy is not an efficient process because all living things need energy to carry out life processes. When a consumer eats another organism, only a small fraction of the energy taken in is used for growth. About 50% of the food is not digested or absorbed and is passed out as waste. Roughly 40% of the energy from food is lost in the form of heat or used by the organism for cellular respiration. Only about 10% of the food eaten is used for growth and is available as energy for the next trophic level in the food chain. This produces a pyramid of energy and numbers in an ecosystem. The greatest amount of energy and the largest population is at the base of the pyramid with the producers. The least amount of energy and the smallest population is at the top of the pyramid in top level consumers. Each trophic level can support fewer organisms, due to the loss of energy as you move up the pyramid. In today’s lab, you will be investigating why different numbers of organisms can survive in different ecosystems.
1. According to the visual on the side, when a snake eats a mouse, how
many J of the original 1,000,000 does it actually get??
2. A hawk requires ten times more energy than a grasshopper- why might that be?
Follow the instructions from the instruction sheet to sample and count the number of grasses ( pinto beans) in Ecosystem 1 and in Ecosystem 2. Then, calculate both your average and the class average:
Table One: Amount of Grass (energy units) in Ecosystem 1 vs. Ecosystem 2
Sample / Ecosystem 1 / Ecosystem 21
2
3
4
My group’s average
Class average
Average ecosystem amount
(class average x 50)
1. Do you think that Ecosystem 1 and Ecosystem 2 will support the same amount and type of organisms? Explain your answer:
Number of Organisms Available / Energy Units Available to Next Level Consumer / Total Energy Absorbed/Consumed / Number of Organisms
Supported
(Transfer to the first column
in the next row)
grass
/ x / 1 energy unit
available per unit of
grass / ÷ / 10 energy units
needed per
grasshopper / = / grasshoppers
grasshoppers / x / 5 energy units
available per grasshopper / ÷ / 30 energy units
needed per
bullfrog / = / bullfrogs
bullfrogs / x / 10 energy units
available per bullfrog / ÷ / 30 energy units
needed per
water snake / = / water snakes
water snakes / x / 10 energy units
available per water snake / ÷ / 55 energy units
needed per
hawk / = / H
hawks
3. Why are the numbers different between grassland and tundra? That is, what is the relationship between the amount of biomass (number of energy units) and the number of organisms that an ecosystem can support?
4. Draw the two sets of numbers on the energy pyramid shown on the side:
Ecosystem 1 Ecosystem 2
5. Based on your observations of both ecosystems, why is it beneficial for all levels of consumers in a food chain if there are large amounts of producers?
6. Why do higher-level consumers such as the hawk need a larger hunting territory than organisms that are lower in the food chain such as a grasshopper?
7. If the amount of grass changes, how does this affect each consumer?
8. Based on your data, why do you think there is a much greater biodiversity of organisms in tropical biomes with lots of rain, compared to biomes with less rainfall and more extreme temperatures?