WS 3.1 Analyzing Marine Food Webs

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WS 3.1 – Analyzing Marine Food Webs

Antarctica is the most inaccessible and least-studied of all the Earth’s continents. To get a better idea of how the organism in Antarctica interact, scientists analyze naturally occurring stable isotopes of nitrogen. All organisms are born with a certain amount of these isotopes in their bodies, about 3.8 parts per thousand. As these organisms eat they retain not only the nitrogen isotopes (δN) they were born with but also the isotopes of nitrogen in the organism that are being consumed. Therefore, as you analyze organisms going up a food web the concentration of nitrogen isotopes (δN) in organism’s increases by a predictable amount and can be used to help determine what trophic level an organism is.

So, dividing the δN composition of different organisms by 3.8 will give an indication of the relative trophic position of each organism in a food web.

1. What are the apex predator(s) on the food chain above?

1. Does a high δN value necessarily mean an organism is a apex predator?

1. What makes these organism apex predators?

1. According to the δN data, how many 3rd level consumers are there? (remember just because there is a 3 in front does not necessarily make them a 3rd level consumer)

1. Provide a rational for why small fish may have a slightly higher δN value than other organisms in their trophic level. What does this indicate about the trophic levels of the organisms they consume?

1. What organism(s) would be considered zooplankton?

1. Which of the 2 penguins obtains more energy through the food they eat?

1. What would happen to crabeater seal populations if the Krill population increased?

1. What would happen to the large fish population if the Weddle seal population increased?

1. What would happen to amphipod populations if the copepod population decreased?

1. What would happen to emperor penguin populations if the leopard seal population decreased?

1. How would a increase in copepods effect Krill populations?

1. What is the only group of organisms that would cause a universal decline in all populations?

1. Can any organism in the food web vary without affecting all other organisms?

1. Why are many marine ecologists recommending against fishing smaller fish lower on the food chain?