Feeding relationships in the Southern Ocean

This task is about reading and interpreting food webs.

There are lots of living things in the cold waters of the Southern Ocean around Antarctica.

Key feeding relationships there are shown in the food web below.

Interpret the food web to answer the following questions:

Question Change answer

e) Krill are small shrimp-like animals that can live up to 5 years – if they can avoid their many predators.

Scientists say that the numbers of krill in the Southern Ocean have dropped by as much as 80% since the 1970's.

On the food web, mark a cross on all the arrows where you think falling krill numbers will have a negative effect on other animals.

e) Krill are small shrimp-like animals that can live up to 5 years – if they can avoid their many predators.

Scientists say that the numbers of krill in the Southern Ocean have dropped by as much as 80% since the 1970's.

On the food web, mark a cross on all the arrows where you think falling krill numbers will have a negative effect on other animals.

Question

f) Penguin population numbers are also falling sharply. Scientists are worried and they blame global warming.

i) Do you think this is justified? Select one

- Yes
- No

ii) Why or why not?

Answers/responses:

		Y10 (08/20006)
a)	Produces own food For example: They don't eat anything because they produce their own food by photosynthesis. They provide energy for others further up the food chain without taking energy from another but making its own.	difficult
a)	Is the food source/is what animals eat directly or indirectly (partially correct answer) For example: They are the start of the food chain. Without them there wouldn't be any other living thing.	moderate
b)	There is more light for photosynthesis in summer, so plankton can gain more energy to breed. For example: Because there is more light, so they can produce energy from photosynthesis.	very difficult
b)	Mention more light (and often greater warmth) without saying why these are advantageous (partially correct answer)	very difficult
c)	Krill numbers drop because there is less plankton for them to eat	moderate
d)	Arrows represent the flow of energy through the food web	very difficult
e)	All arrows except plankton → krill are marked with a cross	difficult
f)	i) Yes or no accepted Response justified by linking to food-web information provided in	moderate
	Response justified by linking to own knowledge For example: Global warming is melting their ice and it's probably too hot and they go in the water and get eaten by killer whales and sea leopards [answered yes]. There are plenty of killer whales and sea leopards that can eat penguins [answered no – see comment below on lack of systems awareness].	difficult
	ii) Response justified with several linked reasons. For example: Because penguins live in cold ice and water and if the krill and plankton is failing because the seas are getting warmer, then the penguins are not only going to have nowhere to live but also less food to eat. The penguin population could be dropping because of lack of food, habitat, or because the seals may be having to start feeding on them because the food source is diminishing.	very difficult

Diagnostic and formative information:

a)	Some students made a very general statement about the position of producers on the food web without saying anything specific about the actual part they play: They start it.
b)	Students who mentioned increased daylight hours seldom linked this to photosynthesis. Some students said it would be warmer in summer, perhaps not realising that the Antarctic Ocean is very cold at all times. A few answers indicated that students had not really thought about whether anywhere else could even be as cold. (The idea of relative temperature change could be explored in this context). The fish that eat them leave for summer to cooler water. Because the krill are trying to keep warm? Not many predators venture in to the heat of the summer. Because it's warmer and they can see predators better on sunny days Some of these answers also hint at another type of mistaken response. 16 percent of students gave answers that indicated they were thinking of plankton as macroscopic rather than microscopic creatures: The melting ice would carry their 'children' away. Because it's easier to breed in winter and the new-borns won't freeze. Because their predators won't be out until later for dinner.
d)	Most students did not seem to know that the arrows on food webs (and food chains) are a shorthand way of signalling the directional flow of energy. The most common response was that arrows show "what eats what". One school was an exception to this pattern, with most students in that school able to say the arrows represented energy flow. (These students were also the most likely to mention photosynthesis in question a) and/or b).) Although the meaning of the arrows is a small point, it encapsulates an important nature of science idea, linked to the key competency Using Languages, Symbols and Texts. That is, scientists agree conventions for commonly used symbols and then all use an agreed symbol in the same way. This idea is covered by Communicating in science in the nature of science strand of the science curriculum.
e)	The most common error involved marking only those arrows directly linked to the krill (23 percent). The students who did this did not appear to have considered the "knock-on" effects higher up the food chains – that is, they were not thinking in terms of whole systems.
f)	65 percent of students thought the claim was justified, 27 percent that it was not justified. Patterns of responses suggested that many students need practice in using evidence to justify their opinions. This links to the key competency Thinking. Most students were able to give one type of justification for their response, whether yes or no. 10 percent (who mostly answered "no") simply stated their opinion on global warming, or "fudged" the justification: Because there could easily be another reason why more penguins are dying. Because that is what I think. Because I don't think there is such a thing as global warming. Global warming is being used as an excuse for everything these days. One student who answered yes justified this by saying: Because scientists mostly know what they are talking about. Students who introduced a factor from their own general knowledge were most likely to mention the impact of habitat changes on penguin numbers: Because global warming is melting the ice and that is their habitat. A few responses hinted that some students do not appreciate contextual differences between Antarctica (where penguins are found) and the Arctic (where they are not found). Because preachers [poachers?] are also killing penguins for oil or sell there skin [answered 'no']. A few students who felt the claim was not justified reasoned that potential habitat changes had been overstated: Can't penguins live in warm places too?? Global warming won't make it like the Bahamas there, so the penguins would [wouldn't?] die because of a slight change in temperature.
f) contd	Although the information provided explicitly linked global warming to food web changes, for many students this link did not seem to carry through to the new context of penguin population changes. This suggests these students were not thinking at even a basic systems level when asked to provide a justification for an opinion. I don't think it is justified to blame the slowly decreasing numbers of penguins on global warming because if penguins are dying it is because they die from lack of food or being eaten by predators. Penguins can survive on land and in water so global warming won't have such an effect on them. A number of students who said the claim was not justified included interesting ideas such as: global warming is something that somehow stands outside biological changes, or global warming is a natural phenomenon rather than human-induced, or a combination of both of these. No because it could be because of other things as well, like lack of food or more predators. Plants and animals have been evolving and dying out since time began. Global warming is a natural cycle of the earth, which is why we have had ice ages and times when there have been no polar ice caps. No because we help global warming so this is part our fault. Global warming is just an excuse we use because man-kind is slowly killing the planet and they need something to blame it on. Another indicator of a lack of systems-level thinking can be seen in answers that gave over-generalised reasons for dismissing the link between dropping penguin numbers and global warming. Because of the hole in the ozone layer [answered yes]. I believe that this is true because the water that this animal is part of could be polluted and then this will pollute their primary food source, plant plankton, they may eat bad food and die. Because it is people making them suffer and people are polluting the streams and the only place they are safe are captivity and it is cruel to do it to an animal [answered 'no'].

Key competencies that could be addressed through this resource are:

Using Languages, Symbols and Texts
Thinking

You are here

Resource user links

Feeding relationships in the Southern Ocean

Feeding relationships in the Southern Ocean

Question 2Change answer

Question 2Change answer

Question 2Change answer

Question 2Change answer

Question Change answer

Question