CTS Guide: Food Chains and Food Webs (K-8) pp 116-117- Section IV Research Summaries
Food Chain/Food Web Concepts and Terminology
Yücel and Özkan (2015) used word association tests with 12 to 14-year-olds. When they were given the term “food chain” students referred to animals, humans, plants and living organisms, but did not use terms such as producer, consumer, herbivore, carnivore, omnivore, trophic level, predator, or prey.
Students frequently misunderstand the concept of a food web when they can’t differentiate between the concept of a food chain and a food web (Grumbine 2012).
Interpreting Food Chains and Food Webs
Çinar (2015) performed word association tests with pre-service student teachers. When given the term “food chain”, the student teachers referred mostly to energy flow. When asked what words they associated with the matter that flows through a food chain, none of the student teachers referred specifically to carbon, though most mentioned carbon dioxide, carbohydrate, oxygen, protein and fat; only one mentioned nitrogen.
Allen (2010): Some students believe that when there is a change in the population of one organism, it only affects the organisms that are adjacent to it in the food chain, such as primary consumers being the only ones affected when plants die. Interpretation of the arrows in food chains was commonly meant to mean “eats”.
Some graphical conventions differ depending on the type of science diagram and domain. This can pose problems for students who are just beginning to encounter food web diagrams since the use of arrows can convey a variety of meanings in other diagrams they have seen (Heiser and Tversky 2006).
Barman, Griffiths and Okebukola (1995): The majority of students in this multinational study described a food chain as showing ‘what eats what’; and only approximately 10% of students used the terms ‘producer’ and ‘consumer’ when asked to explain what is shown by a food chain. When asked to assemble a food chain using pre-printed cards, many students placed the arrows the wrong way around yet when presented with a correct depiction of a food web they did not question the direction of the arrows in the correct representation, even though in most cases it contradicted the students’ own constructions. They also found that students regard the words and pictures in a food chain as representing individual organisms rather than populations of organisms.
Gallegos, Jerezano and Flores (1994) Found that many of the children used their perceptions of an organism’s relative size and ferocity when thinking about predator-prey relationships, and deciding which animals were likely to be herbivores and which were likely to be carnivores. Some children did not consider a plant to be a producer, but still placed it at the beginning of a food chain because it was the smallest, could not defend itself, and could not eat an animal. Confusion about the direction and meaning of the arrows in a food chain was also found to be a commonly reported misunderstanding.
Leach et al. (1992): When students are asked to predict possible effects of a change in a population within a food web, they tend to focus only on single food chains within the web, struggle to trace changes through more than one chain, struggle to think about the impact of a change in a population more than one trophic level away, and are more able to trace changes upwards through a chain than downwards.
A study by Leach at al. (1992) showed few students used the idea of interdependence to explain changes in populations of organisms. When students were asked what the result would be of removing one population from a food web, students responded differently according to which organisms were removed.
Griffiths and Grant (1985): Ample research suggested that school-age children struggle to interpret food chains and food webs.
Schollum (1983): Research suggests that children find it easier to identify predator and prey relationships within food chains when the species are familiar, and particularly when the names are accompanied by pictures. The researcher also compared students’ interpretation of paired diagrams of the same organisms, one with arrows and one without. Some students gave interpretations of the one with arrows that differed from what it was supposed to convey. Some students even said the arrows were going the wrong way.
Dependence on Plants
Driver et al. (1994): Few students appear to relate their ideas about feeding and energy to a framework of ideas about interactions of organisms. Only about half of a sample of undergraduate biology students, when asked about the phrases “life depends on green plants” and “the web of life,” explained these phrases in terms of food chains. Only a minority of these students mentioned harnessing solar energy or photosynthesis as the reason why plants are crucial in the food chain.
Eisen and Stavy (1988): Students from age 13 to the undergraduate level revealed that most of them knew that animals could not exist in a world without plants and suggested this was because animals cannot make their own food. Furthermore, some believed that carnivores could exist if their prey reproduced plentifully.
Transfer of Energy in a Food Web or Food Chain
Various studies have shown that students have limited knowledge of how energy flows through a food web and that energy is a challenging concept for understanding fundamental ecological processes. Understanding representations is key to understanding how energy flows (Wernecke et al. 2018).
Research reveals three commonly held ideas about energy transfer: 1) some students think that the top predator gets all of the energy from the trophic levels beneath it, 2) energy is cumulative as you move up a food chain or food web., and 3) no energy is lost between trophic levels ( Griffiths and Grant 1985).