Food chains and food webs Ena Haniff
Food Chains • A food chain is a simple sequence which shows the flow of energy through an ecosystem (in the form of food) • Energy from the sun is converted to plant matter by producers during the process of photosynthesis • Energy is transferred as the nutrients in food • Each organism is a link and each link is called a feeding level or “trophic level”
Food Chains • A food chain can be represented by a simple diagram as follows: • Grass Deer Tiger • Arrow denotes “ is eaten by” • Arrows are used to show the flow of energy from one trophic level to another
Food Chains • Feeding relationships are shown in a food chain • Food chains begin with a plant or producer (usually) • All other organisms in a food chain are animals or consumers
Questions • How is the sun’s energy transferred to plants? • Plants use the sun’s energy during photosynthesis to produce carbohydrates which is sugar and is a store of energy • How do animals (consumers) obtain their energy? • Animals obtain their energy by eating plants and other animals and use the energy from the carbohydrates. They also build more complex substances (such as proteins) which also stores the energy they obtained from producers
Questions • Why do organisms need energy? • Organisms need energy to carry out all the functions of living things: • Growth • Repair • Reproduction • Movement (animals)
Activity • From the list of organisms, choose three suitable organisms and construct a food chain. • Crab, butterfly, shark, fish, cat, snake, grass, bird, rat, flower, octopus, pig, tiger, deer, lettuce, cow, human, seaweed, • You can construct more than one food chain • Can you spot the producers? • Which organisms are herbivores? • Omnivores? • Carnivores?
Activity Producers Consumers Grass, flower, lettuce, seaweed Crab, butterfly, shark, fish, cat, snake, bird, rat, octopus, pig, tiger, deer, cow, human Herbivores Omnivores Butterfly, deer, cow Pig, human, bird, crab, fish, rat, Carnivores Shark, snake, tiger, octopus
A little more on producers and consumers • Producers make their own food using the sun’s energy • They include green plants, mosses, aquatic plants, phytoplankton in water and certain bacteria • Phytoplankton are microscopic algae that live in water that use photosynthesis to produce their own food and which forms the base of marine food chains
A little more on producers and consumers • Consumers cannot make their own food and need to eat other organisms to obtain energy • There are many types of consumers in a food chain: • Primary • Secondary • Tertiary • Quaternary
A little more on producers and consumers Type of Symbol consumer Description Primary 1° Organisms that consume producers (green plants). They are the first set of consumers and they occupy the 2 nd trophic level Secondary 2° Organisms that consume primary consumers. The are the 2 nd set of consumers and they occupy the 3 rd trophic level Tertiary 3° Organisms that consume secondary consumers. They are the 3 rd set of consumers and they occupy the 4 th trophic level Quaternary 4° Organisms that consume tertiary consumers. They are they 4 th set of consumers and they occupy the 5 th trophic level.
An example • • Grass Deer Human Tiger In this food chain, the grass is the producer. The Deer is the primary consumer Can you identify the secondary and tertiary consumers? Human: Secondary Tiger: Tertiary Can you name the 2 nd feeding or trophic level? The deer
An unusual food chain • • • Recall that in the beginning of the lesson I said that food chains usually begin with producers? Well, here is an exception: Leaf litter Earthworm Bird In this food chain, a producer is not at the beginning. This food chain begins with detritus (decaying organic matter) The Earthworm is a detritivore here (decomposer) It fills the role of returning organic material to inorganic material where it can be used again by plants
Food webs Ena Haniff
Introduction • In the pop up chart, what would happen if I introduced a bird, a rabbit and a snake into the Jungle?
Food webs • In reality, organisms have more than one source of food • Organisms can be a link in more than one food chain • For example the tiger can eat both the deer and the rabbit • And plants are eaten by both the deer and the butterfly • This makes the feeding interactions more complicated
Activity • From the food web shown • Construct a food chain with three links and one with four links
Food web • A food web shows a network of interconnected food chains • It shows the transfer of energy through an ecosystem • It uses arrows to show the transfer of energy
Question • What would happen if all the rats were suddenly removed from this food web?
Possible results • There will be an explosion in the populations of all the organisms that the rat feeds on including grasshoppers, caterpillars, grubs and beetles • These are herbivores; they will consume more plants • Food supplies could be affected • The amount of oxygen produced and carbon dioxide removed from the air could be affected • The owl population would be affected because rats were half of their food supply
Equilibrium • Predators limit the number of prey in an ecosystem and prey limit the number of predators as well. • There is a delicate balance in an ecosystem that can be easily upset if the population of the various organisms are disturbed • An example: swarms of locusts happen under conditions which are favourable to their reproduction; and it wreaks havoc on the food crops when this occurs
Assessment activity • Using any of the organisms provided, construct a simple food web. • Crab, butterfly, shark, fish, cat, snake, grass, bird, rat, flower, octopus, pig, tiger, deer, lettuce, cow, human, seaweed