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 Herbivores Omnivores Carnivores Grass, flower, lettuce, seaweed Crab, butterfly, shark, fish, cat, snake, bird, rat, octopus, pig, tiger, deer, cow, human Herbivores Omnivores Carnivores Butterfly, deer, cow Pig, human, bird, crab, fish, rat, 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 consumer Symbol Description Primary 1° Organisms that consume producers (green plants). They are the first set of consumers and they occupy the 2nd trophic level Secondary 2° Organisms that consume primary consumers. The are the 2nd set of consumers and they occupy the 3rd trophic level Tertiary 3° Organisms that consume secondary consumers. They are the 3rd set of consumers and they occupy the 4th trophic level Quaternary 4° Organisms that consume tertiary consumers. They are they 4th set of consumers and they occupy the 5th 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 2nd 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

Food webs

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?

Activity

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