Big on Biology

A different kind of

World Wide Web

9-12 Science Std: Bio 6f

Food Chains and WebsFood chain: step-by-step sequence that

links together organisms that feed on each othero Ex: bat ate a mosquito that had bitten a

coyote that had eaten a grasshopper that had chewed a leaf

Different Food Chains

Terrestrial (Land-Based)

Marine (Water-Based)

o Food chain supposes that organisms eat only that one particular organismWe know that organisms can eat more than

one type of organismMakes links to different organisms to create

more realistic picture of a food web Food web: complex relationship formed

by interconnecting food chains or feeding relationships signified by arrows

FOOD WEBS

FOOD WEBS

Organisms in the Food Web

Two types of organisms based on where they get their energy (food):

o 1. Autotrophso 2. Heterotrophs

o 1. Autotrophs: organisms capable of obtaining their energy from environmentMost get energy from photosynthesis when

sunlight on plants makes sugarAre called producers since they produce

(make) their energy Ex: all plants, phytoplankton, some

bacteria

Aquatic Producers

o 2. Heterotrophs: organisms that obtain energy from autotrophs or other heterotrophsAre called consumers since they

consume (eat) their energy 3 different kinds of consumers

depending on where they feed in food web:1. Primary consumers2. Secondary consumers3. Decomposers

1. Primary (first-order) consumers: feed directly on autotrophsEat plants only so are considered herbivores (herb/plant eaters)

• Ex: mice, rabbits, deer, cows

Cows are primary consumers because they eat only plants (producer autotrophs)

o 2. Secondary (second-order) consumers: feed on primary consumersEat animals only so are considered carnivores (meat eaters)

• Ex: owls, lions, tigers

Some secondary consumers can also be primary consumers since they are both herbivores and carnivores so are called omnivoresEx: humans, bears

3. Decomposers: feed on remains or bodies of all organisms to make energyEx: bacteria, fungi (mushrooms), some

insects

Food Chains All Have Food Chains All Have Decomposers that Decomposers that Can Feed on Can Feed on AnyAny MemberMember of a Food of a Food ChainChain

Alternative Pathways Maintain Stability in Food Webs

Having alternatives to eat can help stability of food web o Ex: if rabbits in some areas decrease in

population, owls won’t starve, they can focus on mice Less rabbits – more grass - more mice since

more places for mice to hide inIf owls focus on mice, rabbit numbers have a

chance to increaseFood web stays stable since numbers of all

organisms will always go back to original

Maintaining Stability

EATEAT

Owl can eat rabbit or mouse

Worldwide problem has arisen: land to grow producers is being taken over by urban citieso As human population grows, need more

food to feed them, and according to food webs, all human food starts at producers

No land means producers can’t grow No primary consumers will survive No secondary consumers will survive No decomposers will survive

Deforestation

Questions?

The removal of one part from an ecosystem, like the removal of a moving part from a car’s engine, can cause the collapse of an entire food chain. In a food chain, there are predators and

there are prey.Prey – the organism that could be eaten

by another organismPredator – the organisms eating other

organisms

Ex.: Cat = Predator

Mice = Prey

A food chain is a series of predators and preyEx: Coyote Dog Cat Mice

bread crumbs (wheat)

Predators keep the prey population in check.

The prey keep the predators alive by providing food.

predator prey

Ex. Pacific Sea otters mainly eat sea urchins and sea urchins eat kelp (form of seaweed) and little fish hide in the kelp

EAT

EAT

HIDE IN

Hunters used to kill sea otters for their fur. As a result, the number of sea urchins rapidly increased. As the number of sea urchins grew, the amount of kelp went down.

The fish that relied on the kelp for shelter and food also decreased in number.

So killing the sea otters for their fur (nearly becoming extinct), affected sea urchins, which affected the kelp, which affected the fish. (DOMINO EFFECT!!)

EAT

EAT

HIDE IN

• Restoring the Balance Is a Difficult TaskCan the “Domino Effect” be stopped?

oYes! The sea otter was reintroduced (more brought back in) which caused the sea urchin population to get smaller because they are being eaten.

oThe kelp bed have increased and so the number of fish are increasing too.

oThis has “restored the natural balance” of the food chain

This is not always easy to do.