Download TOPIC: Food Chains

TOPIC: Food Chain, Food Web and Food Pyramid
The phrase 'food chain' is a way of indicating how energy moves through an ecosystem.
Food chains are more often called food webs because no organism lives solely on another.
A food chain is a possible route for the transfer of matter and energy (food) through an
ecosystem from autotrophs through heterotrophs and decomposers.
Example of food chains:
• Producer →primary consumer → secondary consumer → tertiary consumer → decomposer
• Grass →rabbit → fox → decomposer (upon the death of the fox)
Components of a Food Chain:
The food chain consists of four main parts:
1. The Sun, which provides the energy for everything on the planet.
2. Producers: these include all green plants. These are also known as autotrophs, since
they make their own food. Producers are able to harness the energy of the sun to make
food. Ultimately, every (aerobic) organism is dependent on plants for oxygen (which is
the waste product from photosynthesis) and food (which is produced in the form of
glucose through photosynthesis). They make up the bulk of the food chain or web.
3. Consumers: In short, consumers are every organism that eats something else. They
include herbivores (animals that eat plants), carnivores (animals that eat other animals),
parasites (animals that live off of other organisms by harming it), and scavengers
(animals that eat dead animal carcasses). Primary consumers are the herbivores, and
are the second largest biomass in an ecosystem. The animals that eat the herbivores
(carnivores) make up the third largest biomass, and are also known as secondary
consumers. This continues with tertiary consumers, etc.
4. Decomposers: These are mainly bacteria and fungi that convert dead matter into
gases such as carbon and nitrogen to be released back into the air, soil, or water.
Fungi, and other organisms that break down dead organic matter are known as
saprophytes. Even though most of us hate those mushrooms or molds, they actually
play a very important role. Without decomposers, the earth would be covered in trash.
Decomposers are necessary since they recycle the nutrients to be used again by
producers.
Types of Food Chains:
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Grazing food chain - The grazing food chain begins with the photosynthetic
fixation of light, carbon dioxide, and water by plants (primary producers) that
produce sugars and other organic molecules. Once produced, these
compounds can be used to create the various types of plant tissues. Primary
consumers or herbivores form the second link in the grazing food chain. They
gain their energy by consuming primary producers. Secondary consumers or
primary carnivores, the third link in the chain, gain their energy by consuming
herbivores.Tertiary consumers or secondary carnivores are animals that
receive their organic energy by consuming primary carnivores.
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Detrital food chain - The detritus food chain differs from the grazing food chain
in several ways:
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the organisms making it up are generally smaller (like algae,
bacteria, fungi, insects, & centipedes)
the functional roles of the different organisms do not fall as neatly
into categories like the grazing food chain's trophic levels.
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detritivores live in environments (like the soil) rich in scattered food
particles. As a result, decomposers are less motile than herbivores
or carnivores.
Decomposers process large amounts of organic matter, converting
it back into its inorganic nutrient form.
Food Web
A food web shows all possible feeding relationships in a community at each trophic
level; represents a network of interconnected food chains.
An example of a food web:
The difference between a food chain and a food web is that a chain is a single strand of
the different levels of energy transfer, where as a food web will show the many strands in a
particular ecosystems such as a forest.
Food Pyramid
A food pyramid, or ecological pyramid, will show population sizes (amount of energy at
that level) in an ecosystem. The pyramid most often decreases, as it gets farther up. In the
example of the food web above, a food pyramid can be created with the clover, the worm, and
the raccoon. There is a much larger abundance of clover than the other two; they will be on the
bottom of the pyramid. The worm will be the next step with a smaller number than clover, but
larger number of raccoon. The raccoon will be on the top of the pyramid with the smallest
number. The pyramid will look like this:
Racoon
Worm
Clover
Interactions Among Organisms
Any relationship in which there is a close and permanent association between
organisms of different species is symbiosis, or “living together”. There are several types of
symbiosis. They are predation, parasitism, commensalism, and mutualism.
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Predation is a relationship in which one organism preys on another as a source of food.
An example of predation is an owl hunting a field mouse.
Parasitism is a relationship in which one organism derives benefit at the expense of the
other. An example of parasitism is a tapeworm living in the intestines of dogs. The
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tapeworm takes nourishment from the dog in which it lives. Pathogens that cause
diseases in plants and animals are parasites. Parasites are responsible for such
diseases as malaria, polio, and influenza in humans. Plant diseases include wheat rust,
corn smut, and Dutch elm disease. If a host dies prematurely from disease, however,
the pathogen is also at risk of dying. As a result, many parasites and their hosts have
evolved a form of mutual tolerance; nevertheless, the host is still harmed in some way.
Commensalism is a relationship in which one organism derives benefit with neither
benefit nor harm to the other. Birds and squirrels nesting in trees and shrubs can be
thought of as examples of commensalism. The benefits are obvious - shelter from the
elements and protection from predators. Host trees and shrubs are not affected by the
presence of nests.
Mutualism is a relationship in which both organisms benefit from each other. An
example of a mutualistic relationship is that of the ant and the acacia tree. The ant
protects the tree from herbivores from eating the tree as well as clearing vegetation
away from the tree that may compete for resources. The tree provides a home for the
ants. Clown fish and sea anemones-bright and colorful clown fish live in and amongst
the tentacles of the sea anemone, which look like beautiful aquatic flowers, but bear
poisonous stinging cells called nematocysts. A slime layer covering the clownfish make
them immune to the stinging cells, and the stinging tentacles of the sea anemone deter
potential predators. The clownfish in turn protect the sea anemone from other fish that
would feed on the anemone. Clownfish laid eggs within the sea anemone, which offers
protection during their incubation and development.
Predator-prey interactions - the interaction between predators and prey involve continuous
evolutionary change; as predators evolve more efficient ways of capturing prey, the prey
evolve ways of avoiding predation. For example:
1. Warning coloration, mimicry, & cryptic coloration:
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Warning coloration - conspicuous markings of an animal that make it
easily recognizable and warn would-be predators that it is a poisonous,
foul-tasting, or dangerous species
mimicry - the advantageous resemblance of one species to another, often
unrelated, species or to a feature of its own environment.
cryptic coloration - an organism matches its background, hiding
(camouflaging) it from predators and/or prey.
2. Chemical defenses
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serve to repel or inhibit potential predators
commonly employed by arthropods, amphibians, & snakes
also used extensively by various types of plants
3. Predator satiation
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timing reproduction so that a maximum number of offspring are produced
in a short period of time, thus satiating predators and allowing a greater
percentage of young to survive
examples of organisms that use this strategy include wildebeest, cicadas,
caribou , and lots of plants
Biogeochemical Cycling
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The transport and transformation of substances in the environment, through life, air,
sea, land, and ice, are known collectively as biogeochemical cycles. These global
cycles include the circulation of certain elements, or nutrients, upon which life and the
earth's climate depend.
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Carbon cycle - the movement of carbon, in its many forms, between the
biosphere, atmosphere, oceans, and geosphere
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plants obtain carbon dioxide from the air and, through photosynthesis,
incorporate carbon into their tissues
producers & consumers - transform part of the carbon in their food back
into carbon dioxide via respiration
decomposers - release the carbon tied up in dead plants & animals into
the atmosphere
Another major exchange of carbon dioxide occurs between the oceans
and the atmosphere. The dissolved CO2 in the oceans is used by marine
biota in photosynthesis.
Two other important processes are fossil fuel burning and changing land
use. In fossil fuel burning, coal, oil, natural gas, and gasoline are
consumed by industry, power plants, and automobiles. Changing land use
is a broad term which encompasses a host of essentially human activities,
including agriculture, deforestation, and reforestation.
Environmental Issues:
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The global carbon cycle is out of balance, making rapid global climate change more
likely. Atmospheric CO2 levels are rising rapidly -- currently, they are 25% above where
they stood before the industrial revolution. Carbon dioxide forms when the carbon in
biomass oxidizes as it burns or decays. Many biological processes set in motion by
people release carbon dioxide. These include burning fossil fuels (coal, oil, & natural
gas), slash-and-burn agriculture, clearing land for permanent pasture, cropland, or
human settlements, accidental and intentional forest burning, and unsustainable logging
and fuelwood collection. Clearing vegetation cover from a forested hectare releases
much of the carbon in the vegetation to the atmosphere, as well as some of the carbon
lodged in the soil. Logging or sustainable fuelwood collection can also degrade
vegetation cover and result in a net release of carbon.
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Nitrogen cycle - Almost all of the nitrogen found in terrestrial ecosystems
originally comes from the atmosphere. Small proportions enter the soil in rainfall
or through the effects of lightning. Most, however, is biochemically fixed within
the soil by specialized micro-organisms like bacteria. Members of the bean family
(legumes) and some other kinds of plants form mutualistic symbiotic relationships
with nitrogen fixing bacterial. In exchange for some nitrogen, the bacteria receive
from the plants carbohydrates and special structures (nodules) in roots where
they can exist in a moist environment. Scientist estimate that biological fixation
globally adds approximately 140 million metric tons of nitogen to ecosystems
every year.