Food Chains

A food chain should be very simple, something you have been studying since primary school; but now we'll take it to the next level.
A typical food chain chain looks like this:

A food chain shows how energy is transfered between organisms
The energy comes as solar energy that plants use to convert into chemical energy (photosynthesis). The herbivores eat the plants, taking some of the energy and then they are prey and the energy is transfered to the predator.
But some of this energy is lost at each stage (or trophic level). In the above example, the grass looses some energy by respiration. And then the rabbit loses energy by heat and waste. And so by the time it gets to the fox a fraction of the original energy gets to it.

Energy Transfer

In an ecosystem there is energy, and this is what allows the organisms to live. This energy mainly comes from one original source: photosynthesis. The plants use this solar energy to produce carbohydrates which are then consumed by other organisms: transfering the energy.
Not all of the energy from sunlight, however, is used by the plants; they are far from efficient. Much sunlight misses the plant, is in the wrong wavelength or lost in the inefficiencies of photosynthesis. We use the term gross primary production to refer to the total energy in the molecules of the plant; and net primary production is the surplus energy not used by the plant itself.
At each level of the food chain energy is lost because it is used by the organism itself for respiration. This limits the number of steps there can be on a food chain.

The diagram above represents quantitatively the efficiency of energy transfer in a food chain. Notice how only about 8% of the energy is transfered from one stage to the next.

Ecological Pyramids

A food chain can be represented quantatively (with numbers) in the form of a pyramid of numbers, below is one for the previous food chain. From this graph we can see there are fewer foxes than rabbits; which makes sense because a fox must eat several rabbits to get enough energy in order to survive.
An ecological pyramid shows the relative sizes of different components at the various trophic levels of a food chain. A trophic level refers to each stage (shown as a horizontal bar on ecological pyramids). There are three types of ecological pyramid we use: numbers, biomass and energy.

The pyramids of numbers shows the raw number of each species at each trophic level. The top example is a typical food chain with a large number of producers but diminishing numbers of consumers. However, if the producer was a tree, followed by insects, then the bottom bar would appear small as many organisms feed on one tree. In this instance the pyramid of biomass is more useful as the tree is much larger.
In the lower example, both the pyramid of numbers and biomass show a smaller producer bar; given what was discussed under the previous heading - this does not make sense. This is because the phytoplankton reproduce very quickly. However, when we represent this information in a pyramid of energy we get a true pyramid.
Plotting the energy will always give a true pyramid because it is impossible to create new energy so a trophic level will always be smaller than the one below it.

Types of Ecological Pyramids

By Debashree Sen, eHow Contributor | updated February 29, 2012

An ecological pyramid is a graphical representation designed to show the number of organisms, energy relationships, and biomass of an ecosystem. They are also called Eltonian pyramids after Charles Elton, who developed the concept of ecological pyramids. Producer organisms (usually green plants) form the base of the pyramid, with succeeding levels above representing the different trophic levels (respective position of the organisms within ecological food chains). Succeeding levels in the pyramid represent the dependence of the organisms at a given level on the organisms at lower level. There are three types of pyramids: of numbers, of biomass, and of energy.

1. Pyramid of Biomass

   • Biomass is renewable organic (living) material. A pyramid of biomass is a representation of the amount of energy contained in biomass, at different trophic levels for a particular time. It is measured in grams per meter2, or calories per meter2. This demonstrates the amount of matter lost between trophic levels. Each level is dependent on its lower level for energy, hence the lower level determines how much energy will be available to the upper level. Also, energy is lost in transfer so the amount of energy is less higher up the pyramid.
     There are two types of biomass pyramids: upright and inverted. An upright pyramid is one where the combined weight of producers is larger than the combined weight of consumers. An example is a forest ecosystem. An inverted pyramid is one where the combined weight of producers is smaller than the combined weight of consumers. An example is an aquatic ecosystem.
     

   2. Pyramid of Numbers

   • The pyramid of numbers represents the number of organisms in each trophic level. This pyramid consists of a plot of relationships between the number herbivores (primary consumers), first level carnivore (secondary consumers), second level carnivore (tertiary consumers) and so forth. This shape varies from ecosystem to ecosystem because the number of organisms at each level is variable
     Upright, partly upright and inverted are the three types of pyramids of numbers. An aquatic ecosystem is an example of upright pyramid where the number of organisms becomes fewer and fewer higher up in the pyramid. A forest ecosystem is an example of a partially upright pyramid, as fewer producers support more primary consumers, but there are less secondary and tertiary consumers. An inverted pyramid of numbers is one where the number of organisms depending on the lower levels grows closer toward the apex. A parasitic food chain is an example.
     

   3. Pyramid of Energy

   • The pyramid of energy represents the total amount of energy consumed by each trophic level. An energy pyramid is always upright as the total amount of energy available for utilization in the layers above is less than the energy available in the lower levels. This happens because during energy transfer from lower to higher levels, some energy is always lost.
     

Food and Energy

Food Chains

A food chain should be very simple, something you have been studying since primary school; but now we'll take it to the next level.
A typical food chain chain looks like this:

A food chain shows how energy is transfered between organisms
The energy comes as solar energy that plants use to convert into chemical energy (photosynthesis). The herbivores eat the plants, taking some of the energy and then they are prey and the energy is transfered to the predator.
But some of this energy is lost at each stage (or trophic level). In the above example, the grass looses some energy by respiration. And then the rabbit loses energy by heat and waste. And so by the time it gets to the fox a fraction of the original energy gets to it.

Energy Transfer

In an ecosystem there is energy, and this is what allows the organisms to live. This energy mainly comes from one original source: photosynthesis. The plants use this solar energy to produce carbohydrates which are then consumed by other organisms: transfering the energy.
Not all of the energy from sunlight, however, is used by the plants; they are far from efficient. Much sunlight misses the plant, is in the wrong wavelength or lost in the inefficiencies of photosynthesis. We use the term gross primary production to refer to the total energy in the molecules of the plant; and net primary production is the surplus energy not used by the plant itself.
At each level of the food chain energy is lost because it is used by the organism itself for respiration. This limits the number of steps there can be on a food chain.

The diagram above represents quantitatively the efficiency of energy transfer in a food chain. Notice how only about 8% of the energy is transfered from one stage to the next.

Ecological Pyramids

A food chain can be represented quantatively (with numbers) in the form of a pyramid of numbers, below is one for the previous food chain. From this graph we can see there are fewer foxes than rabbits; which makes sense because a fox must eat several rabbits to get enough energy in order to survive.
An ecological pyramid shows the relative sizes of different components at the various trophic levels of a food chain. A trophic level refers to each stage (shown as a horizontal bar on ecological pyramids). There are three types of ecological pyramid we use: numbers, biomass and energy.

The pyramids of numbers shows the raw number of each species at each trophic level. The top example is a typical food chain with a large number of producers but diminishing numbers of consumers. However, if the producer was a tree, followed by insects, then the bottom bar would appear small as many organisms feed on one tree. In this instance the pyramid of biomass is more useful as the tree is much larger.
In the lower example, both the pyramid of numbers and biomass show a smaller producer bar; given what was discussed under the previous heading - this does not make sense. This is because the phytoplankton reproduce very quickly. However, when we represent this information in a pyramid of energy we get a true pyramid.
Plotting the energy will always give a true pyramid because it is impossible to create new energy so a trophic level will always be smaller than the one below it.

Food Chains & Food Webs

Do you like to play games? If you do, you will need energy. Every time you run or jump, you are using up energy in your body. How do you get the energy to play? You get energy from the food you eat. Similarly, all living things get energy from their food so that they can move and grow. As food passes through the body, some of it is digested. This process of digestion releases energy.

A food chain shows how each living thing gets its food. Some animals eat plants and some animals eat other animals. For example, a simple food chain links the trees & shrubs, the giraffes (that eat trees & shrubs), and the lions (that eat the giraffes). Each link in this chain is food for the next link. A food chain always starts with plant life and ends with an animal.

1. Plants are called producers because they are able to use light energy from the Sun to produce food (sugar) from carbon dioxide and water.
   
2. Animals cannot make their own food so they must eat plants and/or other animals. They are called consumers. There are three groups of consumers.
   
   
   1. Animals that eat ONLY PLANTS are called herbivores (or primary consumers).
      
   2. Animals that eat OTHER ANIMALS are called carnivores.
      
      
      • carnivores that eat herbivores are called secondary consumers
        
      • carnivores that eat other carnivores are called tertiary consumers
        e.g., killer whales in an ocean food web ... phytoplankton → small fishes → seals → killer whales
      
      
3. Animals and people who eat BOTH animals and plants are called omnivores.
   
4. Then there are decomposers (bacteria and fungi) which feed on decaying matter.
   
   These decomposers speed up the decaying process that releases mineral salts back into the food chain for absorption by plants as nutrients.
   
   Image Map of the Nitrogen Cycle - What happens in the soil?

Do you know why there are more herbivores than carnivores?

In a food chain, energy is passed from one link to another. When a herbivore eats, only a fraction of the energy (that it gets from the plant food) becomes new body mass; the rest of the energy is lost as waste or used up by the herbivore to carry out its life processes (e.g., movement, digestion, reproduction). Therefore, when the herbivore is eaten by a carnivore, it passes only a small amount of total energy (that it has received) to the carnivore. Of the energy transferred from the herbivore to the carnivore, some energy will be "wasted" or "used up" by the carnivore. The carnivore then has to eat many herbivores to get enough energy to grow.

Because of the large amount of energy that is lost at each link, the amount of energy that is transferred gets lesser and lesser ...

1. The further along the food chain you go, the less food (and hence energy) remains available.

The above energy pyramid shows many trees & shrubs providing food and energy to giraffes. Note that as we go up, there are fewer giraffes than trees & shrubs and even fewer lions than giraffes ... as we go further along a food chain, there are fewer and fewer consumers. In other words, a large mass of living things at the base is required to support a few at the top ... many herbivores are needed to support a few carnivores

2. Most food chains have no more than four or five links.
   
   There cannot be too many links in a single food chain because the animals at the end of the chain would not get enough food (and hence energy) to stay alive.
   
   Most animals are part of more than one food chain and eat more than one kind of food in order to meet their food and energy requirements. These interconnected food chains form a food web.
   

Food chains in different habitats:  Desert  |  Coniferous Forest  |  Deciduous Forest  |  Temperate Rainforest 

The following is a possible food web:

Note that the arrows are drawn from food source to food consumers ... in other words, you can substitute the arrows with the words "eaten by" If you are using Internet Explorer, Firefox, Safari or Netscape Navigator (v4) browsers, you may want to have some fun ... creating a possible food web

A change in the size of one population in a food chain will affect other populations.

This interdependence of the populations within a food chain helps to maintain the balance of plant and animal populations within a community. For example, when there are too many giraffes; there will be insufficient trees and shrubs for all of them to eat. Many giraffes will starve and die. Fewer giraffes means more time for the trees and shrubs to grow to maturity and multiply. Fewer giraffes also means less food is available for the lions to eat and some lions will starve to death. When there are fewer lions, the giraffe population will increase.

Energy Pyramids

What is an energy pyramid

Energy pyramid

An energy pyramid is a graphical model of energy flow in a community. The different levels represent different groups of organisms that might compose a food chain. From the bottom-up, they are as follows:

• Producers — bring energy from nonliving sources into the community
• Primary consumers — eat the producers, which makes them herbivores in most communities
• Secondary consumers — eat the primary consumers, which makes them carnivores
• Tertiary consumers — eat the secondary consumers

In some food chains, there is a fourth consumer level, and rarely, a fifth. Have you ever wondered why there are limits to the lengths of food chains?

Why are energy pyramids shaped the way they are?

An energy pyramid’s shape shows how the amount of useful energy that enters each level — chemical energy in the form of food — decreases as it is used by the organisms in that level. How does this happen?
Recall that cell respiration “burns” food to release its energy, and in doing so, produces ATP, which carries some of the energy as well as heat, which carries the rest. ATP is then used to fuel countless life processes. The consequence is that even though a lot of energy may be taken in at any level, the energy that ends up being stored there – which is the food available to the next level — is far less. Scientists have calculated that an average of 90% of the energy entering each step of the food chain is “lost” this way (although the total amount in the system remains unchanged).
The consumers at the top of a food pyramid, as a group, thus have much less energy available to support them than those closer to the bottom. That’s why their numbers are relatively few in most communities. Eventually, the amount of useful energy left can’t support another level. That’s why energy flow is depicted in the shape of a pyramid. The energy that enters a community is ultimately lost to the living world as heat.

Food Energy Pyramids

Flow of energy through a food chain. As energy passes to a higher tropic level, approximately 90% of the useful energy is lost. High tropic levels contain less energy and fewer organisms than lower levels.
At each tropic level in a food chain, energy is used by the organisms at that level to maintain their own life process. Because of the 2nd law of energy, some energy is lost to the surroundings as heat. it is estimated that in going from one tropic level to the next, about 90 % of the energy is lost.
In moving to the next tropic level, only 10 % of the original energy is available. By the third tropic level only 1% of the energy is available.

Food Supply - Eat grain rather than Meat
Energy is used much more efficiently if humans eat plants (first tropic level) instead of meat (second tropic level. A given area of farmland can support more people if the crops are fed directly to people rather than to livestock that people then eat.
For example if a man needs 3,000 Calories per day, then 30,000 Cal beef are needed, which in turn need 300,000 Cal of corn, which in turn means 30,000,000 Cal of sunshine. This works out to be 1.5 acres of corn per day per person. If the person ate corn directly then 10 people could be supported by the same 1.5 acres of corn.

Pyramid of numbers

An ecological pyramid of numbers shows graphically the population of each level in a food chain.
The diagram to the right shows a (nonfictional) example of a five level pyramid of numbers: 10,000 fresh water shrimps support 1,000 bleak, which in turn support 100 perches followed by 10 northern pikes and finally one osprey.

Pyramid of productivity

An ecological pyramid of productivity is often more useful, showing the production or turnover of biomass at each trophic level. Instead of showing a single snapshot in time, productivity pyramids show the flow of energy through the food chain. Typical units would be grams per meter² per year or calories per meter² per year. As with the others, this graph begins with producers at the bottom and places higher trophic levels on top.
When an ecosystem is healthy, this graph produces a standard ecological pyramid. This is because in order for the ecosystem to sustain itself, there must be more energy at lower trophic levels than there is at higher trophic levels. This allows for organisms on the lower levels to not only maintain a stable population, but to also transfer energy up the pyramid. The exception to this generalization is when portions of a food web are supported by inputs of resources from outside of the local community. In small, forested streams, for example gone up greater than could be supported by the local primary production.
When energy is transferred to the next trophic level, typically only 10%^{[citation needed]} of it is used to build new biomass, becoming stored energy (the rest going to metabolic processes). As such, in a pyramid of productivity each step will be 10% the size of the previous step (100, 10, 1, 0.1, 0.01)^{[citation needed]}.
The advantages of the pyramid of productivity:

• It takes account of the rate of production over a period of time.
• Two species of comparable biomass may have very different life spans. Therefore their relative biomasses is misleading, but their productivity is directly comparable.
• The relative energy chain within an ecosystem can be compared using pyramids of energy; also different ecosystems can be compared.
• There are no inverted pyramids.
• The input of solar energy can be added.

The disadvantages of the pyramid of productivity:

• The rate of biomass production of an organism is required, which involves measuring growth and reproduction through time.
• There is still the difficulty of assigning the organisms to a specific trophic level. As well as the organism in the food chains there is the problem of assigning the decomposers and detritivores to a particular trophic level.

Nonetheless, productivity pyramids usually provide more insight into an ecological community when the necessary information is available