Predators (carnivores) come in many shapes and sizes.
Cougar hunts the land. Nautilus hunts the ocean. Blue Darner hunts the sky.
Energy is re-packaged as it transfers along a food chain.
Most food chains are only three or four links long. One food chain in a pond community might be (1) algae eaten by a (2) snail eaten by a (3)painted turtle. Three links.
But say the turtle dies of old age. A (4) crayfish eats part of it. (5) Bacteria and fungi eat the rest of it--they decompose the turtle to get the energy left in its body. Five links.
Since all lives end in death, we can say that all food chains end with bacteria and fungi, the primary decomposers.
Real life is never as simple as the idea of food chains suggests. Instead, the lives in any natural community are a complex system that creates many changing food chains and transfers energy from life to life in all sorts of ways. A grasshopper may be eaten by any of several different bird predators, for example.
• We call this complex combination of energy transfers a food web.
|An actual foodweb showing all the energy transfers taking place is much more complex than what is shown. The diagram just suggests a few possibilities.
At every link in a food web, 90% of the energy is lost. Consumer Cow is only able to use ten per cent of the energy in Producer Grass.
Give yourself a quick test. What does this pyramid show?
Energy does not cycle through a community as life-materials do. It does transfer from life to life, but it gets used up. 90% of the energy is lost at each feeding (trophic) level
Then plants and sunlight do their magic photosynthesis again and make more food.
Review: Producers (plants) are partially eaten by consumers1 (grazing animals), which are sometimes eaten in turn by consumers2 (carnivores), which, when they die are eaten by the decomposers.
At the end of all food chains the energy has been used up, and is replaced by new input of radiant energy from the sun. So energy flows in straight lines through a community and is lost, but is continuously restored to the community by plants, algae, and other photosynthesizers.
||Energy travels in straight lines through food chains and webs and is used up and is replaced by photosynthesis using sunlight
||Nutrients (Life-Materials) travel in circles that do not end. Nutrients have been recycling on Earth for billions of years.
See if you can label this pyramid with the members of additional food chains.
Put yourself in one chain.
|Energy Transfer is Energy Sharing
When we see Earth-life as a whole system (the Biosphere), we think first of the whole rather than of its individual parts. So when a mouse is eaten by a hawk, we can see that first as an energy transfer within the whole system of life.
All lives stay alive on energy transfers and end in death.
When we look at the whole system of the Biosphere, we have choices about how we see it:
• we can choose to see it as a horrible tragedy, a slaughterhouse, or
• we can choose to see it as a system of energy sharing which is essentially cooperative.
All life on Earth survives by feeding on other lives and their leftovers. We live by eating each other. That is the way things are. What is good for the health of the system is not necessarily good for individual lives within that system.
We have to be cautious here about imposing our human moral judgments onto other lives. We don't find it especially ugly when a carrot dies. But when the rabbit who ate the carrot dies, it can be ugly (to humans).
If the rabbit was smeared across a highway by a car, that is ugly. If the energy the rabbit contains is not used by other lives, that may look ugly and wasteful.
But in fact, life is so resourceful that living things always find a way to make a living from whatever is available. What the car did was to shorten the food chain. The crow was happy with the meat he carried back to his nestlings, the sparrow was happy with the fur lining her nest, and forty billion bacteria were living the good life in what was left.
Explore Further in Energy
Explore the Biosphere
top of page