The core patterns studied in Ecosystem Ecology and used in Foodweb Education are energy flow and matter cycles, as these occur in all natural processes at all scales. All systems, whether a single-celled bacteria, the entire biosphere or a washing machine require an energy source to drive the movement of matter within them, giving these patterns broad explanatory power

Thermodynamics is our tool for understanding systems by studying their energy flows. We use the broad but specific definition of energy as ‘the ability to do work’, not just electricity and fuels.


This ensures the vocabulary and patterns are applicable to all natural and human systems, and this point is critical, as energy is a term often overloaded with meaning and a source of confusion. We use the thermodynamic definition of energy, giving topics such as fossil fuels, photosynthesis and eating from the garden the same vocabulary and common energetic origin – sunlight.


Can you name the energy transformations in this picture?


After studying food chains as energy flows, by grades 3-4 students are able to postulate the existence of phytoplankton in Antarctic food webs, and wonder about the ecosystem effects of winter darkness. The same pattern enables understanding energy use in human societies, tracing energy flows from their sources to final heat sinks, whether in a loaf of bread, electric light or vegetables from the garden.


Thermodynamics and energy transformations are to ecological literacy what concepts like whole numbers and addition are to numeracy, providing foundational knowledge that can be applied in all contexts. We feel Education for Sustainability requires a clear commitment to reiterating energy fundamentals, as partial comprehension does not lead to ecological literacy.

A simple description and exercise for understanding the importance of  “looking at everything that goes on around you as an energy flow that starts from a concentrated source – almost always the sun – and ends in diffuse heat radiating out into space is provided by John Michael Greer in his blog post The ways of the Force  which is part of his Green Wizards project :

Let’s look at some examples. A garden bed, to begin with, is a device for collecting energy from the sun by way of the elegant biochemical dance of photosynthesis. Follow a ray of sunlight from the thermonuclear cauldron of the sun, across 93 million miles of hard vacuum and a few dozen miles of atmosphere, until it falls on the garden bed. Around half the sunlight reflects off the plants, which is why the leaves look bright green to you instead of flat black; most of the rest is used by the plants to draw water up from the ground into their stems and leaves, and expel it into the air; a few per cent is caught by chloroplasts – tiny green disks inside the cells of every green plant, descended from blue-green algae that were engulfed but not destroyed by some ancestral single-celled plant maybe two billion years ago – and used to turn water and carbon dioxide into sugars, which are rich in chemical energy and power the complex cascade of processes we call life.

Most of those sugars are used up keeping the plant alive. The rest are stored up until some animal eats the plant. Most of the energy in the plants the animal eats gets used up keeping the animal alive; the rest get stored up, until another animal eats the first animal, and the process repeats. Sooner or later an animal manages to die without ending up in somebody else’s stomach, and its body becomes a lunch counter for all the creatures – and there are a lot of them – that make their livings by cleaning up dead things. By the time they’re finished with their work, the last of the energy from the original beam of sunlight that fell on the garden bed is gone.

Where does it go? Diffuse background heat. That’s the elephant’s graveyard of thermodynamics, the place energy goes to die. Most often, when you do anything with energy – concentrate it, move it, change its form – the price for that gets paid in low-grade heat. All along the chain from the sunlight first hitting the leaf to the last bacterium munching on the last scrap of dead coyote, what isn’t passed onward in the form of stored chemical energy is turned directly or indirectly into heat so diffuse that it can’t be made to do any work other than jiggling molecules a little. The metabolism of the plant generates a trickle of heat; the friction of the beetle’s legs on the leaf generates a tiny pulse of heat; the mouse, the snake, and the coyote all turn most of the energy they take in into heat, and all that heat radiates out into the great outdoors, warming the atmosphere by a tiny fraction of a degree, and slowly spreading up and out into the ultimate heat sink of deep space.


Homework: An exercise, which I’d like to ask those readers studying this material to do several times over the next week, will help get this habit in place. Draw a rough flow chart for one or more versions of this process. Take a piece of paper, draw a picture of the sun at the top, and draw a trash can at the bottom; label the trash can “Background Heat.” Now draw the important components in any system you want to understand, and draw arrows connecting them to show how the energy moves from one component to another. If you’re sketching a natural system, draw in the plants, the herbivores, the carnivores, and the decomposers, and sketch in how energy passes from one to another, and from each of them to the trash can; if you’re sketching a human system, the energy source, the machine that turns the energy into a useful form, and the places where the energy goes all need to be marked in and connected. Do this with a variety of different systems. It doesn’t matter at this stage if you get all the details right; the important thing is to start thinking in terms of energy flow.

Energy flow is a one way road



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