Follow the energy from the Sun along a food chain, then knock out one animal and watch the whole ecosystem react.
Check yourself
In the food chain grass to rabbit to fox, what does each arrow show?
The direction that energy (and biomass) is transferred, from the organism being eaten to the one eating it. So it points from grass to rabbit, and rabbit to fox.
If the foxes are removed, what happens to the rabbits and then the grass?
With no predator, the rabbit population rises. The larger number of rabbits then eats more grass, so the amount of grass falls. Ecosystems are linked, so a change to one part affects the others.
Why is there usually only enough energy for three or four links in a food chain?
Only about a tenth of the energy passes to the next level. The rest is used for movement and warmth, or lost in waste. After a few steps there is too little energy left to support another level.