The arrows in the chain indicate the direction of energy flow and feeding. Energy loss is normal throughout a food chain. For instance, when an animal eats a plant it uses the food to provide energy and raw materials, however some thermal energy is wasted and some plant food is not digestible acting only as roughage. When the different food chains are connected and put together for a habitat, they form a food web . A food web tells you more about a habitat than a food chain as the feeding relationships may be complex.
Some animals change their food source if an organism is in short supply.
Introducing a new species into a food web can have damaging effects. For instance rabbits introduced into Australia in the last century produced a vast population, as they lacked a natural predator. The only way of controlling them was to introduce the rabbit disease myxomatosis, so as to greatly reduce their numbers.