Trophic Levels and Food Webs Answers

Energy is lost ascending each trophic level of the pyramid of energy. Therefore, when quaternary consumers eat tertiary consumers, most of the energy stored in the tertiary consumers' bodies is lost and only 10-15% is passed on to the quaternary consumers. Quaternary consumers, meanwhile, occupy the top position in the pyramid of energy because nothing preys upon them in turn.

Quaternary consumers feed on tertiary consumers and occupy the highest consumer level in a food chain. Because much of the energy is lost at each transfer between trophic levels, only a small amount reaches quaternary consumers, and there is generally not enough energy to support another consumer level above them.

When a predator is eliminated, its prey population may grow because fewer individuals are being eaten. The larger population can use up its food and other resources, creating greater competition. If there is not enough food for all the prey, some may starve.

Decomposers recycle the nutrients in dead organisms allowing it to completely travel through the food web cycle, from producer, to consumer and back again. Without decomposers, dead organic matter would accumulate in an ecosystem until it reached harmful levels. This recycling also applies to quaternary consumers, the predators that generally have no natural enemies, allowing the nutrients in their bodies to be recycled.

Trees are very large compared to the organisms they support, such as insects, birds and rodents. A single tree has much more biomass than the consumers depending upon it, meaning it is still the base of biomass pyramids and pyramids of energy. Therefore even if they are fewer in number trees still occupy the producer level of the trophic pyramid.

Primary consumers such as herbivores only feed on producers. Secondary consumers are predators and feed on primary consumers. The principal difference between the two trophic levels is what they consume.

Primary consumers eat producers, such as plants or algae. Secondary consumers eat primary consumers, such as herbivores.

Decomposers break down dead organisms and waste and return nutrients to the environment. They decompose the remains and waste of organisms at every trophic level, including quaternary consumers. Producers can reuse those nutrients, so decomposers help keep nutrients cycling through the food web.

If the primary predator of a prey species is eliminated, the prey species’ population will increase to the point of overpopulating the ecosystem. This overpopulation will result in depletion of the prey species’ food supplies as more individuals compete for the same resources and can ultimately lead to the prey species starving.

A pyramid of numbers counts organisms, not their size or total biomass. A few large trees can produce enough food and provide habitat for many smaller organisms, so trees may make up the smallest level by number while still serving as producers.