Kristen A. Borsari
All living things need to find nourishment in one way or another, some can find it from many different sources while others only eat one food source: sea gulls will eat fish from the sea of dig through trash inland, pandas will eat only bamboo shoots. Animals have certain nutritional requirements that must be met in order for cell growth to take place. Animals need nutrients to keep their bodies healthy, they all need: glucose (sugars and carbohydrates), lipids (fats), proteins, vitamins and minerals, and water. Each nutrient is found in one type of food or another (Barré, 1998).
Every living organism in a habitat has a niche, a specific role to play within that habitat. There are three main niches: producers, consumers and decomposers. Almost all plants are producers, they provide food for other living things. Consumers eat other living organisms in a habitat, their role is to consume other organisms and be a part of a food web. Decomposers mark the end of the food chain. Fungi and bacteria get rid of dead organisms in a habitat. This is a very general explanation and is a good place to start the children. There is a more inclusive description of niches and food webs. Food chains and food webs are like steps on a ladder, and each step is called a trophic level, and each of the trophic levels fits within these niches. These trophic levels track the transfer of energy and nutrients within a habitat. The first level is the primary producers, which are flowering plants, they provide food for the primary consumers. These are usually herbivores. Primary consumers are eaten by the secondary consumers which can be either omnivore or carnivore. The third level consumer is called the tertiary consumer which may also be either omnivore or carnivore and they consume the secondary consumers. Often there is a fourth level consumer, a quaternary consumer. Some animals can change levels depending on what they are eating and what their meal has eaten (Silverstein, Silverstein & Nunn, 1998).
A food chain explains the pattern of eating and of being eaten, every plant and animal is a part of at least one food chain. When a member of one food chain eats a member of another food chain these chains connect into a food web. Food webs include many plants and animals. Most food chains begin with energy from the sun, plants use the sun's energy and animals eat the plants for energy. All the living things in an habitat are connected in a food web. Food webs work with three parts: plants, herbivores and carnivores/omnivores. Although plants are at the bottom of the food chain, they could not survive without the herbivores, carnivores and omnivores (Kalman and Langille, 1998).
Herbivores
Herbivores are animals that eat the food around them. If an animal survives by eating only plants found in their environment, that animal is an herbivore. Herbivores that eat grass such as cows are called grazers, and animals that eat leaves from trees such as deer are called browsers. Herbivores have large back teeth so they can grind up their food. Herbivores typically have to eat a lot of plants to get enough of the energy they need because plants are hard for their bodies to digest. Most herbivores do not eat an entire plant, they may eat only the leaves, seeds, fruits or flowers. Herbivores are crucial to the food chain, without them, both the food that they eat and the animals that feed on them would suffer. Many of the plants that herbivores feed on depend on them to spread their seeds so new plants can grow in new places. Some plants have seeds that pass unharmed through an animals intestinal tract, when the animal is far away from its last meal and has fully digested the seeds are eliminated from the body and a new plant can grow. Other plants have sticky seeds or pods that adhere to the fur or hair of herbivores. As the animal travels and brushes against trees, rocks, etc. the seeds will drop off and take root. Without an adequate herbivore population, the carnivores that feed on them would have nothing or not enough to eat. Even if they began consuming other carnivores, eventually there would be a shortage of food.
Carnivores
Carnivores are animals that eat other animals, namely herbivores and sometimes other carnivores. When a carnivore hunts or kills another animal for food, it is called a predator, and the animal it eats is called prey. Predators are very important in an habitat, without predators the population of herbivores would grow unchecked until there were not enough plants left to eat. Some carnivores can only feed on a few specific animals due to physical size or shape, as in the case of the anteater which cannot opem its jaws but can use a long sticky tongue to eat ants. There are other carnivores that eat a variety of different foods, such as alligators which will eat just about anything that will wade into or close enough to the water. The teeth of a carnivore are designed to deal with their food. Animals such as lions and wolves have large fang teeth, called canines, they use these for stabbing their prey. Between the canines are incisors, used for cutting into flesh and for cracking open bones are carnassial teeth at the back of the mouth.
Another type of carnivore is the scavenger, which feeds on dead animals. These animals keep the habitat clean by eating the leftovers from a predator's meal or by eating an animal that has died of age or disease. Scavengers are a crucial part of a food web because they prevent the energy of a dead body from being wasted.
Omnivores
Omnivores are animals that eat both plants and animals, because of this adaptation, they will rarely go hungry. They may exist at many points in a food web, depending on the type of food they are eating. Since omnivores eat whatever is available, they will have different diets depending on the season. An example of an omnivore is the raccoon. The raccoon will search many places for its food, it digs up worms and insects, eats fish and frogs, eggs and chicks can be found in trees as well as fruits and berries, and it is not unusual to find a trash can raided by raccoons in the middle of the night! The teeth of omnivores are just as versatile as the animals themselves and these animals frequently use their claws to compensate for strong sharp teeth (Riley, 1998).
Decomposers
Decomposers mark the end of the food chain. When the highest level of the food chain dies, scavengers and decomposers break down and use it along with the remains of other dead organisms from each tropic level. Their job is to make the energy found in those remains is not lost out of the habitat.