Each Type of Community Member Has a Certain Role Or Job to Fulfill in the Community. Ecologists

Bio Text # 2 Mrs. Nichols Biology 1/1A

Each type of community member has a certain role or job to fulfill in the community. Ecologists call this role a niche.

An entire community seems to be dominated by one major activity; food-getting. All plants and animals must have energy in order to carry on their life tasks and maintain homeostasis. Energy is available only through chemical compounds we call “food”. Green plants can make their own food. They represent the food producer niche. Some animals live directly off the green plants. They fulfill the herbivore niche. Others eat other animals – the carnivore niche. Parasites live off the food obtained by other organisms. Scavengers use dead plants and/or animals, as do decomposers that help break down the wastes and dead bodies of all other organisms.

The original source of all energy going into food is the sun. This is because plants that have chlorophyll are able to combine water and carbon dioxide in the presence of light energy and produce sugar. This sugar can be converted to energy as the plant needs it. Of course, some of the sugar is converted into other complex chemicals that permit growth, reproduction, and other life processes.

A community, then, is really a group of plants and animals living together and obtaining food energy from somewhere in the community. Each community species assumes a particular food niche.

It is safe to say that food energy passes through a community in various ways. Each separate way is called a food chain.

An example is the prairie food chain:

 The grass manufactures food. The grass is called a food producer.  The grass is eaten by a prairie dog. It is then the first-order consumer.  A weasel may kill the prairie dog. It is then the second-order consumer.  A bird kills and eats the weasel. It is then the third-order consumer.  This bird, the hawk, will eventually die itself. The wastes and dead organisms are acted on by decomposers, which recycle the nutrients into the soil to then be used by plants. Decomposers may include molds, bacteria, mushrooms, and other fungi. QuickTime™ and a decompressor are needed to see this picture.

Food webs are a network of individual food chains. They give ecologists a realistic picture of the energy relationships in community.

Look at the example:

1. What organisms other than those shown might actually exist in this food web? Some organisms that aren’t shown, but might be in there are worms, maggots, antelope, deer, and humans.

2. What would probably happen to this food web if the grass on the prairie were suddenly to disappear? If the grass on the prairie was to disappear then the animals would die or relocate. The grass is the base of the food chain.

3. What would happen if everything remained the same except that the decomposers disappeared? If everything stayed the same, but the decomposers disappeared, the plants might not grow as fast or lush. There might not be as much biomass because the nutrients aren’t there. Reduce the number and mass of plants.

Food Pyramids

Organisms are not very energy-efficient. Each organism uses a great deal of the energy it takes in just to keep alive, grow, and maintain its homeostatic balance. This is why food is necessary in the first place. While undergoing its life functions, each organism loses energy to the environment in the form of heat. Because of energy loss at each step of food-energy transfer (food chain), the amount of energy available to the next level is decreased.

Ecologists use an energy (food) pyramid concept to help show the amount of energy that passes through organisms in the environment. Because of energy loss, fewer numbers of organisms can be supported at each succeeding food level. Thus as food energy passes form level to level in a food chain, the amount of energy available to the next-higher level decreases.

Example: Pond Food Chain

The number of single-celled algae (producers) runs into the millions; the crustaceans that eat the algae number in the thousands. The number of sunfish that feed on crustaceans is much less. Finally, the number of great blue herons that the sunfish can support may be QuickTime™ and a decompressor are needed to see this picture.

only one. QuickTime™ and a decompressor are needed to see this picture. Because of en