Ecology lecture. “Food Chains.”

Today I’m going to discuss some concepts and terminology related to ecology, specifically, ecosystems and, the classifications of organisms that live there, and, the food chains and food webs within ecosystems.

OK, let’s start with the definition of system: a system is a group of  elements or parts that work together. In any system, those different parts rely, that is, they depend on each other.
We have economic systems, systems of government, and in anatomy, the nervous system. Now in biology, we are going to look at ecosystems,  that is to say, places where organisms rely on each other and, umm, on their environment. Eco, meaning habitat or environment, comes from ecology, which is the branch of biology that studies how organisms interact with their environment. Uh, OK, so, in an ecosystem, the interdependent organisms are plants and animals, and their environment. An ecosystem can be small, like a pond, or even a small aquarium, or it can be big, like a forest or desert.

So, let’s take a look at this illustration of the Great Plains ecosystem. Can anyone tell me the biome this belongs to?  . . .. Yes, that’s right—it’s a grassland, otherwise known as a savannah. Remember, the characteristics of the savannah are: 1) it has an abundance of grasses, 2) it has hot summers, and 3) it receives enough rainfall so that it’s not a desert, but not enough rain for forests to grow.

OK, now, each species in this grassland ecosystem has a habitat and a niche. A species’ habitat is the place where that plant or animal lives within the ecosystem; for example, the buffalo, or bison, lives on the plains, whereas the gopher lives underground. Those, uh, places are those animals’ habitats. And the species’ niche is, the role it plays, in other words, the job it does, within its habitat. The bison eats the buffalo grass and moves from place to place. The flowers and grasses use the sun to produce their own food, through photosynthesis. You will recall that photosynthesis is the chemical process by which plants that contain chlorophyll use sunlight to make food from CO₂ and H₂O, I mean, carbon dioxide and water. As plants and animals interact, there’s a transfer of matter and energy. Now this transfer of energy is, what brings us to food chains and food webs. Within an ecosystem are many food chains, and interconnected food chains constitute, or, uh, make up, a food web.

OK, so let’s look at a food chain in our example of a grassland ecosystem and the terms that are used for the functions of different levels of plants and animals. There are three types of organisms in an ecosystem: producers, consumers, and decomposers. A producer makes its own food. Buffalo grass, clover, uh, dandelions, and wildflowers are all examples of producers in the grassland. At the next level is the consumer. A consumer is an organism that eats other organisms. And there are different levels of consumers, depending on their position in the chain: first order, second order, third order, etc. A grasshopper eats grass and clover, so it’s considered a first-order consumer. A prairie dog eats both grass and grasshoppers; therefore, in one food chain, it is a first-order consumer, but in another food chain, it is a second-order consumer. Hawks and snakes eat prairie dogs, so they are third-order consumers. Bison, or what are commonly known as buffalo, eat grass and clover, so they are first-order consumers.

All right, so we’ve classified the consumers in an ecosystem, and we’ve looked at the producers . . . Now we need to examine the last type of organism in the ecosystem, the decomposers. These organisms, um, decompose, that is, they break down what is left of dead organisms into substances that can in turn be used by producers. Bacteria, in other words, very small one-celled organisms, and fungi, or mushrooms, fall into the category of decomposers. And that completes the cycle of the food chain. On the mid-term, you’ll have to be able to define these terms, give examples, and explain relationships: ecosystem, food chain and web, producer, consumer, the classification of consumers . . . all the terms I’ve explained here today. Our time is up. See you next week.

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