3 Tutorials that teach Food chains and food webs
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Food chains and food webs

Food chains and food webs

Author: Jensen Morgan

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Food Chains and Food Webs

Source: Earth PD http://bit.ly/1ESoBKp Trophic Pyramid CC http://bit.ly/1OdRpTs Food Chain CC http://bit.ly/1EbtPE8 Food Web PD http://bit.ly/1AZryWm

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Hi, I'm Jensen Morgan. We're going to talk about some great concepts in environmental science. Today's topic is food chains and food webs. So let's get started. We're going to talk about trophic levels, food chains, and food webs. Trophic means feeding and nutrition.

Trophic levels in an ecosystem are essentially the hierarchy of feeding and trophic interactions, including the transfer of energy, carbon, and nutrients from one organism to another. This is a trophic pyramid. While it shows up to tertiary consumers, it is possible for there to be a maximum of six trophic levels in an ecosystem. Trophic pyramids illustrate how energy is passed from one level to the next.

Primary producers transform energy from sunlight into biologically useful energy or sugars. Primary productivity is the rate at which producers can obtain energy from sunlight, and it is dependent on sunlight, temperature, and moisture. Of the sunlight that reaches Earth's surface, less than 1% is converted into energy through photosynthesis. The energy captured by primary producers is then moved up the trophic pyramid as higher level consumers eat organisms from the levels blow it.

Secondary productivity is the rate at which consumers convert organic material into biomass. In this sense, biomass describes the dry mass of organic material in an organism, which can be used for energy. However, secondary productivity introduces no new energy into the system. It is entirely dependent on what was produced by primary productivity.

As energy moves up the pyramid, only 10% of energy from the previous level is captured. The other 90% is lost as metabolic heat due to inefficient energy transfer. This loss of energy going up the pyramid is what limits the maximum number of trophic levels to six. There's not enough energy to sustain any higher level.

Important to note, it is far more energy efficient for humans to consume organisms at lower trophic levels, like primary producers, than at the higher levels. Food chains are representations of who eats whom in an ecosystem. See this diagram here? Trophic levels help us distinguish between types of organisms.

That plant is a primary producer, also known as the primary trophic level. On land, they are usually plants, while in the oceans they can be plankton, photosynthetic bacteria, and unicellular algae. That worm could be considered both a primary consumer because it is eating that plant, or a decomposer because it is recycling dead biomass from the plant.

If it is considered a primary consumer, than it is part of the second trophic level. The secondary consumer in this food chain is the turtle, and it is the third trophic level. Finally at the top, the eagle is our tertiary consumer.

While it's not shown in this diagram, that eagle will eventually die and be consumed by decomposers, such as bacteria, which will transform into nutrients to begin that chain again. In general, most predators consume prey that is smaller than they are. So as one goes up the food chain, organisms get larger and larger. Also the larger the organism, the more space is required for that organism to find food, which results in lower population numbers at higher levels of the food chain.

Food webs are diagrams of trophic interactions. They essentially diagram ways that organisms obtain energy from other organisms. The majority of food webs are quite complex and involve many organisms and relationships. As you can see in this food web, these are at the first trophic level. These are the second, also called primary consumers. And these are part of the third trophic level.

Now let's have a recap. We talked about trophic levels, food chains, and food webs. Well, that's all for this tutorial. I look forward to next time. Bye.