Shark Attack!

Lesson Plan - Get It!

Audio:

To understand what is causing the increase in shark attacks, you need to investigate the lifestyle and relationships, known as the ecology, of the organisms at Surf Beach.

Ecology is a branch of biology that deals with the relations of organisms to one another and their physical surroundings. Ecologists use food webs — a series of food chains — to diagram the relationships of organisms in a community.

A food chain is a hierarchical series of organisms, each dependent on the next as a food source. A simple food chain starts with the primary producers.

Primary producers are autotrophic organisms that can synthesize food from organic compounds. There are two types of autotrophs: photoautotrophs and chemoautotrophs.

Photoautotrophs, such as plants, use energy from the sun, combined with carbon dioxide and other nutrients from the soil, to make sugar for food. Plants store the extra sugar, which makes them a perfect start to a food chain. Other common photoautotrophs include algae and cyanobacteria.

Chemoautotrophs use chemosynthesis, which requires chemical energy to build organic compounds. Bacteria found near deep-sea vents where there is no sunlight are chemoautotrophs.

The other organisms in this food chain are all heterotrophs that must consume food to survive. Heterotrophs are more commonly called consumers. You are a consumer!

Consumers are differentiated by their relationship to the producer in categories called trophic levels.

In the food chain pictured above, you can see that the worm is the primary consumer, the owl at the top of the food chain is the final consumer, and there are several other trophic levels of consumers in between.

• Can you think of anything missing from this food chain?

You could have added several things to the food chain. Think about your diet.

• Do you only eat one thing?

Most likely, you eat a variety of things. Even if you only eat hamburgers, you eat beef, a primary consumer, and lettuce or bread from producers. Most consumers eat from a variety of trophic levels.

That's why ecologists use food webs to show the more complex interactions in nature. A food web is a compilation of interconnected food chains illustrating organisms' interactions.

Ecologists use food webs to trace energy and other compounds moving through the environment. In physics, Newton's first law is the law of conservation of energy, which more or less states that energy cannot be created or destroyed.

Energy is essential to trace in a food web because it is the limiting factor in the length of a food chain. When one organism consumes another, it gains energy; however, transferring that energy is inefficient.

Once energy enters a trophic level, it can be used or stored as biomass.

Only the stored energy can be transferred to the next trophic level. As you move up the food chain, the rule is that only 10% of the energy from the previous trophic level can be passed on to the next trophic level.

Besides energy transfer, other compounds can be transferred between trophic levels.

The compounds of most concern to ecologists are toxic pollutants, such as pesticides. Pollutants are of no value to the consumer and are therefore excreted or stored as part of the biomass.

Bioaccumulation occurs when a pollutant is absorbed faster than it is excreted and, therefore, becomes more concentrated and more toxic in organisms as you move up the food chain.

Organisms that live at the top of the food chain, like sharks and humans, are most impacted by bioaccumulation, so monitoring and maintaining safe levels of pollutants is essential.

Continue to the Got It? section to examine the links in the food chain.