Chapter 1 Lesson 3 What is a food web?

Vocabulary Food web: shows how the food chains in an ecosystem connect Competition: struggle between organisms for the same resource Energy pyramid: a model that shows how much energy flows through a food web

What is a food web? A FOOD WEB SHOWS HOW THE FOOD CHAINS IN AN ECOSYTEM OVERLAP AND CONNECT. Take a look at the chains below. In what ways are they connected?

Food webs Food Web Video: Click ME! A food web shows the roles that one organism can have. An example would be that a snake is a predator of a mouse and at the same time is prey for a hawk.

Competition in the web Look at the food web. Can you see any animals that are competing for food?

Competition The snake and the hawk both depending on the mouse for food. They are competing! Competition is the struggle between organisms and the same resource. The resource could be food, water, space, or any other need. The animals will need to compete for the resources. One population may win over another.

Plants compete too! Plants that are trying to grow will try to compete for sunlight, nutrients, and space. An oak tree reduces competition because squirrels take these seeds far from the parent plant . If the acorn sprouts, the young seedlings don’t compete with the parent tree.

Competition What animals may be competing for needs in the food web?

Food web action Game: Click ME! Click ME TOO!

Georgia’s longleaf pines Changes have occurred in the longleaf pines forests of the U.S. Millions of pines were cut down for their timber. Animals depend on the pine ecosystem, if the pines die out, the scrub oak takes over. It will grow and compete with pine seedlings for sunlight. The ecosystem and food web then changes and certain animals become fewer.

Gopher tortoise One important animal of the longleaf pine food web is the gopher tortoise. It eats grasses and other plants (herbivore) and digs burrows to live in. These burrows provide shelter for other animals (snakes, mice, frogs). Over 250 kinds of animals can live in ONE burrow! If the gopher tortoise doesn’t have enough plants to eat, it won’t survive, leaving many animals homeless.

New organisms changing food webs Food webs can change when animal populations change. What else causes changes? In 1935, 2 insects destroyed Australia’s sugarcane fields. The greyback cane beetle and the French’s cane beetle were to blame! Scientists brought in the cane toads as predators to destroy the beetles.

Results of the sugar cane field Scientists thought the toads would eat the beetles. They also thought lizards and birds would eat the toads. They hoped this would keep the toad population from growing too fast. Scientists were wrong! The toads ate frogs, rodents, birds, lizards, and even pets. Animals didn’t want to eat the toads because they tasted bad!! Without any predators, the toad population grew and disrupted the whole food web.

Energy pyramid (video) An energy pyramid is a model that shows how much energy flows through a food web. Producers are at the bottom getting energy from the sun. They use about 90% of this energy to live and grow. They store the other 10% in parts of their stems and leaves. The upper levels of the pyramid are consumers, 10% of the energy stored in plants passes to them. Omnivores and carnivores get energy from the level below them Only 10% of the energy is passed on to each level. Food webs have more consumers than producers!