Food Webs

Food Chain vs food web Many organisms are part of more than one food chain and this creates an interconnected network of food chains, which resembles a web. A food web is a network of food chains that have some links in common.

Reading a Food Web Food webs are just several food chains put together. You read a food web just like you read a food chain. The arrows represent the energy flow from one organism to another.

Competition Competition is the struggle between organisms for the same resource. Organisms compete for food, water, sunlight, and space.

Why are different food chains often linked together? Organisms can be food for many different animals. Also animals can eat more than one type of organism. This causes food chains to overlap creating food webs.

Changing Food Webs If a population of one organism in a food web changes, all the other populations in the food web can be affected. When top carnivores are removed from a food web, prey populations are not longer controlled. Now prey organisms can reproduce without limits. The prey populations will increase and more producers would be needed for their food supply. More and more producers would be eaten by the increasing population and that would lead to less producers.

Red Tide Single populations can grow out of control. A red tide is a sudden explosive growth of single-celled algae in coastal areas. Red tides can occur when nutrient- rich deep water gets brought to the surface after a storm. With so many nutrients in the water, the algae population quickly grows. Toxins produced by the algae can cause the organisms that eat the algae to die. This population change also reduces the food available for fish predators.

Kelp Forests Kelp are giant algae masses. Some kelp forests have been greatly changed by removing the sea otter. Sea otters eat kelp. In the 1800s the sea otters were hunted for their fur. As the population of sea otters decreased the population of sea urchins increased. Sea urchins chew off kelp from the sea floor. As the population increased the kelp floated away. Small fish could not survive without the kelp and died. The organism that depended on the small fish died. Without the sea otter population to control the size of the sea urchin population, the kelp forests almost disappeared. Even if an animal like a sea otter does not eat kelp, can a shortage in kelp affect its food supply? Explain. Yes. Sea otters eat sea urchins, which eat kelp.

Why is it important to have predators in an ecosystem? Predators help to control the size of the prey population.

What occurs when a top carnivore is removed from a food web? Prey populations begin to increase. As they increase in number they consume more producers. When the producer number is low, it causes a food shortage for increased herbivore population. They then begin to die out.

What might happen if a population of producers was removed from a food web? If producers are removed from a food web, there would not be enough food to support the herbivores or primary consumers. When the number of primary consumers is reduced, the secondary consumers would not have enough food sources and they would also become reduced. .

Change in ecosystems by new species Humans can introduce new species to an ecosystem. What is an exotic species? This is a non-native plant and animal species that have been introduced into an environment. These plants and animals can threaten native species.

How new organisms can change food webs Humans introduced zebra mussels into freshwater ecosystems in the United States. These are an exotic species. Zebra mussels are native to eastern Europe and Asia. They were accidentally brought to the U.S. These mussels can attach to ANYTHING! They hitched a ride on ships coming from Europe and Asia. Zebra mussels are tough competitors and reproduce quickly. They also consume large amounts of food. They caused the native species to decline.

Greyback cane beetle and french’s cane beetle These two types of beetles destroyed sugarcane fields in Australia (1935). Scientists brought in cane toads from South America to help control the beetle population since these toads ate beetles. This did not work. The toads did not eat the beetles. They did eat just about everything else like frogs, rodents, birds, and lizards. They did not have a predator so the cane toad population grew out of control. This changed the entire food web and these toads are still causing problems for the native wildlife today.

What are some examples of pests? Roaches Mice Snakes Scorpions Spiders Ants

What type of animal is a zebra mussel? Invertebrate, freshwater mussel Were zebra mussels always found in the United States? No, zebra mussels are not native to the United States.

What would happen if a new animal were brought in to control a specific group of pests in an area? The pests’ food web would be disrupted; other organisms’ food webs may also be changed.

Why are exotic species a problem for some native plants and animals? The exotic species can eat native organisms or they may compete with the native organisms for resources such as food and water.

What are some ways to prevent the introductions of exotic species into an ecosystem? People should make sure if they are traveling from one area to another that their vehicle does not carry live organisms. Boats, airplanes, and other vehicles should be inspected. These vehicles should be cleaned to remove any organisms.

What is an energy pyramid? An energy pyramid is a model that shows how much energy flows through a food web.

Energy Pyramid Producers are at the bottom level. Consumers make up the next levels. They get energy from the organisms in the levels below them. Only 10 percent of the the energy from one level is passed on to the next level. The bottom of the pyramid represents the largest level because it contains the most organisms and it contains the most energy. In any ecosystem, the number of producers is greater than the number of herbivores. There are many more herbivores than carnivores. There are fewer numbers of organisms and less available energy at each higher level of the pyramid.

What does an energy pyramid tell us about food webs? There are many more producers than there are top-level predators. A food web shows relationships between individuals, but it doesn’t represent relative populations size.

In a Mississippi swamp ecosystem, would you expect an alligator or a fish population to be larger? Explain. The fish population should be larger, because they represent a lower level on the pyramid.