Who here has a pet? What type of pet do you have? (Write a list of student pets on the board.) Let's group these animals into different categories. (Have the class work in pairs or small groups to divide the list into different categories. After a few minutes, have the groups share their categories with the class. Example categories: big animals vs. small animals, animals that live inside vs. outside, etc.) How did you decide on your categories? Did you find things that some of the animals had in common? It is important to be able to classify objects into categories so we can study and understand all the patterns of similarities and differences between different living and nonliving things in the world.

Scientists have developed categories to separate different animals as well. They do this in a similar to what we just did — by finding physical characteristics that are unique to certain groups. Of course, there are other ways to classify animals. We could have separated the animals into groups by their behavior or how they get their food. For example, some animals are known as predators and others as prey. Have you heard of those before? A predator is an animal that hunts other animals to eat, such as a fox. Prey is the animal that is hunted and eaten, such as a rabbit.

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Another way to classify animals is by what type of food they eat. Different animals eat different things. An herbivore is an animal that only eats plants. A carnivore is an animal that only eats meat or other animals. Would a meat-eating animal be a predator or prey? (Answer: A predator.) What about an animal that eats both plants and meat? We call these animals omnivores. An omnivore is an animal that eats both plants and other animals. (For example: Skunks are omnivores; they eat insects [bees, grasshoppers, larvae], bird eggs, baby birds, amphibians, as well as fruit and berries.) Which type of animal are you?

Now, why would an engineer care about animals? Engineers work with animals in many different ways. Some engineers study specific animals in great detail and then imitate them to design a technology for use by humans. For example, chemical engineers look at sharks and how they defend themselves from bacteria in the ocean to create new antibiotics to keep humans healthy. The tuna inspired a new sea-going vessel that takes less energy to move. The wings of an airplane were originally designed after the wings of a bird. We call this biomimicry.

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Environmental engineers want to protect animal homes for all kinds of animals, from fish to elephants. They might be involved in environment and resource management, and design technologies to help restore a habitat that was destroyed by natural or human caused disasters. They might work on an environment that has been wrecked by a flood or tornado, or a river that was polluted by a factory. It is important that engineers learn as much as possible about the animals they are working to protect. They must know what types of food each animal in that environment eats as well as its interaction with other animals and its ecosystem.

One way that engineers study how animals interact in an ecosystem is by creating a model of it. A biodome is a model that is designed to represent a particular environment and the community of organisms that live there. When constructing a biodome, engineers must be very careful with interactions between animal predators and prey. Why?

Nature exists through a delicate balance of predators and prey. Animals and plants are interdependent on other species to ensure their existence. A change in one population has an effect on all the other populations in the food chain. For example, grasshoppers eat grass, frogs eat grasshoppers, and snakes eat frogs. If there were so many grasshoppers that there was not enough grass for them to all eat, some grasshoppers might starve and die. A reduction in the grasshopper population would mean that less grass would be eaten. A smaller grasshopper population would also mean that there was less food for the frogs, and that some of the frogs might die. With fewer frogs the grasshopper population may increase. It may not be good to put animals in the biodome that are eaten to extinction by the other animals. Engineers incorporate predators and prey into their biodomes to provide the necessary environment and foods for animals and plant to survive in balance. Today, we are going to learn a little more about animal classification and animal interactions. This will help us think like engineers who are working to design or protect a specific environment.

Why do we need to classify things? It is important to be able to classify things so we can study how they work together or know where they belong. We organize things according to their patterns of similarities and differences. Today, we talked about classifying animals, but what are some other things we could classify? (Possible answers: Plants, books, minerals, toys, students — almost anything.)

What are some of the ways we can classify animals? We can classify them by their physical characteristics, where they live, or even what or how they eat. We learned that a predator is an animal that hunts other animals to eat, such as a fox. Prey is the animal that is hunted and eaten, such as a rabbit. An herbivore is an animal that only eats plants. A carnivore is an animal that only eats meat or other animals. An omnivore is an animal that eats both plants and other animals.

Ongoing predator-prey population changes are natural within an ecosystem. What happens to predators when there is a lot of prey for them to eat? (Answer: They thrive and their numbers increase.) What happens when the amount of prey decreases? (Answer: Some die; their numbers decrease.) Sometimes humans upset the natural balance of the predator-prey relationships, when they alter habitat, displace wildlife or favor one species over others. As a result, sometimes we need to protect a species to keep it from becoming extinct, or arrange for regulated hunting and trapping to keep other species from overpopulating.

What types of engineers might study animals? Environmental engineers study animals to help them figure out the best way to restore habitats and environments that have been damaged. These engineers might also help others study animal interactions in environments and ecosystems by designing and creating biodomes, or small models of environments and the many organisms that live together in balance. Many other engineers use biomimicry to learn from and imitate the characteristics of animals, as they develop new technologies that help humanity and our planet.

Have students calculate the animal population density of their biodome: population density = (# of animals/insects) divided by area (length x width).

Ask students to investigate how engineers are involved with animal biology. Offer extra credit to students who write a paragraph about how this knowledge can be applied.