Kristen A. Borsari
To a fourth grader, habitat will be understood as a 'place where things live'. This simplistic view of habitat is a good place to start, merely by showing colorful pictures of different habitats the students minds will begin classifying the many possibilities of 'places to live.' A habitat shapes the way an organism (not excluding humans) lives. A habitat is a space where the exchange of energy can take place, from thermal radiation to heat conduction, water conduction and water loss, etc. This exchange of energy is what keeps a habitat and an organism from stagnation and consequently extinction.
Exchange is going to be a recurrent word, it benefits to spend some time discussing possible meanings of the word exchange. Students generally know that products such as clothing can be exchanged at a store for different clothing or money. This idea of receiving one service or desired object in return for a giving a service or object (including money) is a workable definition. Students will easily be able to say they love having money, but at one time or another they have
exchanged
that treasured dollar for a new game or toy. Exchange is about value. What is the value of a sandwich? Not much if one has just eaten. However, a day without food and that sandwich will be worth a great deal more, but just how much more? It will be important for students to understand that when animals
exchange
, they consider not the monetary cost but the physical cost of pursuing a food source- will the exertion expend more energy than the intake of the food will provide? Is there a great risk of predation (no sense going out to dinner if one ends up as the main course!)? While this is hard for the students to imagine, have them think of a time when their mom or dad did not want to go to the grocery store because of snow, they decided it would not be a good exchange- too much risk of danger for the food, it's better to go at a safer time.
A habitat also increases or decreases the need for this kind of exchange to take place. When the seasons change, this change in temperature alters the way different species spend the energy.
Fragmentation of Habitats
Habitat fragmentation is when an area of one habitat is made smaller and divided into smaller parts. This is what happens when a habitat is destroyed and parts of it remain. Habitat fragmentation is caused by roads, railroads, canals, powerlines, fences, fire lanes, pipelines and other barriers cut through habitats and inhibit species from moving freely. The real problem comes into play when the edge habitat is taken into consideration. What occurs on the outside edges of a habitat at far different that what occurs on the interior. The edge of a forest has much greater light and a greater possibility of being visited by a non-forest dweller than does the center of the forest. However, if a new cell phone tower needs to be put somewhere in that forest with two service roads for maintenance crews to access the tower from either side, that divides the forest in half. All along those cleared out service roads there are new edges to the forest, creating new interactions between edge species and interior species, interactions that have never occurred before and for which there are no evolutionary adaptations.
Lesson 1
Fragmentation is a more difficult concept for the children to understand. A hands-on approach helps to illustrate the idea and to make it a little more concrete. To introduce the idea, bake two identical cakes with plastic animal miniatures baked inside and show the children. Tell them they are both examples of the same habitat. Cut one of the cakes into 4-5 large pieces. Explain to the children that these are roads through the habitat and ask them if they think it changed what will happen to the animals in that habitat, brainstorm and list their ideas. Pull the pieces apart for the 'fragmented' and have children make detailed observations about what they see. This will get the students thinking how cutting up a habitat, like a cake, changes that space and limits the animals movements to other places within the habitat. from this introduction, the students should be able to generate the meaning of fragmentation. Explain how they need to decide
Lesson 2
Another, and more abstract way of helping the children to understand fragmentation take a roll of masking tape and section off large portions of the room, start with a few and add more 'roads' throughout the day. Label them as large, well-known highways and roads from the area: I-95, I-91, Merritt Parkway, etc. Explain to the children that they are now animals and that they're habitat has been fragmented, review their definition of fragmentation from the day before. Talk about the dangers animals face if they decide to cross highways or busy streets, if they are able to cross at all. The students will begin to make observations about which children will not be able to get to the pencil sharpener, the computers, their reading group, etc. Once these observations have been made, ask them what it would be like if the pencil sharpener was where their winter food source was, the computers were their water source and their reading groups were their fellow animals. Students will quickly realize what a problem fragmentation can be.
An example for discussion with the children: Your mom says, "You may play outside in the yard but stay three feet away from the street." That's fine, you have lots of room to play, draw a diagram on the board of a house with a front yard with a street, shade in an area to represent the three feet away from the street and label the remaining portion as 80 square feet to play (a quick review of area might be needed before discussion). Uh-oh, they need to put a street going along the side of your house where there was just an empty lot before. Draw this road on the diagram and show the children how much play room they lost. Tell them to imagine what it would be like to a have road going through the middle of their yard, and then show them how much play space they lose if they can't go more that three feet close to the edge of that road. Of course that could not really happen, and the children may object to the idea based on that, but it does help them to see how quickly square footage can be lost if edges are off-limits.
Habitat fragmentation can produce extinction of species in other ways. Some animals will not cross any kind of open space because of predators. When this happens species cannot disperse and create new populations. This also affects the plant life of a habitat because many plants depend on animals to disperse their seeds. If the animals are not dispersing, neither are these particular types of plants. Fragmentation is threatening in other ways. Many animals need a great deal of space to move about on to find adequate food. This is especially true as the seasons change and food and water availability also changes. By disabling animals to forage larger habitats and confining them to fragmented habitats, this forces overgrazing and eventual starvation of the species and loss of the habitat (Kareiva and Wennergren, 1995)