介绍:
TPO 1 Lecture 4 Biology
Narrator
Listen to part of a lecture in a biology class.
Professor
For today’s discussion, we’ll review the case study on how some animals have behaviorally adapted to their environments. Now you had to read about two animal species, the Eastern marmot and the Olympic marmot. Marmots are rodents. They are large ground squirrels, about the size of an average house cat. And they live in a variety of habitats. And even though they spend the significant portion of the year hibernating, according to this case study, marmots are still considered excellent subjects for animal behavioral studies. Why is that?
Student
Well, when they are not hibernating, you can find them in open areas. And they are pretty active during the day, which makes them easy to observe, right?
Professor
Uh-huh, so first let’s discuss the Eastern marmots. They reside throughout the eastern region of North America where there is a temperate climate, where the growing season lasts for at least five months of the year, which is when they do all their mating, playing and eating.
Student
Oh, I see. At first I wasn’t sure what growing season meant, just from the reading. But now I get it. It's the amount of time it takes for them to grow, right? So it would be five months?
Professor
Umm? Oh, uh… I’m sorry but no. It has nothing to do with that. It's not about the time it takes for Eastern marmots to grow. It’s when the food is available. That is when it’s not covered in snow and there is no frost covering the grass and, umm, vegetative parts of a plant’s herbs and the flowers the marmots like to eat. So growing season refers to the availability of the food they eat, OK? So now how would you describe the Eastern marmots’ social habits?
Student
Well, they are really territorial, and loners, and just so aggressive even with other Eastern marmots. And their mating ritual is just so impersonal.
Professor
Uh-huh? Now when they emerge in the spring from hibernation, the mating process begins. For them, well, they come together to mate and then they go their separate ways. Then about six to eight weeks after birth, the offspring leave their mothers.
Student
Really? Just six weeks? Is that possible for the offspring to make it on their own so young?
Professor
Well, it’s not as if they aren’t ready for the real world because they are. Remember, they mature quickly and the weather’s nice. Also they live in open fields where there is lots of edible vegetation. So roughly six weeks after birth, Eastern marmots are just old enough to take their chances of surviving in the temperate environment. So how does this relate to their behavior?
Student
Oh, I get it. Since the climate’s not too bad, the Eastern marmots don't have to rely on each other too much and they really don't need to stay together as a family to survive either.
Professor
Uh-ha. Any contrast, the Olympic marmots? What about them?
Student
Well, they live together as a family and take care of their young until they are at least two years old. They’re really friendly with each other. And what I really like is that they even have greeting ceremonies. And they are not at all aggressive and territorial like the Eastern marmots. So their social behavior is so different from Eastern marmots because of the climate where they live? That seems so bizarre.
Professor
Well, the Olympic marmots inhabit meadows high in the Olympic Mountains where the weather conditions are much harsher. So there is a lot more wind and snow. The growing season only lasts about two to three months. So in that much shorter period of time, all the Olympic marmots, male and female, eat, play, work and nurture the young together. Because the climate is so harsh, cooperation increases the survival rate of the Olympic marmots. They keep their young at home until they are physically able to survive on their own. This could explain why the social behavior of the Olympic marmots is so unlike that of the Eastern marmots.
