托福听力TPO8文本(Conversation+Lecture)

　　TPO 8 Lecture 1 Animal Behavior

　　Pro：Well, last time we talked about passive habitat selection, like plants for example, they don't make active choices about where to grow. They are dispersed by some other agent, like the wind.

　　And if the seeds land in a suitable habitat, they do well and reproduce. With active habitat's selection, an organism is able to physically select where to live and breed. And because the animal breeding habitat is so important, we expect animal species to develop preferences for particular types of habitats. Places where their offspring have the best chance for survival. So let's look at the effect the preference can have by looking at some examples, but first let's recap.

　　What do we mean by habitat? Frank?

　　Stu：Well, it's basically the place or environment where an organism normally lives and grows.

　　Pro：Right, and as we discussed, there are some key elements that habitat must contain, food obviously, water, and is got have a right climate and basics for physical protection. And we were sound how important habitat selection is when we look at the habitat were some of the factors are removed, perhaps through habitats' destruction. I just read about a short bird, the plover.

　　The plover lives by the ocean and feeds on small shellfish insects in plants. It blends in with the sand, so it well camouflage from predator birds above. But it lags eggs in shallow depressions in the sand with very little protection around them. So if there are people or dogs on the beach, the eggs and fledglings in the nest are really vulnerable. Outing California weather has been a lot of human development by the ocean. The plovers are now is threaten species. So conservation is tried to recreate a new habitat for them. They made artificial beaches and sun bars in area inaccessible to people and dogs. And the plover population is up quite a bit in those places.

　　Ok. That is an incidence where a habitat is made less suitable. But now, what about the case where animal exhibits a clear choice between two suitable habitats in cases like that. Dose the preference matter? Let's look at the blue warbler.

　　The Blue warbler is a songbird that lives in the North America. They clearly prefer hard wood forests with dense shrubs, bushes underneath the trees. They actually nest in the shrubs, not the trees. So they pretty close to the ground, but these warblers also nest in the forests that have low shrub density. It is usually the younger warblers that next to the area because prefers spots where a lot of shrubs are taken by order more dominant birds.

　　And the choice of habitat seems to affect the reproductive success. Because the order and more experienced birds who nest in the high density shrub areas have significantly more offspring than those in low density areas, which suggests that the choice of where to nest does have impact on the number of chicks they have. But preferred environment doesn't always seem to correlate with greater reproductive success. For example, In Europe, study has been done of blackcap warblers. We just call them blackcaps.

　　Blackcaps can be found in two different environments. Their preferred habitat is forest that near the edge of streams. However, blackcaps also live in pine woods away from water. Study has been done on the reproductive success rate for birds in both areas, and the result showed surprisingly that the reproductive success was essentially the same in both areas--- the preferred and the second choice habitat. Well. Why? It turns out there were actually four times as many bird pairs or couples living in the stream edge habitat compared to the area away from the stream, so this stream edge area had much denser population which meant more members of same species competing for the resources. When into feed on same thing or build their nests in the same places, which lower the suitability of the prime habitat even though its their preferred habitat. So the results of the study suggests that when the number of the competitors in the prime habitat reaches a certain point, the second random habitat becomes just as successful as the prime habitat, just because there are fewer members of the same species living there. So it looks like competition for resources is another important factor in determining if particular habitat is suitable.