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托福听力TPO8原文 Lecture 1-智课教育旗下智课教育
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TPO 8 Lecture 1
Animal Behavior
Pro: OK. 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 selection, an organism is able to
physically select where to live and breed. And because an
animal’s breeding habitat is so important, we’d expect animal
species to have developed preferences for particular types of
habitats, places where their offspring have the best chance of
survival. So let's look at the effect this 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’v discussed, there are some key
elements that a habitat must contain, food obviously, water, it’s
got to have the right climate and spaces for physical protection.
And we saw how important habitat selection is when we look at
habitats where some of these factors are removed, perhaps
through habitat destruction. I just read about a shorebird, the
plover.
The plover lives by the ocean and feeds on small shellfish,
insects and plants. It blends in with the sand, so it’s
well-camouflaged from predator birds above. But it lays its 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 nests are really vulnerable. Out in
California where there has been a lot of human development by
the ocean. The plovers are now a threatened species. So
conservationists tried to recreate a new habitat for them. They
made artificial beaches and sand bars in areas inaccessible to
people and dogs. And the plover population is up quite a bit in
those places.
Ok. That is an instance where a habitat is made less suitable.
But now, what about cases where an animal exhibits a clear
choice between two suitable habitats? In cases like that, does the
preference matter? Well, Let's look at the blue warbler.
The Blue warbler is a songbird that lives in 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’re pretty close to the ground, but these warblers
also nest in forests that have low shrub density. It is usually the
younger warblers that nest in these areas because the preferred
spots where there are a lot of shrubs are taken by the older,
more dominant birds.
And the choice of habitat seems to affect reproductive
success. Because the older, 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 an impact on the number of chicks
they have.
But a preferred environment doesn't always seem to
correlate with greater reproductive success. For example, In
Europe, studies have been done of blackcap warblers. We just
call them blackcaps.
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