听力音频：
L1
讲座
1. What is the lecture mainly about?
Recent efforts to preserve particular amphibian species
Incorrect views about the diversity of amphibian species
Speculations about how the loss of species might affect ecosystems
Ecosystems that have been destroyed as a result of biodiversity losses
2. What point does a student make when he mentions the extinction of the dinosaurs?
Biodiversity can result in conditions that favor some species over others
Biodiversity preservation should be a principal focus of policy makers.
It is possible that not every organism is essential to maintaining life on Earth
The large size of some organisms increases their vulnerability to extinction.
3. Why do the speakers mention a shopping center and a hydroelectric dam?
To identify two construction projects that have had a negative impact on wildlife
To support the claim that it is difficult to reverse a reduction in biodiversity
To illustrate some of the issues involved in ecosystem management
To point out that small changes to construction plans can help protect biodiversity
4. The professor mentions claims made by public officials and others about the role of amphibians in controlling insects. What point does the professor make about those claims?
The claims are likely to lead to greater efforts to protect amphibians
Insufficient evidence exists to determine which claims are correct.
The claims fail to consider the effects of human activity on insect populations.
Officials often make claims without having consulted the most recent scientific evidence
5. What point does the professor make about snakes?
They perform a role similar to that of amphibians in some ecosystems
They provide a better indicator of ecosystem health than amphibians do
It is often difficult to determine the composition of their diet.
In some areas their populations have decreased alongside frog populations.
6. According to the professor, what impact do tadpoles have on some ponds and streams?
They indirectly lead to an increase in the diversity of pond organisms.
They provide certain fish with a critical source of food
They reduce some types of algae while stimulating the growth of other types
They deplete the nutrients available for other pond organisms.
