总论点：American Burying Beetle快灭绝的原因的三个猜测。
猜测三：scavenger mammals和burying beetle竞争食物，使得beetle食物越来越少。
- 听力主要观点提取 -
分论点二：在美国好几种甲壳虫和burying beetle相似，有着相似的生活模式。如果由于栖息地的碎片化就使得burying beetle数量减少，那么其他的甲壳虫也应该减少。但是其他类似的甲壳虫数量并未明显减少。
分论点三：burying beetle有一种特殊的特征，它们的嗅觉很厉害，它们能够在很远的地方就嗅到新鲜的食物。一旦发现食物，burying beetle会在食物上喷一种化学物质来掩盖住猎物的味道，这样scavenger就不能发现猎物，无法与burying beetle竞争食物。
The decline of the American Burying Beetle is very mysterious. Unfortunately, none of the theories you read about can explain why the species is dying out.
First, the pesticide theory is appealing because pesticides definitely can have a powerful effect on the environment. But in the northeastern US, the decline of the beetle population began several years before the first chemical pesticides were introduced there. And in some areas of the Midwestern United States, the beetle population survived for 20 or 30 years after chemical pesticides became widely used there. So in at least two regions of the United States which one had very large beetle populations that pesticides don't seem to have a direct link with the beetles' decline.
Second, there's a problem with the development theory as well. In the United States, there are a number of beetle species related to the American Burying Beetle that have a very similar mode of life and live in very similar habitats. The habitats of these related beetle species have also been fragmented by development. However their populations have not declined significantly. If habitat fragmentation hasn't caused a decline in their related beetle species, there is no reason why it should have caused the decline of the American Burying Beetle.
Third, in thinking about that competition theory, it's important to consider some special characteristics of the burying beetle that the reading did not mention. The burying beetles have a powerful sense of smell, and they can locate new food sources very quickly and from long distances. Once the Beetles find the food, they spray it with a special chemical that blocks its smell. These smell-blocking chemical keeps animals such as the scavenger mammals from being able to find the food. With these important advantages over other species, it doesn't seem likely that increased numbers of competitors could affect the beetle so drastically.