Today, entire populations of frogs, toads, and salamanders are vanishing without a trace. Recent studies implicate a wide array of factors. What is the second greatest cause of decline for threatened species?

Answer: Pollution

Explanation:

There are many population that is about to extinct or has been entered into rare species because of the conditions around them.

The entire population of the organism such as salamanders, frogs are vanishing due to several factors. These factors are killing, invasive species and pollution, climatic conditions, et cetera.

The first factor is killing of organism due to various reasons and second important factor is pollution due to which their growth is decreasing and they are dying.