With a few exceptions, most of the food chains studied by ecologists have a maximum of how many links? 

Food chains are sometimes short because: 

Which ecosystem is characterized by frost-molded landscapes, extremely low temperatures, little precipitation, poor nutrients, and short growing seasons?

NPP (net primary production) in aquatic ecosystems is most often limited by:

Most plants lack symbiotic nitrogen-fixing microorganisms. An addition of nitrogen gas to these plants would:

Which of the following is NOT an abiotic component or condition of an ecosystem?

To be considered ______,an introduced species must begin breeding in its new location and spread widely from its point of introduction causing destruction.

Which ocean zone is basically the open ocean?

Determine whether the underlined portion of the statement is true or false. Habitat destruction is the primary threat to biodiversity.

Which type of forest is found in the broad belt of Eurasia and North America (2/3 in Siberia with the rest in Scandinavia, Alaska, and Canada)?