Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

[EX Q]: Exotic species are also called invasive species because they threaten other species.
[EX A]: Why are exotic species also called invasive species?

[EX Q]: Some plants have stolons, or stems, that run along the ground and are commonly called runners.
[EX A]: Some plants have stolons, or stems, that run along the ground and are commonly called what?

[EX Q]: Net primary productivity is an estimation of all of the organic matter available as food, and involves measuring biomass in terrestrial environments.
[EX A]:
What is an estimation of all of the organic matter available as food, and involves measuring biomass in terrestrial environments?