Question

why the economic impacts of invasive species on agriculture are generally easier to quantify than the economic impacts on invasive species on natural ecosystems?

Answer 1

In agriculture, invasive species interfere the growth of crops. They can use the water and fertilizer of crops and change the crop environment on their favour. So, the growth of crop is disturbed. This can be easily quantified economically.

In natural ecosystem, there are many species interacting with each others. The invasive species may face the competition with each species of the ecosystem. As the ecosystem remains in an equilibrium condition, so the invasive species can't herm them too much. For this reason, the impacts on invasive species on natural ecosystem can't be quantified easily.