Why are invasive species dangerous to the environment?
they pollute the environment.
they are always predators.
they threaten biodiversity.
they bring abiotic factors.

Option C, They threaten biodiversity.

Explanation:

Invasive species are dangerous to the environment as they intrude into any biodiversity and spread up to such an extent that they cause death of native species such as an algal boom in any lake,  spreads in an uncontrollable way and covers the entire lake surface which disrupts the oxygen supply and hence leads to death of organisms with in the lake.  

Death of organisms at a large scale lead to loss of biodiversity in an ecosystem as is the case with the lake.

answer; hydrologic cycle;