The worms alter the ecosystem physically, chemically, and biologically.

Two other introduced species, house cats and house mice, do not alter the ecosystem but directly impact the vole.

For example, birth rate, death rate, migration, and density-dependent predation indirectly alter the ecosystem state by changing population density (a state variable).

Locations where small populations of snail darter are in place should be monitored for invasive species and possible influences from rivers or tributaries that could alter the ecosystem dramatically.

The harvesting of the old growth trees altered the ecosystems they dominated.