Why might ecologists be concerned when new invasive species arrive in an ecosystem?

Ecologists are deeply concerned when there are invasive species in an ecosystem because they have the ability to colonize that particular ecosystem, disrupting its normal routine or functions. These species may arrive naturally through migration but human activity actually poses the greatest threat in bringing invasive species into different locations.
Hope this helped.

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.