I've been stuck on how to reword all this can anyone help?

Question

"An invasive species is non-native to the ecosystem in consideration and causes or is likely to cause economic or environmental harm or harm to human health."

This is what I have so far but I'm not sure if it's any good- Invasive species are just one of many things that can disrupt and drastically change and ecosystem. They are non-native organisms, whose introduction can cause or is likely to cause harm to the economy, the environment and its inhabitants.

Answer 1

It's pretty good.
I'd make a couple of changes, though.

Invasive species are just one of many things that can disrupt and drastically change an ecosystem. They are non-native organisms, whose introduction is likely to cause harm to the economy, the environment and its inhabitants.

Note the words I deleted.

Answer 2

I would not reword it, but quote it (and cite the quote). Otherwise, your rewording is ok.