What do you think invasive species means? It means a plant or animal that invades a food web and messes it up.

What does it mean to invade something? To go into something and disturb its normal life.

Can animals invade? Yes, I know this because the northern pike is an invasive species so you can catch a lot of them and keep a lot of them. 

What about plants? Yes, weeds are invasive species because they come in and steal water and nutrients from other plants.

How might invasive species affect other organisms in their environment? They could kill or eat the other animals and mess up the food web.