Invasive Species
Invasive species are plants or animals that spread fast in a new place and harm what lives there.
Think of it this way
A jar holds a mix of colored marbles in rough balance — red, blue, green, all sharing the space. Then you drop in a handful of orange marbles. The orange ones fill every gap fast and push the others to the edges. Soon the jar is mostly orange, and the other colors barely fit.
Explaining invasive species by grade level
Zebra mussels are tiny clams from far away. They got into lakes where they don't belong. They eat so much food that the fish go hungry. One small clam can cause big harm in a new place.