Okay kiddo, there's something called the "allee effect" which is kind of like when you're playing a game with your friends and you need a certain amount of people to help you win.
Sometimes in nature, some populations of animals or plants need a certain number of individuals around them to keep the group healthy and grow bigger. When there aren't enough of them around, things can start to go wrong.
For example, some animals might need to hunt or mate in big groups, so if there aren't enough of them around they might have a hard time finding enough food or partners. This can lead to fewer babies being born, or even to some of the animals dying off completely.
It's kind of like a snowball effect - once the population gets too small, it can be hard for it to grow again because there aren't enough individuals to help each other out.
Scientists study the allee effect so they can understand how to help these populations of animals or plants survive and thrive.