Let's imagine we have a bunch of different animals living in a big playground. Some are really small like ladybugs, and some are really big like elephants. Species richness means how many different types of animals there are, and body size refers to how big or small each animal is.
Now, let's say we want to know if there are more different types of animals when there are more big animals or more small animals in the playground. Scientists have studied this question and found that there are usually more types of animals when there are more different sizes of animals.
For example, if there are only small animals like ladybugs and ants in the playground, there may be less species richness than if there are small animals like ladybugs AND big animals like elephants. This is because different sizes of animals can use different resources (like food or shelter), so having a variety of sizes can support more types of animals.
Overall, having a mix of small and big animals can help to support a richer variety of animal species.