The relationship between how many animals there are in an area and how big their habitat is was studied for lizards, birds, and mammals worldwide. The idea that more animals mean a larger habitat was not supported by the data. The size of the habitat was more related to the type of environment the animals lived in. The number of animals in an area was influenced by different factors for each group, and not directly linked to the size of their habitat. The previous idea that more animals mean a bigger habitat might not be true, and the reasons for animal numbers and habitat size might be separate.