The researchers studied how dispersal and different environments affect the variety of species in an area. They looked at how species are either replaced or added in different habitats. They found that when there is a lot of movement between areas, new species replace existing ones. But when there is less movement, species are added in a more organized way. In polluted areas, the variety of species decreases, especially when there is little movement between areas. In areas with similar environments, species are replaced more often than added. This shows how the movement of species and the type of environment can change the variety of species in an area.