The study looked at fish and bug types in rivers across the USA to see where there are the most species. They checked data from over 3,000 sites and found that the number of species went up when more sites were studied in each region. The researchers figured out the typical number of species at each site and then saw if some regions had more kinds of species than expected. They found that regions had more species on average than individual sites. The factors affecting bug and fish species were different; like temperature mattered for fish but not for bugs. Also, natural conditions and human activities influenced the number of species. This study gives us new knowledge about where biodiversity hotspots are in the USA and why they are important.