This topic cannot be proven nor disproved easily due to the sheer number of species out there in the regions under comparison. The Amazon river system spans several countries. I’ve kept some tropical fishes originated from the Amazons. Those fishes may not come from Brazil. It may be Peru or other countries. Like for example Peacock bass. Populations of these fishes look the same to me, but scientists may separate them into species. If a particular population is in brazil exclusively and is named a species instead of a subspecies, that will give an impression there is endemism. We see examples in Arrow frogs, orchids, bromeliads. Some plants and creatures evolve to be slightly different due to isolation by physical barriers such as rivers or mountains, deserts.
How is endemism rate calculated ? I guess it is based on some assumptions. I think I’m not going to do those maths. Island endemism appears to be true. Isolation in the Amazons is likely, as rivers can have oxbow lakes. and there are semi arid almost desert regions in Brazil. However, bigger Islands such as Madagascar or Borneo may have a bigger number of unqiue species. In modern times, species may have reached various continents bypassing the isolation formed by oceans.
I mean that a species which is naturally endemic to a country is marked as “native” rather than “endemic” if it has been introduced to another country.
Thanks.
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