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Why can tropical forests on different continents have similar communities but different species?

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World map using color coding to show the distribution of major floral kingdoms, subkingdoms, and regions. Key floral kingdoms include Boreal (green), Neotropical (pink), Paleotropical (yellow), South African or Capensic (purple), Australian (orange), and Antarctic (blue). Boundaries for subkingdoms, regions, and divisions are marked with different colored lines, and major regions such as Indoafrican, North American, and Malesian are labeled across continents. — biogeographic region Floral kingdoms, subkingdoms, and major regions of the world.

Tropical forests on different continents often feature similar biological communities because they share comparable climatic and geologic conditions, which exert similar evolutionary pressures on the organisms living there. This phenomenon leads to convergent evolution, where unrelated or distantly related species independently develop analogous traits or body plans to occupy similar ecological niches. For example, while the specific species differ, different continents may host ecologically equivalent animals—such as the African pygmy hippopotamus and the South American capybara—that have evolved to fill comparable roles in their respective environments.123

The reason these forests contain different species is rooted in their unique geologic histories. Factors such as continental drift and the presence of geographic barriers have historically isolated these regions, leading to the independent evolution of their respective flora and fauna. Consequently, while the "blueprint" of the community remains consistent due to environmental demands, the specific evolutionary lineages available to fill those roles vary by location.14