Maximizing regional biodiversity requires a mosaic of protection levels

Protected areas are the flagship management tools to secure biodiversity from anthropogenic impacts. However, extent which adjacent with distinct protection levels host different species numbers and compositions remains uncertain. Here, using reef fishes, European alpine plants, North American birds, we show that composition of in Strictly Protected, Restricted, Non-Protected is highly dissimilar, whereas number similar, after controlling for environmental conditions, sample size, rarity. We find between 12% 15% only recorded areas, suggesting a non-negligible part regional occurs where human activities less regulated. For imperiled species, proportion reaches 58% 11% 7% highlighting fundamental unique role protected their conditions conservation.