Recent and rapid assembly of an island species–area relationship threatened by human disturbance

The island species–area relationship (ISAR) describes how larger islands support more species. Studies on oceanic archipelagos have shown that ISARs assembled over millions of years have predictable shapes. However, it remains unclear how rapidly “classic” ISARs develop, and how they are formed on much younger systems. Here, we compile a dataset for the fish communities of 79 postglacial peri-Alpine lakes, and report that an ISAR with a classical shape has formed de novo in less than 15,000 years. Despite their very young age, these lakes exhibit an ISAR mirroring older systems, with a characteristic asymptotic shape. Immigration responds primarily to area and saturates, whereas speciation is primarily driven by lake depth. This young ISAR has been reshaped by anthropogenic activities, with species introductions erasing its upper limit. We demonstrate that ISARs can develop rapidly after habitat formation in semi-isolated systems, offering insights into the assembly of ecological patterns.