Climate change and conservation of Caladenia orchids in Western Australia

Understanding how species distributions are being shaped by current rises in atmospheric temperature is of immediate conservation importance. Orchids are a globally threatened plant family, with many species having narrow ranges and low abundances that heighten extinction risk due to rising atmospheric temperature. Using 26 rare and common Caladenia orchid species in Western Australia, we first performed a conservation assessment by calculating the proportion of populations that currently occur in conservation areas. We then compared current range extents with past and future climate scenarios. We performed a niche overlap test with a future climate scenario to test how the current population level climatic niche of these species will change. As some of these orchids frequently hybridize, we then quantified how ecogeographical isolation will change under future climates. Only 27% of all Caladenia populations are currently found in protected areas. Most species had reduced range extents in historically warmer climates. However, only three species will experience range extent contractions under future climate scenarios. The current population climatic niche has a 36% overlap with future climates, indicating that current population level climate conditions will change. Ecogeographical isolation will potentially increase in hybridizing species, thereby acting as a stronger barrier against hybridization. As Caladenia species evolved in seasonally dry conditions, this suggests that there is potential preadaptation to survive under elevated temperatures. Despite their physiological tolerances to elevated temperature, conservation of Caladenia species will depend on the availability of habitat to allow migration within future range limits, and the presence of their key mutualists.