The island marble butterfly (IMB) is an extremely endangered subspecies of the large marble (Euchloe ausonides). It is endemic to the coastal prairies of the northern Salish Sea. Estimates by the National Park Service (NPS) and others suggest that the population is as low as 200 individuals. The IMB is now only found in American Camp, a roughly three-square-kilometer area of San Juan Island National Historical Park.

The IMB relies on coastal prairie environments to survive. Unfortunately, those environments have declined significantly since European settlement of the Salish Sea area - the Washington Department of Fish and Wildlife (WA DFW) estimates that about 97% of the region's costal prairies have been destroyed. Without extensive habitat restoration efforts, the IMB cannot survive indefinitely.

I created habitat suitability models to find more habitat for the butterfly in the Salish Sea ecoregion. These models indicate that the fundamental niche of the butterfly is primarily limited by precipitation and that suitable habitat for the butterfly is limited to areas where its host plants can grow within the rainshadows of the Olympic Mountains and Vancouver Island Ranges. Much of the highest-quality potential habitat is located in the San Juan Islands and on Whidbey Island, but additional potential habitat exists on the Olympic Peninsula and Vancouver Island. Because most potential habitat for the butterfly is located in and around agricultural fields, cooperation with farmers is essential for the butterfly’s conservation. While the island marble may be able to tolerate warmer and drier summers, the indirect effects of climate change such as shifts in phenology and an increase in extreme weather events such as storm surges pose the highest long-term threat to the butterfly’s survival outside of habitat loss. Preserving the butterfly’s current habitat and creating more habitat for the butterfly, especially on San Juan Island, should be the first priority of conservation practitioners working with the species.