Mapping and modeling the distribution of the rosy wolfsnail, Euglandina spp., in Hawaiʻi

Abstract

The rosy wolfsnail (Euglandina spp.) is a carnivorous, highly invasive land snail introduced from Florida to Hawai‘i as biocontrol for the giant African snail (Lissachatina fulica). Listed on the International Union for Conservation of Nature’s “100 of the World’s Worst Invasive Alien Species”, Euglandina spp. have been implicated in the extinction of over 130 Pacific Island land snail species since their release in the mid 1900’s. In Hawai‘i, Euglandina continues to threaten the islands’ imperiled native land snail species–a fauna renowned for its extraordinary diversity and endemism. Land snails are an understudied taxa and little is known about the ecology and spread of Euglandina spp., leaving resource managers with a lack of information. To assess the current distribution of Euglandina spp. across the main Hawaiian islands, a distribution map based on presence-absence data collected during field surveys (2004-present) by the Bishop Museum Malacology Collection and their partners was developed using a geographic information system (GIS). To predict suitable habitat and the potential spread of Euglandina spp. based on elevation, air temperature, and rainfall across Hawai‘i, species distribution models were run using both generalized linear modeling (GLM) and boosted regression trees (BRT). Results showed elevation, air temperature, and rainfall were all significant factors correlated to distribution. Both GLM and BRT models showed areas of suitable habitat for Euglandina on all of the main Hawaiian Islands, with the greatest likelihood of presence in warmer, low-moderate elevations, and on the windward, wetter sides of some islands. For islands mostly under 1000 meters, such as O‘ahu and Kaua‘i, avoidance of Euglandina spp. is unlikely. Only high elevation areas such as Mauna Loa, Mauna Kea, and Haleakalā on Hawai‘i and Maui may be inaccessible to spread. Understanding the current geographical distribution of Euglandina allows us to target ideal locations for predator-free exclosures and identify native snail populations that may be most vulnerable. This study will help to implement effective, island-specific land snail management approaches that consider the potential of Euglandina spp. to inhabit nearly all terrestrial habitats in Hawai‘i within the coming years.