LB 22-228 - CANCELLED - Distributions of non-native snails and slugs within and among islands in the Hawaiian archipelago

Background/Question/Methods:

Limiting the establishment and spread of non-native snails and slugs (hereafter, NNSS) is of critical importance, as they threaten native biodiversity, agriculture, and human health. If we intend to prevent the establishment and spread of NNSS on islands in the Hawaiian archipelago, we must better understand invasion pathways and develop reliable predictors for NNSS distributions and impacts. Our objectives were to: (1) examine NNSS distributions, patterns of richness, and assemblage structure among and within islands to better understand pathways of introduction, and (2) test if native latitudinal origin (temperate or tropical) can predict NNSS species elevation distributions and impact, as most native biodiversity is currently found at higher elevations. To explore these ideas, we analyzed data from a decade-long effort that surveyed 733 sites across the six main Hawaiian Islands: 84 on Kauai (53 low elevation; 31 high elevation); 209 on Oahu (62, 147); 73 on Molokai (16, 57), 18 on Lanai (8, 10), 178 on Maui (40, 138), and 171 on Hawaii (43, 128).

Results/Conclusions:

Oahu (the main port of entry for goods) had higher NNSS richness and more unique species (species only found on one island) than the other islands. However, while NNSS assemblage structure differed among islands, differences were not driven by unique species or by species being found in a higher proportion of sites on Oahu. Additionally, we found larger intra-island differences in assemblage structure with low (0 to 500 m) and high ( > 500 m) elevation areas harboring distinct assemblages. We found that NNSS from temperate and tropical origins dominate assemblages at high and low elevations, respectively, on all islands. Patterns support a ‘hub and spoke’ model with NNSS first becoming established on Oahu, then becoming the source for other islands. However, within island factors associated with elevation are currently more important in structuring assemblages, suggesting that once NNSS become established in the archipelago, few barriers limit their spread to other islands. More effort is needed to prevent both initial introduction to the archipelago and inter-island transport of NNSS. Particular attention should be given to species from temperate regions as they especially threaten high elevation areas that harbor much of the remaining native biodiversity.