Vegetation associations and relative abundance of rodents on St. Eustatius, Caribbean Netherlands
Since the introduction of non-native rodents to the Caribbean region, these invaders have successfully occupied many, if not most, islands where they pose tremendous threats to native biodiversity and ecosystems. The objective of our study was to conduct a preliminary assessment of the relative abundance of invasive alien rodents in different vegetation types on the small Caribbean island of St. Eustatius, which has no native rodent species. We used tracking tunnels (baited ink cards placed in tunnels to identify the prints of animals lured to the card) to determine the presence of rodent species. We collected data in 25 25 m (n ¼ 13) and 5 5m (n ¼ 130) plots to determine whether elevation, number of tree species, canopy cover or other microhabitat components were correlated with rodent relative abundance. Invasive rodents are present in varying relative abundances in rural areas on St. Eustatius. House mice (Mus musculus) were not recorded inside the terrestrial protected areas, whereas black rats (Rattus rattus) were detected in all elevations and all but one vegetation type sampled. We determined significant correlations between some of the habitat characteristics, especially elevation, canopy height, leaf litter cover and number of tree species, which showed significant collinearity with 27 of 45 pairwise comparisons. There was a significant correlation between rodent relative abundance and the number of tree species, but not between elevation, number of living trees, number of shrubs, rainfall, canopy cover, canopy height, leaf litter cover, leaf litter depth, or slope. There was a significant difference within vegetation types for the frequency of traps containing rat versus mouse tracks. Our study was impacted by two major hurricanes in September 2017.