Species richness, community composition, and species distribution patterns in Aleutian plants

Abstract

We conducted an analysis of vascular plant distributional patterns in the Aleutian Islands to identify and quantify the impact of potential Aleutian Island distance dispersal barriers and ecological constraints. Data were collected from Open Access databases, printed floristic accounts, and independent collections made by the primary author to develop an Aleutian Islands floristic database. We documented 520 vascular plant species from 231 genera and 69 families across thirteen well-collected islands in the study area. The most common plant distribution pattern was 'Eastern', though it compared similarly to the 'Western' and 'Widespread' distribution pattern. We calculated and input a classic species assemblage dissimilarity measurement (Jaccard Index), a measurement of phylogenetic dissimilarity (UniFrac), and species richness into non-parametric algorithmic models (TreeNet) based on classic and Aleutians-specific island biogeography hypotheses. Aleutian plant species richness is strongly associated with the equilibrium model variables area and island isolation, as well as distance from the islands to the Alaska Peninsula, and island total stream length. Species composition, using cluster groups of the Jaccard dissimilarity metric between islands, is strongly associated with the landmass groups during the last glacial maximum, maximum island elevation, island isolation and island area. Species composition, using cluster groups of the phylogenetic-derived UniFrac distance metric, is associated with island area, distance from the islands to the Chukotka Peninsula, maximum island elevation, island geologic age, and island isolation. Altogether, this study adds to the growing body of studies extending the classical equilibrium theory of island biogeography to include additional important drivers of diversification on islands such as the landmass during the LGM, or human perturbations affecting extinction rates. Although this study included a compilation of over eighty years of collecting efforts in the Aleutian Islands, it highlights how few "complete" floras have been assembled. The conclusions presented here highlight research targets for gaining continued insights into diversity patterns across the Aleutians.