Support vector machines to map rare and endangered native plants in Pacific islands forests

a r t i c l e i n f o Keywords: Rare species Support vector machines (SVM) Random forests (RF) Biodiversity Digital elevation model (DEM) Vegetation mapping It is critical to know accurately the ecological and geographic range of rare and endangered species for biodiversity conservation and management. In this study, we used support vector machines (SVM) for modeling rare species distribution and we compared it to another emerging machine learning classifier called random forests (RF). The comparison was performed using three native and endemic plants found at low-to mid-elevation in the island of Moorea (French Polynesia, South Pacific) and considered rare because of scarce occurrence records: Lepinia taitensis (28 observed occurrences), Pouteria tahitensis (20 occurrences) and Santalum insulare var. raiateense (81 occurrences). We selected a set of biophysical variables to describe plant habitats in tropical high volcanic islands, including topographic descriptors and an overstory vegetation map. The former were extracted from a digital elevation model (DEM) and the latter is a result of a SVM classification of spectral and textural bands from very high resolution Quickbird satellite imagery. Our results show that SVM slightly but constantly outperforms RF in predicting the distribution of rare species based on the kappa coefficient and the area under the curve (AUC) achieved by both classifiers. The predicted potential habitats of the three rare species are considerably wider than their currently observed distribution ranges. We hypothesize that the causes of this discrepancy are strong anthropogenic disturbances that have impacted low-to mid-elevation forests in the past and present. There is an urgent need to set up conservation strategies for the endangered plants found in these shrinking habitats on the Pacific islands. The detailed knowledge of rare species ecological range and geographic distribution is critical for biodiversity conservation and management (Ferrier, 2002; Rushton et al., 2004). Oceanic islands are famous for their unique biota with high endemism, but also their great vulnerability to anthropogenic disturbances (Caujapé-Castells et al. 2010; Loope et al. 1988) causing the decline of species abundance and distribution, leading sometimes to extinction (Whittaker and Fernandez-Palacios, 2007). As a result, a huge number of endangered species are currently found on island ecosystems (IUCN, 2011). Besides their conservation value, rare species may also play a key role for ecosystem functioning (Lyons and Schwartz, 2001; Lyons et al., 2005). Occurrence records are scarce for rare species resulting in small training sample available for species distribution …