Modeling and mapping species distributions

Abstract

A species' distribution can be characterized by either occurrence probability or population density, defined for all locations in some spatial extent. Defining distribution in terms of these two parameters avoids the ambiguity surrounding the indices of occurrence or abundance produced by many presence-only algorithms. The unmarked package contains methods of tting occurrence and abundance models, and can be used to produce distribution maps with the help of R's GIS capabilities, as is demonstrated in this vignette. Unlike many other tools for modeling species distributions, the models in unmarked account for bias due to spatial and temporal heterogeneity in detection probability. Furthermore, unmarked includes models of population dynamics, allowing one to map quantities such as local colonization or extinction probability.