Abstract
Biological collections, including herbarium specimens, are unique sources of biodiversity data presenting a window on the history of the development and accumulation of knowledge of a specific geographical region. Understanding how the process of discovery impacts that knowledge is particularly important for oceanic islands which are often characterized by both high levels of endemic diversity and high proportions of threatened taxa. The archipelagos of the Macaronesian region (i.e. Azores, Canaries, Savages, Madeira, and Cabo Verde) have been the focus of attention for scientific expeditions since the end of the 17th century. However, there is no integrated study describing the historical process of collecting, discovery and description of its flora. Using as a case study the Cabo Verde endemic angiosperm flora, we review the history of collecting in the flora and apply a Bayesian approach to assess the accumulation of species discovery, through time and space across the nine islands of the archipelago. Our results highlight the central role not only of natural characteristics (e.g. area, age, maximum altitude and average value of the terrain ruggedness index) but also historical factors (i.e. the location of major harbors) for the development of knowledge of the flora. The main factors that have determined the process of species description in the archipelago and how this impact our understanding of diversity patterns across archipelagos are discussed.
Highlights
Understanding global patterns of plant diversity is important for oceanic islands, which are often characterized by high levels of endemic diversity (Warren et al, 2015; Whittaker et al, 2017)
Bayesian Methods to Analyze Historical Collections. One of these characteristics is the presence of a major harbor, a feature that determined the early colonization pattern of the archipelago, and which we modeled as an indicator variable that takes the value of one (1) for the island of Santiago and São Vicente, and the value of zero (0) for the other islands
A detailed list of the main collectors in the Cabo Verde Islands and their dates is provided in Supplementary Table S3
Summary
Understanding global patterns of plant diversity is important for oceanic islands, which are often characterized by high levels of endemic diversity (Warren et al, 2015; Whittaker et al, 2017). Among the most important recent initiatives has been the publication of checklists for each archipelago (e.g. Cabo Verde: Arechavaleta et al, 2005; Madeira and Salvages: Borges et al, 2008; Azores: Borges et al, 2010; Canaries: Arechavaleta et al, 2010). These provide important data for research on biodiversity, but there is still incomplete knowledge about the taxonomy and geographic distribution of most species, the socalled Linnean and Wallacean shortfalls, respectively (Hortal et al, 2015). Rigorous sampling and detailed information on species distributions are not available for the Macaronesian archipelagos, but Bayesian approaches such as that used by Gray and Cavers (2013) have the potential to explain the variation in meta-analyses where levels of taxonomic effort are unequal among islands
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