Master Thesis

Global Analysis of Plant Species Richness on Big, Continental Islands

Corbinian W. Benelli (08/2023-02/2024)

Support: Carl Beierkuhnlein, Anna Walentowitz

Big, continental islands are on average under-researched compared to small oceanic is-lands due to limited funding and time for comprehensive research. This study aims to systematically identify gaps in our understanding of biodiversity by investigating statis-tical irregularities by utilizing commonalities between islands. Various abiotic factors such as geological age, evolutionary time since isolation, forest cover, extent of ice, pop-ulation density, volcanic activity, and distance to the mainland are evaluated in relation to documented plant species richness. Data is collected from the Global Biodiversity In-formation Facility (GBIF) and other available sources for comparison, followed by gen-eralized linear modeling (GLM). A breakpoint analysis is conducted to differentiate big and medium-sized islands, revealing a threshold of 25,000 km². This analysis identifies 44 large islands worldwide that meet the criteria that group into two main clusters. These island agglomerations make it necessary not to examine the data without consideration of their spatial location. The results demonstrate an increase in plant species richness from the poles towards lower latitudes, with apparent peaks in each hemisphere. Big, continen-tal islands appear to experience a decline over time in plant species due to prolonged isolation following the MacArthur-Wilson Species Equilibrium Model, gradually resem-bling the continents. Additionally, there is a clear logarithmic correlation between biodi-versity and the size of continental islands, confirming Robert H. MacArthur's hypothesis regarding this island type. By utilizing a linear trend of plant species density with island size, predictions can be made regarding an island's expected plant species richness, con-sidering its climate and history. 48% of the big, continental islands were identified, whose observed plant species richness cannot be explained by the factors investigated, indicating a research gap in this regard. Foremost among them are Severny Island and Yuzhny Is-land, which are expected to have more plant species than currently recorded in the data-base. These are followed, in descending order of size, by New Guinea, Borneo, Baffin Island, Sumatra, Sulawesi, South Island, Newfoundland, Cuba, Mindanao, Ireland, His-paniola, Sakhalin, Devon Island, Taiwan, New Britain, Prince of Wales Island, Vancou-ver Island, Timor, and Isla de los Estados. This study saves money that can be used for closing the gaps found within plant species knowledge by providing valuable insights on which big, continental islands should be a focus for future efforts to complete the inven-tory of plant species richness.