The role of sea-level fluctuations and human activities in shaping present-day island biodiversity

Funder

Organizational Unit

Publications

Global change in microcosms: Environmental and societal predictors of land cover change on the Atlantic Ocean Islands

Publication . Norder, Sietze J.; F. De Lima, Ricardo; de Nascimento, Lea; Lim, Jun Y.; Fernández-Palacios, José María; Romeiras, Maria M.; Elias, Rui B.; Cabezas, Francisco J.; Catarino, Luís; Ceríaco, Luis M.P.; Castilla-Beltrán, Alvaro; Gabriel, Rosalina; de Sequeira, Miguel Menezes; Rijsdijk, Kenneth F.; Nogué, Sandra; Kissling, W. Daniel; van Loon, E. Emiel; Hall, Marcus; Matos, Margarida; Borges, P.A.V.

Islands contribute enormously to global biodiversity, but their species and ecosystems are highly threatened and often confined to small patches of remaining native vegetation. Islands are thus ideal microcosms to study the local dimensions of global change. While human activities have drastically transformed most islands, the extent to which societal and environmental conditions shape differences in land cover remains unclear. This study analyses the role of contrasting environmental and societal conditions in affecting the extent of native vegetation cover on 30 islands in five Atlantic Ocean archipelagos (Azores, Madeira, Canary Islands, Cape Verde, Gulf of Guinea Islands). We adopt a mixed-method approach in which we combine a statistical analysis of environmental and societal variables with a qualitative reconstruction of historical socioeconomic trends. Statistical results indicate that terrain ruggedness predominantly shapes the extent of remaining native vegetation cover, suggesting that topography constrains human impacts on biodiversity. Overall, environmental variables better explain differences in native vegetation cover between islands than societal variables like human population density. However, throughout history, islands experienced large changes in demography and socioeconomic trends, and therefore modern patterns of native vegetation might also partly reflect these past conditions. While anthropocene narratives often present humans as a global geophysical force, the results show that local environmental context strongly mitigated the degree of human impact on biodiversity. These findings call for integrative approaches to understand the contributions of local human-environment interactions to ongoing global change.

2020-04-25Journal article

Open access

Recent geospatial dynamics of Terceira (Azores, Portugal) and the theoretical implications for the biogeography of active volcanic islands

Publication . Rijsdijk, Kenneth F.; Buijs, Simon; Quartau, Rui; Aguilée, Robin; Norder, Sietze J.; Ávila, Sérgio P.; De Medeiros, Sara Maria Teixeira; Nunes, João Carlos Carreiro; Elias, R.B.; Melo, Carlos S.; Stocchi, Paulo; Koene, Erik F. M.; Seijmonsbergen, A. C. (Harry); De Boer, W. M. (Thijs); Borges, P.A.V.

Ongoing work shows that species richness patterns on volcanic oceanic islands are shaped by surface area changes driven by longer time scale (>1 ka) geological processes and natural sea level fluctuations. A key question is: what are the rates and magnitudes of the forces driving spatial changes on volcanic oceanic islands which in turn affect evolutionary and biogeographic processes? We quantified the rates of surface-area changes of a whole island resulting from both volcanogenic flows and sea level change over the last glacial-interglacial (GI) cycle (120 ka) for the volcanically active island of Terceira, (Azores, Macaronesia, Portugal). Volcanogenic activity led to incidental but long-lasting surface area expansions by the formation of a new volcanic cone and lava-deltas, whereas sea level changes led to both contractions and expansions of area. The total surface area of Terceira decreased by as much as 24% per time step due to changing sea levels and increased by 37% per time step due to volcanism per time step of 10 ka. However, while sea levels nearly continuously changed the total surface area, volcanic activity only impacted total surface area during two time steps over the past 120 ka. The surface area of the coastal and lowland region (here defined as area <300 m) was affected by sea level change (average change of 11% / 10 ka for 120–0 ka) and intra-volcanic change (average change of 17% / 10 ka for 120–0 ka). We discuss the biogeographic implications of the quantified dynamics, and we argue that surface area change is mainly driven by volcanic processes in the early stages of the island’s life cycle, while during the later stages, area change becomes increasingly affected by sea level dynamics. Both environmental processes may therefore affect biota differently during the life cycle of volcanic oceanic islands.

2020-04Journal article

Open access

Island Biogeography in the Anthropocene and Quaternary

Publication . Norder, Sietze Johannes; Matos, Margarida Maria Demony de Carneiro Pacheco de; Borges, Paulo Alexandre Vieira; Rijsdijk, Kenneth Frank

The realization that human activities have a major influence on ecosystems from local to global scales has given rise to the concept of the Anthropocene. However, although the influence of human activities on biodiversity is clearly significant, it remains unclear to what extent the rate and magnitude of biodiversity changes differ from pre-human dynamics. Islands are ideal model systems for understanding the relative contribution of environmental and societal variables to biodiversity change because the onset of human activities on islands can generally be clearly defined. The aim of this PhD thesis is to place human-environment interactions on islands in the context of environmental fluctuations over the Quaternary. The thesis consists of two parts. First, I quantify how island area and isolation have changed over the Quaternary as a result of climate-driven sea-level fluctuations, and analyse how these dynamics have shaped modern biodiversity patterns. Secondly, I study how human activities in the past and present have shaped island ecosystems and landscapes, and compare their rate and magnitude to pre-human dynamics. Overall, the findings of my thesis indicate that modern biodiversity patterns show legacies of past human activities but are also imprinted by environmental dynamics in deep-time. Furthermore, the rate of change following human settlement on islands can largely exceed Quaternary background rates. Therefore, my findings are in line with studies that indicate that human activities have become a major driver in shaping biodiversity across scales. Nonetheless, my comparison of islands worldwide also highlights the diverse ways in which abiotic, biotic, and anthropogenic variables have interacted across individual islands. Therefore, future studies should acknowledge that global biodiversity change can manifest differently across localities. Finally, I emphasize the importance of strengthening interdisciplinary approaches in island biogeography to enhance our understanding of biodiversity changes in the Anthropocene, and how they relate to deeptime dynamics.

2020-04Doctoral thesis

Open access