Abstract
Despite islands contributing only 6.7% of land surface area, they harbor ~20% of the Earth’s biodiversity, but unfortunately also ~50% of the threatened species and 75% of the known extinctions since the European expansion around the globe. Due to their geological and geographic history and characteristics, islands act simultaneously as cradles of evolutionary diversity and museums of formerly widespread lineages—elements that permit islands to achieve an outstanding endemicity. Nevertheless, the majority of these endemic species are inherently vulnerable due to genetic and demographic factors linked with the way islands are colonized. Here, we stress the great variation of islands in their physical geography (area, isolation, altitude, latitude) and history (age, human colonization, human density). We provide examples of some of the most species rich and iconic insular radiations. Next, we analyze the natural vulnerability of the insular biota, linked to genetic and demographic factors as a result of founder events as well as the typically small population sizes of many island species. We note that, whereas evolution toward island syndromes (including size shifts, derived insular woodiness, altered dispersal ability, loss of defense traits, reduction in clutch size) might have improved the ability of species to thrive under natural conditions on islands, it has simultaneously made island biota disproportionately vulnerable to anthropogenic pressures such as habitat loss, overexploitation, invasive species, and climate change. This has led to the documented extinction of at least 800 insular species in the past 500 years, in addition to the many that had already gone extinct following the arrival of first human colonists on islands in prehistoric times. Finally, we summarize current scientific knowledge on the ongoing biodiversity loss on islands worldwide and express our serious concern that the current trajectory will continue to decimate the unique and irreplaceable natural heritage of the world’s islands. We conclude that drastic actions are urgently needed to bend the curve of the alarming rates of island biodiversity loss.
Highlights
Despite islands contributing only 6.7% of land surface area, they harbor ~20% of the Earth’s biodiversity, but ~50% of the threatened species and 75% of the known ex tinctions since the European expansion around the globe
Since the publication of the first Scientists’ Warning to Humanity (Union of concerned scientists, 1992) and its second notice (Ripple et al, 2017), 25 years later, the significance of biodiversity loss and its consequences for our own survival has been a key message. Both calls warned of the main threats to the environment globally and advised urgent actions to avoid the consequences of the last decades’ trajectory and encourage a shift to a more sustainable society
This initiative has resulted in a series of warnings from different scientific communities on specific topics: invasive alien species (Pysek et al, 2020), lake degradation (Jenny et al, 2020), insect extinction (Cardoso et al, 2020), endangered food webs (Heleno et al, 2020), freshwater biodiversity (Albert et al, 2020a), human population growth (Lidicker, 2020), and climate change (Ripple et al, 2021), among others
Summary
Scientists worldwide are becoming increasingly alarmed at the scale and severity of human impacts on our planet (Vitousek et al, 1997; Díaz et al, 2019). Since the publication of the first Scientists’ Warning to Humanity (Union of concerned scientists, 1992) and its second notice (Ripple et al, 2017), 25 years later, the significance of biodiversity loss and its consequences for our own survival has been a key message Both calls warned of the main threats to the environment globally (ozone layer depletion, unsustainable use of resources, habitat and biodiversity loss, climate change, and human population growth) and advised urgent actions (protecting and restoring natural habitats and ecological functions, regulating exploitation of threatened species, promoting sustainable use of resources, supporting environmental education, ensuring investment in nature protection, and providing equal access to education and wealth) to avoid the consequences of the last decades’ trajectory and encourage a shift to a more sustainable society. We highlight great threats to the Earth’s islands and their biodiversity: these fragile ecosystems lie at the intersection of many global threats, making the need for action especially urgent (Gillespie and Clague, 2009; Whittaker et al, 2017; Borges et al, 2019)
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