Global patterns and drivers of the Anthropocene defaunation crisis

Abstract

Global biodiversity is declining at accelerating rates, with growing evidence to suggest that we may be on the brink of the planet’s ‘sixth mass extinction’. Traditionally, the magnitude of this crisis has been estimated using conservation categories from the IUCN Red List. However, these categories provide a static snapshot of species' current extinction risk, neglecting progressive demographic erosions towards extinction. Recently, population trends have emerged as an additional proxy for extinction risk, given that this metric is based on changes in population sizes through time, thus having the potential to indicate a species’ future extinction risk. Despite this advantage, population trends remain largely under-utilised across conservation research. My PhD addresses this gap by examining the current biodiversity crisis using population trends as an additional proxy for extinction risk. My research revealed that 48% of animal species are declining in population sizes, 49% are stable, and only 3% are increasing, Additionally, 33% of species categorised as non-threatened are declining. Integrating conservation categories with population trends revealed that 23% of vertebrates globally are at the highest risk of extinction (threatened declining), primarily in the tropics. Life history traits played a role in the declines of non-threatened vertebrates, while anthropogenic threats influenced taxon-dependent stages. Moreover, only 2% of threatened vertebrates are experiencing population stability or increase. We revealed that the number of species on the verge of becoming categorised as threatened (1,830 Near Threatened declining species) is 31-fold higher than the number of species on the verge of becoming non-threatened (59 Vulnerable increasing species). Based on this latent extinction risk, we revealed that extinction risk hotspots are predicted to expand in geographic magnitude across each vertebrate taxonomic class. For amphibians in particular, we revealed 41% of species are at the highest extinction risk (threatened declining), predominantly in the Neotropics and Sri Lanka. Life history traits influenced declines in non-threatened species, while environmental factors influenced declines in threatened species. Finally, our assessment of the role of UV-B in amphibian extinctions revealed that increasing UV-B radiation predicted the likelihood of being both threatened and declining for temperate salamanders, while decreasing UV-B predicted declining population sizes for temperate frogs and low elevation tropical frog species. Overall, this thesis suggests that our understanding of biodiversity loss is underestimated when using conservation categories alone. The integration of extinction risk proxies provides a nuanced identification of species on the brink of extinction, aiding to anticipate potential oncoming crises in certain taxa and factors contributing to this increasing risk, offering a pre-emptive approach for conservation.

Date of Award	Dec 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	NERC QUADRAT
Supervisor	Daniel Pincheira-Donoso (Supervisor) & Paul Caplat (Supervisor)