Publications by authors named "Anthony D Barnosky"

Unlabelled: Cores from Searsville Lake within Stanford University's Jasper Ridge Biological Preserve, California, USA, are examined to identify a potential GSSP for the Anthropocene: core JRBP2018-VC01B (944.5 cm-long) and tightly correlated JRBP2018-VC01A (852.5 cm-long).

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Unlabelled: We use a combination of proxy records from a high-resolution analysis of sediments from Searsville Lake and adjacent Upper Lake Marsh and historical records to document over one and a half centuries of vegetation and socio-ecological change-relating to logging, agricultural land use change, dam construction, chemical applications, recreation, and other drivers-on the San Francisco Peninsula. A relatively open vegetation with minimal oak () and coast redwood () in the late 1850s reflects widespread logging and grazing during the nineteenth century. Forest and woodland expansion occurred in the early twentieth century, with forests composed of coast redwood and oak, among other taxa, as both logging and grazing declined.

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Concern for megafauna is increasing among scientists and non-scientists. Many studies have emphasized that megafauna play prominent ecological roles and provide important ecosystem services to humanity. But, what precisely are 'megafauna'? Here, we critically assess the concept of megafauna and propose a goal-oriented framework for megafaunal research.

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In the face of the current global ecological crisis and the threats it poses to human survival and security, the fundamental solution is to resolve the deep contradiction between conservation and economic development. We considered the 3 key and basic questions of why to protect, how much to protect, and where to protect natural areas. Human survival depends on functioning ecosystems and the ecosystem services they provide.

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We explore the risk that self-reinforcing feedbacks could push the Earth System toward a planetary threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and cause continued warming on a "Hothouse Earth" pathway even as human emissions are reduced. Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene.

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Conservation of species and ecosystems is increasingly difficult because anthropogenic impacts are pervasive and accelerating. Under this rapid global change, maximizing conservation success requires a paradigm shift from maintaining ecosystems in idealized past states toward facilitating their adaptive and functional capacities, even as species ebb and flow individually. Developing effective strategies under this new paradigm will require deeper understanding of the long-term dynamics that govern ecosystem persistence and reconciliation of conflicts among approaches to conserving historical versus novel ecosystems.

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Article Synopsis
  • Human activities are changing the Earth in a big way, leading to talks about a new time period called the Anthropecene.
  • This period is marked by items made by humans, like plastics and metals, showing up in the Earth’s layers.
  • These changes also include rising sea levels, climate problems, and many animals going extinct faster than before.
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The oft-repeated claim that Earth's biota is entering a sixth "mass extinction" depends on clearly demonstrating that current extinction rates are far above the "background" rates prevailing between the five previous mass extinctions. Earlier estimates of extinction rates have been criticized for using assumptions that might overestimate the severity of the extinction crisis. We assess, using extremely conservative assumptions, whether human activities are causing a mass extinction.

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Loss of megafauna, an aspect of defaunation, can precipitate many ecological changes over short time scales. We examine whether megafauna loss can also explain features of lasting ecological state shifts that occurred as the Pleistocene gave way to the Holocene. We compare ecological impacts of late-Quaternary megafauna extinction in five American regions: southwestern Patagonia, the Pampas, northeastern United States, northwestern United States, and Beringia.

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Localized ecological systems are known to shift abruptly and irreversibly from one state to another when they are forced across critical thresholds. Here we review evidence that the global ecosystem as a whole can react in the same way and is approaching a planetary-scale critical transition as a result of human influence. The plausibility of a planetary-scale 'tipping point' highlights the need to improve biological forecasting by detecting early warning signs of critical transitions on global as well as local scales, and by detecting feedbacks that promote such transitions.

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Palaeontologists characterize mass extinctions as times when the Earth loses more than three-quarters of its species in a geologically short interval, as has happened only five times in the past 540 million years or so. Biologists now suggest that a sixth mass extinction may be under way, given the known species losses over the past few centuries and millennia. Here we review how differences between fossil and modern data and the addition of recently available palaeontological information influence our understanding of the current extinction crisis.

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Earth has experienced five major extinction events in the past 450 million years. Many scientists suggest we are now witnessing a sixth, driven by human impacts. However, it has been difficult to quantify the real extent of the current extinction episode, either for a given taxonomic group at the continental scale or for the worldwide biota, largely because comparisons of pre-anthropogenic and anthropogenic biodiversity baselines have been unavailable.

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Earth's most recent major extinction episode, the Quaternary Megafauna Extinction, claimed two-thirds of mammal genera and one-half of species that weighed >44 kg between approximately 50,000 and 3,000 years ago. Estimates of megafauna biomass (including humans as a megafauna species) for before, during, and after the extinction episode suggest that growth of human biomass largely matched the loss of non-human megafauna biomass until approximately 12,000 years ago. Then, total megafauna biomass crashed, because many non-human megafauna species suddenly disappeared, whereas human biomass continued to rise.

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Estimates of paleodiversity patterns through time have relied on datasets that lump taxonomic occurrences from geographic areas of varying size per interval of time. In essence, such estimates assume that the species-area effect, whereby more species are recorded from larger geographic areas, is negligible for fossil data. We tested this assumption by using the newly developed Miocene Mammal Mapping Project database of western North American fossil mammals and its associated analysis tools to empirically determine the geographic area that contributed to species diversity counts in successive temporal bins.

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Article Synopsis
  • Scientists are debating whether humans or climate change caused the extinction of big animals called megafauna a long time ago.
  • Evidence shows that humans played a role in some places, but climate changes also played a big part, especially in the Northern Hemisphere.
  • In Australia, new studies suggest humans may have caused extinctions too, but the link to climate is less clear, so more research is needed to fully understand what happened everywhere.
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Article Synopsis
  • Scientists discovered a lot of old animal fossils in Porcupine Cave, Colorado, which help us understand how animals reacted to climate changes long ago.
  • They found 127 different animal species from the mid-Pleistocene period, including 30 that were seen for the first time.
  • The research showed that smaller animals were more affected by warming climates, but the overall balance of animal communities stayed stable for a really long time, even before humans came along.
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To provide empirical evidence of species boundaries and the role of climatic change in affecting evolution, we documented evolution of the sagebrush vole, Lemmiscus curtatus, through hundreds of thousands of years by following populations from the middle Pleistocene to the present. We found that: (i) extant representatives of the species culminate a morphological transition that was initiated within an unusually arid and warm interglacial period, perhaps related to the shift from glacial-interglacial cycles dominated by a 41,000 year periodicity to those dominated by a 100,000 year rhythm; and (ii) sympatry of extant and extinct morphotypes persisted for more than 800,000 years. This exceptionally detailed tracing of extinct populations into extant ones suggests that species such as the one we studied are real entities in space, that their boundaries become fuzzy (although potentially diagnosable) through time and that unusual climatic warming may initiate significant evolutionary change manifested at the morphological level.

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