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John R. Stewart

Bio: John R. Stewart is an academic researcher from Bournemouth University. The author has contributed to research in topics: Pleistocene & Population. The author has an hindex of 30, co-authored 89 publications receiving 4348 citations. Previous affiliations of John R. Stewart include Natural History Museum & University of Murcia.


Papers
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Journal ArticleDOI
TL;DR: Overall, it seems clear that there is large variation in both the size of refugia and the duration during which species are confined to them, which has implications for the role ofRefugia in the evolution of species and their genetic diversity.
Abstract: Climate change in the past has led to significant changes in species' distributions. However, how individual species respond to climate change depends largely on their adaptations and environmental tolerances. In the Quaternary, temperate-adapted taxa are in general confined to refugia during glacials while cold-adapted taxa are in refugia during interglacials. In the Northern Hemisphere, evidence appears to be mounting that in addition to traditional southern refugia for temperate species, cryptic refugia existed in the North during glacials. Equivalent cryptic southern refugia, to the south of the more conventional high-latitude polar refugia, exist in montane areas during periods of warm climate, such as the current interglacial. There is also a continental/oceanic longitudinal gradient, which should be included in a more complete consideration of the interaction between species ranges and climates. Overall, it seems clear that there is large variation in both the size of refugia and the duration during which species are confined to them. This has implications for the role of refugia in the evolution of species and their genetic diversity.

1,036 citations

Journal ArticleDOI
TL;DR: Increasing evidence suggests that the well-studied European southern and eastern refugia for thermophilous animal and plant taxa were supplemented by cryptic refugias in northern Europe during the Late Pleistocene, which could partially explain the ‘nonanalogue' mammalian assemblages of the Late pleistocene.
Abstract: Viewed from a geological perspective, present-day animal and plant communities in many parts of the world have a remarkably short history. The environmental revolution at the end of the Pleistocene, a mere 10 000 years ago, triggered major shifts in the ranges of species and hence composition of communities. Present-day communities in the boreal and temperate zones assembled at this time by combining species that survived the northern environment of the Last Cold Stage with those returning from more temperate refugia. Increasing evidence suggests that the well-studied European southern and eastern refugia for thermophilous animal and plant taxa were supplemented by cryptic refugia in northern Europe during the Late Pleistocene. These northern refugia would have been in areas of sheltered topography that provided suitable stable microclimates, and could partially explain the ‘nonanalogue' mammalian assemblages of the Late Pleistocene. They also have implications for phylogeography and speciation.

854 citations

Journal ArticleDOI
12 May 2017-Science
TL;DR: Using targeted enrichment of mitochondrial DNA, it is shown that cave sediments represent a rich source of ancient mammalian DNA that often includes traces of hominin DNA, even at sites and in layers where no Hominin remains have been discovered.
Abstract: Although a rich record of Pleistocene human-associated archaeological assemblages exists, the scarcity of hominin fossils often impedes the understanding of which hominins occupied a site. Using targeted enrichment of mitochondrial DNA, we show that cave sediments represent a rich source of ancient mammalian DNA that often includes traces of hominin DNA, even at sites and in layers where no hominin remains have been discovered. By automation-assisted screening of numerous sediment samples, we detected Neandertal DNA in eight archaeological layers from four caves in Eurasia. In Denisova Cave, we retrieved Denisovan DNA in a Middle Pleistocene layer near the bottom of the stratigraphy. Our work opens the possibility of detecting the presence of hominin groups at sites and in areas where no skeletal remains are found.

248 citations

Journal ArticleDOI
16 Mar 2012-Science
TL;DR: Data from ancient genomes of Neandertals and Denisovans coupled with improved understanding of the role of refugia in driving evolution during the Ice Ages suggest that such refugias were important in the pace and pattern of change.
Abstract: Although an African origin of the modern human species is generally accepted, the evolutionary processes involved in the speciation, geographical spread, and eventual extinction of archaic humans outside of Africa are much debated. An additional complexity has been the recent evidence of limited interbreeding between modern humans and the Neandertals and Denisovans. Modern human migrations and interactions began during the buildup to the Last Glacial Maximum, starting about 100,000 years ago. By examining the history of other organisms through glacial cycles, valuable models for evolutionary biogeography can be formulated. According to one such model, the adoption of a new refugium by a subgroup of a species may lead to important evolutionary changes.

238 citations

Journal ArticleDOI
TL;DR: The Pleistocene is an excellent model case for the effects of rapid climate change, as the authors experience at the moment, on the ecology of plants and animals.

223 citations


Cited by
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Journal ArticleDOI
TL;DR: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols used xiii 1.
Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

14,171 citations

Journal ArticleDOI
07 Jun 2012-Nature
TL;DR: Evidence that the global ecosystem as a whole is approaching a planetary-scale critical transition as a result of human influence is reviewed, highlighting the need to improve biological forecasting by detecting early warning signs of critical transitions.
Abstract: There is evidence that human influence may be forcing the global ecosystem towards a rapid, irreversible, planetary-scale shift into a state unknown in human experience. Most forecasts of how the biosphere will change in response to human activity are rooted in projecting trajectories. Such models tend not anticipate critical transitions or tipping points, although recent work indicates a high probability of those taking place. And, at a local scale, ecosystems are known to shift abruptly between states when critical thresholds are passed. These authors review the evidence from across ecology and palaeontology that such a transition is being approached on the scale of the entire biosphere. They go on to suggest how biological forecasting might be improved to allow us to detect early warning signs of critical transitions on a global, as well as local, scale. 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. It is also necessary to address root causes of how humans are forcing biological changes.

1,571 citations

Journal ArticleDOI
TL;DR: Range edges are characterized by increased genetic isolation, genetic differentiation, and variability in individual and population performance, but evidence for decreased abundance and fitness is lacking, and a better fusion of experimentation and theory will advance understanding of the causes of range limits.
Abstract: Species range limits involve many aspects of evolution and ecology, from species distribution and abundance to the evolution of niches. Theory suggests myriad processes by which range limits arise, including competitive exclusion, Allee effects, and gene swamping; however, most models remain empirically untested. Range limits are correlated with a number of abiotic and biotic factors, but further experimentation is needed to understand underlying mechanisms. Range edges are characterized by increased genetic isolation, genetic differentiation, and variability in individual and population performance, but evidence for decreased abundance and fitness is lacking. Evolution of range limits is understudied in natural systems; in particular, the role of gene flow in shaping range limits is unknown. Biological invasions and rapid distribution shifts caused by climate change represent large-scale experiments on the underlying dynamics of range limits. A better fusion of experimentation and theory will advance our understanding of the causes of range limits.

1,534 citations

Journal ArticleDOI
TL;DR: Overall, it seems clear that there is large variation in both the size of refugia and the duration during which species are confined to them, which has implications for the role ofRefugia in the evolution of species and their genetic diversity.
Abstract: Climate change in the past has led to significant changes in species' distributions. However, how individual species respond to climate change depends largely on their adaptations and environmental tolerances. In the Quaternary, temperate-adapted taxa are in general confined to refugia during glacials while cold-adapted taxa are in refugia during interglacials. In the Northern Hemisphere, evidence appears to be mounting that in addition to traditional southern refugia for temperate species, cryptic refugia existed in the North during glacials. Equivalent cryptic southern refugia, to the south of the more conventional high-latitude polar refugia, exist in montane areas during periods of warm climate, such as the current interglacial. There is also a continental/oceanic longitudinal gradient, which should be included in a more complete consideration of the interaction between species ranges and climates. Overall, it seems clear that there is large variation in both the size of refugia and the duration during which species are confined to them. This has implications for the role of refugia in the evolution of species and their genetic diversity.

1,036 citations