Frédérik Saltré | Flinders University of South Australia (original) (raw)
Papers by Frédérik Saltré
Frontiers in Conservation Science
Global Ecology, College of Science and Engineering, Flinders University, Adelaide, SA, Australia,... more Global Ecology, College of Science and Engineering, Flinders University, Adelaide, SA, Australia, 2 Australian Research Council Centre of Excellence for Australian Biodiversity and Heritage, EpicAustralia.org, Adelaide, SA, Australia, Department of Biology, Stanford University, Stanford, CA, United States, Department of Biological Sciences, Macquarie University, Sydney, NSW, Australia, 5 Instituto de Ecología, Universidad Nacional Autónoma de México, Ciudad de México, Mexico, Department of Science, Technology, and Society, Virginia Tech, Blacksburg, VA, United States, Millennium Alliance for Humanity and the Biosphere, Department of Biology, Stanford University, Stanford, CA, United States, 8 Energy and Resources Group, University of California, Berkeley, Berkeley, CA, United States, 9 The Rocky Mountain Biological Laboratory, Crested Butte, CO, United States, Missouri Botanical Garden, St Louis, MO, United States, Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR, United States, Global Footprint Network, Oakland, CA, United States, Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, United States, 14 La Kretz Hall, Institute of the Environment and Sustainability, University of California, Los Angeles, Los Angeles, CA, United States
Nature Human Behaviour, 2021
Archaeological data and demographic modelling suggest that the peopling of Sahul required substan... more Archaeological data and demographic modelling suggest that the peopling of Sahul required substantial populations, occurred rapidly within a few thousand years and encompassed environments ranging from hyper-arid deserts to temperate uplands and tropical rainforests. How this migration occurred and how humans responded to the physical environments they encountered have, however, remained largely speculative. By constructing a high-resolution digital elevation model for Sahul and coupling it with fine-scale viewshed analysis of landscape prominence, least-cost pedestrian travel modelling and high-performance computing, we create over 125 billion potential migratory pathways, whereby the most parsimonious routes traversed emerge. Our analysis revealed several major pathways—superhighways—transecting the continent, that we evaluated using archaeological data. These results suggest that the earliest Australian ancestors adopted a set of fundamental rules shaped by physiological capacity...
Extinctions stemming from environmental change often trigger trophic cascades and coextinctions. ... more Extinctions stemming from environmental change often trigger trophic cascades and coextinctions. However, it remains unclear whether trophic cascades were a large contributor to the megafauna extinctions that swept across several continents in the Late Pleistocene. The pathways to megafauna extinctions are particularly unclear for Sahul (landmass comprising Australia and New Guinea), where extinctions happened earlier than on other continents. We investigated the role of bottom-up trophic cascades in Late Pleistocene Sahul by constructing pre-extinction (~ 80 ka) trophic network models of the vertebrate community of Naracoorte, south-eastern Australia. These models allowed us to predict vertebrate species’ vulnerability to cascading extinctions based on their position in the network. We tested whether the observed extinctions could be explained by bottom-up cascades, or if they should be attributed to other external causes. Species that disappeared from the community were more vulne...
Frontiers in Conservation Science
We report three major and confronting environmental issues that have received little attention an... more We report three major and confronting environmental issues that have received little attention and require urgent action. First, we review the evidence that future environmental conditions will be far more dangerous than currently believed. The scale of the threats to the biosphere and all its lifeforms—including humanity—is in fact so great that it is difficult to grasp for even well-informed experts. Second, we ask what political or economic system, or leadership, is prepared to handle the predicted disasters, or even capable of such action. Third, this dire situation places an extraordinary responsibility on scientists to speak out candidly and accurately when engaging with government, business, and the public. We especially draw attention to the lack of appreciation of the enormous challenges to creating a sustainable future. The added stresses to human health, wealth, and well-being will perversely diminish our political capacity to mitigate the erosion of ecosystem services on...
Nature Communications
The peopling of Sahul (the combined continent of Australia and New Guinea) represents the earlies... more The peopling of Sahul (the combined continent of Australia and New Guinea) represents the earliest continental migration and settlement event of solely anatomically modern humans, but its patterns and ecological drivers remain largely conceptual in the current literature. We present an advanced stochastic-ecological model to test the relative support for scenarios describing where and when the first humans entered Sahul, and their most probable routes of early settlement. The model supports a dominant entry via the northwest Sahul Shelf first, potentially followed by a second entry through New Guinea, with initial entry most consistent with 50,000 or 75,000 years ago based on comparison with bias-corrected archaeological map layers. The model’s emergent properties predict that peopling of the entire continent occurred rapidly across all ecological environments within 156–208 human generations (4368–5599 years) and at a plausible rate of 0.71–0.92 km year−1. More broadly, our methods...
The causes of Sahul’s megafauna extinctions remain uncertain, although multiple, interacting fact... more The causes of Sahul’s megafauna extinctions remain uncertain, although multiple, interacting factors were likely responsible. To test hypotheses regarding plausible ecological mechanisms underlying these extinctions, we constructed the first stochastic, age-structured models for 13 extinct megafauna species from five functional/taxonomic groups, as well as 8 extant species within these groups for comparison. Perturbing specific demographic rates individually, we tested which species were more demographically susceptible to extinction, and then compared these relative sensitivities to the fossil-derived extinction chronology. Here we show that the macropodiformes were the most resilient to extinction, followed by carnivores, monotremes, vombatiform herbivores, and large birds. Five of the eight extant species were as or more susceptible than were the extinct species. There was no clear relationship between extinction susceptibility and the extinction chronology for any perturbation s...
Feral cats are one of the most destructive invasive predators worldwide. Due to the high risk of ... more Feral cats are one of the most destructive invasive predators worldwide. Due to the high risk of pushing native species to extinction in Australia, density-reduction or eradication campaigns can greatly improve the persistence probability and recovery of native fauna. Kangaroo Island — Australia’s third-largest island — was recently nominated as a complete cat-eradication site by the federal government. Because most population density-reduction campaigns are costly and not effective in the long term, mathematical models predicting optimal culling regimes can guide management plans, especially if they include estimates of costs under different policy decisions. We constructed a stochastic population model with cost estimates to test the relative effectiveness and cost-efficiency of two main culling scenarios for Kangaroo Island to 2030: (1) constant proportional annual cull, and (2) high initial culling followed by a constant proportional maintenance cull. We also examined the effect...
Nature Communications
The mechanisms leading to megafauna (>44 kg) extinctions in Late Pleistocene (126,000—12,000 y... more The mechanisms leading to megafauna (>44 kg) extinctions in Late Pleistocene (126,000—12,000 years ago) Australia are highly contested because standard chronological analyses rely on scarce data of varying quality and ignore spatial complexity. Relevant archaeological and palaeontological records are most often also biased by differential preservation resulting in under-representated older events. Chronological analyses have attributed megafaunal extinctions to climate change, humans, or a combination of the two, but rarely consider spatial variation in extinction patterns, initial human appearance trajectories, and palaeoclimate change together. Here we develop a statistical approach to infer spatio-temporal trajectories of megafauna extirpations (local extinctions) and initial human appearance in south-eastern Australia. We identify a combined climate-human effect on regional extirpation patterns suggesting that small, mobile Aboriginal populations potentially needed access to ...
Ecology and Evolution
This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Ecography
The koala's Phascolarctos cinereus distribution is currently restricted to eastern and southeaste... more The koala's Phascolarctos cinereus distribution is currently restricted to eastern and southeastern Australia. However, fossil records dating from 70 ± 4 ka (ka = 10 3 yr) from southwestern Australia and the Nullarbor Plain are evidence of subpopulation extinctions in the southwest at least after the Last Interglacial (~128-116 ka). We hypothesize that koala sub-population extinctions resulted from the eastward retraction of the koala's main browse species in response to unsuitable climatic conditions. We further posit a general reduction in the distribution of main koala-browse trees in the near future in response climate change. We modelled 60 koala-browse species and constructed a set of correlative species distribution models for five time periods: Last Interglacial (~128-116 ka), Last Glacial Maximum (~23-19 ka), Mid-Holocene (~7-5 ka), present (interpolations of observed data, representative of 1960-1990), and 2070. We based our projections on five hindcasts and one forecast of climatic variables extracted from WorldClim based on two general circulation models (considering the most pessimistic scenario of high greenhousegas emissions) and topsoil clay fraction. We used 17 dates of koala fossil specimens identified as reliable from 70 (± 4) to 535 (± 49) ka, with the last appearance of koalas at 70 ka in the southwest. The main simulated koala-browse species were at their greatest modelled extent of suitability during the Last Glacial Maximum, with the greatest loss of koala habitat occurring between the Mid-Holocene and the present. We predict a similar habitat loss between the present and 2070. The spatial patterns of habitat change support our hypothesis that koala extinctions in the southwest, Nullarbor Plain and central South Australia resulted from the eastward retraction of the dominant koala-browse species in response to long-term climate changes. Future climate patterns will likely increase the extinction risk of koalas in their remaining eastern ranges.
Global change biology, Mar 1, 2018
The current distribution of species, environmental conditions and their interactions represent on... more The current distribution of species, environmental conditions and their interactions represent only one snapshot of a planet that is continuously changing, in part due to human influences. To distinguish human impacts from natural factors, the magnitude and pace of climate shifts, since the Last Glacial Maximum, are often used to determine whether patterns of diversity today are artefacts of past climate change. In the absence of high-temporal resolution palaeoclimate reconstructions, this is generally done by assuming that past climate change occurred at a linear pace between widely spaced (usually, ≥1,000 years) climate snapshots. We show here that this is a flawed assumption because regional climates have changed significantly across decades and centuries during glacial-interglacial cycles, likely causing rapid regional replacement of biota. We demonstrate how recent atmosphere-ocean general circulation model (AOGCM) simulations of the climate of the past 21,000 years can provide...
Climatic Change, 2013
ABSTRACT Paleo-data suggest that East African mountain treelines underwent an altitudinal shift d... more ABSTRACT Paleo-data suggest that East African mountain treelines underwent an altitudinal shift during the Last Glacial Maximum (LGM). Understanding the ecological and physiological processes underlying treeline response to such past climate change will help to improve forecasts of treeline change under future global warming. In spite of significant improvements in paleoclimatic reconstruction, the climatic conditions explaining this migration are still debated and important factors such as atmospheric CO2 concentration, the impact of lapse rate decreasing temperature along altitudinal gradients and rainfall modifications due to elevation have often been neglected or simplified. Here, we assess the effects of these different factors and estimate the influence of the most dominant factors controlling changes in past treeline position using a multi-proxy approach based on simulations from BIOME4, a coupled biogeography and biogeochemistry model, modified to account for the effect of elevation on vegetation, compared with pollen, and isotopic data. The results indicate a shift in mountain vegetation at the LGM was controlled by low pCO2 and low temperatures promoting species morphologically and physiologically better adapted to LGM conditions than many trees composing the forest belt limit. Our estimate that the LGM climate was cooler than today’s by −4.5 °C (range: −4.3 to −4.6 °C) at the upper limit of the treeline, whereas at 831 m it was cooler by −1.4 °C (range: −2.6 to −0.6 °C), suggests that a possible lapse rate modification strongly constrained the upper limit of treeline, which may limit its potential extension under future global warming.
Scientific Data, 2019
The 2016 version of the FosSahul database compiled non-human vertebrate megafauna fossil ages fro... more The 2016 version of the FosSahul database compiled non-human vertebrate megafauna fossil ages from Sahul published up to 2013 in a standardized format. Its purpose was to create a publicly available, centralized, and comprehensive database for palaeoecological investigations of the continent. Such databases require regular updates and improvements to reflect recent scientific findings. Here we present an updated FosSahul (2.0) containing 11,871 dated non-human vertebrate fossil records from the Late Quaternary published up to 2018. Furthermore, we have extended the information captured in the database to include methodological details and have developed an algorithm to automate the quality-rating process. The algorithm makes the quality-rating more transparent and easier to reproduce, facilitating future database extensions and dissemination. FosSahul has already enabled several palaeoecological analyses, and its updated version will continue to provide a centralized organisation of...
Scientific Reports, 2019
The first peopling of Sahul (Australia, New Guinea and the Aru Islands joined at lower sea levels... more The first peopling of Sahul (Australia, New Guinea and the Aru Islands joined at lower sea levels) by anatomically modern humans required multiple maritime crossings through Wallacea, with at least one approaching 100 km. Whether these crossings were accidental or intentional is unknown. Using coastal-viewshed analysis and ocean drift modelling combined with population projections, we show that the probability of randomly reaching Sahul by any route is <5% until ≥40 adults are 'washed off' an island at least once every 20 years. We then demonstrate that choosing a time of departure and making minimal headway (0.5 knots) toward a destination greatly increases the likelihood of arrival. While drift modelling demonstrates the existence of 'bottleneck' crossings on all routes, arrival via New Guinea is more likely than via northwestern Australia. We conclude that anatomically modern humans had the capacity to plan and make open-sea voyages lasting several days by at least 50,000 years ago. Increased attention to maritime landscapes over the last two decades has re-invigorated investigation into the role of coastal environments and sea travel in the behavioural evolution of our species. New evidence has fundamentally changed our understanding of the cognitive capacity of anatomically modern humans 1,2 , genetic ancestry 3 , dispersal patterns from Africa 4 and the peopling of new environments 5,6. However, the role of coastlines and coastal resources in the dispersal of modern humans has been much debated. Proponents of a coastal migration model for H. sapiens out of Africa argue that coastlines would have provided for a fast, directional population expansion with predictable resources and supplies of potable water 7. Those opposing, point out that there is little direct evidence to support a coastal-highway hypothesis and that there is evidence that early humans were able to make use of savanna and rainforest environments 2,8. More recent papers propose a less dichotomous model featuring flexibility, involving use of coasts and estuaries, but not exclusively relying on them 4,5,9. Whatever the reality, it is clear that the ability to make even rudimentary watercraft and move directionally over water, both across large rivers and in traversing unknown sections of coastline, would have given H. sapiens a selective advantage over other hominins. Australia and the islands to its north (the Wallacean Archipelago) have been at the forefront of this debate because the maritime crossing from Sunda to Sahul requires lengthy water crossings that appear to have been beyond the capacity of earlier hominins.
Nature Ecology and Evolution, 2019
The timing, context and nature of the first people to enter Sahul is still poorly understood owin... more The timing, context and nature of the first people to enter Sahul is still poorly understood owing to a fragmented archaeological record. However, quantifying the plausible demographic context of this founding population is essential to determine how and why the initial peopling of Sahul occurred. We developed a stochastic, age-structured model using demographic rates from hunter-gatherer societies, and relative carrying capacity hindcasted with LOVECLIM’s net primary productivity for northern Sahul. We projected these populations to determine the resilience and minimum sizes required to avoid extinction. A census founding population of between 1,300 and 1,550 individuals was necessary to maintain a quasi-extinction threshold of ≲0.1. This minimum founding population could have arrived at a single point in time, or through multiple voyages of ≥130 people over ~700–900 years. This result shows that substantial population amalgamation in Sunda and Wallacea in Marine Isotope Stages 3–4 provided the conditions for the successful, large-scale and probably planned peopling of Sahul.
Biology Letters, 2018
The last large marsupial carnivores-the Tasmanian devil (Sarcophilis harri-sii) and thylacine (Th... more The last large marsupial carnivores-the Tasmanian devil (Sarcophilis harri-sii) and thylacine (Thylacinus cynocephalus)-went extinct on mainland Australia during the mid-Holocene. Based on the youngest fossil dates (approx. 3500 years before present, BP), these extinctions are often considered synchronous and driven by a common cause. However, many published devil dates have recently been rejected as unreliable, shifting the youngest mainland fossil age to 25 500 years BP and challenging the synchronous extinction hypothesis. Here we provide 24 and 20 new ages for devils and thylacines, respectively, and collate existing, reliable radiocarbon dates by quality-filtering available records. We use this new dataset to estimate an extinction time for both species by applying the Gaussian-resampled, inverse-weighted McInerney (GRIWM) method. Our new data and analysis definitively support the synchronous-extinction hypothesis, estimating that the mainland devil and thylacine extinctions occurred between 3179 and 3227 years BP.
Global Change Biology, 2018
The current distribution of species, environmental conditions and their interactions represent on... more The current distribution of species, environmental conditions and their interactions represent only one snapshot of a planet that is continuously changing, in part due to human influences. To distinguish human impacts from natural factors, the magnitude and pace of climate shifts, since the Last Glacial Maximum, are often used to determine whether patterns of diversity today are artefacts of past climate change. In the absence of high-temporal resolution palaeoclimate reconstructions, this is generally done by assuming that past climate change occurred at a linear pace between widely spaced (usually, ≥1,000 years) climate snapshots. We show here that this is a flawed assumption because regional climates have changed significantly across decades and centuries during glacial-interglacial cycles, likely causing rapid regional replacement of biota. We demonstrate how recent atmosphere-ocean general circulation model (AOGCM) simulations of the climate of the past 21,000 years can provide credible estimates of the details of climate change on decadal to centennial timescales, showing that these details differ radically from what might be inferred from longer timescale information. High-temporal resolution information can provide more meaningful estimates of the magnitude and pace of climate shifts, the location and timing of drivers of physiological stress, and the extent of novel climates. They also produce new opportunities to directly investigate whether short-term climate variability is more important in shaping biodiversity patterns rather than gradual changes in long-term climatic means. Together, these more accurate measures of past climate instability are likely to bring about a better understanding of the role of palaeoclimatic change and variability in shaping current macroecological patterns in many regions of the world.
It has been diffi cult to access projections of global-scale climate change with high temporal re... more It has been diffi cult to access projections of global-scale climate change with high temporal resolution spaning the late
Pleistocene and Holocene. Th is has limited our ability to discern how climate fl uctuations have aff ected species ’ range
dynamics and extinction processes, turn-over in ecological communities and changes in genetic diversity. PaleoView is a
new freeware tool, which provides a comprehensive but easy-to-use way to generate and view paleoclimate data at temporal
and spatial resolutions suitable for detecting biotic responses to major climate shifts since the last glacial maximum.
Regional to global scale simulations of temperature, precipitation, humidity and mean sea level pressure can be generated
from PaleoView as gridded or time series data at time intervals as short as a decade for any period during the last 21 000 yr.
Th ey can be viewed using a built-in geographical user interface or saved as data fi les. Modelled climate reconstructions
are based on daily simulation output from the Community Climate System Model ver. 3 (CCSM3). Th is global coupled
atmosphere – ocean – sea ice – land general circulation model accurately reproduces major climatic features associated with
the most recent deglaciation event, and predicts present-day patterns of climate conditions with verifi ed hindcast skill. By
providing a portal for readily accessing climate reconstructions at high temporal resolutions, PaleoView can help to better
establish the consequences of past climate fl uctuations on macro-ecological patterns of biological and genetic diversity.
NATURE CLIMATE CHANGE | VOL 6 | OCTOBER 2016 | www.nature.com/natureclimatechange 909 U nderstand... more NATURE CLIMATE CHANGE | VOL 6 | OCTOBER 2016 | www.nature.com/natureclimatechange 909 U nderstanding, predicting and mitigating the impacts of global change on biodiversity poses one of the most crucial challenges for ecologists, conservation biologists and resource managers this century 1,2 . Models forecast that human-induced climate change is likely to cause extinctions, both directly and in synergy with other threatening processes, but the range of estimates for its total impact remain worryingly large 3 . A more evidencefocused approach to global change ecology is required to gain deeper insights into the likely effect of shifts in climate and other environmental change on biodiversity over the coming decades to centuries 4 , and so to design effective conservation strategies that mitigate climate-driven biodiversity loss 5 . New research emerging at the frontiers between palaeoecology, climatology, population genetics and quantitative ecology is proving useful for uncovering past responses of species and populations to global environmental change 6,7 . However, the practical application of this long-term retrospective knowledge (derived from palaeoecological archives and proxies) in modern strategies to mitigate future climate-driven biodiversity loss has so far been limited, in part due to barriers that constrain the flow of information and collaboration between palaeoecologists and conservation biologists 8 .
The study of palaeo-chronologies using fossil data provides evidence for past ecological and evol... more The study of palaeo-chronologies using fossil data provides evidence for past ecological and evolutionary processes, and is therefore useful for predicting patterns and impacts of future environmental change. However, the robustness of inferences made from fossil ages relies heavily on both the quantity and quality of available data. We compiled Quaternary non-human vertebrate fossil ages from Sahul published up to 2013. This, the FosSahul database, includes 9,302 fossil records from 363 deposits, for a total of 478 species within 215 genera, of which 27 are from extinct and extant megafaunal species (2,559 records). We also provide a rating of reliability of individual absolute age based on the dating protocols and association between the dated materials and the fossil remains. Our proposed rating system identified 2,422 records with high-quality ages (i.e., a reduction of 74%). There are many applications of the database, including disentangling the confounding influences of hypothetical extinction drivers, better spatial distribution estimates of species relative to palaeo-climates, and potentially identifying new areas for fossil discovery.
Frontiers in Conservation Science
Global Ecology, College of Science and Engineering, Flinders University, Adelaide, SA, Australia,... more Global Ecology, College of Science and Engineering, Flinders University, Adelaide, SA, Australia, 2 Australian Research Council Centre of Excellence for Australian Biodiversity and Heritage, EpicAustralia.org, Adelaide, SA, Australia, Department of Biology, Stanford University, Stanford, CA, United States, Department of Biological Sciences, Macquarie University, Sydney, NSW, Australia, 5 Instituto de Ecología, Universidad Nacional Autónoma de México, Ciudad de México, Mexico, Department of Science, Technology, and Society, Virginia Tech, Blacksburg, VA, United States, Millennium Alliance for Humanity and the Biosphere, Department of Biology, Stanford University, Stanford, CA, United States, 8 Energy and Resources Group, University of California, Berkeley, Berkeley, CA, United States, 9 The Rocky Mountain Biological Laboratory, Crested Butte, CO, United States, Missouri Botanical Garden, St Louis, MO, United States, Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR, United States, Global Footprint Network, Oakland, CA, United States, Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, United States, 14 La Kretz Hall, Institute of the Environment and Sustainability, University of California, Los Angeles, Los Angeles, CA, United States
Nature Human Behaviour, 2021
Archaeological data and demographic modelling suggest that the peopling of Sahul required substan... more Archaeological data and demographic modelling suggest that the peopling of Sahul required substantial populations, occurred rapidly within a few thousand years and encompassed environments ranging from hyper-arid deserts to temperate uplands and tropical rainforests. How this migration occurred and how humans responded to the physical environments they encountered have, however, remained largely speculative. By constructing a high-resolution digital elevation model for Sahul and coupling it with fine-scale viewshed analysis of landscape prominence, least-cost pedestrian travel modelling and high-performance computing, we create over 125 billion potential migratory pathways, whereby the most parsimonious routes traversed emerge. Our analysis revealed several major pathways—superhighways—transecting the continent, that we evaluated using archaeological data. These results suggest that the earliest Australian ancestors adopted a set of fundamental rules shaped by physiological capacity...
Extinctions stemming from environmental change often trigger trophic cascades and coextinctions. ... more Extinctions stemming from environmental change often trigger trophic cascades and coextinctions. However, it remains unclear whether trophic cascades were a large contributor to the megafauna extinctions that swept across several continents in the Late Pleistocene. The pathways to megafauna extinctions are particularly unclear for Sahul (landmass comprising Australia and New Guinea), where extinctions happened earlier than on other continents. We investigated the role of bottom-up trophic cascades in Late Pleistocene Sahul by constructing pre-extinction (~ 80 ka) trophic network models of the vertebrate community of Naracoorte, south-eastern Australia. These models allowed us to predict vertebrate species’ vulnerability to cascading extinctions based on their position in the network. We tested whether the observed extinctions could be explained by bottom-up cascades, or if they should be attributed to other external causes. Species that disappeared from the community were more vulne...
Frontiers in Conservation Science
We report three major and confronting environmental issues that have received little attention an... more We report three major and confronting environmental issues that have received little attention and require urgent action. First, we review the evidence that future environmental conditions will be far more dangerous than currently believed. The scale of the threats to the biosphere and all its lifeforms—including humanity—is in fact so great that it is difficult to grasp for even well-informed experts. Second, we ask what political or economic system, or leadership, is prepared to handle the predicted disasters, or even capable of such action. Third, this dire situation places an extraordinary responsibility on scientists to speak out candidly and accurately when engaging with government, business, and the public. We especially draw attention to the lack of appreciation of the enormous challenges to creating a sustainable future. The added stresses to human health, wealth, and well-being will perversely diminish our political capacity to mitigate the erosion of ecosystem services on...
Nature Communications
The peopling of Sahul (the combined continent of Australia and New Guinea) represents the earlies... more The peopling of Sahul (the combined continent of Australia and New Guinea) represents the earliest continental migration and settlement event of solely anatomically modern humans, but its patterns and ecological drivers remain largely conceptual in the current literature. We present an advanced stochastic-ecological model to test the relative support for scenarios describing where and when the first humans entered Sahul, and their most probable routes of early settlement. The model supports a dominant entry via the northwest Sahul Shelf first, potentially followed by a second entry through New Guinea, with initial entry most consistent with 50,000 or 75,000 years ago based on comparison with bias-corrected archaeological map layers. The model’s emergent properties predict that peopling of the entire continent occurred rapidly across all ecological environments within 156–208 human generations (4368–5599 years) and at a plausible rate of 0.71–0.92 km year−1. More broadly, our methods...
The causes of Sahul’s megafauna extinctions remain uncertain, although multiple, interacting fact... more The causes of Sahul’s megafauna extinctions remain uncertain, although multiple, interacting factors were likely responsible. To test hypotheses regarding plausible ecological mechanisms underlying these extinctions, we constructed the first stochastic, age-structured models for 13 extinct megafauna species from five functional/taxonomic groups, as well as 8 extant species within these groups for comparison. Perturbing specific demographic rates individually, we tested which species were more demographically susceptible to extinction, and then compared these relative sensitivities to the fossil-derived extinction chronology. Here we show that the macropodiformes were the most resilient to extinction, followed by carnivores, monotremes, vombatiform herbivores, and large birds. Five of the eight extant species were as or more susceptible than were the extinct species. There was no clear relationship between extinction susceptibility and the extinction chronology for any perturbation s...
Feral cats are one of the most destructive invasive predators worldwide. Due to the high risk of ... more Feral cats are one of the most destructive invasive predators worldwide. Due to the high risk of pushing native species to extinction in Australia, density-reduction or eradication campaigns can greatly improve the persistence probability and recovery of native fauna. Kangaroo Island — Australia’s third-largest island — was recently nominated as a complete cat-eradication site by the federal government. Because most population density-reduction campaigns are costly and not effective in the long term, mathematical models predicting optimal culling regimes can guide management plans, especially if they include estimates of costs under different policy decisions. We constructed a stochastic population model with cost estimates to test the relative effectiveness and cost-efficiency of two main culling scenarios for Kangaroo Island to 2030: (1) constant proportional annual cull, and (2) high initial culling followed by a constant proportional maintenance cull. We also examined the effect...
Nature Communications
The mechanisms leading to megafauna (>44 kg) extinctions in Late Pleistocene (126,000—12,000 y... more The mechanisms leading to megafauna (>44 kg) extinctions in Late Pleistocene (126,000—12,000 years ago) Australia are highly contested because standard chronological analyses rely on scarce data of varying quality and ignore spatial complexity. Relevant archaeological and palaeontological records are most often also biased by differential preservation resulting in under-representated older events. Chronological analyses have attributed megafaunal extinctions to climate change, humans, or a combination of the two, but rarely consider spatial variation in extinction patterns, initial human appearance trajectories, and palaeoclimate change together. Here we develop a statistical approach to infer spatio-temporal trajectories of megafauna extirpations (local extinctions) and initial human appearance in south-eastern Australia. We identify a combined climate-human effect on regional extirpation patterns suggesting that small, mobile Aboriginal populations potentially needed access to ...
Ecology and Evolution
This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Ecography
The koala's Phascolarctos cinereus distribution is currently restricted to eastern and southeaste... more The koala's Phascolarctos cinereus distribution is currently restricted to eastern and southeastern Australia. However, fossil records dating from 70 ± 4 ka (ka = 10 3 yr) from southwestern Australia and the Nullarbor Plain are evidence of subpopulation extinctions in the southwest at least after the Last Interglacial (~128-116 ka). We hypothesize that koala sub-population extinctions resulted from the eastward retraction of the koala's main browse species in response to unsuitable climatic conditions. We further posit a general reduction in the distribution of main koala-browse trees in the near future in response climate change. We modelled 60 koala-browse species and constructed a set of correlative species distribution models for five time periods: Last Interglacial (~128-116 ka), Last Glacial Maximum (~23-19 ka), Mid-Holocene (~7-5 ka), present (interpolations of observed data, representative of 1960-1990), and 2070. We based our projections on five hindcasts and one forecast of climatic variables extracted from WorldClim based on two general circulation models (considering the most pessimistic scenario of high greenhousegas emissions) and topsoil clay fraction. We used 17 dates of koala fossil specimens identified as reliable from 70 (± 4) to 535 (± 49) ka, with the last appearance of koalas at 70 ka in the southwest. The main simulated koala-browse species were at their greatest modelled extent of suitability during the Last Glacial Maximum, with the greatest loss of koala habitat occurring between the Mid-Holocene and the present. We predict a similar habitat loss between the present and 2070. The spatial patterns of habitat change support our hypothesis that koala extinctions in the southwest, Nullarbor Plain and central South Australia resulted from the eastward retraction of the dominant koala-browse species in response to long-term climate changes. Future climate patterns will likely increase the extinction risk of koalas in their remaining eastern ranges.
Global change biology, Mar 1, 2018
The current distribution of species, environmental conditions and their interactions represent on... more The current distribution of species, environmental conditions and their interactions represent only one snapshot of a planet that is continuously changing, in part due to human influences. To distinguish human impacts from natural factors, the magnitude and pace of climate shifts, since the Last Glacial Maximum, are often used to determine whether patterns of diversity today are artefacts of past climate change. In the absence of high-temporal resolution palaeoclimate reconstructions, this is generally done by assuming that past climate change occurred at a linear pace between widely spaced (usually, ≥1,000 years) climate snapshots. We show here that this is a flawed assumption because regional climates have changed significantly across decades and centuries during glacial-interglacial cycles, likely causing rapid regional replacement of biota. We demonstrate how recent atmosphere-ocean general circulation model (AOGCM) simulations of the climate of the past 21,000 years can provide...
Climatic Change, 2013
ABSTRACT Paleo-data suggest that East African mountain treelines underwent an altitudinal shift d... more ABSTRACT Paleo-data suggest that East African mountain treelines underwent an altitudinal shift during the Last Glacial Maximum (LGM). Understanding the ecological and physiological processes underlying treeline response to such past climate change will help to improve forecasts of treeline change under future global warming. In spite of significant improvements in paleoclimatic reconstruction, the climatic conditions explaining this migration are still debated and important factors such as atmospheric CO2 concentration, the impact of lapse rate decreasing temperature along altitudinal gradients and rainfall modifications due to elevation have often been neglected or simplified. Here, we assess the effects of these different factors and estimate the influence of the most dominant factors controlling changes in past treeline position using a multi-proxy approach based on simulations from BIOME4, a coupled biogeography and biogeochemistry model, modified to account for the effect of elevation on vegetation, compared with pollen, and isotopic data. The results indicate a shift in mountain vegetation at the LGM was controlled by low pCO2 and low temperatures promoting species morphologically and physiologically better adapted to LGM conditions than many trees composing the forest belt limit. Our estimate that the LGM climate was cooler than today’s by −4.5 °C (range: −4.3 to −4.6 °C) at the upper limit of the treeline, whereas at 831 m it was cooler by −1.4 °C (range: −2.6 to −0.6 °C), suggests that a possible lapse rate modification strongly constrained the upper limit of treeline, which may limit its potential extension under future global warming.
Scientific Data, 2019
The 2016 version of the FosSahul database compiled non-human vertebrate megafauna fossil ages fro... more The 2016 version of the FosSahul database compiled non-human vertebrate megafauna fossil ages from Sahul published up to 2013 in a standardized format. Its purpose was to create a publicly available, centralized, and comprehensive database for palaeoecological investigations of the continent. Such databases require regular updates and improvements to reflect recent scientific findings. Here we present an updated FosSahul (2.0) containing 11,871 dated non-human vertebrate fossil records from the Late Quaternary published up to 2018. Furthermore, we have extended the information captured in the database to include methodological details and have developed an algorithm to automate the quality-rating process. The algorithm makes the quality-rating more transparent and easier to reproduce, facilitating future database extensions and dissemination. FosSahul has already enabled several palaeoecological analyses, and its updated version will continue to provide a centralized organisation of...
Scientific Reports, 2019
The first peopling of Sahul (Australia, New Guinea and the Aru Islands joined at lower sea levels... more The first peopling of Sahul (Australia, New Guinea and the Aru Islands joined at lower sea levels) by anatomically modern humans required multiple maritime crossings through Wallacea, with at least one approaching 100 km. Whether these crossings were accidental or intentional is unknown. Using coastal-viewshed analysis and ocean drift modelling combined with population projections, we show that the probability of randomly reaching Sahul by any route is <5% until ≥40 adults are 'washed off' an island at least once every 20 years. We then demonstrate that choosing a time of departure and making minimal headway (0.5 knots) toward a destination greatly increases the likelihood of arrival. While drift modelling demonstrates the existence of 'bottleneck' crossings on all routes, arrival via New Guinea is more likely than via northwestern Australia. We conclude that anatomically modern humans had the capacity to plan and make open-sea voyages lasting several days by at least 50,000 years ago. Increased attention to maritime landscapes over the last two decades has re-invigorated investigation into the role of coastal environments and sea travel in the behavioural evolution of our species. New evidence has fundamentally changed our understanding of the cognitive capacity of anatomically modern humans 1,2 , genetic ancestry 3 , dispersal patterns from Africa 4 and the peopling of new environments 5,6. However, the role of coastlines and coastal resources in the dispersal of modern humans has been much debated. Proponents of a coastal migration model for H. sapiens out of Africa argue that coastlines would have provided for a fast, directional population expansion with predictable resources and supplies of potable water 7. Those opposing, point out that there is little direct evidence to support a coastal-highway hypothesis and that there is evidence that early humans were able to make use of savanna and rainforest environments 2,8. More recent papers propose a less dichotomous model featuring flexibility, involving use of coasts and estuaries, but not exclusively relying on them 4,5,9. Whatever the reality, it is clear that the ability to make even rudimentary watercraft and move directionally over water, both across large rivers and in traversing unknown sections of coastline, would have given H. sapiens a selective advantage over other hominins. Australia and the islands to its north (the Wallacean Archipelago) have been at the forefront of this debate because the maritime crossing from Sunda to Sahul requires lengthy water crossings that appear to have been beyond the capacity of earlier hominins.
Nature Ecology and Evolution, 2019
The timing, context and nature of the first people to enter Sahul is still poorly understood owin... more The timing, context and nature of the first people to enter Sahul is still poorly understood owing to a fragmented archaeological record. However, quantifying the plausible demographic context of this founding population is essential to determine how and why the initial peopling of Sahul occurred. We developed a stochastic, age-structured model using demographic rates from hunter-gatherer societies, and relative carrying capacity hindcasted with LOVECLIM’s net primary productivity for northern Sahul. We projected these populations to determine the resilience and minimum sizes required to avoid extinction. A census founding population of between 1,300 and 1,550 individuals was necessary to maintain a quasi-extinction threshold of ≲0.1. This minimum founding population could have arrived at a single point in time, or through multiple voyages of ≥130 people over ~700–900 years. This result shows that substantial population amalgamation in Sunda and Wallacea in Marine Isotope Stages 3–4 provided the conditions for the successful, large-scale and probably planned peopling of Sahul.
Biology Letters, 2018
The last large marsupial carnivores-the Tasmanian devil (Sarcophilis harri-sii) and thylacine (Th... more The last large marsupial carnivores-the Tasmanian devil (Sarcophilis harri-sii) and thylacine (Thylacinus cynocephalus)-went extinct on mainland Australia during the mid-Holocene. Based on the youngest fossil dates (approx. 3500 years before present, BP), these extinctions are often considered synchronous and driven by a common cause. However, many published devil dates have recently been rejected as unreliable, shifting the youngest mainland fossil age to 25 500 years BP and challenging the synchronous extinction hypothesis. Here we provide 24 and 20 new ages for devils and thylacines, respectively, and collate existing, reliable radiocarbon dates by quality-filtering available records. We use this new dataset to estimate an extinction time for both species by applying the Gaussian-resampled, inverse-weighted McInerney (GRIWM) method. Our new data and analysis definitively support the synchronous-extinction hypothesis, estimating that the mainland devil and thylacine extinctions occurred between 3179 and 3227 years BP.
Global Change Biology, 2018
The current distribution of species, environmental conditions and their interactions represent on... more The current distribution of species, environmental conditions and their interactions represent only one snapshot of a planet that is continuously changing, in part due to human influences. To distinguish human impacts from natural factors, the magnitude and pace of climate shifts, since the Last Glacial Maximum, are often used to determine whether patterns of diversity today are artefacts of past climate change. In the absence of high-temporal resolution palaeoclimate reconstructions, this is generally done by assuming that past climate change occurred at a linear pace between widely spaced (usually, ≥1,000 years) climate snapshots. We show here that this is a flawed assumption because regional climates have changed significantly across decades and centuries during glacial-interglacial cycles, likely causing rapid regional replacement of biota. We demonstrate how recent atmosphere-ocean general circulation model (AOGCM) simulations of the climate of the past 21,000 years can provide credible estimates of the details of climate change on decadal to centennial timescales, showing that these details differ radically from what might be inferred from longer timescale information. High-temporal resolution information can provide more meaningful estimates of the magnitude and pace of climate shifts, the location and timing of drivers of physiological stress, and the extent of novel climates. They also produce new opportunities to directly investigate whether short-term climate variability is more important in shaping biodiversity patterns rather than gradual changes in long-term climatic means. Together, these more accurate measures of past climate instability are likely to bring about a better understanding of the role of palaeoclimatic change and variability in shaping current macroecological patterns in many regions of the world.
It has been diffi cult to access projections of global-scale climate change with high temporal re... more It has been diffi cult to access projections of global-scale climate change with high temporal resolution spaning the late
Pleistocene and Holocene. Th is has limited our ability to discern how climate fl uctuations have aff ected species ’ range
dynamics and extinction processes, turn-over in ecological communities and changes in genetic diversity. PaleoView is a
new freeware tool, which provides a comprehensive but easy-to-use way to generate and view paleoclimate data at temporal
and spatial resolutions suitable for detecting biotic responses to major climate shifts since the last glacial maximum.
Regional to global scale simulations of temperature, precipitation, humidity and mean sea level pressure can be generated
from PaleoView as gridded or time series data at time intervals as short as a decade for any period during the last 21 000 yr.
Th ey can be viewed using a built-in geographical user interface or saved as data fi les. Modelled climate reconstructions
are based on daily simulation output from the Community Climate System Model ver. 3 (CCSM3). Th is global coupled
atmosphere – ocean – sea ice – land general circulation model accurately reproduces major climatic features associated with
the most recent deglaciation event, and predicts present-day patterns of climate conditions with verifi ed hindcast skill. By
providing a portal for readily accessing climate reconstructions at high temporal resolutions, PaleoView can help to better
establish the consequences of past climate fl uctuations on macro-ecological patterns of biological and genetic diversity.
NATURE CLIMATE CHANGE | VOL 6 | OCTOBER 2016 | www.nature.com/natureclimatechange 909 U nderstand... more NATURE CLIMATE CHANGE | VOL 6 | OCTOBER 2016 | www.nature.com/natureclimatechange 909 U nderstanding, predicting and mitigating the impacts of global change on biodiversity poses one of the most crucial challenges for ecologists, conservation biologists and resource managers this century 1,2 . Models forecast that human-induced climate change is likely to cause extinctions, both directly and in synergy with other threatening processes, but the range of estimates for its total impact remain worryingly large 3 . A more evidencefocused approach to global change ecology is required to gain deeper insights into the likely effect of shifts in climate and other environmental change on biodiversity over the coming decades to centuries 4 , and so to design effective conservation strategies that mitigate climate-driven biodiversity loss 5 . New research emerging at the frontiers between palaeoecology, climatology, population genetics and quantitative ecology is proving useful for uncovering past responses of species and populations to global environmental change 6,7 . However, the practical application of this long-term retrospective knowledge (derived from palaeoecological archives and proxies) in modern strategies to mitigate future climate-driven biodiversity loss has so far been limited, in part due to barriers that constrain the flow of information and collaboration between palaeoecologists and conservation biologists 8 .
The study of palaeo-chronologies using fossil data provides evidence for past ecological and evol... more The study of palaeo-chronologies using fossil data provides evidence for past ecological and evolutionary processes, and is therefore useful for predicting patterns and impacts of future environmental change. However, the robustness of inferences made from fossil ages relies heavily on both the quantity and quality of available data. We compiled Quaternary non-human vertebrate fossil ages from Sahul published up to 2013. This, the FosSahul database, includes 9,302 fossil records from 363 deposits, for a total of 478 species within 215 genera, of which 27 are from extinct and extant megafaunal species (2,559 records). We also provide a rating of reliability of individual absolute age based on the dating protocols and association between the dated materials and the fossil remains. Our proposed rating system identified 2,422 records with high-quality ages (i.e., a reduction of 74%). There are many applications of the database, including disentangling the confounding influences of hypothetical extinction drivers, better spatial distribution estimates of species relative to palaeo-climates, and potentially identifying new areas for fossil discovery.