ArticlePDF Available

Abstract

Researchers are divided about the relative importance of people versus climate in triggering the Late Holocene extinctions of the endemic large-bodied fauna on the island of Madagascar. Specifically, a dramatic and synchronous decline in arboreal pollen and increase in grass pollen ca 1000 yr ago has been alternatively interpreted as evidence for aridification, increased human activity, or both. As aridification and anthropogenic deforestation can have similar effects on vegetation, resolving which of these factors (if either) led to the demise of the megafauna on Madagascar has remained a challenge. We use stable nitrogen isotope (δ15N) values from radiocarbon-dated subfossil vertebrates to disentangle the relative importance of natural and human-induced changes. If increasing aridity were responsible for megafaunal decline, then we would expect an island-wide increase in δ15N values culminating in the highest values at the time of proposed maximum drought at ca 1000 yr ago. Alternatively, if climate were relatively stable and anthropogenic habitat alteration explains the palynological signal, then we would anticipate little or no change in habitat moisture, and no systematic, directional change in δ15N values over time. After accounting for the confounding influences of diet, geographic region, and coastal proximity, we find no change in δ15N values over the past 10 000 yr, and no support for a period of marked, geographically widespread aridification culminating 900-950 yr ago. Instead, increases in grasses at around that time may signal a transition in human land use to a more dedicated agro-pastoralist lifestyle, when megafaunal populations were already in decline. Land use changes ca 1000 yr ago would have simply accelerated the inevitable loss of Madagascar's megafauna.


Island-wide aridity did not trigger recent megafaunal extinctions in
Madagascar

Crowley, Brooke; Godfrey, Laurie; Bankoff, Richard; Perry, George; Culleton,
Brendan; Kennett, Douglas; Sutherland, Mike; Samonds, Karen; Burney, David
A.
!"!!
#$"
%&
"&"
!!&!&
"'!
!&!()
*"
(+,-)!""!"
!.
"&
+,-!!
&'!&
!""
&"
&&+,-!!'
&&
&+,-!!&&
/&
00,.&

&#
&!!"
1
... Paleoclimate proxies from southwest Madagascar, particularly records of δ18O which serve as proxies for precipitation and evidence dry and wet periods, indicate a highly variable climate over the past millennium, including a series of extreme drought events (Figure 7-2;Faina et al. 2021;Hixon et al. 2021;Razanatsoa 2019). These changes overlap with megafaunal extinction events (e.g., Li et al. 2020;Virah-Sawmy et al. 2010) and landscape-scale ecological shifts, some of which are directly related to changes in human subsistence practices meant to cope with such environmental instability (Crowley et al. 2017;Godfrey et al. 2019). ...
... Such datasets are crucial for understanding landscape scale dynamics of human-environment interaction, but also require highly resolved paleoclimatic records to model the effects of environmental change on human behavior (d'Alpoim Guedes et al. 2016;Davis 2019b). Extensive paleoclimate work has been conducted on Madagascar and its surrounding regions (e.g., Burney 1999;Crowley et al. 2017;de Boer et al. 2014;Dewar and Richard 2007b;Douglass and Zinke 2015;Godfrey et al. 2019;Grove et al. 2012;Hixon et al. 2018;Kull 2000;Kull et al. 2012;Scroxton et al. 2017;Virah-Sawmy et al. 2009Voarintsoa et al. 2017;Zinke et al. 2004). However, no studies on Madagascar have yet applied marine paleoclimate records to archaeological data. ...
Thesis
People on Madagascar have coped with environmental change for millennia. Present-day environmental change, however, is negatively impacting the livelihoods and sustainability of coastal communities on Madagascar. As a result of increasing climate-driven impacts on livelihoods and economic development initiatives, community settlement strategies are shifting towards increased sedentism. This dissertation investigates settlement patterns of mobile foraging populations, their drivers, and ecological effects in Late Holocene Madagascar. Specifically, I investigate environmental links to settlement patterns via remotely sensed environmental and archaeological data and radiocarbon chronology from identified archaeological deposits. While most studies of settlement distribution focus on socioecological drivers, in this project I also devote attention to the ecological legacy effects of human settlement by looking at the geochemical and spectral properties of archaeologically inhabited areas. In this way, this dissertation seeks a holistic understanding of settlement distribution in Southwest Madagascar extending from its driving forces to its long-lasting effects on ecological systems. Using a predictive modeling protocol rooted in ideal distribution models from human behavioral ecology, I use machine learning algorithms to extract culturally significant environmental variables from Sentinel-2 satellite images. These data then aid in exploring the degree to which resource distribution is correlated with settlement density, whether Allee effects account for settlement patterns, and the resulting ecological impact of foraging activity on the Malagasy landscape over thousands of years. Identified cultural deposits are visited during ground investigations to survey and excavate different areas to acquire temporal information (e.g., 14C dates, ceramics, etc.). Based on this newly generated archaeological settlement record, these data are incorporated into spatial point process models (PPMs), a form of regression analysis, of archaeological settlements to investigate the relationship between environmental conditions and settlement distributions. PPMs help to reveal external ecological relationships as well as dispersive or cohesive properties between archaeological points. Finally, using an automated remote sensing procedure employing a combination of Sentinel-2 and PlanetScope imagery and random forest models, I quantify the extent of cultural niche construction resulting from foraging communities in the Velondriake Marine Protected Area in southwest Madagascar since the Late Holocene. Altogether, this dissertation demonstrates that foraging communities in Late Holocene Madagascar settled the landscape according to the principles of an ideal free distribution with Allee effects, meaning that a strong mix between environmental and social factors, including active landscape modification (or niche construction) drove settlement choice. Specifically, the presence of freshwater sources, community defense, and social cohesion were among the most significant drivers of settlement patterns, followed by marine resource access (i.e., coral reefs). Additionally, it appears that almost 20% of the Velondriake region has been anthropogenically modified, demonstrating that foraging communities leave quantifiable and long-lasting impacts on ecological systems. Over the last millennium, communities in the Velondriake region have maintained close social connections, which have shifted geographically over the last several hundred years. Settlements appear to reflect a variety of long-term and seasonal occupations that exploited a variety of marine habitats including coastal coral reefs, oceans, and mangrove forests.
... Thus we consider the period of established and continuous human habitation to be the time frame encompassing~2500 years BP onward [3][4][5]32,33 , when the human population expanded and started to have a strong impact on the island's ecosystems. Third, there is uncertainty about whether the recent extinctions were mainly caused by humans, natural changes or a combination of both 6,[34][35][36][37] . For some species, an anthropogenic cause of extinction has been suggested 38 . ...
Article
Full-text available
Many of Madagascar’s unique species are threatened with extinction. However, the severity of recent and potential extinctions in a global evolutionary context is unquantified. Here, we compile a phylogenetic dataset for the complete non-marine mammalian biota of Madagascar and estimate natural rates of extinction, colonization, and speciation. We measure how long it would take to restore Madagascar’s mammalian biodiversity under these rates, the “evolutionary return time” (ERT). At the time of human arrival there were approximately 250 species of mammals on Madagascar, resulting from 33 colonisation events (28 by bats), but at least 30 of these species have gone extinct since then. We show that the loss of currently threatened species would have a much deeper long-term impact than all the extinctions since human arrival. A return from current to pre-human diversity would take 1.6 million years (Myr) for bats, and 2.9 Myr for non-volant mammals. However, if species currently classified as threatened go extinct, the ERT rises to 2.9 Myr for bats and 23 Myr for non-volant mammals. Our results suggest that an extinction wave with deep evolutionary impact is imminent on Madagascar unless immediate conservation actions are taken.
... As in other parts of the world once human populations began to expand, their activities had substantial impacts on local biota. This process resulted in landscape transforma-tion from ca. 300 CE onward (35,36) and subsequent extinction of Madagascar's once rich megafauna (here defined as vertebrates >10 kg) through a combination of hunting and habitat displacement (34,(37)(38)(39)(40). These extinctions may have accelerated as a result of a shift from hunting and foraging to herding and farming as the predominant methods of obtaining food, which brought land clearance and transformation to agricultural land (41). ...
Article
Full-text available
Madagascar's biota is hyperdiverse and includes exceptional levels of endemicity. We review the current state of knowledge on Madagascar's past and current terrestrial and freshwater biodiversity by compiling and presenting comprehensive data on species diversity, endemism, and rates of species description and human uses, in addition to presenting an updated and simplified map of vegetation types. We report a substantial increase of records and species new to science in recent years; however, the diversity and evolution of many groups remain practically unknown (e.g., fungi and most invertebrates). Digitization efforts are increasing the resolution of species richness patterns and we highlight the crucial role of field- and collections-based research for advancing biodiversity knowledge and identifying gaps in our understanding, particularly as species richness corresponds closely to collection effort. Phylogenetic diversity patterns mirror that of species richness and endemism in most of the analyzed groups. We highlight humid forests as centers of diversity and endemism because of their role as refugia and centers of recent and rapid radiations. However, the distinct endemism of other areas, such as the grassland-woodland mosaic of the Central Highlands and the spiny forest of the southwest, is also biologically important despite lower species richness. The documented uses of Malagasy biodiversity are manifold, with much potential for the uncovering of new useful traits for food, medicine, and climate mitigation. The data presented here showcase Madagascar as a unique "living laboratory" for our understanding of evolution and the complex interactions between people and nature. The gathering and analysis of biodiversity data must continue and accelerate if we are to fully understand and safeguard this unique subset of Earth's biodiversity.
... Importantly, while inappropriate priors can result in false signal of synchronicity in ABC analyses, we show our data have substantial power to detect asynchronous divergence under informed divergence time priors Oaks et al., 2014). In agreement with our results, several studies have shown that glacial cycles across Madagascar's ecoregions were not ubiquitous, and island-wide patterns are at least partially influenced by species-specific responses even in shared environments (Burney, 1987(Burney, , 1996Burney et al., 2004;Crowley et al., 2017;Gasse & Van Campo, 1998;Goodman & Jungers, 2014). ...
Article
A long history of isolation coupled with complex landscapes makes Madagascar ideal for exploring the historical factors that have shaped patterns of population diversity and endemism. Many species‐level studies have suggested Late Quaternary climate change may have influenced population dynamics in the tropics, but unique biomes and individual species properties may have driven idiosyncratic responses to these shifts. Here, we use community‐scale population genetic data to investigate the impact of Quaternary climate cycles on shared demographic response and investigate the contributions of both biotic and abiotic factors which shape these demographic trajectories. Madagascar. Reptiles and Amphibians. Using community‐scale population genetic data, we implement a hierarchical approximate Bayesian computation approach to evaluate the degree of synchronous population expansion during glacial cycles across herpetofaunal assemblages both within and across discrete biomes and taxonomic groups. We use Bayesian model averaging to identify intrinsic and extrinsic conditions predictive of individualistic demographic change. We find that demographic responses are not uniform across groups, with more than 50% of all populations showing signal of recent expansion. Our explanatory models indicate species occupying narrow elevational ranges had a higher probability of expansion, while amphibian assemblages showed higher genetic diversity and greater departures from population neutrality. Expansion events were largely asynchronous, with coexpansion found in less than half of all populations. Exceptionally, 69%–74% of all humid‐restricted populations coexpanded during the start of the Last Glacial Period at around 100 kya, supporting the hypothesis of a more extensive humid forest cover for Madagascar during this time. We show that differences in life history and regional biogeography have contributed to patterns of richness and endemism found across Madagascar, and historical connectivity across humid forests has been an important factor in shaping present‐day diversity and endemism on Madagascar, particularly for amphibians.
Article
Full-text available
People could have hunted Madagascar’s megafauna to extinction, particularly when introduced taxa and drought exacerbated the effects of predation. However, such explanations are difficult to test due to the scarcity of individual sites with unambiguous traces of humans, introduced taxa, and endemic megaherbivores. We excavated three coastal ponds in arid SW Madagascar and present a unique combination of traces of human activity (modified pygmy hippo bone, processed estuarine shell and fish bone, and charcoal), along with bones of extinct megafauna (giant tortoises, pygmy hippos, and elephant birds), extirpated fauna (e.g., crocodiles), and introduced vertebrates (e.g., zebu cattle). The disappearance of megafauna from the study sites at ~ 1000 years ago followed a relatively arid interval and closely coincides with increasingly frequent traces of human foraging, fire, and pastoralism. Our analyses fail to document drought-associated extirpation or multiple millennia of megafauna hunting and suggest that a late combination of hunting, forest clearance, and pastoralism drove extirpations.
Article
Archaeoprimatology intertwines archaeology and primatology to understand the ancient liminal relationships between humans and nonhuman primates. During the last decade, novel studies have boosted this discipline. This edited volume is the first compendium of archaeoprimatological studies ever produced. Written by a culturally diverse group of scholars, with multiple theoretical views and methodological perspectives, it includes new zooarchaeological examinations and material culture evaluations, as well as innovative uses of oral and written sources. Themes discussed comprise the survey of past primates as pets, symbolic mediators, prey, iconographic references, or living commodities. The book covers different regions of the world, from the Americas to Asia, along with studies from Africa and Europe. Temporally, the chapters explore the human-nonhuman primate interface from deep in time to more recent historical times, covering both extinct and extant primate taxa. This anthology of archaeoprimatological studies will be of interest to archaeologists, primatologists, anthropologists, art historians, paleontologists, conservationists, zoologists, historical ecologists, philologists, and ethnobiologists.
Chapter
Archaeoprimatology intertwines archaeology and primatology to understand the ancient liminal relationships between humans and nonhuman primates. During the last decade, novel studies have boosted this discipline. This edited volume is the first compendium of archaeoprimatological studies ever produced. Written by a culturally diverse group of scholars, with multiple theoretical views and methodological perspectives, it includes new zooarchaeological examinations and material culture evaluations, as well as innovative uses of oral and written sources. Themes discussed comprise the survey of past primates as pets, symbolic mediators, prey, iconographic references, or living commodities. The book covers different regions of the world, from the Americas to Asia, along with studies from Africa and Europe. Temporally, the chapters explore the human-nonhuman primate interface from deep in time to more recent historical times, covering both extinct and extant primate taxa. This anthology of archaeoprimatological studies will be of interest to archaeologists, primatologists, anthropologists, art historians, paleontologists, conservationists, zoologists, historical ecologists, philologists, and ethnobiologists.
Article
Objectives The Holocene arrival of humans on Madagascar precipitated major changes to the island's biodiversity. The now-extinct, endemic “subfossil” megafauna of Madagascar were likely hunted by early human inhabitants. Perhaps in part due to preferential hunting of larger prey, no surviving endemic species on Madagascar is >10 kg. Moreover, some subfossil bones of extant lemurs are considerably larger than those of the modern members of their species, but subfossil versus modern locale differences for the comparisons conducted to date lead to uncertainty about whether these size differences reflect in situ change or pre-existing ecogeographic variation. Here, we revisited this question with samples from nearby locales. Materials and Methods We used high-resolution 3D scan data to conduct comparative morphological analyses of subfossil and modern skeletal remains of one of the larger extant lemurs, Verreaux's sifakas (Propithecus verreauxi) from subfossil and modern sites only ~10 km apart: Taolambiby (bones dated to 725–560—1075–955 cal. years before present) and Beza Mahafaly Special Reserve, respectively. Results The mean aggregate score for all subfossil elements (n = 12; 0.089 ± 0.117) is significantly greater than that for the modern individuals (n = 31; 0.009 ± 0.045; t-test; p = 0.039). We found that the average subfossil sifaka bone is ~9% larger than that of modern sifakas (permutation test p = 0.037). Discussion We cannot yet conclude whether this size difference reflects evolutionary change or an archaeological aggregation/taphonomic process. However, if this is a case of phyletic dwarfism in response to human size-selective harvesting pressures then the estimated rate of change is greater than those previously calculated for other archaeological cases of this phenomenon.
Article
Full-text available
Madagascar experienced a major faunal turnover near the end of the first millenium CE that particularly affected terrestrial, large-bodied vertebrate species. Teasing apart the relative impacts of people and climate on this event requires a focus on regional records with good chronological control. These records may document coeval changes in rainfall, faunal composition, and human activities. Here we present new paleontological and paleoclimatological data from southwestern Madagascar, the driest part of the island today. We collected over 1500 subfossil bones from deposits at a coastal site called Antsirafaly and from both flooded and dry cave deposits at Tsimanampesotse National Park. We built a chronology of Late Holocene changes in faunal assemblages based on 65 radiocarbon-dated specimens and subfossil associations. We collected Frontiers in Ecology and Evolution | www.frontiersin.org 1 September 2021 | Volume 9 | Article 742203 Godfrey et al. Holocene Extinction in SW Madagascar stalagmites primarily within Tsimanampesotse but also at two additional locations in southern Madagascar. These provided information regarding hydroclimate variability over the past 120,000 years. Prior research has supported a primary role for drought (rather than humans) in triggering faunal turnover at Tsimanampesotse. This is based on evidence of: (1) a large freshwater ecosystem west of what is now the hypersaline Lake Tsimanampesotse, which supported freshwater mollusks and waterfowl (including animals that could not survive on resources offered by the hypersaline lake today); (2) abundant now-extinct terrestrial vertebrates; (3) regional decline or disappearance of certain tree species; and (4) scant local human presence. Our new data allow us to document the hydroclimate of the subarid southwest during the Holocene, as well as shifts in faunal composition (including local extirpations, large-vertebrate population collapse, and the appearance of introduced species). These records affirm that climate alone cannot have produced the observed vertebrate turnover in the southwest. Human activity, including the introduction of cattle, as well as associated changes in habitat exploitation, also played an important role.
Conference Paper
Faunal remains at archaeological sites can be used to address direct anthropogenic impacts on ecosystems. However, due to the late arrival of modern humans to Madagascar the decline of megafauna on the island, particularly of giant lemurs, remains under debate. Currently, direct evidence of human skeletal modifications and hunting of megafauna is limited. In addition, methods previously used to address the extent of post mortem processing of megafauna, including cut mark morphology, are time-consuming, introduce unwanted measurement errors, and are prohibitively expensive for large samples. However, 3D digital microscopy can address these limitations and provide detailed morphometric analysis (e.g. depth, width, and length) of potential bone modifications associated with human butchery. In this poster, we test the use of 3D digital microscopy using a Keyence 3D digital Microscope VHX-2000E to analyze bone modifications on epoxy resin positive casts of femora and humeri from Pachylemur, Palaeopropithecus, and Archaeolemur from four paleontological sites in Southwest Madagascar including Ampasambazimba, Beloha Anavoha, Tsirave, and Manombo Toliara. Preliminary results of our analysis show an overall improvement (<1mm) in morphometric data of cut marks compared to previous methods and lends archaeological support to the role of human hunting in Malagasy megafaunal decline. In addition, frequencies of modification in this study average 1-3% at Ampasambazimba, Beloha Anavoha, and Manombo Toliara, and 13% at Tsirave suggest potential site bias. Future work will address this bias and use 3D microscopic image stitching to identify tool class and usage patterns in megafaunal butchery.