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Island-wide aridity did not trigger recent megafaunal extinctions in Madagascar

May 2016
Ecography 40(8)

DOI:10.1111/ecog.02376

Authors:

Brooke Erin Crowley

University of Cincinnati

Laurie Godfrey

University of Massachusetts Amherst

Richard Bankoff

Pennsylvania State University

George H Perry

Pennsylvania State University

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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.

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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

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Thesis

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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.

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Full-text available

Nov 2022

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.

Part III - Africa

Article

Aug 2022

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.

Lemur Hunting in Madagascar’s Present and Past: The Case of Pachylemur

Chapter

Aug 2022

Potential evolutionary body size reduction in a Malagasy primate ( Propithecus verreauxi ) in response to human size‐selective hunting pressure

Article

Jan 2022

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.

Teasing Apart Impacts of Human Activity and Regional Drought on Madagascar’s Large Vertebrate Fauna: Insights From New Excavations at Tsimanampesotse and Antsirafaly

Article

Full-text available

Sep 2021

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.

Terrestrial eco-regions of africa and Madagascar: A conservation assessment

Article

Full-text available

Jan 2004

Pastoralists, Warriors and Colonists: The Archaeology of Southern Madagascar

Book

Jan 2010

The application of 3D digital microscopy in identifying evidence of human butchery of extant lemurs

Conference Paper

Jan 2015

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.

Extinct Madagascar: Picturing the Island's Past

Book