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

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.

A new late Pleistocene subfossil site (Tsaramody, Sambaina basin, central Madagascar) with implications for the chronology of habitat and megafaunal community change on Madagascar's Central Highlands

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“…Burney, , , ; Burney & Flannery, ; Burney et al ., , ; Godfrey & Irwin, ; Goodman & Jungers, ; MacPhee et al ., ). However, the importance of climate change has been challenged (Burns et al ., ; Crowley et al ., ; Godfrey et al ., ; Hixon et al ., ). To resolve this question, it is critical to track changes in faunal composition through recent geological time, paying particular attention to how distributions were affected by climate before human arrival.…”

“…Megafaunal extinction is widely believed to have been induced by humans, either directly (via hunting) or indirectly (via landscape transformation), aided by Late Pleistocene and Holocene climatic change (e.g. 2016;Crowley et al, 2017;Godfrey et al, 2019;Hixon et al, 2018). To resolve this question, it is critical to track changes in faunal composition through recent geological time, paying particular attention to how distributions were affected by climate before human arrival.…”

Anthropogenic threats can have cascading homogenizing effects on the phylogenetic and functional diversity of tropical ecosystems

“…Madagascar's bioclimatic zones comprise humid, subhumid, montane, dry, and subarid environments with distinct geographic features and vegetation patterns (Humbert 1955, Cornet 1974, Schatz 2000. These five broad climatic zones have been widely adopted and incorporated in numerous insightful taxonomic, evolutionary, ecological, conservation and biogeographic studies (Megson et al 2009, Buerki et al 2010, Irwin et al 2010, Brown et al 2014, Blair et al 2015, Vieilledent et al 2016, Crowley et al 2017, Wahlert et al 2017. Although the montane bioclimate is fairly limited in area ( Fig.…”

Using palaeoecology to determine baseline ecological requirements and interaction networks for de‐extinction candidate species

“…However, dietary stable isotopes can also be influenced by factors other than diet, such as d 15 N values, which are also affected by aridity (e.g. Crowley et al 2016;D ıaz et al 2016). In some instances, these influences can be insidious and not detected unless complementary evidence of diet is also used (Turney, Hunt & Burrows 2002;Rawlence et al 2016).…”