Exploring the influence of ancient and historic megaherbivore extirpations on the global methane budget.
Globally, large-bodied wild mammals are in peril. Because "megamammals" have a disproportionate influence on vegetation, trophic interactions, and ecosystem function, declining populations are of considerable conservation concern. However, this is not new; trophic downgrading occurred in the past, including the African rinderpest epizootic of the 1890s, the massive Great Plains bison kill-off in the 1860s, and the terminal Pleistocene extinction of megafauna. Examining the consequences of these earlier events yields insights into contemporary ecosystem function. Here, we focus on changes in methane emissions, produced as a byproduct of enteric fermentation by herbivores. Although methane is ∼ 200 times less abundant than carbon dioxide in the atmosphere, the greater efficiency of methane in trapping radiation leads to a significant role in radiative forcing of climate. Using global datasets of late Quaternary mammals, domestic livestock, and human population from the United Nations as well as literature sources, we develop a series of allometric regressions relating mammal body mass to population density and CH4 production, which allows estimation of methane production by wild and domestic herbivores for each historic or ancient time period. We find the extirpation of megaherbivores reduced global enteric emissions between 2.2-69.6 Tg CH4 y(-1) during the various time periods, representing a decrease of 0.8-34.8% of the overall inputs to tropospheric input. Our analyses suggest that large-bodied mammals have a greater influence on methane emissions than previously appreciated and, further, that changes in the source pool from herbivores can influence global biogeochemical cycles and, potentially, climate.
Department of Biology, University of New Mexico, Albuquerque, NM 87131; fasmith@unm.edu.
Felisa A
FA
Smith
Department of Biology, University of New Mexico, Albuquerque, NM 87131;
John I
JI
Hammond
Department of Biology, University of New Mexico, Albuquerque, NM 87131;
Meghan A
MA
Balk
Climate, Ocean, Sea Ice Modeling, Los Alamos National Laboratory, Los Alamos, NM 87545;
Scott M
SM
Elliott
Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013.
S Kathleen
SK
Lyons
Department of Biology, University of New Mexico, Albuquerque, NM 87131;
Melissa I
MI
Pardi
Department of Biology, University of New Mexico, Albuquerque, NM 87131;
Catalina P
CP
Tomé
Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013.
Peter J
PJ
Wagner
Department of Biology, University of New Mexico, Albuquerque, NM 87131;
Marie L
ML
Westover
D000693:Anaerobiosis; D063147:Animal Distribution; D000818:Animals; D000829:Animals, Domestic; D000835:Animals, Wild; D016164:Bison; D002980:Climate; D004063:Digestion; D004196:Disease Outbreaks / Q000266:history / Q000662:veterinary; D017753:Ecosystem; D005060:Europe; D053476:Extinction, Biological; D005285:Fermentation; D017752:Greenhouse Effect; D060434:Herbivory; D049690:History, Ancient; D006802:Human Activities; D006801:Humans; D007053:Ice; D008322:Mammals / Q000378:metabolism*; D008697:Methane / Q000032:analysis* / Q000378:metabolism; D063148:Plant Dispersal; D010945:Plants, Edible; D012301:Rinderpest / Q000266:history
D007053:Ice; D008697:Methane
Anthropocene; bison overkill; megaherbivores; rinderpest; trophic downgrading