title: Scaling methane emissions in ruminants and global estimates in wild populations.
abstract: Methane (CH4) emissions by human activities have more than doubled since the 1700s, and they contribute to global warming. One of the sources of CH4is produced by incomplete oxidation of feed in the ruminant's gut. Domestic ruminants produce most of the emissions from animal sources, but emissions by wild ruminants have been poorly estimated. This study (i) scales CH4against body mass in 503 experiments in ruminants fed herbage, and assesses the effect of different sources of variation, using published and new data; and (ii) it uses these models to produce global estimates of CH4emissions from wild ruminants. The incorporation of phylogeny, diet and technique of measuring in to a model that scales log10CH4gd-1against log10body mass (kg), reduces the slope, from 1.075 to 0.868, making it not significantly steeper than the scaling coefficient of metabolic requirements to body mass. Scaling models that include dry matter intake (DMI) and dietary fiber indicate that although both increase CH4, dietary fiber depresses CH4as the levels of DMI increases. Cattle produces more CH4per unit of DMI than red deer, sheep or goat, and there are no significant differences between CH4produced by red deer and sheep. The average estimates of global emissions from wild ruminants calculated using different models are smaller (1.094-2.687Tgy-1) than those presented in the reports of the Intergovernmental Panel on Climate Change (15Tgyr-1). Potential causes to explain such discrepancy are the uncertainty on the world's wild ruminant population size, and the use of methane output from cattle, a high methane producer, as representative methane output of wild ruminants. The main limitation researchers' face in calculating accurate global CH4emissions from wild ungulates is a lack of reliable information on their population sizes.
authors.affiliation: Grupo PAIDI RNM118, Estación Biológica de Doñana, CSIC, Sevilla 41092, Spain; Ungulate Research Unit, CRCP, University of Córdoba, Córdoba, Spain; James Hutton Institute, Craigiebuckler, AB15 8QH Aberdeen, Scotland, UK. Electronic address: j.perezbarberia@gmail.com.
authors.forename: F J
authors.initials: FJ
authors.lastname: Pérez-Barbería
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000706:statistics & numerical data; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D000835:Animals, Wild / Q000502:physiology; D057231:Climate Change; D004784:Environmental Monitoring; D008697:Methane / Q000032:analysis*; D012418:Ruminants / Q000502:physiology*
chemical_list: D000393:Air Pollutants; D008697:Methane
keywords: GHG inventory; Meta-analysis; Methane emissions; Phylogeny; Ruminants