Carrion decomposition and nutrient cycling in a semiarid shrub-steppe ecosystem

Vertebrate carrion decomposition and nutrient cycling have both direct and indirect effects on the soil properties, fauna, and. ora associated with an animal's carcass. While few comprehensive quantitative studies have been undertaken, those that have show considerable variability in decomposition processes and rates, their regulating variables, and the resultant ecosystem effects. In this two-part study, decomposition rates of vertebrate species were measured in a semiarid, shrub-steppe environment (Wyoming, USA). First, decomposition loss rates of mass, energy, and nutrients were measured for rat carcasses (Rattus norvegicus) in four seasons and two microsites (surface and underground burrows). Decomposition rates varied significantly between microsites (burrow > surface in spring and summer) and among seasons (spring > summer > autumn approximate to winter), with mass loss amounts linearly correlated with ambient air temperatures. Energy and nutrient losses were related to phased carcass organ/tissue losses, with energy, K, Na, N, and S being lost more quickly than skeletal components (P, Mg, Ca). Overall, the nutrient loss sequence was K = Na > N = S > P = Mg > Ca. Carcass quality (N concentration) declined through time as a function of decay stage. Second, decomposition rates of 10 vertebrate species (mule deer [Odocoileus hemionus], dog [Canis familiaris], white-tailed jackrabbit [Lepus townsendii], Uinta ground squirrel [Spermophilus armatus], least chipmunk [Tamias minimus], deer mouse [Peromyscus maniculatus], Magpie [Pica hudsonia], Sage Sparrow [Amphispiza belli], terrestrial garter snake [Thamnophis elegans], and northern leopard frog [Lithobates pipiens]) were measured with vertebrate scavengers present or absent. Mass loss rates varied among species and were generally faster in the presence of scavengers. Carcass body mass, N content, or labile/recalcitrant fractions did not correlate with decomposition rate, though surface area to volume ratios of mammal carcasses were positively correlated with wet-mass decomposition rate. Nutrient measures of sub-carcass soils showed soil N, P, and Na increased during decomposition. Increased soil nutrient amounts represented up to 15.6% of the available carcass N, 28.8% of carcass P, and 28.7% of carcass Na. At a landscape scale in the shrub steppe ecosystem, carrion decomposition constituted < 1% of the nutrient-cycling budget but contributed significantly to localized soil nutrient dynamics.