Effects of animal husbandry on secondary production and trophic efficiency at a regional scale

IRISARRI J.G. N.; OESTERHELD, M; GOLLUSCIO, R.A; J.M. PARUELO

ECOSYSTEMS (NEW YORK. PRINT)

SPRINGER

Lugar: Berlin; Año: 2014 vol. 17 p. 738 - 749

1432-9840

Agricultural systems are expected to have higher net secondary production (NSP) than natural systems as a result of higher trophic efficiency and lower interannual variability. These differences, however, have not been quantified across regional gradients. We compiled a dataset of herbivore biomass, consumption, NSP, annual precipitation, and aboveground net primary production (ANPP) for extensive livestock farms across a wide precipitation gradient in Argentina. We compared these data with worldwide published studies of natural systems. In a double-logarithmic scale, NSP of agricultural systems increased with ANPP from semiarid to subhumid systems and decreased from subhumid to humid systems, a response that contrasted with the linear positive increase of natural systems. Compared to natural systems dominated by homeotherms, E troph (NSP:ANPP) in agricultural systems in semiarid areas was 8 times higher, due to a 2 times higher E consump (Consumption:ANPP) and a 4 times higher E prod (NSP:Consumption). In subhumid areas, E troph was 46 times higher, due to a 13.7 times higher E consump and a 3.3 times higher E prod. In humid areas, E troph was 5 times higher, due to a 2.5 times higher E consump and a 2 times higher E prod. The interannual variation of herbivore biomass, a major determinant of NSP, was 60 % lower in agricultural than in natural systems dominated by homeotherms, and was decoupled from the variability of precipitation. Agricultural systems reach higher NSP by (1) diverting a major proportion of ANPP from the detritus to the grazing chain, (2) converting more efficiently consumption into NSP, and (3) stabilizing herbivore biomass across years.