Evaluating socio-economic change in the Andes using oribatid mite abundances as indicators of domestic animal densities

Tracking social and economic change in Andean societies prior to the invasion of the Spanish has always been a difficult task, especially given that these cultures failed to develop any form of written record. Here we present a new method of reconstructing socio-economic shifts in a rural setting from the analysis of the frequency of oribatid mite remains present in a sedimentary lake sequence. Oribatid mites are soil-dwelling microarthropod detritivores, some of which inhabit areas of grassland pasture. One of the primary controls governing their abundance in such habitats is the level of animal dung present. We propose that past fluctuations in mite remains can be related to the density of domestic animals using the area of pasture and, by extension, may provide a proxy for broad-scale social and economic change through time. To test this hypothesis, we analysed a high-resolution (∼6 years) mite record from a sequence of well-dated sediments from Marcacocha, a climatically sensitive lake site located close to an important Inca trading route across the Andes. The timing and magnitude of mite fluctuations at Marcacocha since the 1530s show remarkable correspondence with a series of major, well-documented socio-economic shifts in the region relating to political and climatic pressures. This provided the confidence to extend the record back a further 700 years and reconstruct changes in domestic herbivore densities for a period of time that lacks historical documentation and thereby infer changes in human occupation of the basin. In particular, high mite abundances appear to correspond clearly with the rapid rise and fall of the Inca Empire (c. AD 1400–1532). We argue that small lake basins such as Marcacocha may be particularly suitable for obtaining continuous oribatid mite records and providing the possibility of reconstructing large herbivore abundances in the Andes and elsewhere.