A potential new proxy for tracking livestock densities and associated anthropogenic activity

When the Spanish conquistadors arrived in Peru in the 1530s, the highly advanced Inca state was the largest empire to have existed in the Americas, stretching from the present day Colombian border to central Chile. The Inca owed much of their spectacular success to the practices and infrastructure of earlier societies (which they had freely-adopted), as well as to their innovative adaptation strategies in the face of climatic change. However, the details surrounding the expansion, success and ultimate collapse of all these so-called pre-Columbian cultures are still poorly understood, in part because they failed to develop any form of written language and so left no documentary evidence behind. Questions relating to population size, trading activities, land use and large-scale demographic change are therefore difficult to resolve from archaeological evidence alone. This problem (by no means unique to South America) also highlights the difficulty faced by contemporary interdisciplinary climate research, which is becoming increasingly interested in how societies have responded and adapted to past climatic pressures so that models for predicting future responses under global warming scenarios might be tested.

One way of addressing this problem is provided by the reliance of these early Andean agro-pastoral societies on their livestock, which was crucially important both as a valuable food, wool, fuel and fertiliser resource, but also as a means of facilitating trade between the coast, highlands and rainforest. Being able to estimate the changing densities of livestock on the landscape could provide a first order assessment of land-use, trading strength and population migration through time (especially if considered alongside other palaeoenvironmental evidence). Promising new data from Marcacocha, a well-studied 4200-year lake record from highland Peru, has suggested a link between the quantities of camelid (chiefly llama) dung deposited in pasture areas on trading routes and the abundance of soil-dwelling mites preserved in the sediments of those grazing areas. Mites are micro-arthropods, familiar in domestic settings for inhabiting carpets and mattresses. However, some species live exclusively in moist grasslands, where they break down organic matter to provide a rich food source. Pasture mite abundances are known to respond directly to nutrient fluxes via livestock dung and their remains are often well preserved in lake sediments (as at Marcacocha).

This project proposes to apply rigorous scientific procedures to the promising Marcacocha material to test the hypothesis that mite remains can track livestock density changes through time. We have three lines of approach. The first is to use detailed taxonomy to properly identify the species present and, using what we know of their modern habitat requirements, to derive an environmental history of the sequence. Certain mite taxa may even provide evidence for particular animal groups, e.g. camelids and/or introduced livestock (e.g. cattle, sheep). The second approach is to compare the mite data against a more established proxy for detecting large animals, namely the spores of dung-inhabiting fungi (e.g. Sporormiella). Whilst spore preservation can be problematic in some settings, we know that they are present at Marcacocha. By 'calibrating' the mite data against that derived from spores (never before attempted), we will be able to develop an alternative and potentially more sensitive means of detecting herbivore presence in situations when Sporormiella evidence is lacking. Finally, we will compare the new mite (and spore) data against the other proxy evidence for anthropogenic change at Marcacocha to build up a much more detailed interpretation of the history of the region.

Development of this novel technique has applications not only across the Andes, but also in other pastoral settings (e.g. Greenland Norse) and in the study of more ancient megafaunal extinctions.

The main beneficiaries of the proposed research beyond the academic realm (see separate statement) fall into two categories:

1. Young people and interested members of the public will benefit via an increased understanding of the scientific approaches taken to understanding past climates, the key questions that drive archaeological science, the unresolved questions around the socio-economic development of past cultures and their response to climatic forcing, and our current knowledge of natural climate variability. The engagement of the research team with undergraduate students as part of their normal duties will contribute to the basic training of the next generation of young scientists and policy makers in the UK.

2. Environmentally-based NGOs working in South America and concerned with biodiversity conservation and sustainable land-use management practices in the Andes (e.g. the Asociación Ecosistemas Andinos, ECOAN). Today's Andean communities continue to face significant environmental pressures brought on by global warming, including reduced fresh water availability and land degradation. Organisations such as ECOAN will benefit from high-resolution datasets that document land-use changes over time in response to climatic variability and will help to inform ongoing policy decisions in conjunction with modelled climate change scenarios.

Our engagement activities will draw on our connection with the Natural History Museum (NHM) that will enable us to reach a very diverse audience indeed. Nature Live events are popular interactive sessions with visitors to the Museum and, furthermore, are made available via their website for subsequent video streaming. The proposed project web-pages in English and Spanish (also hosted by the NHM) will communicate the findings of the project to a variety of potential users, both academic and non-specialist alike. Furthermore, our media engagement will publicise the project locally, nationally and internationally; previous experience will allow us to target Latin American (i.e. Spanish language) outlets in particular. More local engagement (via pro-active talks for organisations such as the Geologists' and Geographical Associations) will help to inform and inspire young scientists.

The direct societal or economic impact of this research is difficult to quantify, but through the generation of high-quality new data sets that have implications for understanding human responses to climatic change, this research programme will ensure that the UK remains an important centre for tackling key earth system science questions.