Rodent Middens

2356 PLANT MACROFOSSIL METHODS AND STUDIES/Rodent Middens Kolstrup, E. (1980). Climate and stratigraphy in northwestern Alticola (mountain voles) and Ochotona (pikas) in Europe between 30 000 BP and 13 000 BP, with special reference central Asia, and Leporillus (stick-nest rats) in to The Netherlands. Med. Rijks Geol. Dienst 32(15), 181–253. Australia. The studies of South American middens Kultti, S., Va¨liranta, M., Sarmaja-Korjonen, K., et al. (2003). have mostly concerned pollen analysis, although a Palaeoecological evidence of changes in vegetation and climate during the Holocene in the pre-Polar Urals, northeast European few plant macrofossil records have been developed Russia. Journal of Quaternary Science 18(6), 503–520. (Betancourt et al., 2000; Latorre et al., 2002). The Kultti, S., Oksanen, P. and Va¨liranta, M. (2004). Holocene tree studies of hyrax middens from the Middle East and line, permafrost, and climate dynamics in the Nenets region, desert regions of Africa have focused mainly on East European Arctic. Canadian Journal of Earth Sciences 41, pollen (Scott and Vogel, 2000). The few studied 1141–1158. Lang, G. (1994). Quarta¨re Vegetationsgeschichte Europas. Fischer Stick-nest rat middens in Australia are all of late Verlag, Jena, Germany. Holocene age (Pearson, 1999). Little research has Lotter, A. F. and Birks, H. J. B. (2003). The Holocene palaeolim- been done on porcupine middens in North nology of Sa¨gistalsee and its environmental history—A synth- America, although these middens are known to esis. Journal of Paleolimnology 30, 333–342. Rasmussen, P. and Anderson, N. J. (2005). Natural and anthro- persist as long as 25,000 years in arid conditions pogenic forcing of aquatic macrophyte development in a shal- (Betancourt et al., 1986). The middens of North low Danish lake during the last 7000 years. Journal of American packrats have yielded by far the most Biogeography 32, 1993–2005. well-studied records of late Pleistocene plant Scheffer, M., Hosper, S. H., Meijer, M.-L., Moss, B. and Jeppesen, macrofossils. This article focuses primarily on this E. (1993). Alternative equilibria in shallow lakes. TREE 8, 275–279. remarkable record. Smol, J. P. (2002). Pollution of Lakes and Rivers. A Paleoenvironmental Perspective. Arnold, London. Va¨liranta, M. (2005). Plant Macrofossil Evidence of Changes in North American Packrat Middens Aquatic and Terrestrial Environments in North-eastern European Russia and Finnish Lapland since Late Weichselian. Packrats, or woodrats, are the native North PhD thesis No. 181, Department of Geology, University of American rats of the genus Neotoma (Fig. 1). There Helsinki. ISSN 1795-3499, ISBN 952-10-2153-5 (PDF). are 21 species in this genus. These rats are broadly Wasylikowa, K. (2005). Palaeoecology of Lake Zeribar, Iran, in the Pleniglacial, Lateglacial and Holocene, reconstructed from distributed, ranging from Arctic Canada to plant macrofossils. The Holocene 15, 720–735. Nicaragua. They are a very successful group, and only a few species inhabit desert and semi-arid regions. While packrats are not strict herbivores, plants are by far the most important part of their Rodent Middens diets. Packrats live in dens. Regardless of size, each den is occupied by one individual, or the female and S A Elias, Royal Holloway, University of London, Surrey, UK her young. These dens range from piles of sticks ª 2007 Elsevier B.V. All rights reserved. Introduction The study of Pleistocene terrestrial environments has tended to focus mainly on the middle and high latitude regions where water-lain deposits (lake sediments, peat bogs, fluvial deposits) tend to be well preserved. By their very nature, most desert and semi-arid regions offer few if any archives of waterlain sediments for such studies. However, an important, if unexpected archive of Pleistocene desert environments does exist, in the form of rodent middens. Rodent middens are pro- duced by Neotoma (packrats) and Erethizon (porcupine) in North America; Lagidium (viscacha), Phyllotis (leaf-eared mice), Abrocoma (chinchilla rats) and Octodontomys (mountain degu) in South Figure 1 Photograph of a packrat (Neotoma), the principle America; Procavia (rock hyrax) and Petromus agent of plant materials that become incorporated into packrat (Dassie rat) in Africa and the Middle East; middens (photo courtesy of Corel Corporation). PLANT MACROFOSSIL METHODS AND STUDIES/Rodent Middens 2357 fossils, because the packrat is the primary agent that accumulates the materials found in middens. They eat a wide variety of plants, and the unconsumed pieces of these plants eventually form the bulk of the plant macrofossils in midden records. Because of the rodent’s food preferences, plant macrofossil records from middens do not represent the full spec- trum of regional vegetation; nevertheless, the variety of plant species found in these assemblages can be truly remarkable. Dial and Czaplewski (1990) discussed the problems of potential bias in packrat midden plant macrofossil assemblages. Their study concluded that if several middens are studied from a Figure 2 Packrat (Neotoma) midden sample from a rock shelter at Emery Falls, Grand Canyon, Arizona. Photo by Thomas Van given region, then the contemporaneous plant species Devender The shiny surface is amberat (dried packrat urine). diversity of that region may be fairly represented in Note fossil conifer needles that have weathered out from the the suite of midden samples. A study of paired sam- broken edge of the midden. ples of modern vegetation communities and paired samples of ancient communities was used to investi- under shrubs or trees to more elaborate shelters in gate the probability that the absence of a plant taxon caves and rock shelters. In the arid Southwest, these from a packrat midden implies absence from the dens often include tightly-packed bundles of cactus ancient plant community where the packrat lived stems that deter predators. Besides bedding material (Nowak et al., 2000). The probability of the occur- and food plants, packrats also accumulate other rence of a false inference was calculated to be from objects from the surrounding landscape. These 7–11%, depending on the taxon. Lyford et al. (2004) objects, plus packrat feces, are cemented together studied the contents of 59 modern packrat (Neotoma by successive layers of dried rat urine to form a mid- cinerea) middens in escarpments and canyons in three den (Fig. 2). The crystalized urine layers encapsulate states in the Rocky Mountain region. They found plant materials and rat feces to form a hardened that these middens are highly reliable sensors for mass, called amberat. When protected from direct the presence of key woody plant species, such as rainfall and high humidity, amberat is extremely Juniperus osteosperma (Utah juniper) and J. scopu- resistant to decomposition. It secures biological spe- lorum (Rocky Mountain juniper), but that other con- cimens (plant parts, bones, insects, etc.) into a kind of ifers were occasionally absent from modern middens desiccated time capsule, documenting the ancient life if their presence in the local vegetation cover was less of the region. Middens of late Holocene age have than 20% of the canopy cover. been found throughout the western United States and southwestern Canada (Hebda et al., 1990). In How Middens Are Analyzed the arid regions of the southwestern United States and northern Mexico, many packrat middens have Packrat midden analysis methods have been remained intact beyond the limit of the radiocarbon described by Spaulding et al. (1990). Most ancient dating method (>45,000 years). packrat middens are indurated (hardened almost to Packrat ecology has been described by Vaughan the consistency of rock), and resemble blocks of (1990). Packrats require succulent plants for food, asphalt. Amberat forms a tough, outer rind that and they must have shelter, as they do not have the resists erosion and decomposition (Fig. 1). When metabolic mechanisms for water retention found in moist, amberat is sticky. It is this stickiness that some other rodents. The dens are often built in rock often cements middens to the walls of caves or rock shelters, crevices, and caves, where there is a micro- shelters. Midden samples are taken by the removal of climate that is significantly buffered from ambient discrete horizontal sections of midden, often using climatic conditions. The annual variation of tempera- hammers and chisels. Each sample is radiocarbon- tures in packrat dens from mid- to high latitudes is as dated, because successive layers in a midden may little as 15 C. Packrat middens accumulate as long as have been deposited at widely-spaced time intervals, a den is occupied. In sheltered localities, these mid- or occasionally in random order. Radiocarbon dates dens may accumulate for millennia, as favorable den- are often obtained from packrat fecal pellets, or from ning sites are inhabited by succeeding generations of plant macrofossils. The majority of middens are of packrats. Packrat middens are an unusual source of Holocene and late Wisconsin age (Fig. 3). 2358 PLANT MACROFOSSIL METHODS AND STUDIES/Rodent Middens samples discussed here have been taken from canyons and rocky hillsides, just above the desert floor. In the American Southwest, no Pleistocene middens have been sampled at elevations greater than 2,500 m. The elevational distribution of midden samples reflects regional physiography. Sites south of 36 latitude generally occur at elevations below 1,500 m, while more northerly

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