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The consequences of climate change vary over space and time. Effective studies of human responses to climatically induced environmental change must therefore sample the environmental diversity experienced by specific societies. We reconstruct population histories from A.D. 600 to 1280 in six environmentally distinct portions of the central Mesa Verde region in southwestern Colorado, relating these to climate-driven changes in agricultural potential. In all but one subregion, increases in maize-niche size led to increases in population size. Maize-niche size is also positively correlated with regional estimates of birth rates. High birth rates continued to accompany high population levels even as productive conditions declined in the A.D. 1200s. We reconstruct prominent imbalances between the maize-niche size and population densities in two subregions from A.D. 1140 to 1180 and from A.D. 1225-1260. We propose that human responses in those subregions, beginning by the mid-A.D. 1200s, contributed to violence and social collapse across the entire society. Our findings are relevant to discussions of how climate change will affect contemporary societies.Las consecuencias del cambio climático varían a través del tiempo y espacio. Por lo tanto, estudios efectivos de las respuestas humanas al cambio ambiental climáticamente inducido tienen que muestrear la diversidad ambiental experimentada por sociedades específicas. Nosotros reconstruimos historias poblacionales desde 600 hasta 1.200 d.C. en seis porciones ambientalmente distintas de la región central de Mesa Verde, en el suroeste de Colorado, relacionándolas con cambios climáticamente inducidos en el potencial agrícola. En todas menos una de las subregiones, aumentos en la extensión del nicho del maíz llevaron a incrementos en el tamaño poblacional. La extensión del nichodel maíz también está positivamente correlacionada con estimaciones regionales de tasas de natalidad. Las altas tasas de natalidad continuaron acompañando altos niveles poblacionales aún cuando las condiciones productivas declinaron en el 1.200 d.C. Nosotros reconstruimos desbalances destacados entre el tamaño del nicho del maíz y las densidades poblacionales en dos subregiones desde 1.140 a 1.180 años d.C. y desde 1.225 a 1.260 años d.C. Proponemos que, comenzando a mediados del 1.200 d.C., las respuestas humanas en estas subregiones contribuyeron a la violencia y al colapso social a través de toda la sociedad. Nuestros hallazgos son relevantes para las discusiones acerca de cómo el cambio climático afectará a las sociedades contemporáneas.

Paleosol macromorphology, petrography and stable isotope geochemistry of carbonate nodules from Permo–Triassic (P–T) boundary strata of the central Karoo basin, South Africa are presented in order to evaluate their utility as geochemical archives of Permian–Triassic paleoatmospheric chemistry and their potential to provide a terrestrial carbon isotope chemostratigraphy for correlation with contemporaneous global marine δ 13 C records. Paleosol morphologies across P–T boundary strata of the central Karoo basin indicate the region was a poorly drained, seasonally to continuously flooded bottomland. Radiaxial calcite, microspar and micrite microtextures are observed in the calcite nodules associated with P–T paleosol profiles. Micritic calcite is typical of soil carbonate that forms in well-drained soils characterized by open-system gaseous diffusion between the soil and global atmosphere, whereas more coarsely crystalline textures and radiaxial calcite are more typical of crystallization in phreatic environments with limited gaseous diffusion between the soil and global atmosphere. In this regard, only those nodules composed of micritic calcite can be considered as a potentially reliable source of proxy information for paleoatmospheric δ 13 C values across the P–T boundary. The δ 13 C values of all carbonate nodules from two overlapping measured sections near Carlton Heights, South Africa range from − 24.4‰ to − 1.8‰, whereas micritic calcite nodule δ 13 C values range from − 7.0‰ to − 21.3‰. Comparison of calcite δ 13 C values with penecontemporaneous organic matter δ 13 C values indicate that calcite δ 13 C values δ 13 C values. Rather, these more negative carbonate nodule δ 13 C values likely reflect calcite crystallization under poorly drained, swampy conditions characterized by a semi-closed chemical system that evolved independently of Earth's troposphere. Therefore, previously reported negative carbon isotope shift(s) measured from carbonate nodules in the Karoo basin P–T strata do not provide a record of atmospheric δ 13 C, and probably do not provide a viable carbon isotope stratigraphy that can be realistically correlated with global P–T marine carbon isotope stratigraphies.

We examined the influence of ecological (diet, swamp use, and rainfall) and social (intergroup interaction rate) factors on ranging behavior in one group of western gorillas (Gorilla gorilla gorilla) during a 16-month study. Relative to mountain gorillas, western gorillas live in habitats with reduced herb densities, more readily available fruit (from seasonal and rare fruit trees), and, at some sites, localized large open clearings (swamps and “bais”). Ranging behavior reflects these ecological differences. The daily path length (DPL) of western gorillas was longer (mean=2,014 m) than that of mountain gorillas, and was largely related to fruit acquisition. Swamp use occurred frequently (27% of days) and incurred a 50% increase in DPL, and 77% of the variation in monthly frequency of swamp use was explained by ripe fruit availability within the swamp, and not by the absence of resources outside the swamp. The annual home-range size was 15.4 km2. The western gorilla group foraged in larger areas each month, and reused them more frequently and consistently through time compared to mountain gorillas. In contrast to mountain gorillas, intergroup encounters occurred at least four times more frequently, were usually calm rather than aggressive, and had no consistent effect on DPL or monthly range size for one group of western gorillas. High genetic relatedness among at least some neighboring males [Bradley et al., Current Biology, in press] may help to explain these results, and raises intriguing questions about western gorilla social relationships. Am J Primatol 64:207–222, 2004. © 2004 Wiley-Liss, Inc.

The most severe mass extinction of marine species and terrestrial vertebrates and plants is associated with the Permian–Triassic boundary (∼251 Ma). The extinction interval is also marked by the disappearance of most Late Permian gymnosperm palynomorphs at a layer containing solely the abundant remains of fungi. This ‘fungal spike’ apparently represents widespread devastation of arboreous vegetation. Stratigraphic and palynological study of the Carlton Heights section in the southern Karoo Basin of South Africa revealed a 1-m-thick fungal spike zone that occurs simultaneously with the last appearance of typically Late Permian gymnosperm pollen. The plant extinction and fungal spike zone are found above the last occurrence of Late Permian mammal-like reptiles of the Dicynodont Zone at other Karoo sections. Using the fungal event as a time line in marine and non-marine sections allows placement of the marine extinctions and the extinction of terrestrial plants and reptiles within a brief crisis interval of less than about 40 000 years at the end of the Permian.

Studies of the relative effects of growing conditions on specific maize ( Zea mays L.) characters enhance interpretation of archaeological maize specimens. To understand better the contribution of moisture as a source of maize variation, this study documents morphological variability of ear, cob and kernel characters by examining a single south-western U.S. cultivar (Tohono O'odham flour maize) grown in 2 consecutive years under five controlled irrigation treatments. Variability in timing and amounts of irrigation water, as well as differences in the timing of rain between the 2 years, resulted in several statistically significant differences in morphological characters. Particularly relevant to the south-western archaeological record of predominantly dryland farming, data from the treatment irrigated only at planting demonstrated differences in maize morphology and grain yield attributable primarily to variability in rain. One character generally recorded on archaeological specimens, row number, was among those least affected by irrigation treatment and rain timing. Cupule width, another often recorded archaeological character, was moderately affected by moisture. For the combined 2-year experiment, characters listed in order from least to most affected were: kernel weight, pith diameter, row number, kernel volume, ratio of kernel width to kernel length, ratio of ear diameter to ear length, kernel thickness, cupule depth, ratio of kernel thickness to kernel length, ear diameter, ear weight, cupule width, cob diameter, ear length, rachis segment length, kernel length, and kernel width. This single cultivar study complements earlier studies of environmental effects on the morphology of maize characters. To determine if moisture effects can mask race-identifying characters, additional controlled-environment studies of other south-western maize cultivars should be conducted. The contribution of moisture, either as irrigation treatment or rain, to reproductive part morphology and grain yield must be considered in the interpretation of archaeological maize.

The most severe mass extinction of marine species and terrestrial vertebrates and plants is associated with the Permian-Triassic (P-Tr) boundary (~253 Ma). In order to investigate the relative timing of the biotic crises in terrestrial and marine environments, we studied the stratigraphy, paleomagnetism, and palynology of the Carlton Heights section in the southern Karoo Basin, South Africa. Stratigraphic and palynological study at Carlton Heights revealed the abrupt disappearance of Late Permian gymnosperm taxa and replacement by Triassic palynomorphs just below the boundary between the Balfour Formation and the Katberg sandstone, at a layer characterized by abundant remains of fungi. This “fungal spike” occurs globally in marine and terrestrial P-Tr boundary sections, and thus can be used to correlate the extinctions of marine fauna and terrestrial land plants and vertebrates in the P-Tr boundary interval. Our results suggest that the extinction of mammal-like reptiles at the end of the Permian may have preceded the fungal event and land-plant extinction within an interval of less than ~100,000 years, and possibly less than ~25,000 years.