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Many mammalian populations conform spatially and temporally to Bergmann's rule. This ecogeographic pattern is driven by selection for larger body masses by cooler temperatures and smaller ones by warming temperatures. However, it is unclear whether the response to warming or cooling temperatures is (a)symmetrical. Studies of the evolutionary record suggest that mammals evolve smaller body sizes more rapidly than larger ones, suggesting that it may be “easier” to adapt to warming climates than cooling ones. Here, we examine the potential asymmetrical response of mammals to past temperature fluctuations. We use the fossil midden record of the bushy-tailed woodrat, Neotoma cinerea, a well-studied animal that generally conforms to Bergmann's rule, to test the ability of populations to respond to warming versus cooling climate throughout its modern range in western North America over the late Quaternary. We quantified the response to temperature change, as characterized by the Greenland Ice Sheet Project 2 temperature record, using N. cinerea presence/absence and “darwins.” Our results show that populations within the modern range of N. cinerea show little difference between warming and cooling events. However, northern, peripheral populations are absent during older, cooler periods, possibly due to climate or taphonomy. Our study suggests adaptation in situ may be an underestimated response to future climate change.
The Neotoma Paleoecology Database is a community-curated data resource that supports interdisciplinary global change research by enabling broad-scale studies of taxon and community diversity, distributions, and dynamics during the large environmental changes of the past. By consolidating many kinds of data into a common repository, Neotoma lowers costs of paleodata management, makes paleoecological data openly available, and offers a high-quality, curated resource. Neotoma’s distributed scientific governance model is flexible and scalable, with many open pathways for participation by new members, data contributors, stewards, and research communities. The Neotoma data model supports, or can be extended to support, any kind of paleoecological or paleoenvironmental data from sedimentary archives. Data additions to Neotoma are growing and now include >3.8 million observations, >17,000 datasets, and >9200 sites. Dataset types currently include fossil pollen, vertebrates, diatoms, ostracodes, macroinvertebrates, plant macrofossils, insects, testate amoebae, geochronological data, and the recently added organic biomarkers, stable isotopes, and specimen-level data. Multiple avenues exist to obtain Neotoma data, including the Explorer map-based interface, an application programming interface, the neotoma R package, and digital object identifiers. As the volume and variety of scientific data grow, community-curated data resources such as Neotoma have become foundational infrastructure for big data science.
In western North America, pollen data from highland lakes are often used to reconstruct vegetation on the adjacent lowlands. Plant macrofossils and pollen from packrat middens now provide a means to evaluate such reconstructions. On the basis of pollen diagrams from the Chuska Mountains, H. E. Wright, Jr., A. M. Bent, B. S. Hansen, and L. J. Maher, Jr., ((1973), Geological Society of America Bulletin, 84 , 1155–1180) arrived at conservative estimates for late Pleistocene depression of highland conifers. In their interpretation, a proposed slight depression of 500 m for lower tree line precluded expansion of Pinus ponderosa into elevations now in desertscrub. Instead, it was suggested that pinyon pine and Artemisia occupied the lowland plateaus. Packrat midden records on either side of the Chuskas fail to verify this model. Early Holocene middens from Chaco Canyon, New Mexico, and a terminal Pleistocene midden from Canyon de Chelly, Arizona, show that blue spruce, limber pine, Douglas fir, dwarf juniper, and Rocky Mountain juniper expanded at least down to 1770 m elevation Neither Colorado pinyon nor ponderosa pine was found as macrofossils in the middens. Artemisia pollen percentages are high in the terminal Pleistocene midden, as they are in the Chuska Mountain pollen sequence, suggesting regional dominance by sagebrush steppe. Of 38 taxa identified, only 3 are shared by middens dated 11,900 and 3120 yr B.P. from Canyon de Chelly, indicating a nearly complete turnover in the flora between the late Pleistocene and late Holocene. Although corn was previously thought to have been introduced to the Colorado plateaus after 2200 yr B.P., the midden dated 3120 yr B.P. contains pollen of corn and other indicators of incipient agriculture.
Records of Holocene vegetation and climate change at low elevations (<2000 m) are rare in the central Rocky Mountain region. We developed a record of Holocene vegetation and climate change from 55 14C-dated woodrat middens at two low-elevation sites (1275 to 1590 m), currently vegetated by Juniperus osteosperma woodlands, in the northern Bighorn Basin. Macrofossil and pollen analyses show that the early Holocene was cooler than today, with warming and drying in the middle Holocene. During the Holocene, boreal (Juniperus communis, J. horizontalis) and montane species (J. scopulorum) were replaced by a Great Basin species (J. osteosperma). J. osteosperma colonized the east side of the Pryor Mountains 4700 14C yr B.P. Downward movement of lower treeline indicates wetter conditions between 4400 and 2700 14C yr B.P. Increased aridity after 2700 14C yr B.P. initiated expansion of J. osteosperma from the east to west side of the Pryor Mountains.
Temperature profoundly influences the physiology and life history characteristics of organisms, particularly in terms of body size. Because so many critical parameters scale with body mass, long-term temperature fluctuations can have dramatic impacts. We examined the response of a small mammalian herbivore, the bushy-tailed woodrat ( Neotoma cinerea), to temperature change from 20,000 yr B.P. to present, at five sites within the Colorado Plateau. Our investigations focused on the relationship between temperature, plant composition and abundance, and woodrat size. Body size was estimated by measuring fossil fecal pellets, a technique validated in earlier work. We found significant and highly covariable patterns in body mass over the five locations, suggesting that responses to temperature fluctuations during the late Quaternary have been very similar. Although woodrat mass and the occurrence of several plant species in the fossil record weresignificantly correlated, in virtually all instances changes in woodrat size preceded changes in vegetational composition. These results may be due to the greater sensitivity of woodrats to temperature, or to the shorter generation times of woodrats as compared to most plants. An alternative hypothesis is that winter temperatures increased before summer ones. Woodrats are highly sensitive to warmer winters, whereas little response would be expected from forest/woodland plants growing at their lower limits. Our work suggests that woodrat size is a precise paleothermometer, yielding information about temperature variation over relatively short-term temporal and regional scales.
So-called annual banding has been identified in a number of speleothems in which the number of bands approximates the time interval between successive U-series dates. The apparent annual resolution of speleothem records, however, remains largely untested. Here we statistically compare variations in band thickness from a late Holocene stalagmite in Carlsbad Cavern, Southern New Mexico, USA, with three independent tree-ring chronologies form the same region. We found no correspondence. Although there may be various explanations for the discordance, this limited exercise suggests that banded stalagmites should be held to the same rigorous standards in chronology building and climatic inference as annually resolved tree rings, corals, and ice cores.
Advancements in ancient DNA analyses now permit comparative molecular and morphological studies of extinct animal dung commonly preserved in caves of semiarid regions. These new techniques are showcased using a unique dung deposit preserved in a late glacial vizcacha (Lagidium sp.) midden from a limestone cave in southwestern Argentina (38.5° S). Phylogenetic analyses of the mitochondrial DNA show that the dung originated from a small ground sloth species not yet represented by skeletal material in the region, and not closely related to any of the four previously sequenced extinct and extant sloth species. Analyses of pollen and plant cuticles, as well as analyses of the chloroplast DNA, show that the Cuchillo Curá ground sloth browsed on many of the same herb, grass, and shrub genera common at the site today, and that its habitat was treeless Patagonian scrub-steppe. We envision a day when molecular analyses are used routinely to supplement morphological identifications and possibly to provide a time-lapse view of molecular diversification.
A new packrat midden chronology from Playas Valley, southwestern New Mexico, is the first installment of an ongoing effort to reconstruct paleovegetation and paleoclimate in the U.S.A.–Mexico Borderlands. Playas Valley and neighboring basins supported pluvial lakes during full and/or late glacial times. Plant macrofossil and pollen assemblages from nine middens in the Playas Valley allow comparisons of two time intervals: 16,000–10,000 and 4000–0 14C yr B.P. Vegetation along pluvial lake margins consisted of open pinyon–juniper communities dominated by Pinus edulis, Juniperus scopulorum, Juniperus cf. coahuilensis, and a rich understory of C4 annuals and grasses. This summer-flowering understory is also characteristic of modern desert grassland in the Borderlands and indicates at least moderate summer precipitation. P. edulis and J. scopulorum disappeared or were rare in the midden record by 10,670 14C yr B.P. The late Holocene is marked by the arrival of Chihuahuan desert scrub elements and few departures as the vegetation gradually became modern in character. Larrea tridentata appears as late as 2190 14C yr B.P. based on macrofossils, but may have been present as early as 4095 14C yr B.P. based on pollen. Fouquieria splendens, one of the dominant desert species present at the site today, makes its first appearance only in the last millennium. The midden pollen assemblages are difficult to interpret; they lack modern analogs in surface pollen assemblages from stock tanks at different elevations in the Borderlands.
Animals respond to climatic change by adapting or by altering distributional patterns. How an animal responds is influenced by where it is positioned within its geographic range; the probability of extirpation is increased near range boundaries. Here, we examine the impact of Holocene climatic fluctuations on a small mammalian herbivore, the bushy-tailed woodrat (Neotoma cinerea), at five locations within south central Idaho and northwestern Utah. Previous work demonstrated that woodrats adapt to temperature shifts by altering body size. We focus here on the relationship between body mass, temperature, and location within the geographic range. Body mass is estimated by measuring fossil fecal pellets, a technique validated in earlier work. Overall, we find the predicted phenotypic response to climate change: animals were larger during cold periods, and smaller during warmer episodes. However, we also identify several time periods when changes in environmental temperature exceeded the adaptive flexibility of N. cinerea. A smaller-bodied species, the desert woodrat (N. lepida) apparently invaded lower elevation sites during the mid-Holocene, despite being behaviorally and physically subordinate to N. cinerea. Analysis of contemporary patterns of body size and thermal tolerances for both woodrat species suggests this was because of the greater heat tolerance of N. lepida. The robust spatial relationship between contemporary body size and ambient temperature is used as a proxy to reconstruct local climate during the Holocene.
Patterns of climate and C4plant abundance in the southwestern United States during the last glaciation were evaluated from isotopic study of herbivore tooth enamel. Enamel δ13C values revealed a substantial eastward increase in C4plant consumption for Mammuthusspp., Bisonspp., Equusspp., and Camelopsspp. The δ13C values were greatest in Bisonspp. (−6.9 to +1.7‰) and Mammuthusspp. (−9.0 to +0.3‰), and in some locales indicated C4-dominated grazing. The δ13C values of Antilocaprids were lowest among taxa (−12.5 to −7.9‰) and indicated C3feeding at all sites. On the basis of modern correlations between climate and C4grass abundance, the enamel data imply significant summer rain in parts of southern Arizona and New Mexico throughout the last glaciation. Enamel δ18O values range from +19.0 to +31.0‰ and generally increase to the east. This pattern could point to a tropical or subtropical source of summer rainfall. At a synoptic scale, the isotope data indicate that interactions of seasonal moisture, temperature, and lowered atmospheric pCO2determined glacial-age C4abundance patterns.
Thirteen packrat (Neotoma spp.) and two porcupine (Erethizon dorsatum) middens from 1555 to 1690 m elevation from the Sacramento Mountains, New Mexico, provide an 18,000-yr vegetation record in the northern Chiuahuan Desert. The vegetation sequence is a mesic, Wisconsin fullglacial (18,000–16,000 yr B.P.) pinyon-juniper-oak woodland; a xeric, early Holocene (ca. 11,000–8000 yr B.P.) juniper-oak woodland; a middle Holocene (ca. 8000-4000 yr B.P.) desert-grassland; and a late Holocene (ca. 4000 yr B.P. to present) Chihuahuan desertscrub. The frequency of spring freezes and summer droughts in the late Wisconsin probably set the northern limits of Pinus edulis and Juniperus monosperma at about 34°N, or 6° south of today's limit. Rising summer tempratures in the early Holocene eliminated pinyon and other mesic woodland plants from the desert lowlands and allowed the woodland to move upslope. At this time pinyon-juniper woodland and pine forest dominated by Pinus ponderosa probably began their spectacular Holocene expansions to the north. Continued warming in the middle Holocene led to very warm summers with strong monsoons, relatively dry, cold winters, and widespread desert-grasslands. Desertscrub communities in the northern Chihuahuan Desert did not develop until the late Holocene when the biseasonal rainfall shifted slightly back toward the winter, catastrophic winter freezes decreased, and droughts in all seasons increased. The creosote bush desertscrub corridor across the Continental Divide between the Chihuahuan and Sonoran deserts was probably connected for the first time since the last interglaciation.
Buffelgrass, a highly competitive and flammable African bunchgrass, is spreading rapidly across both urban and natural areas in the Sonoran Desert of southern and central Arizona. Damages include increased fire risk, losses in biodiversity, and diminished revenues and quality of life. Feasibility of sustained and successful mitigation will depend heavily on rates of spread, treatment capacity, and cost–benefit analysis. We created a decision support model for the wildland–urban interface north of Tucson, AZ, using a spatial state-and-transition simulation modeling framework, the Tool for Exploratory Landscape Scenario Analyses. We addressed the issues of undetected invasions, identifying potentially suitable habitat and calibrating spread rates, while answering questions about how to allocate resources among inventory, treatment, and maintenance. Inputs to the model include a state-and-transition simulation model to describe the succession and control of buffelgrass, a habitat suitability model, management planning zones, spread vectors, estimated dispersal kernels for buffelgrass, and maps of current distribution. Our spatial simulations showed that without treatment, buffelgrass infestations that started with as little as 80 ha (198 ac) could grow to more than 6,000 ha by the year 2060. In contrast, applying unlimited management resources could limit 2060 infestation levels to approximately 50 ha. The application of sufficient resources toward inventory is important because undetected patches of buffelgrass will tend to grow exponentially. In our simulations, areas affected by buffelgrass may increase substantially over the next 50 yr, but a large, upfront investment in buffelgrass control could reduce the infested area and overall management costs.
Widespread, organic-rich diatomaceous deposits are evidence for formerly wetter times along the margins of the central Atacama Desert, one of the driest places on Earth today. We mapped and dated these paleowetland deposits at three presently waterless locations near Salar de Punta Negra (24.5°S) on the western slope of the Andes. Elevated groundwater levels supported phreatic discharge into wetlands during two periods: 15,900 to ~ 13,800 and 12,700 to ~ 9700 cal yr BP. Dense concentrations of lithic artifacts testify to the presence of paleoindians around the wetlands late in the second wet phase (11,000?–9700 cal yr BP). Water tables dropped below the surface before 15,900 and since 8100 cal yr BP, and briefly between ~ 13,800 and 12,700 cal yr BP. This temporal pattern is repeated, with some slight differences, in rodent middens from the study area, in both paleowetland and rodent midden deposits north and south of the study area, and in lake level fluctuations on the adjacent Bolivian Altiplano. The regional synchroneity of these changes points to a strengthening of the South American Monsoon — which we term the "Central Andean Pluvial Event" — in two distinct intervals (15,900–13,800 and 12,700–9700 cal yr BP), probably induced by steepened SST gradients across the tropical Pacific (i.e., La Niña-like conditions).
Rodent (Abrocoma, Lagidium, Phyllotis) middens collected from 2350 to 2750 m elevation near Arequipa, Peru (16°S), provide an ∼9600-yr vegetation history of the northern Atacama Desert, based on identification of >50 species of plant macrofossils. These midden floras show considerable stability throughout the Holocene, with slightly more mesophytic plant assemblages in the middle Holocene. Unlike the southwestern United States, rodent middens of mid-Holocene age are common. In the Arequipa area, the midden record does not reflect any effects of a mid-Holocene mega drought proposed from the extreme lowstand (100 m below modern levels, >6000 to 3500 yr B.P.) of Lake Titicaca, only 200 km east of Arequipa. This is perhaps not surprising, given other evidence for wetter summers on the Pacific slope of the Andes during the middle Holocene as well as the poor correlation of summer rainfall among modern weather stations in the central Andes-Atacama Desert. The apparent difference in paleoclimatic reconstructions suggests that it is premature to relate changes observed during the Holocene to changes in El Niño Southern Oscillation modes.
Plant macrofossils from 33 rodent middens sampled at three sites between 2910 and 3150 m elevation in the main canyon of the Río Salado, northern Chile, yield a unique record of vegetation and climate over the past 22,000 cal yr BP. Presence of low-elevation Prepuna taxa throughout the record suggests that mean annual temperature never cooled by more than 5°C and may have been near-modern at 16,270 cal yr BP. Displacements in the lower limits of Andean steppe and Puna taxa indicate that mean annual rainfall was twice modern at 17,520–16,270 cal yr BP. This pluvial event coincides with infilling of paleolake Tauca on the Bolivian Altiplano, increased ENSO activity inferred from a marine core near Lima, abrupt deglaciation in southern Chile, and Heinrich Event 1. Moderate to large increases in precipitation also occurred at 11,770–9550 (Central Atacama Pluvial Event), 7330–6720, 3490–2320 and at 800 cal yr BP. Desiccation occurred at 14,180, 8910–8640, and 4865 cal yr BP. Compared to other midden sites in the region, early Holocene desiccation seems to have happened progressively earlier farther south. Emerging trends from the cumulative midden record in the central Atacama agree at millennial timescales with improved paleolake chronologies for the Bolivian Altiplano, implying common forcing through changes in equatorial Pacific sea-surface temperature gradients.
Cores and cross sections from 133 limber pine (Pinus flexilis James) and Douglas fir (Pseudotsuga menziesii (Mirbel) Franco) at four sites were used to estimate annual (July to June) precipitation in the Yellowstone National Park region for the period from AD 1173 to 1998. Examination of the long-term record shows that the early 20th century was markedly wet compared to the previous 700 yr. Extreme wet and dry years within the instrumental period fall within the range of past variability, and the magnitude of the worst-case droughts of the 20th century (AD 1930s and 1950s) was likely equaled or exceeded on numerous occasions before AD 1900. Spectral analysis showed significant decadal to multidecadal precipitation variability. At times this lower frequency variability produces strong regime-like behavior in regional precipitation, with the potential for rapid, high-amplitude switching between predominately wet and predominately dry conditions. Over multiple time scales, strong Yellowstone region precipitation anomalies were almost always associated with spatially extensive events spanning various combinations of the central and southern U.S. Rockies, the northern U.S.–Southern Canadian Rockies and the Pacific Northwest.
Plant macrofossils from 38 packrat middens spanning the last ~ 33,000 cal yr BP record vegetation between ~ 650 and 900 m elevation along the eastern escarpment of the Sierra San Pedro Mártir, northern Baja California. The middens span most of the Holocene, with a gap between ~ 4600 and 1800 cal yr BP, but coverage in the Pleistocene is uneven with a larger hiatus between 23,100 and 14,400 cal yr BP. The midden flora is relatively stable from the Pleistocene to Holocene. Exceptions include Pinus californiarum, Juniperus californica and other chaparral elements that were most abundant > 23,100 cal yr BP and declined after 14,400 cal yr BP. Despite being near the chaparral/woodland-desertscrub ecotone during glacial times, the midden assemblages reflect none of the climatic reversals evident in the glacial or marine record, and this is corroborated by a nearby semi-continuous pollen stratigraphy from lake sediments. Regular appearance of C4 grasses and summer-flowering annuals since 13,600 cal yr BP indicates occurrence of summer rainfall equivalent to modern (JAS average of ~ 80–90 mm). This casts doubt on the claim, based on temperature proxies from marine sediments in the Guaymas Basin, that monsoonal development in the northern Gulf and Arizona was delayed until after 6200 cal yr BP.
Lacustrine deposits exposed around Lake Aricota, Peru (17° 22′S), a 7.5-km2 lake dammed by debris flows, provide a middle to late Holocene record of lake-level fluctuations. Chronological context for shoreline deposits was obtained from radiocarbon dating of vascular plant remains and other datable material with minimal 14C reservoir effects (<350 yr). Diatomites associated with highstands several meters above the modern lake level indicate wet episodes. Maximum Holocene lake level was attained before 6100 14C yr B.P. and ended ∼2700 14C yr B.P. Moderately high lake levels occurred at 1700 and 1300 14C yr B.P. The highstand at Lake Aricota during the middle Holocene is coeval with a major lowstand at Lake Titicaca (16°S), which is only 130 km to the northeast and shares a similar climatology. Comparisons with other marine and terrestrial records highlight emerging contradictions over the nature of mid-Holocene climate in the central Andes.
Fire and vegetation records at the City of Rocks National Reserve (CIRO), south-central Idaho, display the interaction of changing climate, fire and vegetation along the migrating front of single-leaf pinyon (Pinus monophylla) and Utah juniper (Juniperus osteosperma). Radiocarbon dating of alluvial charcoal reconstructed local fire occurrence and geomorphic response, and fossil woodrat (Neotoma) middens revealed pinyon and juniper arrivals. Fire peaks occurred ~ 10,700–9500, 7200–6700, 2400–2000, 850–700, and 550–400 cal yr BP, whereas ~ 9500–7200, 6700–4700 and ~ 1500–1000 cal yr BP are fire-free. Wetter climates and denser vegetation fueled episodic fires and debris flows during the early and late Holocene, whereas drier climates and reduced vegetation caused frequent sheetflooding during the mid-Holocene. Increased fires during the wetter and more variable late Holocene suggest variable climate and adequate fuels augment fires at CIRO. Utah juniper and single-leaf pinyon colonized CIRO by 3800 and 2800 cal yr BP, respectively, though pinyon did not expand broadly until ~ 700 cal yr BP. Increased fire-related deposition coincided with regional droughts and pinyon infilling ~ 850–700 and 550–400 cal yr BP. Early and late Holocene vegetation change probably played a major role in accelerated fire activity, which may be sustained into the future due to pinyon–juniper densification and cheatgrass invasion.