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Geology topics

Julio L. Betancourt

Publications and source records attributed to Julio L. Betancourt.

At least 19 recordsLinked to original sources
USGS2026

A 40,000-year packrat midden series from Cataviña, central Baja California, Mexico

Thirty packrat ( Neotoma spp.) middens collected from boulder fields near Cataviña, Baja California, Mexico, at 640–680 m elevation provide the first long chronology of macrofossils and pollen spanning the late Quaternary in the Central Desert of Baja California. Midden plant macrofossil and pollen assemblages document a rich chaparral/woodland assemblage during the last glacial and early Holocene dominated by Parry pinyon ( Pinus quadrifolia ) and California juniper ( Juniperus californica ) until 11,630 cal yr BP. This indicates chaparral/woodland had a much more extensive distribution in what are now desert elevations in northern and central Baja California. In contrast to late glacial and early Holocene midden records from northeastern Baja, the Cataviña middens of the same age lack plants adapted to warm season precipitation, suggesting that decreased temperatures and evapotranspiration during the growing season and enhanced winter precipitation, with little contribution from summer rains, supported the lowering of chaparral/woodland species distributions in central Baja California. Cataviña middens also record endemic desert plant taxa mixed in with chaparral/woodland species during the Pleistocene, persisting throughout the Holocene, followed by the quick arrival of other desert species after ∼11,000 cal yr BP. Baja California remains a high-potential yet poorly sampled area for packrat midden research in North America.

Baja California↗
USGS2025

Establishing historical baselines of arthropod assemblages using rodent paleomiddens

Aim Arthropods are under-represented in paleoecological studies but are critical agents in ecological processes. Despite rigorous documentation of diverse arthropod assemblages from ancient rodent (or paleo) middens worldwide, their use for studying ancient arthropod diversity has stalled in recent decades. Here, we review published studies to identify how paleomidden arthropods can be leveraged to address significant questions in ecology and synthesise spatiotemporal trends in ancient arthropod diversity. Location Global with a focus on the Americas. Time Period From ~40,000 to 100 years before present. Major Taxa Studied Fossil arthropods preserved in rodent paleomiddens. Methods We identified four primary objectives in ecology that can be advanced using paleomidden arthropod fossils: the reconstruction of ancient biodiversity, the elucidation of mechanisms and processes driving arthropod range shifts, the incorporation of arthropods into ancient trophic webs, and the assessment of adaptive responses to changing environments. Results We identified 20 papers reporting arthropod remains, of which 14 provided data suitable for quantitative analyses. Although no significant differences in arthropod community diversity were found across broad geographic regions, substantial differences in community structure were observed. In North America, we also detected a decline in arthropod diversity from 10 to 5 ka BP, driven primarily by the absence of high-diversity assemblages during this period. Main Conclusions Paleomidden arthropods remain an underutilised ecological resource that can be leveraged to improve the inferential scope of arthropod research across spatiotemporal gradients. Collaboration between paleo- and neoecologists could help expand the sampling of ancient and modern arthropod communities, particularly those associated with paleomiddens, to create high-resolution datasets spanning important periods in biogeographical history. Paleomidden arthropods will remain a fundamental component for understanding arthropod biodiversity changes in the past, present, and future.

Global Ecology and Biogeography↗
USGS2024

New uses for ancient middens: Bridging ecological and evolutionary perspectives

Rodent middens provide a fine-scale spatiotemporal record of plant and animal communities over the late Quaternary. In the Americas, middens have offered insight into biotic responses to past environmental changes and historical factors influencing the distribution and diversity of species. However, few studies have used middens to investigate genetic or ecosystem level responses. Integrating midden studies with neoecology and experimental evolution can help address these gaps and test mechanisms underlying eco-evolutionary patterns across biological and spatiotemporal scales. Fully realizing the potential of middens to answer cross-cutting ecological and evolutionary questions and inform conservation goals in the Anthropocene will require a collaborative research community to exploit existing midden archives and mount new campaigns to leverage midden records globally.

Trends in Ecology and Evolution↗
USGS2022

Transporting timbers to Chaco Canyon: How heavy, how many carriers and how far/fast?

A total of 200,000+ large timbers were transported >75 km to Chaco Canyon, a political and religious center in the precontact U.S. Southwest, using only human power. Previous researchers reported that typical primary roof beams (vigas) of Chacoan Great Houses averaged 0.22 m in diameter and 5 m in length with a mass of 275 kg. However, the 275 kg mass appears to be a miscalculation. Here, we calculate that a ponderosa pine timber of the stated dimensions would have a mass between 85–140 kg depending on the water content. While still a prodigious load, this recalculated mass requires revisions to estimates of the labor, time, and energy required to build Great Houses at Chaco. Based on contemporary measurements on professional load carriers and soldiers, we estimate that as few as two people could have carried an 85 kg timber across 100 km in as few as 21 h of active walking.

Kiva↗
USGS2021

Grassification and fast-evolving fire connectivity and risk in the Sonoran Desert, United States

In the southwestern United States, non-native grass invasions have increased wildfire occurrence in deserts and the likelihood of fire spread to and from other biomes with disparate fire regimes. The elevational transition between desertscrub and montane grasslands, woodlands, and forests generally occurs at ∼1,200 masl and has experienced fast suburbanization and an expanding wildland-urban interface (WUI). In summer 2020, the Bighorn Fire in the Santa Catalina Mountains burned 486 km 2 and prompted alerts and evacuations along a 40-km stretch of WUI below 1,200 masl on the outskirts of Tucson, Arizona, a metropolitan area of >1M people. To better understand the changing nature of the WUI here and elsewhere in the region, we took a multidimensional and timely approach to assess fire dynamics along the Desertscrub-Semi-desert Grassland ecotone in the Catalina foothills, which is in various stages of non-native grass invasion. The Bighorn Fire was principally a forest fire driven by a long-history of fire suppression, accumulation of fine fuels following a wet winter and spring, and two decades of hotter droughts, culminating in the hottest and second driest summer in the 125-yr Tucson weather record. Saguaro ( Carnegia gigantea ), a giant columnar cactus, experienced high mortality. Resprouting by several desert shrub species may confer some post-fire resiliency in desertscrub. Buffelgrass and other non-native species played a minor role in carrying the fire due to the patchiness of infestation at the upper edge of the Desertscrub biome. Coupled state-and-transition fire-spread simulation models suggest a marked increase in both burned area and fire frequency if buffelgrass patches continue to expand and coalesce at the Desertscrub/Semi-desert Grassland interface. A survey of area residents six months after the fire showed awareness of buffelgrass was significantly higher among residents that were evacuated or lost recreation access, with higher awareness of fire risk, saguaro loss and declining property values, in that order. Sustained and timely efforts to document and assess fast-evolving fire connectivity due to grass invasions, and social awareness and perceptions, are needed to understand and motivate mitigation of an increasingly fire-prone future in the region.

Arizona↗
USGS2021

Recovery and analysis of ancient beetle DNA from subfossil packrat middens using high-throughput sequencing

The study of ancient DNA is revolutionizing our understanding of paleo-ecology and the evolutionary history of species. Insects are essential components in many ecosystems and constitute the most diverse group of animals. Yet they are largely neglected in ancient DNA studies. We report the results of the first targeted investigation of insect ancient DNA to positively identify subfossil insects to species, which includes the recovery of endogenous content from samples as old as ~ 34,355 ybp. Potential inhibitors currently limiting widespread research on insect ancient DNA are discussed, including the lack of closely related genomic reference sequences (decreased mapping efficiency) and the need for more extensive collaborations with insect taxonomists. The advantages of insect-based studies are also highlighted, especially in the context of understanding past climate change. In this regard, insect remains from ancient packrat middens are a rich and largely uninvestigated resource for exploring paleo-ecology and species dynamics over time.

Scientific Reports↗
USGS2021

High- and low-latitude forcings drive Atacama Desert rainfall variations over the past 16,000 years

Late Quaternary precipitation dynamics in the central Andes have been linked to both high- and low-latitude atmospheric teleconnections. We use present-day relationships between fecal pellet diameters from ashy chinchilla rats ( Abrocoma cinerea ) and mean annual rainfall to reconstruct the timing and magnitude of pluvials (wet episodes) spanning the past 16,000 years in the Atacama Desert based on 81 14 C-dated A. cinerea paleomiddens. A transient climate simulation shows that pluvials identified at 15.9 to 14.8, 13.0 to 8.6, and 8.1 to 7.6 ka B.P. can be linked to North Atlantic (high-latitude) forcing (e.g., Heinrich Stadial 1, Younger Dryas, and Bond cold events). Holocene pluvials at 5.0 to 4.6, 3.2 to 2.1, and 1.4 to 0.7 ka B.P. are not simulated, implying low-latitude internal variability forcing (i.e., ENSO regime shifts). These results help constrain future central Andean hydroclimatic variability and hold promise for reconstructing past climates from rodent middens in desert ecosystems worldwide.

Science Advances↗
USGS2020

Seasonality of biological and physical systems as indicators of climatic variation and change

Evidence-based responses to climate change by society require operational and sustained information including biophysical indicator systems that provide up-to-date measures of trends and patterns against historical baselines. Two key components linking anthropogenic climate change to impacts on socio-ecological systems are the periodic inter- and intra-annual variations in physical climate systems (seasonality) and in plant and animal life cycles (phenology). We describe a set of national indicators that reflect sub-seasonal to seasonal drivers and responses of terrestrial physical and biological systems to climate change and variability at the national scale. Proposed indicators and metrics include seasonality of surface climate conditions (e.g., frost and freeze dates and durations), seasonality of freeze/thaw in freshwater systems (e.g., timing of stream runoff and durations of lake/river ice), seasonality in ecosystem disturbances (e.g., wildfire season timing and duration), seasonality in vegetated land surfaces (e.g., green-up and brown-down of landscapes), and seasonality of organismal life-history stages (e.g., timings of bird migration). Recommended indicators have strong linkages to variable and changing climates, include abiotic and biotic responses and feedback mechanisms, and are sufficiently simple to facilitate communication to broad audiences and stakeholders interested in understanding and adapting to climate change.

Climatic Change↗
USGS2020

Paleo-metagenomics of North American fossil packrat middens: Past biodiversity revealed by ancient DNA

Fossil rodent middens are powerful tools in paleoecology. In arid parts of western North America, packrat ( Neotoma spp.) middens preserve plant and animal remains for tens of thousands of years. Midden contents are so well preserved that fragments of endogenous ancient DNA (aDNA) can be extracted and analyzed across millennia. Here, we explore the use of shotgun metagenomics to study the aDNA obtained from packrat middens up to 32,000 C 14 years old. Eleven Illumina HiSeq 2500 libraries were successfully sequenced, and between 0.11% and 6.7% of reads were classified using Centrifuge against the NCBI “nt” database. Eukaryotic taxa identified belonged primarily to vascular plants with smaller proportions mapping to ascomycete fungi, arthropods, chordates, and nematodes. Plant taxonomic diversity in the middens is shown to change through time and tracks changes in assemblages determined by morphological examination of the plant remains. Amplicon sequencing of ITS2 and rbcL provided minimal data for some middens, but failed at amplifying the highly fragmented DNA present in others. With repeated sampling and deep sequencing, analysis of packrat midden aDNA from well-preserved midden material can provide highly detailed characterizations of past communities of plants, animals, bacteria, and fungi present as trace DNA fossils. The prospects for gaining more paleoecological insights from aDNA for rodent middens will continue to improve with optimization of laboratory methods, decreasing sequencing costs, and increasing computational power.

Ecology and Evolution↗
USGS2020

Unfamiliar territory: Emerging themes for ecological drought research and management

Novel forms of drought are emerging globally, due to climate change, shifting teleconnection patterns, expanding human water use, and a history of human influence on the environment that increases the probability of transformational ecological impacts. These costly ecological impacts cascade to human communities, and understanding this changing drought landscape is one of today’s grand challenges. By using a modified horizon-scanning approach that integrated scientists, managers, and decision-makers, we identified the emerging issues in ecological drought that represent key challenges to timely and effective responses. Here we review the themes that most urgently need attention, including novel drought conditions, the potential for transformational drought impacts, and the need for anticipatory drought management. This horizon scan and review provides a roadmap to facilitate the research and management innovations that will support forward-looking, co-developed approaches to reduce the risk of drought to our socio-ecological systems during the 21 st century.

One Earth↗
USGS2020

Climate dipoles as continental drivers of plant and animal populations

Ecological processes, such as migration and phenology, are strongly influenced by climate variability. Studying these processes often relies on associating observations of animals and plants with climate variability indices, such as the El Niño–Southern Oscillation. A characteristic of climate indices is the simultaneous emergence of opposite extremes of temperature and precipitation across continental scales, known as climate dipoles. The role of climate dipoles in shaping ecological and evolutionary processes has been largely overlooked. We review emerging evidence that climate dipoles can entrain species dynamics, and offer a framework for identifying ecological dipoles using broad-scale biological data. Given future changes in climatic and atmospheric processes, climate and ecological dipoles will likely shift in their intensity, distribution, and timing.

Trends in Ecology and Evolution↗
USGS2019

Investigating (a)symmetry in a small mammal’s response to warmingand cooling events across western North America over the late Quaternary

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 warmingclimates 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.” Ourresults 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.

Quaternary Research↗
USGS2018

Anticipatory natural resource science and management for a changing future

Prolonged shifts in long‐term average climate conditions and increasing variability in short‐term weather conditions affect ecological processes, and represent a fundamental challenge for natural resource management. Recent and forthcoming advances in climate predictability may offer novel opportunities, but capitalizing on these opportunities will require focusing scientific research on understanding the links between climate and ecological responses over multiple timescales, fostering programmatic links among science and management agencies, and developing new and flexible decision‐making frameworks. Anticipating short‐ to near‐term climate conditions can help managers mitigate land degradation driven by unfavorable conditions and promote actions that make the most of favorable conditions. Similarly, anticipating long‐term, multidecadal climate trajectories can help managers to identify those species and communities that are most likely to remain viable throughout the 21st century. A focus on “anticipatory science and management” could substantially bolster natural resource planning and management but will require long‐term investment and widespread adoption.

Frontiers in Ecology and the Environment↗
USGS2018

Iterative near-term ecological forecasting: Needs, opportunities, and challenges

Two foundational questions about sustainability are “How are ecosystems and the services they provide going to change in the future?” and “How do human decisions affect these trajectories?” Answering these questions requires an ability to forecast ecological processes. Unfortunately, most ecological forecasts focus on centennial-scale climate responses, therefore neither meeting the needs of near-term (daily to decadal) environmental decision-making nor allowing comparison of specific, quantitative predictions to new observational data, one of the strongest tests of scientific theory. Near-term forecasts provide the opportunity to iteratively cycle between performing analyses and updating predictions in light of new evidence. This iterative process of gaining feedback, building experience, and correcting models and methods is critical for improving forecasts. Iterative, near-term forecasting will accelerate ecological research, make it more relevant to society, and inform sustainable decision-making under high uncertainty and adaptive management. Here, we identify the immediate scientific and societal needs, opportunities, and challenges for iterative near-term ecological forecasting. Over the past decade, data volume, variety, and accessibility have greatly increased, but challenges remain in interoperability, latency, and uncertainty quantification. Similarly, ecologists have made considerable advances in applying computational, informatic, and statistical methods, but opportunities exist for improving forecast-specific theory, methods, and cyberinfrastructure. Effective forecasting will also require changes in scientific training, culture, and institutions. The need to start forecasting is now; the time for making ecology more predictive is here, and learning by doing is the fastest route to drive the science forward.

Proceedings of the National Academy of Sciences of↗
USGS2018

Past and future global transformation of terrestrial ecosystems under climate change

Impacts of global climate change on terrestrial ecosystems are imperfectly constrained by ecosystem models and direct observations. Pervasive ecosystem transformations occurred in response to warming and associated climatic changes during the last glacial-to-interglacial transition, which was comparable in magnitude to warming projected for the next century under high-emission scenarios. We reviewed 594 published paleoecological records to examine compositional and structural changes in terrestrial vegetation since the last glacial period and to project the magnitudes of ecosystem transformations under alternative future emission scenarios. Our results indicate that terrestrial ecosystems are highly sensitive to temperature change and suggest that, without major reductions in greenhouse gas emissions to the atmosphere, terrestrial ecosystems worldwide are at risk of major transformation, with accompanying disruption of ecosystem services and impacts on biodiversity.

Science↗
USGS2017

Late Quaternary environmental dynamics in the Atacama Desert reconstructed from rodent midden pollen records

In the past two decades, much has been learned about the late Quaternary climate history of the Atacama Desert with some details still unclear about the seasonality, timing and extent of wet and dry phases. Modern climate studies reveal that, far from exhibiting a unique pattern, seasonal precipitation originates from many sources and mechanisms. For the last 16 ka, we attempt to sort out these complexities in pollen records from four fossil rodent midden series spanning 22°–25°S in northern Chile. Widespread wet conditions prevailed during the late Pleistocene and early Holocene, particularly between 13 and 9 ka, evidenced by <400 m lowering of pollen zones (plant communities) compared to today. Regional differences in the timing and magnitude of this displacement may be related to the prevailing source (tropical/extra‐tropical) or mode (NNW/SE) of tropical precipitation through time. Wet conditions persisted well into the early Holocene, lasting ∼1–1.5 ka longer than previously suggested. The pollen record suggests extreme drying ∼8 ka, possibly associated with a northward shift of the Inter Tropical Convergence Zone, tracking minimum insolation values at subtropical latitudes during the austral summer. The establishment of conditions similar to today happened ∼4 ka.

Journal of Quaternary Science↗