Geology topics

Brett R. Riddle

Publications and source records attributed to Brett R. Riddle.

3 recordsLinked to original sources

USGS2022

Integrating Earth–life systems: A geogenomic approach

For centuries, scientists have recognized and worked to understand how Earth’s mutable landscape and climate shape the distribution and evolution of species. Here, we describe the emerging field of geogenomics, which uses the reciprocal and deep integration of geologic, climatic, and population genomic data to define and test cause–effect relationships between Earth and life at intermediate spatial and temporal scales (i.e., the mesoscale). Technological advances now power the detailed reconstruction of landscape and evolutionary histories, but transdisciplinary collaborations and new quantitative tools are needed to better integrate Earth–life data. Geogenomics can help build a more unified theory and characterize the boundary conditions under which geologic and climatic processes generate new biodiversity, how species’ responses differ, and why.

Trends in Ecology & Evolution↗

USGS2016

Ecology, distribution, and predictive occurrence modeling of Palmers chipmunk ( Tamias palmeri ): a high-elevation small mammal endemic to the Spring Mountains in southern Nevada, USA

Although montane sky islands surrounded by desert scrub and shrub steppe comprise a large part of the biological diversity of the Basin and Range Province of southwestern North America, comprehensive ecological and population demographic studies for high-elevation small mammals within these areas are rare. Here, we examine the ecology and population parameters of the Palmer’s chipmunk ( Tamias palmeri ) in the Spring Mountains of southern Nevada, and present a predictive GIS-based distribution and probability of occurrence model at both home range and geographic spatial scales. Logistic regression analyses and Akaike Information Criterion model selection found variables of forest type, slope, and distance to water sources as predictive of chipmunk occurrence at the geographic scale. At the home range scale, increasing population density, decreasing overstory canopy cover, and decreasing understory canopy cover contributed to increased survival rates.

Nevada↗

USGS2002

Ploidy race distributions since the Last Glacial Maximum in the North American desert shrub, Larrea tridentata

A classic biogeographic pattern is the alignment of diploid, tetraploid and hexaploid races of creosote bush ( Larrea tridentata ) across the Chihuahuan, Sonoran and Mohave Deserts of western North America. We used statistically robust differences in guard cell size of modern plants and fossil leaves from packrat middens to map current and past distributions of these ploidy races since the Last Glacial Maximum (LGM). Glacial/early Holocene (26–10 14 C kyr bp or thousands of radiocarbon years before present) populations included diploids along the lower Rio Grande of west Texas, 650 km removed from sympatric diploids and tetraploids in the lower Colorado River Basin of south-eastern California/south-western Arizona. Diploids migrated slowly from lower Rio Grande refugia with expansion into the northern Chihuahuan Desert sites forestalled until after ~4.0 14 C kyr bp . Tetraploids expanded from the lower Colorado River Basin into the northern limits of the Sonoran Desert in central Arizona by 6.4 14 C kyr bp . Hexaploids appeared by 8.5 14 C kyr bp in the lower Colorado River Basin, reaching their northernmost limits (~37°N) in the Mohave Desert between 5.6 and 3.9 14 C kyr bp . Modern diploid isolates may have resulted from both vicariant and dispersal events. In central Baja California and the lower Colorado River Basin, modern diploids probably originated from relict populations near glacial refugia. Founder events in the middle and late Holocene established diploid outposts on isolated limestone outcrops in areas of central and southern Arizona dominated by tetraploid populations. Geographic alignment of the three ploidy races along the modern gradient of increasingly drier and hotter summers is clearly a postglacial phenomenon, but evolution of both higher ploidy races must have happened before the Holocene. The exact timing and mechanism of polyploidy evolution in creosote bush remains a matter of conjecture.

Arizona, Baja California, Baja California Sur, Cal↗