Geology topics

Bradford D. Hollingsworth

Publications and source records attributed to Bradford D. Hollingsworth.

3 recordsLinked to original sources

USGS2025

Desert ecosystems shape diversification in glossy snakes (genus Arizona) requiring a re-alignment of evolutionary and conservation units

Subspecies are often targets for conservation, yet many lack the genetic data necessary to validate their status as distinctive evolutionary lineages. In 2016, conservationists faced this issue when designating the California glossy snake, Arizona elegans occidentalis , as a Species of Special Concern in California, a decision prompted by population declines and habitat loss but absent of genetic information about its evolutionary integrity. To address this knowledge gap, we collected genomic and mitochondrial data from a rangewide sample of the Arizona elegans complex ( n = 257) and characterized genetic structure at varying spatial scales. We confirmed an east–west phyletic division within the A. elegans complex that correlates with an ecotone between the Sonoran and Chihuahuan Deserts and pinpoint the separation to a ∼20 km area in southeastern Arizona, USA. Individuals recognized as A. e. occidentalis do not form a genetically cohesive unit within a more inclusive western clade that is sister to the endemic Arizona pacata in Baja California, México. We synonymize four subspecies circumscribed by the western clade and recognize a new species Arizona occidentalis to re-align the taxonomy with the phylogeographic structure. Most of the diversity within A. occidentalis occurs in California, with three major lineages corresponding separate desert biomes. We revise the conservation units within A. occidentalis to mirror these lineages and address concerns regarding habitat loss in transitional environments along the western edge of its range. This work underscores the importance of aligning taxonomy, evolutionary identity, and management units to design the most effective conservation strategies.

Molecular Phylogenetics and Evolution↗

USGS2025

The Southwestern Pond Turtle (Actinemys pallida) in Baja California, Mexico: New localities and persistent threats

The Southwestern Pond Turtle ( Actinemys pallida ), the only native freshwater turtle in Baja California, is experiencing alarming population declines, echoing global patterns observed in freshwater turtles. We conducted comprehensive field surveys across the major drainages of northwestern Baja California to delineate the species' current distribution, identify critical threats to its persistence, and provide guidance for conservation actions. We documented the continued presence of A. pallida at 27 sites across 10 watersheds, ranging from sea level to 1,525 m in elevation. These include nine historically known sites and 18 newly recorded localities. The most pervasive threats we identified were habitat degradation, the proliferation of invasive aquatic species, and unsustainable water extraction. Despite these pressures, our findings confirm that A. pallida still occupies much of its historical range. However, urgent ecological research is needed to inform evidence-based strategies that ensure the long-term viability of this imperiled species.

Baja California↗

USGS2023

Prioritizing the risk and management of introduced species in a landscape with high indigenous biodiversity

Risk analysis protocols for prioritizing the management of non-native species are numerous, yet few incorporate risk and management in the same analysis or accommodate a broad diversity of taxa outside of a specific geographic area. We adapted a protocol that accounts for these factors to address non-native animal species in the Southern California/Northern Baja California Coast Ecoregion near the international border in San Diego County, an area with high indigenous biodiversity and high numbers of species of conservation concern. This stepwise, semi-quantitative protocol is applicable to any animal group in any predefined geographic area, relies on consensus-building among taxonomic experts, and has been vetted through previous use and in peer-reviewed literature. Our results show that the final prioritization was driven mainly by management feasibility, with top-ranked species having multitrophic effects that favor other non-native invaders over native residents. Conditions within the assessment area required some modification to the protocol as it was originally designed, namely a shift in emphasis from eradication to control, given that eradication is implausible for most non-native species in the assessment area. We call attention to taxon-specific issues that surfaced during the analysis, identify areas for improvement in this first-ever risk assessment for invasive animal species in the Natural Communities Conservation Plan/Habitat Conservation Plan (NCCP/HCP) reserve system of San Diego County, and provide suggestions for further refinement of the protocol. This study builds on the effort to standardize risk analysis for invasive species globally, given that many of the same invaders present threats to indigenous biodiversity worldwide.

California↗