We think of range maps as static representations of where plants and animals belong. It doesn't often occur to us that maps are just snapshots of a constantly changing world. In the Mojave Desert, two sister species of desert ground squirrel coexist nearly side by side. A field guide's range maps will tell you where those species live right now. But those maps also convey hints out of Deep Time, and those hints can explain not only why the squirrels live where they do, but also how the two species evolved in their own directions.

Host Chris Clarke shares the story of those sister species: the Mohave and Round-tailed ground squirrels. One is doing well and is abundant. The other has been designated as a threatened species. Each of them is a library of history... if we know how to read them.

Chris also announces the launch of our Fellowship for Desert Reporting: prospective Fellows can start by filling out the application form at https://thedamn.org/fellowship-application.

Resources 

Mohave ground squirrels

• California Department of Fish and Wildlife: Mohave Ground Squirrel
  Species overview, conservation status, recordings and access to the state conservation strategy.
  CDFW Mohave Ground Squirrel
• Philip Leitner, “Current Status of the Mohave Ground Squirrel: An Update Covering the Period 2013–2020”
  Reviews the animal’s current distribution, apparent losses from portions of its historical range and continuing conservation concerns.
  Status update PDF
• Mohave Ground Squirrel Technical Advisory Group
  CDFW’s archive of technical documents and meeting materials from researchers, agencies and other specialists.
  Technical Advisory Group
• Mohave Ground Squirrel Conservation Council: Publications
  A bibliography covering the species’ taxonomy, ecology, genetics, distribution and conservation.
  Publications list

Separation, contact and hybridization

• Kayce C. Bell and Marjorie D. Matocq, “Regional Genetic Subdivision in the Mohave Ground Squirrel: Evidence of Historic Isolation and Ongoing Connectivity in a Mojave Desert Endemic”
  Animal Conservation 14 (2011): 371–381. Examines genetic structure and historical isolation within Mohave ground squirrel populations.
  Article and abstract
• Philip Leitner, Jennifer S. Rippert and Marjorie D. Matocq, “Genetic Structure Across a Contact Zone Between Xerospermophilus Ground Squirrels in Southern California”
  Western North American Naturalist 77 (2017): 152–161. Documents both species and genetically admixed animals near Hinkley. It also reports expansion across the former barrier of no more than approximately 30 kilometers—an average of no more than five meters per year.
  Full article
• “Distribution and Genetic Status of Xerospermophilus Ground Squirrels in the Barstow Region”
  Includes useful maps of trapping records and genetically identified Mohave, round-tailed and hybrid or backcrossed animals around Barstow and Hinkley.
  CDFW-hosted report

Mojave River and vanished lakes

• Marith C. Reheis et al., “Geomorphic History of Lake Manix, Mojave Desert, California: Evolution of a Complex Terminal Lake Basin”
  Geomorphology 392 (2021). A detailed modern synthesis of the lake basin’s development, changing river routes, tectonics and climate history.
  USGS publication page
• USGS: Surficial Geology and Stratigraphy of Pleistocene Lake Manix
  Detailed geologic mapping of Lake Manix, its component basins and the deposits exposed by the Mojave River and Afton Canyon.
  USGS Lake Manix map and report
• Marith Reheis and Joanna Redwine, “Lake Manix Shorelines and Afton Canyon Terraces: Implications for Incision of Afton Canyon”
  Discusses the overflow of Lake Manix and relatively rapid initial incision of Afton Canyon at approximately 25,000 calibrated years ago.
  USGS publication record
• USGS: Mojave River and Associated Lakes
  An accessible introduction to the Mojave River, Lake Manix, Lake Mojave and the modern Soda and Silver Lake playas.
  Mojave River and Associated Lakes

Range maps and Joshua trees

• USGS: High-resolution distribution maps for western and eastern Joshua trees
  Describes empirical and modeled range maps for Yucca brevifolia and Yucca jaegeriana across four states.
  USGS Joshua tree distribution study
• Smith et al., “Genome-Scale Data Resolves the Timing of Divergence in Joshua Trees”
  American Journal of Botany 108 (2021). Estimates that the two Joshua tree species diverged approximately 100,000–200,000 years ago.
  Journal article