Dietary modifications of packrats in response to changing plant communities: Evidence from fossil plant cuticles spanning >55,000 years in Sonoran Desert packrat middens

• This is the first cuticle study from fossil woodrat middens in North America.
• Preferential collection of favored foods appears to augment macrofossil abundances.
• Fecal pellet cuticles show a broad Pleistocene to Holocene change in woodrat diet.
• Cuticle analysis helped to refine timing of species arrivals and disappearances.
• A broad diet portends well for woodrats' ability to adapt to anthropogenic warming.

Plant cuticles in fecal pellets from 45 Neotoma middens from northeastern Baja California, Mexico were analyzed to explore woodrat dietary composition spanning >55,000 years. Pleistocene cuticles were dominated by the more mesic and/or chaparral-type extralocals Juniperus californica, Nolina, Agave cf. deserti, Salvia, and Simmondsia chinensis. Cylindoputia/Opuntia cuticles were abundant throughout both the Pleistocene and Holocene. Together, these species comprised the bulk of the woodrats’ diet during the last ice age. The glacial-interglacial transition showed the replacement of extralocals in the diet by more xeric desert scrub species, especially Acacia greggii, Larrea tridentata, Olneya tesota, and Prosopis glandulosa var. torreyana. The main dietary species were all also highly abundant as macrofossils, suggesting preferential collection of favored foods. Interestingly, J. californica and Nolina cuticles persisted >1500 years after disappearing from macrofossils, while O. tesota cuticles appeared 4160 years earlier. It is possible that consumption of particularly prized foods at times they were less abundant left little material for incorporation into middens. Analyzing cuticles along with macrofossils from middens provides complimentary information about woodrat dietary preferences, helps refine the timing of species arrivals/disappearances, and shows how diets shifted with changing climatic conditions.