Paleoclimatic Implications of Holocene Plant Remains from the Sierra Bacha, Sonora, Mexico

Abstract

A total of 93 plant taxa were identified from 11 packrat (Neotoma sp.) midden samples from the Sierra Bacha on the coast of the Gulf of California near Puerto Libertad, Sonora, Mexico. Nine indurated samples have radiocarbon dates ranging from 9970 to 320 yr B.P. Sonoran desertscrub was present on rocky slopes throughout the Holocene. Early Holocene assemblages dominated by Fouquieria columnaris (boojum tree) reflect vegetation and climate more like modern Baja California with greater winter rainfall and cooler summers. Middle Holocene vegetation was essentially modern with modest indications of greater monsoonal rainfall even though cold-water upwelling locally inhibits summer precipitation. The results are similar to all previous midden reconstructions of early and middle Holocene climates in the Sonoran Desert, but contradict general atmospheric circulation model simulations.

Alternative glacial-interglacial refugia demographic hypotheses tested on Cephalocereus columna-trajani (Cactaceae) in the intertropical Mexican drylands

“…This demographic dynamic is well supported by palaeoecological analyses of macrofossils from Neotoma middens, which point out expansion ranges of floristic elements associated with an increase in aridity during the Holocene interglacial period. Accordingly, xerophytic species persisted in semi-deserts located at low elevations in Sonora and Baja California throughout the last glacial period, from where they reached their current distribution after range expansion at approximately 4 to 8 kyr [20–21]. Theses findings are consistent with the Glacial Refugium Hypothesis (GRH), which is widely accepted for temperate species in the mid latitudes of the Northern Hemisphere.…”

Phylogeography of the Western Lyresnake (Trimorphodon biscutatus): testing aridland biogeographical hypotheses across the Nearctic–Neotropical transition

“…During glacial periods, cooler, wetter conditions allowed the expansion of woodland trees and shrubs into areas formerly occupied by desert, restricting arid regions to lowland basins below 300 m a.s.l. at more southerly latitudes, and forming pluvial lakes in lowland areas (Van Devender & Spaulding 1979; Van Devender 1990a, b; Van Devender et al . 1994; Holmgren et al .…”

Microsatellite variation among diverging populations of Drosophila mojavensis

“…Genetic variation in Mojave populations may reflect a very recent reduction in the effective population size as all loci show relatively high and equivalent reductions in heterozygosity and n e . The origin of these populations and demographic events could be explained by the north and south migration of the frost‐sensitive host cacti during the Pleistocene glaciation cycles (Van Devender, 1990; Van Devender et al. , 1994), leaving relictual populations using prickly pear and barrel cacti as hosts in these areas.…”