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There are many abandoned mines throughout the Arizona Sonoran Desert region and their environmental impact is yet to be fully understood. It was hypothesized that mining would result in decreased microbiome diversity, although some bacteria may adapt to the mine waste conditions. Soil samples were collected from three different mines in the Sonoran Desert and matched control sites. Soil total DNA was extracted and analyzed via 16S rRNA sequencing and analysis. Elemental analysis of the soils by x-ray fluorescence showed very different concentrations of toxic elements between the mine soils and the control sites. The concentrations of Pb, As, and Cu were as high as 8.1%, 0.72%, and 0.33%, respectively, of the soil mass at the mine soils, and thus much different than the control soils. There was an overall decrease in soil microbiome diversity and species richness in mine samples. Overall, approximately 50% of assigned Operational Taxonomic Units (OTU) overlapped between mine and control soil samples. Additionally, a total of 12 OTUs were detected within all mine soil samples and none of the control soil samples, suggesting these bacteria do not naturally occur in undisturbed desert soils within this region and instead were able to adapt to the extreme conditions of the former mines. One of these 12 bacteria was found to be a previously undescribed species that appears to be closely related to the phylum Chloroflexi.
Both black-tailed jackrabbits (Lepus californicus) and antelope jackrabbits (L. alleni) have been reported to prefer less densely vegetated habitats over densely vegetated habitats. Studies comparing trends of antelope jackrabbit numbers in differing habitats are lacking however. From 2012 to 2019 we conducted walking transect surveys in two different grassland types where jackrabbits occur. We found antelope jackrabbit densities to be significantly lower in a semidesert grassland site protected from grazing when compared to a grazed site in Sonoran savanna grassland (p < 0.01). While antelope jackrabbit densities in the temperate, densely vegetated semidesert grassland site declined over time in the absence of fire, and increased after burning, antelope jackrabbit densities fluctuated at a higher level independently without the presence of fire in more sparsely vegetated Sonoran savanna grassland. We attribute these changes in antelope jackrabbit numbers in the two survey sites to the animal′s preference for open annual grasslands in a tropic-subtropic environment as compared to grasslands composed of dense perennial bunch-grasses.
Opuntia cespitosa (Cactaceae, previously known under the synonym O. humifusa) is found over eastern North America, yet its populations are very sparse and small despite effective vegetative reproduction. Their edaphic preferences are poorly known, and may limit the distribution and success of the species. Soils were sampled for %O.M. (organic matter), %sand, %silt, %clay, pH, and kg/ha of P, K, Ca, Mg, and Zn in 33 populations over a wide area of eastern North America. Tissue testing was carried out in three populations. Opuntia cespitosa occurs over a wide variety of nutrient conditions and soil textures, including both acidic and alkaline soils, though soil nutrients were generally poor and thin. Populations of the species occurred on soils with very high levels of calcium that could be toxic for other plants, exceeding 20,000 kg/ha in some areas. Plants in these areas also had high Ca tissue levels, also common in desert cacti. Kruskal-Wallis and Spearman′s correlation results suggest that population size was not related to the soil attributes tested, but does indicate that areas mowed by large mowers have larger populations. This may be the result of local vegetative spread of fragments by mowers.
We collected harvest and survey information on ∼800 antelope jackrabbits (Lepus alleni) and 27 black-tailed jackrabbits (L. californicus) from 2009 to 2020. These data indicated that abundance varied annually and that the antelope jackrabbit population in the study area neither increased nor decreased greatly during the 12 years of the study, while black-tailed jackrabbit numbers remained low. The reasons for population changes in antelope jackrabbits appear complex and include variations in recruitment rate that were not positively related to precipitation amounts that could not be used to predict hunter success. Correlation coefficients between antelope jackrabbit hunt success and the numbers of antelope jackrabbits seen on belt transects weakly correlated with an index to bobcat (Lynx rufus) abundance indicating that further understanding of jackrabbit population dynamics will require investigating factors that affect changes in annual survival rate.