Peer Leader Essays from the Desert Southwest: The Practice of Leading Learning

At semester’s end at the University of Texas at El Paso and at the University of Texas of the Permian Basin, faculty members directing the PLTL Programs invite Peer Leaders to reflect on their experience, to describe their challenges, and to offer their personal advice. For the benefit of future Peer Leaders, here are their stories, reflections, observations, and advice about leadership and the practice of leading.

A phenotypic characterization of Rarámuri Criollo cattle introduced into the Southwestern United States

Our objective was to describe key phenotypic characteristics of a population of Rarámuri Criollo (RC) cattle introduced from the Copper Canyon of Chihuahua, México into the Southwestern United States almost two decades ago. We recorded 26 phenotypic traits of 37 RC individuals including mature cows, first-calf heifers, and mature bulls raised at the USDA-ARS Jornada Experimental Range in southern New Mexico. This herd of RC cattle exhibited intermediate body sizes compared to the smaller Corriente and larger Texas Longhorn and Florida Cracker cattle. Coat colors were similar to those described for other Criollo biotypes but horn shape and size of RC appear to be different than that of other US-based Criollo breeds. Though smaller than commercial beef breeds, RC cattle appear to be well-matched to the Southwestern US environments as evidenced by previous studies that evaluated their grazing behavior, weight gains, and carcass quality. Rarámuri Criollo cattle are a genetic resource whose conservation could be critically important for climate change adaptation of ranches in the desert Southwest.

Aquatic Habitat Bird Occurrences at Photovoltaic Solar Energy Development in Southern California, USA

The development of photovoltaic (PV) utility-scale solar energy (USSE) in the desert Southwest has the potential to negatively affect birds through collision mortality. Based on early patterns in fatality monitoring data, the lake effect hypothesis (LEH) was developed and suggested that birds misinterpret PV solar panels for water. As the LEH was only recently defined and inference beyond bird mortality is limited, our research objective was to examine the species composition, abundance, and distribution of live and dead aquatic habitat birds at five PV solar facilities and paired reference areas in southern California. Further, we collected data from a small regional lake as an indicator of the potential aquatic habitat bird community that could occur at our study sites. Using an ordination analysis, we found the lake grouped away from the other study sites. Although the bird community (live and dead) at the solar facilities contained aquatic habitat species, Chao’s diversity was higher, and standardized use was more than an order of magnitude higher at the lake. Finally, we did not observe aquatic habitat bird fatalities in the desert/scrub and grassland reference areas. Thus, the idea of a “lake effect” in which aquatic habitat birds perceive a PV USSE facility as a waterbody and are broadly attracted is likely a nuanced process as a PV solar facility is unlikely to provide a signal of a lake to all aquatic habitat birds at all times.

Analyzing a phenological anomaly in Yucca of the southwestern United States

Yucca in the American desert Southwest typically flowers in early spring, but a well-documented anomalous bloom event occurred during an unusually cold and wet late fall and early winter 2018–2019. We used community science photographs to generate flowering presence and absence data. We fit phenoclimatic models to determine which climate variables are explanatory for normal flowering, and then we tested if the same conditions that drive normal blooming also drove the anomalous blooming event. Flowering for Yucca brevifolia (Joshua tree) and Yucca schidigera (Mojave yucca) is driven by complex, nonlinear interactions between daylength, temperature, and precipitation. To our surprise, early-season flowering odds are highest in colder and drier conditions, especially for Joshua trees, but increase with precipitation late-season. However, the models used to fit normal blooming overpredicted the number of anomalous blooms compared to what was actually observed. Thus, predicting anomalous flowering events remains a challenge for quantitative phenological models. Because our model overpredicted the number of anomalous blooms, there are likely other factors, such as biotic interactions or other seasonal factors, which may be especially important in controlling what is presumed to be rare, out-of-season flowering in desert-adapted Yucca.

Kissing Bug Intrusions into Homes in the Southwest United States

Kissing bugs readily enter homes in the Sonoran Desert and bite the residents. Their saliva is highly antigenic, causing local and systemic skin reactions and life-threatening anaphylaxis. We attempted to determine what characteristics of homesites may have contributed to home intrusion by kissing bugs. Extensive and detailed information about the homes and the home environment was collected from 78 homeowners in Tucson who suffered kissing bug intrusions. Homeowners collected 298 Triatoma rubida in and around their homes. Of the homes entered by kissing bugs, 29 of 46 (63%) contained bugs harboring Trypanosoma cruzi. Although in the aggregate, homeowners were bitten > 2200 times, no individual tested positive for Chagas disease (N = 116). Although yearly intrusion likely occurs in some homes, T. rubida does not domiciliate within homesites in the Desert Southwest. We conclude there is little risk to homeowners for Chagas disease given the current behavior of resident kissing bugs and absent ingesting kissing bug fecal matter.

Predicting Phenological Anomaly: a Case Study of Yucca in the Southwestern United States

Yucca in the American desert Southwest typically flowers in early spring, but a well-documented anomalous bloom event occurred during an unusually cold and wet late fall and early winter 2018–2019. We used citizen science photographs as a means to generate flowering presence and absence data. We fit phenoclimatic models to determine which climate variables are explanatory for normal flowering, and then we tested if the same conditions that drive normal blooming also drove the anomalous blooming event. Flowering for Y. brevifolia and Y. schidigera is driven by complex, nonlinear interactions between daylength, temperature, and precipitation. To our surprise, early-season flowering odds are highest in colder and drier conditions, especially for Joshua trees, but increase with precipitation late-season. However, the models used to fit normal blooming overpredicted the number of anomalous blooms compared to what was actually observed. Thus, predicting anomalous flowering events remains a challenge for quantitative phenological models. Because our model overpredicted the number of anomalous blooms, there are likely other factors, such as biotic interactions or other seasonal factors, which may be especially important in controlling what is presumed to be rare, out-of-season flowering in desert-adapted Yucca.

Atmospheric Precipitable Water and its Correlation with Clear Sky Infrared Temperature Observations

Total precipitable water (TPW) in the atmosphere is the vertically integrated amount of atmospheric water in all of its phases. TPW is a valuable predictor for weather forecasting, and it is routinely measured using radiosondes, ground-based global positioning systems (GPS), sun photometers, or microwave radiometers. The use of these sophisticated instruments limits the number of TPW measurement sites, which affects the accuracy of forecast models in regards to storm formation, strength, and the potential for precipitation. We have analyzed this relationship for the much drier climate zone found in the Desert Southwest, specifically over Socorro, New Mexico (34° N, 107° W). Daily measurements of the ground and zenith sky temperatures have been made at Socorro for two complete annual cycles using infrared thermal sensors. Radiosonde TPW measurements from National Weather Service stations located in nearby Albuquerque, and Santa Theresa, New Mexico, are input into our dataset and analysed via a newly developed computational tool. Our results show that an exponential relationship between TPW and zenith sky temperature also holds for the Desert Southwest, but with parameters that are different than those obtained for the Gulf Coast. Model simulations can accurately reproduce the observed relationship between TPW and temperature, and the results suggest that half of the signal in temperature is directly related to direct changes in opacity due to changes in TPW, while the other half is due to changes in air temperature that usually accompany changes in TPW.

Phylogeography of Cedros and Tiburón Island Mule Deer in North America’s Desert Southwest

Though mule deer (Odocoileus hemionus) persist in robust populations throughout most of their North American distribution, habitat loss, unregulated hunting, and other factors have reduced their historical range in México. Two of the 6 putative subspecies inhabiting México’s deserts and Baja California peninsula are of conservation concern, occupying islands in the Pacific Ocean (Odocoileus hemionus cerrosensis on Cedros Island: endangered) and Sea of Cortés (Odocoileus hemionus sheldoni on Tiburón Island: threatened). Focusing on the desert southwest (n = 448), we sampled Tiburón (n = 22) and Cedros (n = 15) Island mule deer using contemporary samples and natural history museum specimens to complete a phylogeographic evaluation of the species complex, and assess the phylogeography of these insular subspecies. Both insular subspecies formed endemic haplotype lineages, consistent with island biogeographic theory. Bayesian skyline plots were consistent with Holocene demographic expansion. Cedros Island deer were genetically most similar to adjacent mainland Baja California deer, but exhibited a suite of unique haplotypes and reduced genetic variation. Tiburón Island deer haplotypes unexpectedly nested within a mainland lineage found in distant New Mexico, rather than the adjacent mainland Sonoran lineage. Such findings suggest the importance of postglacial climate fluctuations and biotic community turnover in the phylogeographic history of mule deer in the desert southwest. Our genetic data corroborates cultural, archaeological, and phenotypic evidence supporting Cedros and Tiburón deer endemicity and subspecies status. Reduced genetic variation, divergence from mainland populations, and demographic trends on both islands indicate that conservation, monitoring, and management are critical to ensure persistence of these endemic insular subspecies.

Late summer organic tomato production with heat tolerant tomato cultivars

Field production of organic fresh-market tomatoes in the U.S. Desert Southwest is desired by local producers and consumers. Tomato yield and fruit quality can be seriously impacted by heat stress (HS) and beet curly top virus (BCTV) infection of the main-season crop. We examined delayed planting of HS tolerant cultivars as a strategy for avoiding and mitigating these abiotic and biotic stressors. In 2016, seven putative HS tolerant cultivars, and one considered to be heat susceptible, were transplanted to the field in mid-summer to avoid peak populations of beet leafhopper (Circulifer tenellus), the vector of BCTV. In 2017, seven HS tolerant cultivars, one heat-susceptible, and two hot-set hybrid cultivars were transplanted in mid-summer. Fruit set was above 75% for most entries, including the heat-susceptible checks. Open-pollinated (OP) and hybrid cultivars exhibited a range of yields from 21.3 to 148.6 Mg/ha and fruit quality ratings from poor to excellent. The OP check ‘Super Sioux’ displayed consistently good yield and quality across years. The correlation between fruit set and yield was low (R2 = 0.29) and significant only at the 0.10 level (P<0.09). The incidence of curly top (incited by BCTV infection) was less than 10% in both years, indicating mid-summer planting aided disease avoidance. ‘Flamenco’, the earliest variety, and two later maturing varieties ‘Florida 91’ and ‘Skyway 687’, are recommended for further evaluation. Mid-summer planting of small and medium-fruited tomato cultivars appears to be a viable option for organic fresh-market tomato production for the fall market in the Southwest USA

Connecting the Land Surface to Droughts: How Transpiration, Canopy Evaporation, and Ground Evaporation Impact Droughts Across the North American Continent

&lt;p&gt;Land surface moisture plays a crucial role in precipitation patterns across the globe. Evapotranspiration (the combination of ground evaporation (E), canopy evaporation (I), and transpiration (T)) from the land surface can influence precipitation through local recycling and the propagation of moisture to downwind regions. However, the role of the land surface and of T, E, and I individually in these two processes are not well understood and limit our understanding of the role of the land surface for both drought onset and intensification. Here we use a version of the Community Earth System Model (CESM1.2 with the Community Atmosphere Model CAM5 and the Community Land Model CLM5) with online water tracers to directly track and quantify the movement of T, E and I moisture across North America for the 1985&amp;#8211;2015 period. Initial findings suggest that over 50% of summer precipitation for much of central and northern US and Canada comes from the land surface. The tracers also suggest that, with the exception of the US west coast and desert southwest, 40-60% of land precipitation across the continent comes from the T component. The connection between land surface moisture and drought episodes are examined for different regions of North America. The individual roles of T, E, and I in shaping droughts are also examined.&lt;/p&gt;