Sonoran Desert Of Central Arizona Research Articles

Living on the edge: The sensitivity of arthropods to development and climate along an urban-wildland interface in the Sonoran Desert of central Arizona.

Preservation of undeveloped land near urban areas is a common conservation practice. However, ecological processes may still be affected by adjacent anthropogenic activities. Ground-dwelling arthropods are a diverse group of organisms that are critical to ecological processes such as nutrient cycling, which are sensitive to anthropogenic activities. Here, we study arthropod dynamics in a preserve located in a heavily urbanized part of the Sonoran Desert, Arizona, U.S.. We compared arthropod biodiversity and community composition at ten locations, four paired sites representing the urban edge and one pair in the Preserve interior. In total, we captured and identified 25,477 arthropod individuals belonging to 287 lowest practical taxa (LPT) over eight years of sampling. This included 192 LPTs shared between interior and edge sites, with 44 LPTs occurring exclusively in interior sites and 48 LPTs occurring exclusively in edge sites. We found two site pairs had higher arthropod richness on the preserve interior, but results for evenness were mixed among site pairs. Compositionally, the interior and edge sites were more than 40% dissimilar, driven by species turnover. Importantly, we found that some differences were only apparent seasonally; for example edge sites had more fire ants than interior sites only during the summer. We also found that temperature and precipitation were strong predictors of arthropod composition. Our study highlights that climate can interact with urban edge effects on arthropod biodiversity.

Using Bioacoustics to Examine Vocal Phenology of Neotropical Migratory Birds on a Wild and Scenic River in Arizona

Passive acoustic recorders have been used successfully as automated survey tools to detect terrestrial wildlife. However, few studies have monitored Neotropical migratory bird use of riparian forest habitat using this technology. Within dryland ecosystems, the forests along rivers support high bird diversity. Many bird species of conservation concern require these floodplain forest habitats for foraging, migration stop-overs, and breeding. Few studies have explored the use of acoustic records in riverine systems designated for conservation for their natural resource value via the Wild and Scenic Rivers Act in the USA. Using acoustic recorders, we document vocal activity of four riparian-obligate species (Bell’s Vireo, Vireo bellii; Summer Tanager, Piranga rubra; Yellow Warbler, Setophaga petechial; and Yellow-billed Cuckoo, Coccyzus americanus) to determine species occurrence along a Wild and Scenic River. We established three study reaches along the perennial Lower Verde River, in the Sonoran Desert of central Arizona, USA. Nine acoustic recorders were used over the period of 80–120 days during the summer of 2018. We measured vegetation composition and structure in 100 m2 plots paired with acoustic recorders. Visualizing vocal activity showed that three species were calling and singing at each reach; whereas, one species, the cuckoo, had fewer recordings and occurred later in the summer. We demonstrate the utility of acoustic monitoring even when applied to rare birds in complex riparian habitats. This information is important for land management and conservation efforts concerning these species of interest and identifying important habitat features in Southwestern US riparian woodlands.

Off‐highway vehicle road networks and kit fox space use

ABSTRACTOff‐highway vehicle (OHV) use is popular for outdoor recreation across the United States, with especially high levels of participation in Arizona and the American Southwest. Road networks related to OHV recreation have the potential to influence kit fox (Vulpes macrotis) space use intensity. To evaluate the potential impacts of OHV road networks to kit fox space use, we conducted a study during 2010–2013 in 2 areas of the Sonoran Desert in central Arizona. We used an observational approach to determine the importance of road density to kit fox space use, relative to other measured environmental variables. We monitored 22 collared individuals and used linear mixed models and an information‐theoretic approach to develop models of intensity of space use for seasons of relatively low (e.g., 33% of yearly OHV use observed) and high (e.g., 67% of yearly OHV use observed) OHV use. We found road density to be the most important predictor of space use for kit foxes, relative to other measured environmental variables. Space use was negatively associated with road density during winter (Oct–Mar), which coincided with kit fox breeding, denning, and pupping activities and was the season of relatively higher OHV use. Road density in OHV use areas is an important seasonal predictor of, and can negatively influence, kit fox space use. OHV road networks may lead to effective habitat loss for kit foxes and managers must consider how OHV recreational opportunities should be balanced with habitat conservation for species like kit fox. © 2016 The Wildlife Society.

Toe-cut terraces

Alluvial fans and fluvial terraces occur in nearly all climatic settings and often coexist within the same drainage basin. These landforms play an important role in understanding the geomorphic, hydrologic, sedimentologic and erosional histories of a basin. The juxtaposition of fans and fluvial terraces, in some instances, can lead to misinterpretation in distinguishing traditional fluvial terraces from the truncated toe of tributary alluvial fans. This becomes particularly troublesome for those attempting to interpret results from published field studies where fan-cut terrace, truncated alluvial fan, toe-cut alluvial fan, alluvial terrace, and incision of the lower end of a fan piedmont all refer to the same genetic landform. We call for use of the term “toe-cut terrace” to represent this landform. We also present criteria to aid in the identification of toe-cut terraces, defined as an abandoned alluvial surface, formed by the truncation of the distal portion of tributary alluvial fans by streams flowing obliquely or perpendicular to the fan surface. Truncation occurs through lateral erosion (“toe-cutting”) or through vertical incision by the trunk drainage lowering the base-level of the alluvial fan. This results in incision into the fan surface abandoning the fan’s depositional surface at a higher level above the modern floodplain – a form that often resembles a fluvial terrace. A case study from the Sonoran Desert in central Arizona illustrates a sequence of abandoned alluvial surfaces that resemble fluvial terraces, but use of the proposed criteria reveal the presence of both toe-cut terraces and traditional fluvial terraces formed by the abandonment of the rivers former floodplain.

Winter Activity of the Sonoran Desert Tortoise (Gopherus morafkai) in Central Arizona

Little is known regarding the activity of desert tortoises during winter, especially for the Sonoran Desert Tortoise (Gopherus morafkai). We observed adult, juvenile, and hatchling G. morafkai active during November, December, January, and February at 3 field sites in upland Sonoran Desert in central Arizona. At 1 site all individuals under observation (n = 36), including males, females, and hatchlings, emerged from hibernacula to drink during the first heavy (> 20 mm) rainfall event (December); at all 3 sites, females were observed active (basking, foraging) during winter much more frequently than were males.

Variation in monsoon precipitation drives spatial and temporal patterns of Larrea tridentata growth in the Sonoran Desert

Summary 1. Broad-scale patterns of above-ground net primary production (ANPP) are closely coupled to climate features, particularly the distribution and magnitude of rainfall. In arid and semi-arid regions, however, the precipitation regime, together with local geomorphology and plant life history traits, combine to regulate soil water availability and patterns of growth, complicating simple correlations with climatic variables. 2. To better understand the drivers of plant growth in desert ecosystems, we characterized the rates and spatial heterogeneity of stem elongation by the dominant perennial shrub, creosote bush (Larrea tridentata) in the northern Sonoran Desert of Arizona (USA). Estimates of stem growth were made over a 5-year period (2006–2010) from 60 plots at 15 sites spanning c. 120 km across the Central Arizona–Phoenix (CAP) Long-term Ecological Research (LTER) area. 3. We observed both the highest and lowest rates of stem growth during summer, and these patterns were related to the amount of monsoon rainfall and local rates of water infiltration. The relationship between growth and precipitation in the summer was nonlinear, with rates increasing more than eightfold at plots receiving more than 100 mm of seasonal rainfall. Conversely, growth during the winter/spring was intermediate in magnitude, similar among years and poorly correlated with seasonal precipitation. 4. The spatial heterogeneity of stem growth also differed markedly between seasons and was greater both within and among sites during summer compared to winter/spring growing periods. At broad scales, spatial heterogeneity of shrub growth was correlated with seasonal changes in the spatial variability of rainfall across the study area. At small spatial scales, greater heterogeneity during the summer appears linked to local soil properties that influence infiltration and water availability following monsoon storms. 5. Overall, the strong, nonlinear growth response by L. tridentata to monsoon rainfall suggests that the recurrence interval of wet summer seasons is an important driver of ANPP for this long-lived shrub. More generally, our results illustrate how regional climate variability and local soil properties can interact to influence the rates and heterogeneity of desert plant growth at multiple scales.

DIETS OF ADULTS AND LAMBS OF DESERT BIGHORN SHEEP DURING YEARS OF VARYING RAINFALL IN CENTRAL ARIZONA

Abstract Effects of unpredictable, variable rainfall in arid systems on diets of adults and lambs of desert bighorn sheep (Ovis canadensis) are poorly understood. We determined associations based on analysis of feces between amounts of rainfall and composition and similarity (overlap and diversity) of diets of adults and lambs, and relationships between diets of adults and lambs, in the Sonoran Desert of central Arizona during 1999–2003. Drought occurred in 2 of 3 years during sampling of feces of adults, and in 1 of 3 years during sampling of feces of lambs. Composition and diversity of diets of adults were comparable during years of drought and normal rainfall, except that diets were not correlated between years when severe drought (31% of long-term average rainfall) followed normal rainfall. Composition and diversity of diets of lambs also were independent of amounts of rainfall, but dietary overlap between and within age groups was greater during years of increasing rainfall compared to previous years...

Exposure to solar UV-B radiation accelerates mass and lignin loss of Larrea tridentata litter in the Sonoran Desert

We assessed whether exposure to solar ultraviolet-B radiation (UV-B) affects the mass loss of Larrea tridentata (creosotebush) litter in the Sonoran Desert of central Arizona. We placed three types of litter (leaves, twigs, or a natural mixture of leaves, twigs, and seeds) in bags constructed of UV-B-transmitting or UV-B- absorbing filter material that allowed either 85% (near-ambient UV-B treatment) or 15% (reduced UV-B treatment) of the biologically effective solar UV-B to reach litter inside the bags. Bags were placed outdoors for 4-5 months during the winter at two sites: a balcony or on the soil surface of the desert. Mass loss of leaf litter was greater under near-ambient UV-B than reduced UV-B at both sites: 21 (near-ambient) vs. 18% (reduced) on the balcony, and 18 vs. 14% at the desert site. Mass loss of twig litter was also greater under near-ambient UV-B at the desert site. Mass loss of the natural mixture of litter was also greater when exposed to near-ambient UV-B on the balcony, and tended to be greater at the desert site. We estimate that about 14-22% of the total mass loss of leaf litter during our 4-5 month experiments was attributable to solar UV- B exposure. Leaf litter exposed to near-ambient UV-B had lower concentrations of lignin, and fats and lipids, and slightly higher concentrations of holocellulose. The greater mass loss of litter under near-ambient UV-B appeared mainly attributable to loss of lignin, although losses of fats and lipids were also appreciable. A primary reason for greater mass loss of litter under solar UV-B appeared to be photodegradation, partic- ularly of lignin.

DIETS OF SYMPATRIC BOBCATS AND COYOTES DURING YEARS OF VARYING RAINFALL IN CENTRAL ARIZONA

We collected fecal samples (scats) of sympatric bobcats (Lynx rufus) and coyotes (Canis latrans) between 2000 and 2003 in a 53,600-ha area of the Upper Sonoran Desert in central Arizona. Our objective was to investigate composition, diversity, and overlap of diets of bobcats and coyotes in relation to varying rainfall in the Sonoran Desert of central Arizona. In general, bobcats ate more rodents than did coyotes, and coyotes ate more lagomorphs, large prey, and fruit/seeds than did bobcats. Composition of bobcat diets was independent of differences among years in annual rainfall and seasonal rainfall during summer–autumn (May–October) and winter–spring (November–April). Composition of coyote diets also was independent of drought conditions among years during summer–autumn, but coyotes ate more large prey and fewer rodents during years with winter–spring drought. Seasonally, bobcats ate more rodents than did coyotes in summer–autumn and winter–spring, whereas coyotes ate more lagomorphs than did bobcats during winter–spring, and more large prey and fruit/seeds in both seasons. Coyotes ate more large prey and lagomorphs during winter–spring, when seasonal rainfall was higher, and more fruit/seeds in summer–autumn, when seasonal rainfall was lower. Diversity of diets was consistently higher for coyotes than for bobcats, and increased for bobcats but not for coyotes during winter–spring drought and during higher seasonal rainfall in winter–spring. Overlap of diets between predators was independent of rainfall levels. We suggest that bobcats in the Sonoran Desert are more selective, specialized predators and that coyotes are more generalist, opportunistic predators. We hypothesize that, although diversity of bobcat food items and composition of coyote diets differ with varying rainfall in the Sonoran Desert, patterns of feeding strategy are independent of seasonal differences in precipitation and effects of drought, and bobcats and coyotes partition food resources independently of varying rainfall.

Spatial and temporal variation in islands of fertility in the Sonoran Desert

In many arid and semi-arid ecosystems, canopy trees and shrubs have a strong positive influence on soil moisture and nutrient availability, creating islands of fertility where organic matter and nutrients are high relative to areas outside the canopy. Previous studies of canopy effects on soil processes have rarely considered how landscape context may modulate these effects. We measured the effects of velvet mesquite trees (Prosopis velutina) on soil moisture and the biogeochemistry of nitrogen at different positions along a topographic gradient from upland desert to riparian zone in the Sonoran Desert of central Arizona. We also examined how landscape position and patterns of precipitation interact to determine the influence of P. velutina on soil moisture, N availability assessed using ion exchange resins, net N mineralization and net nitrification, and microbial biomass C and N. P. velutina clearly created islands of fertility with higher soil organic matter, net N mineralization and net nitrification rates, and microbial biomass under mesquite canopies. These effects were consistent across the landscape and showed little temporal variability. Magnitude and direction of effect of mesquite on soil moisture changed with landscape position, from positive in the upland to negative in the terrace, but only when soil moisture was >4%. Resin N showed responses to mesquite that depended on precipitation and topographic position, with highest values during wet seasons and under mesquite on terraces. We suggest changes in proximity of P. velutina to groundwater lead to shifts in biogeochemical processes and species interactions with change in landscape position along a topographic gradient.

Ploidy race distributions since the Last Glacial Maximum in the North American desert shrub, Larrea tridentata

Abstract A classic biogeographic pattern is the alignment of diploid, tetraploid and hexaploid races of creosote bush (Larrea tridentata) across the Chihuahuan, Sonoran and Mohave Deserts of western North America. We used statistically robust differences in guard cell size of modern plants and fossil leaves from packrat middens to map current and past distributions of these ploidy races since the Last Glacial Maximum (LGM). Glacial/early Holocene (26–10 14C kyr bp or thousands of radiocarbon years before present) populations included diploids along the lower Rio Grande of west Texas, 650 km removed from sympatric diploids and tetraploids in the lower Colorado River Basin of south‐eastern California/south‐western Arizona. Diploids migrated slowly from lower Rio Grande refugia with expansion into the northern Chihuahuan Desert sites forestalled until after ~4.0 14C kyr bp. Tetraploids expanded from the lower Colorado River Basin into the northern limits of the Sonoran Desert in central Arizona by 6.4 14C kyr bp. Hexaploids appeared by 8.5 14C kyr bp in the lower Colorado River Basin, reaching their northernmost limits (~37°N) in the Mohave Desert between 5.6 and 3.9 14C kyr bp. Modern diploid isolates may have resulted from both vicariant and dispersal events. In central Baja California and the lower Colorado River Basin, modern diploids probably originated from relict populations near glacial refugia. Founder events in the middle and late Holocene established diploid outposts on isolated limestone outcrops in areas of central and southern Arizona dominated by tetraploid populations. Geographic alignment of the three ploidy races along the modern gradient of increasingly drier and hotter summers is clearly a postglacial phenomenon, but evolution of both higher ploidy races must have happened before the Holocene. The exact timing and mechanism of polyploidy evolution in creosote bush remains a matter of conjecture.

Ontogenetic Variation in Growth and Sexual Size Dimorphism in a Central Arizona Population of the Western Diamondback Rattlesnake (Crotalus atrox)

The western diamondback rattlesnake (Crotalus atrox) is sexually dimorphic (adult males larger than females) throughout its range. A comprehensive analysis of the ecological and evolutionary sources of sex differences in growth and size requires a detailed understanding of growth trajectories during ontogeny. We studied a population of C. atrox in the upper Sonoran Desert of central Arizona. Specifically, we asked at what point during ontogeny males and females diverge in size: at birth, during juvenile growth, or as mature adults? We used mark-recapture data and a novel analysis of rattle characteristics to test for sex differences during each of these three ontogenetic stages. Our analyses suggest that male and female neonates are similar in size. Juvenile growth rates also appear to be uniform between sexes. However, males and females begin to diverge in size beyond sexual maturity, when female but not male growth rates become undetectable given our recapture intervals. Our results indicate that, when partitioned into its lifecycle components, sexual size dimorphism can be expressed at different stages and may be affected by a variety of behavioral, bioenergetic, and selective forces. Accordingly, studies of proximate and ultimate causation in sexual size dimorphism may benefit from consideration of the ontogeny of size separately in males and females.

Convergent Evolution in Perching and Patrolling Site Preferences of Some Hilltopping Insects of the Sonoran Desert

Males of the pompilid wasp, Hemipepsis ustulata, defend palo verde trees on mountain ridges in the Sonoran Desert. The preferences of the wasps for different trees on one ascending ridge remained essentially the same over four spring flight seasons. The wasps preferred large trees high on the ridge. Other insects unrelated to the wasp behaved similarly and focused their territorial or non-territorial mate-searching on or near the same sites most preferred by the wasps. Convergent preferences of hilltopping male insects may reflect the capacity of the compound eye of insects to detect some distant landmarks more easily than others. The prominent ridges that rise from the upland Sonoran Desert of central Arizona attract a diversity of insects, including tarantula hawk wasps, various butterflies, and bot flies. In the spring months males of these hilltopping species patrol or perch in or near conspicuous palo verdes (Cercidium microphyllum) growing on the backbone of the ridges. There they await the arrival of receptive females. Males of some species defend their patrolling or perching locations; in other species males exhibit little or no aggression toward conspecifics. But whether territorial or not, hilltopping males are not distributed evenly along ascending mountain ridges. Previous studies (Alcock, 1981, 1983a,b; Alcock and Schaefer, 1983) of three territorial members of the hilltopping complex (a pompilid wasp, Hemipepsis ustulata; a hairstreak butterfly, Atlides halesus; and a rodent bot fly, Cuterebra sp.) have documented that: (1) certain locations are much more likely to be occupied than others by territorial males, (2) territorial preferences appear to be stable from year to year, and (3) different species have similar preferences for available territory sites. The purpose of this report is (1) to provide new data on the year to year stability of territorial preferences of the wasp Hemipepsis ustulata, (2) to identify the key parameters of perch sites that determine their relative attractiveness to the wasps, and (3) to present new evidence showing that other species, both territorial and non-territorial, rank available mate- locating sites along a ridge in much the same order as the wasp.

Hilltop territoriality in a Sonoran desert bot fly (Diptera: Cuterebridae)

Males of an undescribed species of Cuterebra bot fly defend territories along ridge tops in the Sonoran desert of central Arizona. The most consistently occupied site, an 18 m 2 territory at the peak of a ridge, was usually defended by a single male for the entire (2–2.5 h) flight period of the morning. An average of five other males visited the peaktop territory each day from mid-February to early June and engaged in chases with the resident before departing. The resident male was very likely to return the next day but was generally ousted by a successful usurper on this or the third day of his tenure. The behaviour of males of this species of Cuterebra resembles that of several other members of the genus, especially C. latifrons. The landmark-based territoriality of these flies is similar to lek territoriality as defined from mammalian and avian examples.