Colorado Desert Of California Research Articles

Whole community shotgun metagenomes of two biological soil crust types from the Mojave Desert.

We present six whole community shotgun metagenomic sequencing data sets of two types of biological soil crusts sampled at the ecotone of the Mojave Desert and Colorado Desert in California. These data will help us understand the diversity and function of biocrust microbial communities, which are essential for desert ecosystems.

A Genetic Assessment of the Recovery Units for the Mojave Population of the Desert Tortoise, Gopherus agassizii

ABSTRACT In the 1994 Recovery Plan for the Mojave population of the desert tortoise, Gopherus agassizii, the US Fish and Wildlife Service established 6 recovery units by using the best available data on habitat use, behavior, morphology, and genetics. To further assess the validity of the recovery units, we analyzed genetic data by using mitochondrial deoxyribonucleic acid (mtDNA) sequences and nuclear DNA microsatellites. In total, 125 desert tortoises were sampled for mtDNA and 628 for microsatellites from 31 study sites, representing all recovery units and desert regions throughout the Mojave Desert in California and Utah, and the Colorado Desert of California. The mtDNA revealed a great divergence between the Mojave populations west of the Colorado River and those occurring east of the river in the Sonoran Desert of Arizona. Some divergence also occurred between northern and southern populations within the Mojave population. The microsatellites indicated a low frequency of private alleles and a signif...

EPISODIC DEATH ACROSS SPECIES OF DESERT SHRUBS

Extreme events shape population and community trajectories. We report episodic mortality across common species of thousands of long-lived perennials individually tagged and monitored for 20 years in the Colorado Desert of California following severe regional drought. Demographic records from 1984 to 2004 show 15 years of virtual stasis in populations of adult shrubs and cacti, punctuated by a 55-100% die-off of six of the seven most common perennial species. In this episode, adults that experienced reduced growth in a lesser drought during 1984-1989 failed to survive the drought of 2002. The significance of this event is potentially profound because population dynamics of long-lived plants can be far more strongly affected by deaths of adults, which in deserts potentially live for centuries, than by seedling births or deaths. Differential mortality and rates of recovery during and after extreme climatic events quite likely determine the species composition of plant and associated animal communities for at least decades. The die-off recorded in this closely monitored community provides a unique window into the mechanics of this process of species decline and replacement.

Ontogenetic shift from facilitation to competition in a desert shrub

Summary Spatiotemporal responses to habitat conditions are important components of plant population and community dynamics. Plant stage or size is a common predictor of plant performance for a range of ecological conditions, including responses to neighbours. Plant response to local conditions varies from seedling establishment through to senescence, with strong implications for population regulation. I investigated size‐dependent responses to near adult neighbours among a uniquely quantitative sample of mapped juvenile and adult bur‐sage (Ambrosia dumosa), a common shrub in the Colorado Desert of California. Analyses of juvenile establishment and survival for two 5‐year census periods from 1984 to 1989 and 1989 to 1994 determined that germination and survival was greater for juveniles located under adults compared with away from adults. However, analyses of neighbour effects on growth of plants from the 1984 cohort showed that near adult neighbours improved juvenile growth over the 10‐year interval from 1984 to 1994, but reduced adult growth. A size‐dependent, ontogenetic shift occurs because neighbouring adult plants significantly improve the demographic performance of juveniles, but diminish that of larger established plants. The ontogenetic niche shift may be a useful framework to describe such differential responses of juvenile and adult plants. The utility of this framework is that responses to spatial and temporal variability in the environment are clearly demonstrated through ontogenetic constraints on plant performance, which provide an alternative mechanism of coexistence within and between species.

Movement, Home Range, and Activity Patterns of the Horned Lizard, Phrynosoma mcallii

Abstract Sixty-nine telemetered Phrynosoma mcallii from the Colorado Desert in California were relocated for up to nine months to examine activity patterns, home-range sizes and overlap, distance traveled between relocations, and onset and duration of hibernation. Total area used by the lizards ranged from 651–59,237 m2. Males had significantly larger mean summer home ranges and traveled significantly further than females. The duration of winter dormancy for eight telemetered lizards was 85 ± 8 (mean ± SE) days. Nearly all telemetered lizards were underground by mid-November and emerged as early as late December. Telemetered P. mcallii were out in the open or underneath a shrub throughout the day during spring and fall. They retreated into burrows to escape the midday summer heat. When out in the open, males perched on an elevated surface 19.0% of the time, whereas females perched 4.3%. Telemetered lizards exhibited considerable overlap among their home ranges; males shared 11% of their home ranges with f...

Nearest-Neighbour Relationships of Overlapping Circles and the Dispersion Pattern of Desert Shrubs

(1) Most techniques for analysing the dispersion of plant individuals in populations assume that the objects in question are points. When applied to populations of desert shrubs, these techniques often indicate significantly uniform dispersion. (2) The growth patterns of some plants may result in the overlap and fusion of separate individuals to form a clump that cannot be distinguished from that produced by a single individual. This inability to distinguish intimately fused individuals creates a bias toward perceiving uniformity as the techniques of dispersion analysis are based on theory relating to the dispersion of dimensionless points. (3) Simberloff's technique of analysis of nearest-neighbour relationships of nonoverlapping circles can be adapted to overlapping circles that become indistinguishable at some critical minimum separation distance and thus provides a technique for pattern analysis under these circumstances. (4) Analysis of the dispersion of Larrea tridentata in the Colorado Desert of California demonstrates that its clumped growth pattern creates a strong bias toward the perception of uniformity with techniques based on the point-dispersion theory.

Resource Utilization by Desert Quail: Time and Energy, Food and Water

Time—energy budgets (TEB) of Gambel's Quail (Callipepla gambelii) were compiled during two summers in the Colorado Desert of California. Quail spent 6.77 h/d foraging, 6.2 h/d inactive during daylight hours, and 11.02 h/d inactive at night. Field metabolic rate (FMR) calculated from this activity budget was 81.8 kJ/d. Of this, 47.3 kJ/d was expended during foraging, 12.6 kJ/d in daytime inactivity, and 20.4 kJ/d in nighttime inactivity. Despite the extremely hot thermal environment (maximum ambient temperature °45°C), there was no energy cost above resting levels for thermoregulation. FMR was also measured simultaneously with doubly labeled water (DLW), and averaged 90.8 kJ/d. TEB and DLW values agreed to within 6% when differences in measurement period were taken into account. A laboratory validation study indicated that DLW and balance methods agreed to within 5%. The FMR of C. gambelii was only 40% of that predicted for a bird of its body mass. This low FMR is primarily the result of a low resting metabolic rate (RMR): 51% of the predicted basal rate in 1981, and 70% of predicted in 1982. The basis and significance of this low and variable RMR are unclear. Energy assimilation efficiency, measured in laboratory feeding experiments with a mixed seed and arthropod diet, was 60.3%. An individual quail in the field thus required 150.3 kJ/d in its diet, representing a dry matter intake of 8.1 g/d. A diet of seeds alone provides insufficient water for Gambel's Quail in summer, so they must either incorporate moist food items in their diet or drink free water. It was calculated that over the course of a year, a population of Gambel's Quail consumes seeds with a total energy content °15% as great as that in seeds consumed by a population of desert rodents or harvester ants in the same area. Gambel's Quail thus may be important factors in the competition for resources among desert granivores, particularly because they can eat one of their competitors (harvester ants).

Decomposition of Ocotillo (Fouquieria splendens) Wood in the Colorado Desert of California

The weight loss of stem sections of ocotillo (Fouquieria splendens) was determined for 11 years in the Colorado Desert of California. Weight of a stem section was a function of original weight, time in the field and presence or absence of termites. A section weighing 10 g is estimated to have a half-life of 29 years without termites and 17 years if termites find the section. Small sections of stem decayed slightly more rapidly than larger sections. INTRODUCTION Decomposition in desert ecosystems is considered to be a slow process and, because of this, there can be more dead than live aboveground biomass (Hadley and Szarek, 1981). There are few measurements of natural rates of decomposition in deserts; however, examples of such studies include Haverty and Nutting (1975), who measured loss in wood due to termites over a period of one year; Comanor and Staffeldt (1978), who documented loss of weight by creosote bush (Larrea tridentata) parts over 5 months, and Fowler and Whitford (1980), who examined L. tridentata litter in bags over a period of 1-2 months. The purpose of this note is to report results of a study of weight loss in pieces of ocotillo (Fouquieria splendens) stem over 11 years. The study was prompted by a question about the stability of ocotillo populations: dead ocotillos are common in the western Colorado Desert of California, but small living individuals are very rare. Either dead ocotillos take a very long time to decay and, hence, the rarity of small living individuals reflects stationary recruitment or the population in the Colorado Desert of California is in a state of decline, with high rates of death and decomposition and a low rate of recruitment. This work was conducted at the southern end of the Anza-Borrego State Park, California (33 N lat, 116 W long). The area is a bajada between the Coyote Mountains to the N and the Jacumba Mountains to the W. The substrate is recent alluvium made up of locally derived andesitic volcanic rock mixed with granite and sedimentary rocks from the surrounding hills. The area is finely dissected with a microtopography of small water courses. The elevation is 275 m above sea level. In addition to Fouquieria splendens, Larrea tridentata, Ambrosia dumosa, Opuntia echinocarpa, 0. bagelovii and Encelia farinosa are abundant. METHODS Stems of living ocotillo were collected in January 1971 at the study site, cut into sections ca. 8.5 cm long (range 8.0-9.5 cm), dried at 85 C for 2 weeks, and then weighed to the nearest milligram. Average weight of the dried sections was 15.1 g 4 7.8 SD (range 5.0-30.9 g, n = 22). A wire was fastened around 15 sections together with a numbered metal tag. In the field, wires were fastened to wooden stakes and sections were left on the soil surface. Two sections were collected in 1972, 1973, 1974, 1977 and 1978. Five sections were collected in 1982. All sections were randomly selected. Sand was brushed from the sections, they were dried at 85 C and then weighed to determine loss. Analysis is based on a simple model in which the final weight is related to original weight by an allometric function:

Contrasts in energy intake and expenditure in sit-and-wait and widely foraging lizards.

Daily energy metabolism and water flux were measured with doubly labeled water in the free-living insectivorous lizards Cnemidophorus tigris (mean body mass 15.7 g) and Callisaurus draconoides (8.6 g) in June 1979 in the Colorado Desert of California. C. tigris was an active forager; it spent 91% of its 5-h daily activity period in movement. C. draconoides was a sit-and-wait predator; it spent less than 2% of its 10-h activity period in movement. C. tigris had significantly higher rates of field energy metabolism and water influx (210 Jg-1 day-1, 36.8 ul H2O g-1 day-1, N=19) than C. draconoides (136, 17.1, N=18). There were no significant differences between the sexes within either species.The extra costs of free existence were calculated from differences between field metabolic rates and maintenance costs estimated from laboratory respirometry. Rates of energy metabolism during the field activity period were about 1.5x resting levels at 40° C (∼field active body temperature) for C. draconoides and 3.3 x resting levels at 40° C (∼field active body temperature) for the more active C. tigris. Feeding rates calculated from water influx data were 13.3 mg g-1 day-1 for C. tigris and 5.8 mg g-1 day-1 for C. draconoides. Though C. tigris had a high rate of energy expenditure, its foraging efficiency [Formula: see text] was higher than C. draconoides'.

Seasonal Variation of Lipid Content in the Mosquito Culiseta inornata1

Fat body development in adult female Culiseta inornata (Diptera: Culicidae) was determined between Sept., 1975 and Feb., 1977. Fat body hypertrophy began in Mar., with 26% of dry body wt as lipid (DBWL) but increased to 64% DBWL by June, when overt activity ended. In Sept., when activity resumed, until Feb., fat body hypotrophy was apparent as DBWL remained below 21%. These seasonal variations in lipid content support the theory of aestivation by adult C. inornata in the Colorado Desert of California.

The Ecology of Culiseta inornata in the Colorado Desert of California: Seasonal Abundance, Gonotrophic Status, and Oviparity of Adult Mosquitoes1

In the Colorado Desert of California, female Culiseta inornata (Diptera: Culicidae) were active from Sept.-June, while males were active from Oct.-May. In airborne populations, during Oct. through Feb., nullipars comprised 40% or less of the empty females examined. Parous females alone were captured in Sept., and from Mar.-June. Among resting females, the occurrence of nullipars varied directly with changing population level in Oct. and Nov. (between 0 and 50% of empty females=nulliparous), but inversely with levels during Feb. and Mar. (100% of empty females=nulliparous). Aestival populations of C. inornata were inferred to consist of small numbers of females who either possess fully developed oocytes, or have completed at least one gonotrophic cycle. Male C. inornata do not survive the summer.

Sympatric Relationships of the Kangaroo Rats, Dipodomys merriami and Dipodomys agilis

Dipodomys merriami collinus and Dipodomys agilis cabezonae are two heteromyid rodents that occur in partial sympatry on the western edge of the Colorado Desert in California. Activity patterns, interspecific behavior and water requirements were investigated in the laboratory and correlated with the relative distributions of these species in the field. D. m. collinus and D. a. cabezonae were trapped in a vegetation cline along an altitudinal topographic gradient. There was a reversal of relative abundance of these two species along this cline. This study revealed apparent subspecific differences in the ability of D. agilis to produce concentrated urine, but no apparent differences under the midly stressful environmental conditions were noted between D. agilis and D. merriami .

Seasonal Adaptations in Photosynthesis and Respiration in Four Desert Shrubs Growing in Situ

Field measurements of carbon dioxide exchange and carbohydrate resources show that physiological adaptations occur in the shrubs Larrea divaricata, Encelia farinosa, Hymenoclea salsola, and Acacia greggii growing in situ in the Colorado Desert of California. L. divaricata, the most widely distributed shrub of the North American deserts, exhibited the greatest seasonal adaptation in the field. This study supports the hypothesis that adaptive temperature acclimations occur in plants.

Water Economy of the White-Crowned Sparrow and Its Use of Saline Water

range are the arid portions of southern California and adjacent regions (Grinnell and Miller, 1944). It is one of the most conspicuous winter-visitant sparrows in Joshua Tree National Monument, located in the transition between the Mojave Desert and the Colorado Desert in California (Miller and Stebbins, 1964). In addition Banks (1963) reports the occurrence of large flocks of White-crowned Sparrows (not subspecifically designated) on several of the desert islands in the Gulf of California during March and April 1962. The physiology of photoperiodically influenced phenomena in the White-crowned Sparrow has been intensively investigated by Farner and his colleagues (for example, Farner, 1964); King (1964) has recently reported on its metabolism and body temperature, and Morton (1965) has analyzed its food intake and feeding periodicity. In spite of these many investigations and in spite of its frequent habitation of xeric situations in the winter, information on the water relations of the Whitecrowned Sparrow is fragmentary. This investigation undertakes to examine the water economy of the Whitecrowned Sparrow in order to expand our knowledge of its general biology. Specifically, the study attempts to assess the ability of the White-crowned Sparrow to maintain water balance on the desert and to utilize saline water that may be present in desert springs and as sea water in portions of its winter range.

Adaptations of the Amphibian, Scaphiopus couchi, to Desert Conditions

Spade-foot toads (Scaphiopus couchi) have been discovered recently in the Colorado Desert of California (Sonoran Desert), a region averaging approximately 2' 2 inches of rainfall per year and having very high summer temperatures (to 50 C). This is one of the driest and hottest areas in North America. The species was apparently more widely distributed along the California side of the Colorado River in an earlier pluvial period. The animals now found there appear to be relict populations that have survived in a few isolated situations (in dry washes and at the, edge of sand dunes), due to special environmental conditions. Adults remain in burrows beneath dense vegetation during dry periods. Toads living at the sand dunes presumably bury themselves in a permanently wet layer in the sand. Adults appear to retain several layers of partially shed skin, which presumably form semi-impermeable membranes that reduce moisture loss. Body fluids of field animals just after emergence contain very high osmotic concentrations (approximately 20 o/oo compared to hydrated animals (7 to 8 o/oo). This also presumably tends to reduce water loss, perhaps even to aid in extracting moisture from a damp environment. In the laboratory, eggs require less than 48 hours for hatching at room temperature, and tadpoles produce legs within ten days. Observations indicate they, develop even more rapidly under field conditions. Young toads kept in the laboratory grew to approximately one-half adult size within three months. An extreme local drought is currently in its 20th year. However, this drought has probably been exceeded in intensity in the not-too-distant past. Consequently, these conditions have probably been experienced by members of this species previously. Therefore, there is little reason to believe the present drought necessarily will eliminate the California populations of S. couchi.

Limnology, Sedimentation, and Microorganisms of the Salton Sea, California

The Salton Sea, originally a fresh-water lake formed by the flood of the Colorado River in 1905, is located in the center of the Colorado Desert of California. By 1929, the water of the lake had become almost as saline as ocean water because of intense evaporation and solution of salts present on the floor of the basin before the flood. In recent years, in spite of the high rate of evaporation, excessive runoff from irrigation water has maintained and even raised the level of the lake. Evaluation of the water budget has made it possible to anticipate future changes in the chemical composition of the water— i.e., an increase in the amount of sulfates is predicted for the future. Measurements with a current cross and studies of salinity distribution indicate a counter-clockwise current pattern in the Salton Sea. Sands, silts, and clays are deposited in that order from the shore line to the center of the lake. The water content, amount of calcium carbonate, and textural characteristics indicate that most of the sediments of the Salton Sea were derived from the suspended load of the Colorado River, whereas the mineralogical study suggests that some of the sediments have a local origin. Two entirely different methods of computing the rate of sedimentation and of calculating the amount of calcium carbonate in the sediments give results of the same order of magnitude. The large amount of calcium carbonate is partly due to precipitation and partly to transportation by Colorado River water. Foraminifera are the most abundant microorganisms in the lake. Several ecological factors influence their distribution; among these factors, chlorinity and temperature are not important, depth may be important by its effect on other factors, but the variation in the pH of the sediments is significant. The living foraminiferal assemblage is due to accidental introduction, but the natural effect of environmental conditions has resulted in the creation of a dwarf fauna and many malformed individuals. In contrast to conditions in the ocean, abundance of species decreases offshore; however, as in the ocean, the number of living Foraminifera increases greatly after a bloom of phytoplankton. The average productivity of the Salton Sea is greater than that of the oceans. Conclusions derived from this study were applied to sediments deposited in the same basin during the past and made it possible to suggest a late Pliocene or early Pleistocene age for the Borrego formation and a Pleistocene age for the Brawley formation.

Physiology of Man in the Desert

THE possibility that American troops might be required to fight in the desert caused a team of physiologists to go to the Colorado Desert in California during the summers of 1942 and 1943. Their efforts were mainly concentrated first on the effects of the environment and level of physical activity on the rate of sweating and on the water requirements of man, and secondly, on the physiological effects of water depletion. Physiology of Man in the Desert By E. F. Adolph and Associates. (Monographs in the Physiological Sciences.) Pp. xiii + 357. New York and London: Interscience Publishers, Inc., 1947.) 39s.

The Colorado Desert of California: Its Origin and Biota

The Colorado Desert of California: Its Origin and Biota