Southwestern California Research Articles

College Undergraduate Ritalin Abusers in Southwestern California: Protective and Risk Factors

During the past five years, a few studies have reported that college students are using stimulants such as Ritalin without a prescription. To date, studies on college Ritalin/Adderall use have been from samples in the eastern or midwestern U.S. This study was designed to examine risk and protective factors associated with Ritalin/Adderall use among a college sample in Southern California. Our findings indicate that 11.2% of students reported past year and over 4% reported past 30 day use of Ritalin/Adderall. In our final analysis, students with lower GPAs, in a fraternity/sorority, not in a committed relationship, and who smoke and use other drugs were more likely to report past year and past 30 day Ritalin/Adderall use. Implications for prevention programming of these findings are discussed.

Doc at a Distance

A team of scientists from the US Army's Telemedicine and Advanced Technology Research Center is working to develop a new generation of remotely-controlled surgical robots that would allow military doctors, stationed safely distant from the front line, to perform operations without once putting their hands on patients. Part of the High Altitude Platforms Mobile Robotics Telesurgery project, this endeavor aims to demonstrate the concept of remote robotic surgery in the field, using a rugged surgical robot and an airborne communications link. With medical vehicles equipped with such remote-controlled robots, surgical care can be provided to soldiers in a lot less time than it would take to evacuate them to the nearest base or hospital. The team hopes these robots could also be used to bring advanced medical care not just to soldiers but to people in remote locations lacking in specialized physicians. A prototype of these remote-controlled robots is undergoing field testing at an isolated site north of Simi Valley in southwestern California to evaluate how well it performs outside the controlled environment of an operating with less than ideal conditions

Aspects of alluvial fan shape indicative of formation process: A case study in southwestern California with application to Mojave Crater fans on Mars

Longitudinal profiles from six alluvial fans surveyed in southwestern California have quantitative attributes that can distinguish formation processes. The radial slope of fans where debris flow processes dominated is constant while fluvially‐fed fans have a concave‐upward shape. We find the power law regression of upstream slope‐distance profiles is the preferred approach for assessing concavity. Concavity index, the exponential determined via power law regression analysis, is an accurate reflection of the magnitude of the concavity and thus a qualitative measure of the relative influence of fluvial processes on the fan. Fan length and surface gradient are inversely correlated: debris flow fans are shorter and steeper (>15°) than their fluvial counterparts. The results of this investigation provide criteria to evaluate hypothesized formation processes and provide constraints on the amount of fluid and timescales involved in the generation of comparably‐sized fans within Mojave Crater, Mars.

Eotetranychus lewisi

<i>Eotetranychus lewisi</i>

Edge effects of an invasive species across a natural ecological boundary

Natural habitats adjacent to human-modified areas often suffer edge effects stemming from physical disturbance, elevated predator densities, or invasive species. Although seldom documented, detrimental edge effects can also occur at natural ecological boundaries. Here I examine the spatial pattern and ecological effects of a biological invasion at well-delineated and abrupt edges between riparian corridors and coastal sage scrub at 10 sites in southwestern California. The invasive Argentine ant Linepithema humile thrives in moist riparian corridors but decreases greatly in number with increasing distance into adjacent dry scrub habitats. As L. humile numbers decrease, both the number of native ant workers and the number of native ant species captured in pitfall traps increase. Argentine ants appear to suppress native ants within at least 50 m of riparian corridors, but these effects diminish to undetectable levels by 200 m. At comparable uninvaded sites neither the number of native ant workers nor the number of native ant species captured in pitfall traps varies significantly across riparian-scrub edges. Areas subject to this edge effect may be sinks both for native ants and for organisms that depend on them for food or services. In general edge effects occurring at natural boundaries should receive increased attention as they might disrupt ecosystems not greatly altered by human activity.

Evidence that queens do not influence nestmate recognition in Argentine ants

Introduced populations of many invasive ants exhibit low levels of intraspecific aggression. Argentine ants (Linepithema humile), for example, maintain expansive supercolonies in many parts of their introduced range. Recent studies demonstrate that variation in nestmate recognition in L. humile can derive from both environmental and genetic sources. In some ants, pheromones emitted by queens also influence nestmate-recognition behavior. To test if such a phenomenon occurs in Argentine ants, we examined whether levels of intraspecific aggression vary as a function of queen presence or absence in experimental lab colonies. For each of four known supercolonies from southwestern California, we set up a pair of experimental colonies and randomly assigned replicates within each pair to treatment (queen removal) and control (no queen removal) groups. Using two different behavioral assays, we then measured aggressive behavior for ten days, removed queens from colonies in the treatment group, and continued to monitor aggression in both experimental groups for an additional 65 days. Both assays yielded qualitatively similar results: intraspecific aggression remained high throughout the experiment in both experimental groups. These results suggest that L. humile queens fail to influence levels of intraspecific aggression in introduced populations.

Neutralization of venoms from two Southern Pacific Rattlesnakes ( Crotalus helleri) with commercial antivenoms and endothermic animal sera

The Southern Pacific Rattlesnake ( Crotalus helleri) is found in southwestern California (USA), southward through north Baja California (MX) into the northern part of southern Baja California (MX). In this study, the venoms from two Southern Pacific Rattlesnakes were characterized. The two venoms were different in color, concentration, and enzyme activities. Two commercial antivenoms neutralized both C. helleri venoms differently. Antivipmyn (Fab 2H) and CroFab (FabO) neutralized both venoms but had different ED 50. Four times more Fab 2H antivenom was required to neutralize the C. helleri venom No. 011-084-009 than the venom from the snake No. 010-367-284. The hemorrhagic activity of two C. helleri venoms were neutralized differently by endothermic animal sera having a natural resistance to hemorrhagic activity of snake venoms. Opossums and Mexican ground squirrel sera did not neutralize the hemorrhagic activity of the venom No. 010-367-284. The sera of gray woodrats and hispid cotton rats neutralized all hemorrhagins in both C. helleri venoms. This is the first reported case in which opossum serum has not neutralized hemorrhagic activity of pit viper venom. Differences in the compositions of C. helleri venoms and their ability to be neutralized may help explain why snakebites are a difficult medical problem to treat and why effective polyvalent antivenoms are difficult to produce.

Dynamic reserve site selection

We analyze the problem of choosing sites through time to include in a network of biological reserves for species conservation. When sites cannot all be protected immediately, and excluded sites are threatened by development, planning should factor in both expected biodiversity benefits of sites and development risk. We formulate this problem as a stochastic dynamic integer-programming problem. We find that the timing of selections is critical; conservation budgets available up front yield significantly greater biodiversity protection. We also compare results using optimal and heuristic algorithms. The theory is applied to vertebrate and development threat data from southwestern California.

Variation in top‐down control of avian reproductive success across a fragmentation gradient

Understanding mechanisms that inhibit population persistence in fragmentation‐sensitive species is a key to conservation and management. It has become clear that species vary in their sensitivity to habitat fragmentation caused by urbanization and other land uses. We studied variation in avian reproductive success in coastal sage scrub habitat across a fragmentation gradient (interior of large habitat blocks (&gt;2300 ha)→edge of large habitat blocks→large habitat fragments (37–80 ha)→small habitat fragments (5–17 ha)) in urban southwestern California. We focused on four species of birds: the shrub‐nesting wrentit (Chamaea fasciata) and California towhee (Pipilo crissalis) and the ground‐nesting spotted towhee (P. maculatus) and rufous‐crowned sparrow (Aimophila ruficeps). Snake abundance was the best predictor of nest failure in the ground‐nesting species, whereas abundance of avian predators (Corvidae, Mimidae) was associated with nest failure of the wrentit and a combination of snake and avian predator abundance was correlated with nest failure of the California towhee. Avian nest predator abundance increased across the fragmentation gradient; by contrast, snake abundance decreased across this gradient. As a result, top‐down control of reproductive success in populations of the spotted towhee and rufous‐crowned sparrow was largely absent in habitat fragments. These two species enjoyed much higher nest success on fragments yet, paradoxically, both species are sensitive to fragmentation whereas the shrub‐nesting species are not. Our findings suggest that another process – perhaps differential survivorship or dispersal – yields reduced abundance of ground‐nesting species in habitat fragments. Studies of top‐down control and trophic cascades in fragmented landscapes should reflect that the strength of top‐down forces across a landscape varies with characteristics of predator and prey and their autecological responses to ecological gradients.

Paleoecology of a Middle Wisconsin Deposit from Southern California

Analysis of a buried deposit in the Diamond Valley of southern California has revealed well-preserved pollen, wood, and diatom remains. Accelerator mass spectrometry dates of 41,200±2100 and 41,490±1380 14C yr B.P. place this deposit in marine isotope stage 3. Diatoms suggest a shallow lacustrine environment. Pollen data suggest that several plant communities were present near the site, with grassland, scrub, chaparral, forest, and riparian communities represented. Comparison with modern pollen suggests similarities with montane forests in the nearby San Bernardino and San Jacinto ranges, indicating vegetation lowering by at least 900 m elevation and temperatures 4°–5°C cooler than today. An increase in high-elevation conifer pollen documents climatic cooling near the profile top. Early-profile diatoms are typical of warm water with high alkalinity and conductivity, whereas later diatoms suggest a higher flow regime and input of cooler water into the system. We suggest that the sequence is part of the cooling phase of an interstadial Dansgaard–Oeschger cycle. Records of the middle Wisconsin period are rare in southern California, but the Diamond Valley site is similar to records from Tulare Lake in the San Joaquin Valley and the ODP Site 893A record from Santa Barbara Basin. It is probable that the Diamond Valley assemblage is a local expression of a vegetation type widespread in the ranges and basins of southwestern California during the middle Wisconsin.

The Recent Rainfall Climatology of the Mediterranean Californias

In this work, recent (1948‐2001) rainfall data in a southwestern California station (San Diego) and a northwestern Baja California station (Ensenada) within a region called Mediterranean California, around 33 8N, 1178W, are studied. Cumulative annual means are used as indicators of climatological variability; but the entire datasets are analyzed by modeling the histogram of each set as a Weibull distribution probability density function, f . The climatology of both stations, defined simply as the arithmetic average, is compared with their theoretical mean; that is, the first moment of f . It is assumed that this comparison would be indicative of the reliability of the available rainfall climatologies. If these assumptions hold, in particular if the data is indeed Weibull distributed, it can be concluded that the climatological annual mean precipitation in this region is slightly overestimated at this time.

Phylogeography and Systematics of the Peromyscus eremicus Species Group and the Historical Biogeography of North American Warm Regional Deserts

Phylogeographic relationships among 26 populations from throughout the geographic range of the Peromyscus eremicus species group are described based on sequence data for a 699-bp fragment of the mitochondrial DNA COIII gene. Distance, maximum-likelihood, and maximum-parsimony analyses of phylogenetic trees generated under four separate character-weighting strategies and representing five alternative biogeographic hypotheses revealed the existence of a cryptic species (Peromyscus fraterculus, previously included under P. eremicus) on the Baja California Peninsula and adjacent southwestern California and two distinct forms of P. eremicus, one from the Mojave, Sonoran, and northwestern Chihuahuan regional deserts (West) and one from the remainder of the Chihuahuan Desert (East). Distinctiveness of P. fraterculus is supported by previous morphometric and allozyme analyses, including comparisons with neighboring P. eremicus and parapatric P. eva, with which P. fraterculus shares a sister taxon relationship. Divergence of the eva + fraterculus, West + East eremicus, and P. merriami haplotype lineages likely occurred in the late Neogene (3 Ma), in response to northern extension of the Sea of Cortéz and elevation of the Sierra Madre Occidental; divergence of eva from fraterculus is concordant with the existence of a trans-Peninsular seaway during the Pleistocene (1 Ma); and divergence of West from East eremicus occurred during the Pleistocene pluvial–interpluvial cycles, but well before the Wisconsinan glacial interval. The sequence of divergence within the eremicus species group and causal association of geological events of the Neogene and Holocene provide a working hypothesis against which phylogeographic patterns among other arid-adapted species of the warm regional deserts of North America may be compared.

Phylogeography of the California mountain kingsnake, Lampropeltis zonata (Colubridae).

The phylogeography of the California mountain kingsnake, Lampropeltis zonata, was studied using mitochondrial DNA sequences from specimens belonging to the seven recognized subspecies and collected throughout the range of the species. Maximum parsimony and maximum likelihood methods identified a basal split within L. zonata that corresponds to southern and northern segments of its distribution. The southern clade is composed of populations from southern California (USA) and northern Baja California, Mexico. The northern clade is divided into two subclades, a 'coastal' subclade, consisting of populations from the central coast of California and the southern Sierra Nevada Mountains of eastern California, and a 'northeastern' subclade, mainly comprised of populations north of the San Francisco Bay and from the majority of the Sierra Nevada. We suggest that past inland seaways in southwestern California and the embayment of central California constituted barriers to gene flow that resulted in the two deepest divergences within L. zonata. Throughout its evolutionary history, the northern clade apparently has undergone instances of range contraction, isolation, differentiation, and then expansion and secondary contact. Examination of colour pattern variation in 321 living and preserved specimens indicated that the two main colour pattern characters used to define the subspecies of L. zonata are so variable that they cannot be reliably used to differentiate taxonomic units within this complex, which calls into question the recognition of seven geographical races of this snake.

Miocene Paleogeography of Southwestern California and Its Implications Regarding Basin Terminology

A new palinspastic reconstruction for the latest Oligocene of southwestern California is created by: (1) backsliding the eastern part of the western Transverse Ranges west of the curved San Gabriel-Sierra Madre fault in a counterclockwise, rotational, left-slip direction in order to close the gap created by medial Miocene transrotational extension of the easternmost Los Angeles basin; and (2) bending the rocks in the westernmost Transverse Ranges, west of the Santa Monica Mountains, through an additional counterclockwise backrotation until they are in contact with the present southern California coast. This reconstruction restores Eocene forearc basin deposits of the southern California coast and the western Transverse Ranges regions into straight alignment with Eocene forearc-basin deposits to the north in the San Rafael Mountains. During the Oligocene, this forearc basin was divided into two depositional basins that received mostly nonmarine deposits. The northern of the two basins is named the DiSoCuMa depositional basin and the southern one the AnaVent depositional basin. Subsidence occurred during the early Miocene and flooded the two basins with marine deposits. During the medial Miocene, subsidence continued as the western side of the AnaVent basin (today's western Transverse Ranges) began to pull away from the southern California coast and rotate clockwise around its northern end. This transrotational process served to enlarge both basins by crustal extension and produced extensive areas of volcanism. Throughout the late Miocene, transrotation and subsidence continued, the basins grew in size and depth to their present configuration, and internal isostatic adjustments produced several new marine depositional basins within the previous two-basin framework.

Abstract: Miocene Paleogeography of Southwestern California

Abstract: Miocene Paleogeography of Southwestern California

Abstract: Miocene Palinspastic Restoration of Southwestern California

Abstract: Miocene Palinspastic Restoration of Southwestern California

Regional isotope effects and application to hydrologic investigations in southwestern California

Stable isotopic compositions of locally derived and imported surface and groundwaters in southwestern California provide a quantitative background for assessment of a variety of hydrologie and meteorologie questions. Geographically controlled meteoric water isotope‐ratio variations in the maritime climate zone of southwestern California show best fit δD dependence on latitude (−2.0‰ per degree), distance inland (−21‰ per 100 km), and elevation (−10‰ per kilometer). Meteoric and evaporative fractionations provide distinctive isotopic signatures that permit tracing of transported waters, as well as identification of watersheds for those precipitated locally. This regional framework of evaporative and meteoric isotope fractionation trends permits interpretation of local recharge and subsurface hydrology in the San Jacinto region. Similar techniques may be applied to other regions in southwestern California where differing source watersheds, surface or subsurface transport, and mixing provide significant variations in groundwater isotopic composition.

Reserve selection as a maximal covering location problem

Many alternative approaches have been proposed for setting conservation priorities from a database of species (or communities) by site. We present a model based on the premise that reserve selection or site prioritization can be structured as a classic covering problem commonly used in many location problems. Specifically, we utilize a form of the maximal covering location model to identify sets of sites which represent the maximum possible representation of specific species. An example application is given for vertebrate data of Southwestern California, which is then compared to an iterative solution process used in previous studies. It is shown that the maximal covering model can quickly meet or exceed iterative models in terms of the coverage objective and automatically satisfies a complementarity objective. Refinements to the basic model are also proposed to address additional objectives such as irreplaceability and flexibility.

Dust deposition in southern Nevada and California, 1984–1989: Relations to climate, source area, and source lithology

Dust samples collected annually for 5 years from 55 sites in southern Nevada and California provide the first regional source of information on modern rates of dust deposition, grain size, and mineralogical and chemical composition relative to climate and to type and lithology of dust source. The average silt and clay flux (rate of deposition) in southern Nevada and southeastern California ranges from 4.3 to 15.7 g/m2/yr, but in southwestern California the average silt and clay flux is as high as 30 g/m2/yr. The climatic factors that affect dust flux interact with each other and with the factors of source type (playas versus alluvium), source lithology, geographic area, and human disturbance. Average dust flux increases with mean annual temperature but is not correlated to decreases in mean annual precipitation because the regional winds bring dust to relatively wet areas. In contrast, annual dust flux mostly reflects changes in annual precipitation (relative drought) rather than temperature. Although playa and alluvial sources produce about the same amount of dust per unit area, the total volume of dust from the more extensive alluvial sources is much larger. In addition, playa and alluvial sources respond differently to annual changes in precipitation. Most playas produce dust that is richer in soluble salts and carbonate than that from alluvial sources (except carbonate‐rich alluvium). Gypsum dust may be produced by the interaction of carbonate dust and anthropogenic or marine sulfates. The dust flux in an arid urbanizing area may be as much as twice that before disturbance but decreases when construction stops. The mineralogic and major‐oxide composition of the dust samples indicates that sand and some silt is locally derived and deposited, whereas clay and some silt from different sources can be far‐traveled. Dust deposited in the Transverse Ranges of California by the Santa Ana winds appears to be mainly derived from sources to the north and east.

The question of prehistoric agriculture among the western Yumans

Agriculture fanned an important part of the subsistence system of the prehistoric: Yuman-speaking peoples who lived along or near the lower Colorado River. Some recent scholars have argued that the Yumans of nnorthwestern Baja California and southwestern California also practiced agriculture prehistorically. A critical review of the evidence fills to fails any substantial support for that conclusion.