Arizona-New Mexico Research Articles

A possible link between wildfire aerosol and North American Monsoon precipitation in Arizona–New Mexico

ABSTRACTPrevious research highlights the dominant role of Pacific sea surface temperatures (SSTs) and their associated large‐scale teleconnections in modulating the North American monsoon (NAM). At the regional scale, feedbacks associated with land‐surface boundary conditions have been shown to provide ‘memory’ in the system. Here, a previously unexplored second‐order linkage between aerosol generated by late‐spring wildfires and subsequent summer precipitation delivered by the NAM in the Arizona‐New Mexico (AZNM) region is proposed. Correlations between June/July organic carbon and elemental carbon (OC/EC) in Inter‐agency Monitoring of Protected Visual Environments (IMPROVE) aerosol data (Gila Wilderness and Bandelier) and NAM precipitation in southern AZNM over the period 1994–2012 are shown to be negative (r = –0.4), suggesting that active antecedent wildfire seasons tend to be immediately followed by a weak late summer monsoon. This result is consistent with a previous study linking precipitation and area burned in wildfires in AZNM. A survey of extant literature suggests a sound basis for potential mechanisms related to convective processes and cloud microphysics, and furthermore suggests that this forcing could be of similar magnitude to well‐documented land‐based second‐order NAM forcings (antecedent snowpack and soil moisture, vegetation, and mineral dust). Based on these results, we believe that the role of aerosols in modulating summer precipitation deserves further investigation both observationally and in modeling studies. If indeed wildfire smoke does contribute to the modulation of NAM intensity, by virtue of its close temporal association with NAM season, it may well represent a factor that could contribute effectively to improved seasonal prediction of summer precipitation in the NAM region.

Direct and semi-direct radiative effects of anthropogenic aerosols in the Western United States: Seasonal and geographical variations according to regional climate characteristics

The direct and semi-direct radiative effects of anthropogenic aerosols on the radiative transfer and cloud fields in the Western United States (WUS) according to seasonal aerosol optical depth (AOD) and regional climate are examined using a regional climate model (RCM) in conjunction with the aerosol fields from a GEOS-Chem chemical-transport model (CTM) simulation. The two radiative effects cannot be separated within the experimental design in this study, thus the combined direct- and semi-direct effects are called radiative effects hereafter. The CTM shows that the AOD associated with the anthropogenic aerosols is chiefly due to sulfates with minor contributions from black carbon (BC) and that the AOD of the anthropogenic aerosol varies according to local emissions and the seasonal low-level winds. The RCM-simulated anthropogenic aerosol radiative effects vary according to the characteristics of regional climate, in addition to the AOD. The effects on the top of the atmosphere (TOA) outgoing shortwave radiation (OSRT) range from −0.2 Wm−2 to −1 Wm−2. In Northwestern US (NWUS), the maximum and minimum impact of anthropogenic aerosols on OSRT occurs in summer and winter, respectively, following the seasonal AOD. In Arizona-New Mexico (AZNM), the effect of anthropogenic sulfates on OSRT shows a bimodal distribution with winter/summer minima and spring/fall maxima, while the effect of anthropogenic BC shows a single peak in summer. The anthropogenic aerosols affect surface insolation range from −0.6 Wm−2 to −2.4 Wm−2, with similar variations found for the effects on OSRT except that the radiative effects of anthropogenic BC over AZNM show a bimodal distribution with spring/fall maxima and summer/winter minima. The radiative effects of anthropogenic sulfates on TOA outgoing longwave radiation (OLR) and the surface downward longwave radiation (DLRS) are notable only in summer and are characterized by strong geographical contrasts; the summer OLR in NWUS (AZNM) is reduced (enhanced) by 0.52 Wm−2 (1.14 Wm−2). The anthropogenic sulfates enhance (reduce) summer DLRS by 0.2 Wm−2 (0.65 Wm−2) in NWUS (AZNM). The anthropogenic BC affect DLRS noticeably only in AZNM during summer. The anthropogenic aerosols affect the cloud water path (CWP) and the radiative transfer noticeably only in summer when convective clouds are dominant. Primarily shortwave-reflecting anthropogenic sulfates decrease and increase CWP in AZNM and NWUS, respectively, however, the shortwave-absorbing anthropogenic BC reduces CWP in both regions. Due to strong feedback via convective clouds, the radiative effects of anthropogenic aerosols on the summer radiation field are more closely correlated with the changes in CWP than the AOD. The radiative effect of the total anthropogenic aerosols is dominated by the anthropogenic sulfates that contribute more than 80% of the total AOD associated with the anthropogenic aerosols.

Mechanisms Controlling Precipitation in the Northern Portion of the North American Monsoon

Abstract Key mechanisms important for the simulation and better understanding of the precipitation of the North American monsoon (NAM) were analyzed in this paper. Three experiments with the Providing Regional Climates for Impacts Studies (PRECIS) regional climate model, the Hadley Centre Regional Model version 3P (HadRM3P), driven by different boundary conditions were carried out. After a detailed analysis of the moisture and low-level winds derived from the models, the authors conclude that the Gulf of Mexico (GoM) moisture and the Great Plains low-level jet (GPLLJ) play an important role in the northern portion of the NAM. Moreover, the realistic simulation of these features is necessary for a better simulation of precipitation in the NAM. Previous works suggest that the influence of moisture from the GoM in Arizona–New Mexico (AZNM) takes place primarily via the middle- and upper-tropospheric flow (above 700 mb). However, it is shown here that if the GoM does not supply enough moisture and the GPLLJ at lower levels (below 700 mb) does not reach the AZNM region, then a dry westerly flow dominates that area and the summer precipitation is below normal. The implications of these findings for studies of climate change are demonstrated with the analysis of two general circulation models (GCMs) commonly used for climate change prediction, which are shown not to reproduce correctly the GPLLJ intensity nor the moisture in the GoM. This implies that the precipitation in AZNM would not be correctly represented by a regional model driven by these GCMs.

Simulations of the 2004 North American Monsoon: NAMAP2

Abstract The second phase of the North American Monsoon Experiment (NAME) Model Assessment Project (NAMAP2) was carried out to provide a coordinated set of simulations from global and regional models of the 2004 warm season across the North American monsoon domain. This project follows an earlier assessment, called NAMAP, that preceded the 2004 field season of the North American Monsoon Experiment. Six global and four regional models are all forced with prescribed, time-varying ocean surface temperatures. Metrics for model simulation of warm season precipitation processes developed in NAMAP are examined that pertain to the seasonal progression and diurnal cycle of precipitation, monsoon onset, surface turbulent fluxes, and simulation of the low-level jet circulation over the Gulf of California. Assessment of the metrics is shown to be limited by continuing uncertainties in spatially averaged observations, demonstrating that modeling and observational analysis capabilities need to be developed concurrently. Simulations of the core subregion (CORE) of monsoonal precipitation in global models have improved since NAMAP, despite the lack of a proper low-level jet circulation in these simulations. Some regional models run at higher resolution still exhibit the tendency observed in NAMAP to overestimate precipitation in the CORE subregion; this is shown to involve both convective and resolved components of the total precipitation. The variability of precipitation in the Arizona/New Mexico (AZNM) subregion is simulated much better by the regional models compared with the global models, illustrating the importance of transient circulation anomalies (prescribed as lateral boundary conditions) for simulating precipitation in the northern part of the monsoon domain. This suggests that seasonal predictability derivable from lower boundary conditions may be limited in the AZNM subregion.

RUDD CREEK PUEBLO: A LATE TULAROSA PHASE VILLAGE IN EAST CENTRAL ARIZONA

Rudd Creek Pueblo is a late Tularosa phase (A.D. 1225-1300) village located in the Upper Little Colorado region south of Springerville, Arizona. In 1996, Arizona State University, in cooperation with the Arizona Game and Fish Department, conducted archaeological fieldwork at Rudd Creek. This paper summarizes the results of that field season, which included the clearing of disturbed fill from a number of looted rooms, as well as limited test excavations in two great kivas, undisturbed rooms, and extramural areas. Comparison of the archaeology of Rudd Creek Pueblo with other Tularosa phase settlements in the Mogollon highlands along the Arizona-New Mexico border highlights key dimensions of variability in thirteenth century settlement in this area. Our investigations suggest that future research focusing on Tularosa phase settlements has the potential to contribute greatly to current debates in Southwest archaeology concerning migration, exchange, and population aggregation.

Hydrology, Geomorphology and Management: Implications for Sustainability of Native Southwestern Fishes

Native southwestern fishes have declined markedly in range and numbers. The factors responsible for their decline are many and varied. However, the primary stressors to native fish assemblages in southwestern rivers and streams are habitat alteration and introduction of non-native species. We present data that compare the fish assemblages in two desert rivers—the Gila and Verde (Arizona-New Mexico)—over a period of 7–12 years, respectively. We also present data on hydrographs, broadscale and local geomorphology, and past fisheries, water, and land management activities. Peak flow, mean volume of flow, variability of flow, canyon-bound and broad alluvial reaches, dams, and introduced fishes are all either directly or indirectly related to fish assemblages in southwestern rivers and streams. We suggest that three primary influencing factors—two natural and one human induced (hydrograph, geomorphology, management)—are critical features in delimiting native fish assemblages. Conserving and sustaining native fish assemblages in these and other southwestern rivers and streams will require land managers to address all aspects of these three major influencing factors with administrative and legal mandates.

The Effects of the Gulf of California SSTs on Warm-Season Rainfall in the Southwestern United States and Northwestern Mexico: A Regional Model Study

Abstract The impacts of the sea surface temperatures (SSTs) in the northern Gulf of California (GC) on warm-season rainfall in the Arizona–New Mexico (AZNM) and the northwestern Mexico (NWM) regions associated with the North American monsoon (NAM) are examined from two sets of seasonal simulations in which different SSTs were prescribed in the GC. The simulations reproduced important features in the low-level mesoscale circulations and upper air fields around the time of monsoon rainfall onset in AZNM such as sea-breeze-like diurnal variations in the low-level winds between the GC and the land, development of south-southeasterly winds over the GC and the western slope of the Sierra Madre Occidental after the onset of rainfall, and the strengthening of the 500-hPa high over AZNM around the onset of monsoon rainfall in AZNM. The simulated temporal variations in the upper air fields and daily rainfall, as well as the mesoscale circulation around the GC, suggest that the GC SSTs affect the water cycle around the GC mainly by altering mesoscale circulation and water vapor fluxes, but they have minimal impacts on the onset timing of monsoon rainfall in NWM and AZNM. With higher SSTs in the NGC, rainfall in NWM and AZNM increases in response to enhanced water vapor fluxes from the GC into the land. The enhanced onshore component of the low-level water vapor fluxes from the GC with higher GC SSTs results from two opposing effects: weakened sea-breeze-like circulation between the GC and the surrounding lands that tends to reduce the water vapor fluxes from the GC, and increased evaporation from the GC that tends to increase the water vapor fluxes. The simulations also suggest that the development of south-southeasterly low-level winds over the GC after monsoon rainfall onset plays an important role in enhancing rainfall as longer fetches over the GC can provide more water vapor into the low atmosphere.

Precipitation variability associated with the North American Monsoon in the 20th century

An analysis of century‐long precipitation data shows that the interseasonal and continental‐scale variations of precipitation anomalies associated with interannual variations of the North American Monsoon (NAM) are notably different between the two periods of 1901–1962 and 1963–1994. In Arizona‐New Mexico (AZ‐NM), wet (dry) summers are preceded by dry (wet) winters only after 1962. Another characteristic of the NAM variability, a summer rainfall pattern of wetter (drier) AZ‐NM, and drier (wetter) Great Plains (GP), is observed only after 1962, as well. The strongest contrast in summer rainfall anomalies appears between AZ‐NM and the southeastern U.S. for 1901–1962, while it appears between AZ‐NM and the GP for 1963–1994. For the period after 1962, the precipitation variability obtained here show the same features found in earlier studies. Causes of the observed changes in the precipitation characteristics around 1960 are not clear due to a lack of large–scale atmospheric and oceanic data before 1950.

Interannual Variability of the North American Warm Season Precipitation Regime

Interannual variability of the North American warm season-precipitation regime is examined in three regions of the United States and Mexico: Arizona-New Mexico, northwest Mexico, and southwest Mexico. Daily observed precipitation over the United States and Mexico for a 26-yr (1963-88) period and various fields from the National Centers for Environmental Prediction-National Center for Atmospheric Research Reanalysis are used to compare and contrast hydrologic conditions and atmospheric circulation features associated with early, late, wet, and dry monsoons in each region. Relationships between anomalous monsoon behavior and the El Nino-Southern Oscillation phenomenon are examined. Some factors associated with the atmosphere's lower boundary conditions that might influence the interannual variability of the warm season precipitation regime are discussed. The mean seasonal evolution of the North American monsoon system is characterized by the regular northward progression of heavy precipitation from southern Mexico by early June to the southwestern United States by early July. While the seasonal normal rainfall and its variability are largest in southwest Mexico, the mean seasonal percent departure from normal is largest in Arizona-New Mexico. Wet (dry) monsoons in southwest Mexico tend to occur during La Nina (El Nino). This association is attributed, in part, to the impact of local sea surface temperature anomalies on the land-sea thermal contrast, hence the strength of the monsoon. There is also a weak association between dry monsoons in Arizona-New Mexico (northwest Mexico) and La Nina (El Nino). Wet summer monsoons in Arizona-New Mexico tend to follow winters characterized by dry conditions in the southwestern United States and vice versa. Although the onset and duration of the monsoon are quite regular in each region, the precise date of onset in a given region is highly variable and likely to be unrelated to the date of onset in the other regions. Early monsoons in Arizona-New Mexico tend to have heavy seasonal rainfall while late monsoons in northwest Mexico tend to have deficient seasonal rainfall. The onset date in southwest Mexico is not related to seasonal rainfall. However, interannual fluctuations in rainfall over the entire monsoon region for the 2-month period after onset in southwest Mexico are highly correlated, suggesting that knowledge of the starting date in southwest Mexico may be useful for analyzing, understanding, and possibly predicting these fluctuations.

The Pediatric Infectious Disease Journal® Newsletter

The Pediatric Infectious Disease Journal® Newsletter

Geographic variation and systematics of monospermous Juniperus (cupressaceae) from the Chihuahua Desert based on rapds and terpenes

Random amplified polymorphic DNAs (RAPDs) and the steam volatile leaf terpenoids of Juniperus erythrocarpa, J. monosperma var. monosperma, J. m. var. gracilis and J. pinchotii were analyzed by principal coordinate analyses and contour mapping. Juniperus monosperma var. gracilis was elevated to specific rank as J. angosturana R. P. Adams nom. nov.; J. erythrocarpa var. erythrocarpa was treated as a segregate of J. pinchotii; and J. erythrocarpa var. coahuilensis was accepted as a distinct species, J. coahuilensis (M. Martinez) Gaussen ex. R. P. Adams. Geographic and chemical analyses of J. coahuilensis suggests that hybridization and introgression with J. angosturana has been factor in the variation of this taxon. RAPDs and terpene data supported the recognition of Arizona-New Mexico populations of J. coahuilensis as a new variety, J. c. var. arizonica R. P. Adams, var. nov. In addition, several terpenoids previously reported as unknown are now identified.

Partitioning of copper and zinc in the sediments and porewaters of a high-elevation alkaline lake, east-central Arizona, U.S.A.

In Pacheta Lake, a high-elevation alkaline lake proximal to the smelting region of southern Arizona-New Mexico, concentrations of transition metal ions in pore waters and co-existing sediments were compared. Copper, Fe, Mn and Zn have been partitioned among operationally defined sediment solid phases (exchangeable sites, organic complexes, amorphous oxides, crystalline oxides, sulfides and residual silicates) and their concentrations in interstitial waters were measured. Concentrations are reported as a function of depth in the sediment column. The diagenetic environment is described and cycling mechanisms postulated for the above metals. Selective, sequential extraction of metals from lake sediments showed different binding mechanisms for Cu and Zn, the former most strongly associated with organic complexes, and the latter with iron oxyhydroxides. This difference has strong implications for selective metal remobilization under variable environmental conditions, both naturally and anthropogenically induced. Copper and zinc in porewaters were estimated to diffuse to overlying waters at 12.8 and 21.9 μg/cm 2/a, respectively. These fluxes are large enough to account for observed concentrations of Cu and Zn in overlying waters. No sediment metal contamination was directly attributable to smelting activity. However, this study does document a flux from sediments, which have accumulated Cu and Zn, to overlying waters no longer receiving trace metal deposition from now inactive smelters.

Regional Diversity of Insects in North America

Data on the regional distribution in America north of Mexico of >3,550 insect species belonging to a representative sample of taxonomically relatively well-known groups, chiefly families, shows that more species occur in southern regions (71% of all species occur south of a line along state boundaries from the Arizona-California to Georgia-South Carolina borders) than in northern regions (50% of all species occur north of the Oregon-California to New England-New York borders). More species occur in western regions (73% only west of Manitoba, Canada, to Texas) than in eastern regions (56%). Texas-Oklahoma and Arizona-New Mexico contain the most species, followed by California, Georgia-Florida, and the mid-Atlantic region (New York and other states). The percentages of species recorded in different areas depend on the state of knowledge as well as on the geographical restriction of the groups. Knowledge of most groups of North American insects is inadequate for any meaningful distributional analysis of the sort carried out for these representative samples. Although about one-third of the species analyzed are relatively widespread, the many geographic differences confirm that quantifying biodiversity (especially for purposes of preservation or management) requires local or regional, and not just global, analyses.

Effects of uranium mining discharges on water quality in the Puerco River basin, Arizona and New Mexico

Abstract From 1967 until 1986, uranium mine dewatering increased dissolved gross alpha, gross beta, uranium and radium activities and dissolved selenium and molybdenum concentrations in the Puerco River as indicated by time trends, areal patterns involving distance from the mines and stream discharge. Additionally, increased dissolved uranium concentrations were identified in groundwater under the Puerco River from where mine discharges entered the river to approximately the Arizona-New Mexico State line about 65 km downstream. Total mass of uranium and gross alpha activity released to the Puerco River by mine dewatering were estimated as 560 Mg (560 × 106 g) and 260 Ci, respectively. In comparison, a uranium mill tailings pond spill on 16 July 1979, released an estimated 1.5 Mg of uranium and 46 Ci of gross alpha activity. Mass balance calculations for alluvial ground water indicate that most of the uranium released did not remain in solution. Sorption of uranium on sediments and uptake of uranium by plants probably removed the uranium from solution.

The Mesozoic Mogollon Highlands, Arizona: An Early Cretaceous Rift Shoulder

The Mogollon Highlands have long been considered the southern source terrane for much of the early-to-middle Mesozoic fluvial sedimentary rocks of the southern Colorado Plateau. Because of the lack of Mesozoic sedimentary strata in the Mogollon region, many workers have suggested these highlands were located in central Arizona and New Mexico. New evidence suggests that during the Triassic and most of the Jurassic, a large highland did not exist in central Arizona-New Mexico but was present as a continental margin volcanic arc in southern Arizona and northern Mexico. At this time, central Arizona would be more aptly called the Mogollon Slope. Early Jurassic Navajo-equivalent sands were blown south from the Colorado Plateau area, across the Mogollon Slope, to become intercalated with volcanics along the northeast side of the arc. The first good evidence for a structural and topographic highland in the Mogollon area is in the Early Cretaceous, when the uplifted northeast flank of the Bisbee rift basin tilted...

Density and Production of Seeded Range Grasses in Southeastern Arizona (1970-1982)

Density and Production of Seeded Range Grasses in Southeastern Arizona (1970-1982)

Seasonal Movements of Mexican Freetail Bats Tadarida brasiliensis mexicana Banded in the Great Plains

Records of band recoveries from 170,000 bats banded in northern Oklahoma between 1952 and 1968 are summarized to present an account of the migratory habits of the Great Plains population of this species. Winter range lies between 20° and 29°N, and between the Gulf of Mexico and the interior of the Mexican Plateau. Maximum recorded distance from banding site to point of recovery is 1,840 km. One bat was recovered in its natal cave after making eight migra- tory circuits. A theory regarding the use of olfaction in long-range navigation is presented. The Mexican freetail bat has been known since 1956 to be a migratory species (Villa, 1956; Glass, 1958, 1959; Villa and Cockrum, 1963). Since the first discovery of long-range migration, Constantine (1967) has summarized his data on activity patterns and recorded numerous records of movements to and from Carlsbad Cavern. Cockrum (1969) summarized data he obtained in northwestern Mexico and southern Arizona. He recognzied four discrete populations, those in California and western Arizona which perform only local or short-range movements, and those of the intermontane desert and the Great Plains, which perform long migratory flights. The Arizona-New Mexico population migrates south along the Sierra Madre Occidental and the west coast of Mexico at least as far as the state of Sinaloa; the Great Plains population moves southward through Texas and along the Sierra Madre Oriental into eastern and south-central Mexico. Cockrum recorded two instances of movement of banded bats from Carlsbad to Arizona and northern Sonora, and Constantine recorded three recoveries of his Carlsbad bands in Arizona and one in Sinaloa. These records constitute the only evi- dence of intermixing between the Great Plains and Interior Desert populations. Between 1952 and 1968 the author and his graduate students banded approximately 170,000 of these bats in western Oklahoma. In the early years bats were banded without regard to age, but from 1962 to 1968, about 120,000 neonates were banded, males and females in about equal numbers. The bats came from four caves less than 80 km apart, whose populations constantly intermingle. These four caves constitute the northernmost nursery aggregation of freetail bats in the Great Plains and collectively con- tain an estimated >3 million fledged bats in late summer when all neonates are fully capable of flight. By using a different-colored band each year, with colors being repeated only at 5-year intervals, it was possible to recognize our bats, as opposed to bats banded elsewhere, and to recognize year classes, without capturing bats to read the numbers. From 329 bands actually read, and many hundreds more seen and recognized as ours, it appears that a large part of the population returns each year to its natal area. However, numerous summer records (Fig. 9) indicate that many bats of both sexes

Predatory behavior and prey selection by army ants in a desert-grassland habitat

Colonies of Neivamyrmex nigrescens conduct extensive nocturnal raids on other ants and termites in the desert-grassland of Arizona-New Mexico. We collected quantitative data on several aspects of raiding to pinpoint differences due to colony size and behavioral phase. In the nomadic phase, colonies began raiding at sunset and continued until dawn. Larger colonies covered more area, discovered more prey sites, and collected more booty than smaller colonies, but there were no systematic changes in raid intensity over the course of the nomadic phase. In the statary phase, raiding occurred less frequently and was less intense when it occurred; however, at the end of this phase, raiding was similar to nomadic phase raids in extent, duration, and booty captured.

The Navajo Homestead: Situation and Site

The Navajo Homestead: Situation and Site Stephen C. Jett* Spread over some 16 million acres (c. 6.5 million ha) of Arizona, New Mexico, and Utah is a cultural landscape quite distinct from that of the nation's dominant Anglo-American culture. It is a landscape created by the more than 150,000 Navajo, the nation's most numerous Indian tribe. Several centuries ago, the ancestral Navajo migrated to the Southwest from what is now western Canada, bringing with them settlement patterns characteristic of Northern Hunters.1 Despite the eventual adoption of an economy based on subsistence sheepherding and farming, the Navajo have retained, in modified form, their northern habits of settlement. These include a dispersed population, qualified by small agglomerations representing economically cooperating extended families ("homestead groups").2 Villages and towns have never characterized Navajo settlement.1 Single-individual and nuclear-family residences, as well as larger homestead-group agglomerations, form homesteads (popularly , "camps") consisting of one or more dwellings and, usually, * Dr. Jett is a Professor of Geography at the University of California, Davis. Field and archival work for this project was supported by intramural research grants of that institution. Aid was received from many individuals and libraries, but particular thanks are due David M. Brugge and Virginia Evelyn Spencer. My Navajo informant was Chauncey Neboyia, of Canyon de Chelly, Arizona. 1 Homer Aschmann, "Athapaskan Expansion in the Southwest," Yearbook, Association of Pacific Coast Geographers, Vol. 32 (1970), pp. 79-97. 2 Stephen C. Jett, "Origins of Navajo Settlement Patterns," Annals, Association of American Geographers, Vol. 68 (1978), pp. 351-362. ;i Elliot G. Mclntire, "Central Place Studies on the Navajo Reservation: A Special Case," Yearbook, Association of Pacific Coast Geographers, Vol. 29 (1967), pp. 91-96. 101 102ASSOCIATION OF PACIFIC COAST GEOGRAPHERS corrals and other structures. Typically, each homestead group maintains permanent dwellings at two or more camps, which are occupied in response to changing seasonal availabilities of, and requirements for, farmland, pasturage, firewood, and stock water—or, today, wage-work opportunities, schools and shopping, and the like. Homestead Morphology In the broadest sense, a Navajo homestead may consist of anything from a simple log-and-brush summer shade (ramada) or tent, to a grouping of 20 or more hogans (traditional circular or polygonal dwellings), houses, and shades, one or more corrals, and often, other structures such as privies, beehive ovens, animal shelters, root cellars , sudatories, and the like.4 A camp may be the permanent homesite or temporary camp of an individual, a nuclear family, or a man and his plural wives and their children; or, it may comprise the several dwellings and other structures belonging to members of a homestead group which, in addition to the aforementioned relatives, may include grandparents, siblings and their spouses and children, and occasionally other persons. Sometimes, too, loose clusters of dwellings of adjacent homestead groups may be fairly close to each other, forming what appears to be a single large camp or small hamlet . There is, therefore, no "typical" Navajo homestead, although a 4 "Camp" is often used but seldom defined. Richards defined it as being a household's or extended family's residence cluster, geographically or socially isolated from neighboring clusters; Cara E. Richards, "Modem Residence Patterns Among The Navajo," El Palacio, Vol. 70 (1963), p. 26. For detailed descriptions and bibliography of dwelling types and homesteads, see Cosmos Mindeleff, "Navajo Houses," Bureau of American Ethnology, Annual Report 17 (1898), pp. 475-517; Virginia Evelyn Spencer, "The Geography of Navajo Dwelling Types with Special Reference to Black Creek Valley, Arizona-New Mexico," unpublished M.A. thesis, Department of Geography, University of California, Davis, 1969; Virginia E. Spencer and Stephen C. Jett, "Navajo Dwellings of Rural Black Creek Valley, Arizona-New Mexico," Plateau, Vol. 43 (1971), pp. 159-175; Stephen C. Jett and Virginia Evelyn Spencer, Navajo Architecture: Forms, History, and Distributions (Tucson, University of Arizona Press), in press; John Leslie Landgraf, Land-Use in the Ramah Navajo Area, Peabody Museum of American Archaeology and Ethnology Papers, Vol. 42, No. 1 (1954), pp. 47-51; Edwin N. Wilmsen, "The House of the Navajo," Landscape, Vol. 10 (1960), pp. 15-19. YEARBOOK · VOLUME 42 · 1980103 couple of hogans (or, today...

Recruitment behavior, home range orientation and territoriality in harvester ants, Pogonomyrmex

1. Scouts of the harvester ant Pogonomyrmex barbatus, P. maricopa and P. rugosus which discovered a new rich foraging area recruit nestmates by laying a trail with poison gland contents from the feeding site to the nest. Laboratory experiments have shown that Pogonomyrmex workers are stimulated to follow the trail by the trail pheromone alone. 2. The biological significance of the recruitment behavior was analyzed in the mesquite-acacia desert in Arizona-New Mexico, where the three species occur sympatrically. P. maricopa recruits less efficiently to food sources than does P. barbatus and P. rugosus. Generally the recruitment activity depends on a number of parameters of the food source, such as distance to the nest, density of the seed fall and size of the grains. 3. The recruitment activity is also affected by the presence, absence or distance of hostile neighboring colonies. 4. The use of chemically and visually marked trunk trails which originate from recruitment trails, guarantees and efficient partitioning of foraging grounds. It could be demonstrated that trunk trails, used by P. barbatus and P. rugosus during foraging and homing, have the effect of avoiding aggressive confrontations between neighboring colonies of the same species. They channel the mass of foragers of hostile neighboring nests into diverging directions, before each ant pursues its individual foraging exploration. This channeling subtly partitions the foraging grounds and allows a much denser nest spacing pattern than a foraging strategy without trunk trails, such as that employed by P. maricopa. 5. The behavioral mechanisms which maintain overdispersion both within and between species of Pogonomyrmex were investigated. Aggressive confrontations at the colony level and aggressive expulsion of foundress queens from the nest territories of mature colonies play thereby a major role. Observational as well as experimental data led to the conclusion that the farther away from its nest the intruder is, the less vigorous are the aggressive confrontations with the defenders. Only when neighboring colonies are located too close together will increased aggressive interactions eventually lead to the emigration of the weaker colony. 6. P. barbatus and P. rugosus have a wide niche overlap, whereas P. maricopa seems to be more specialized in regard to food. This is consistent with the findings that interspecific territoriality between P. barbatus and P. rugosus is considerably more developed than between these species on the one side and P. maricopa on the other. 7. Although foundress queens, which venture into a territory of a conspecific mature colony are fiercely attacked, most of them are not injured, but rather dragged or carried to the territorial border and then released. 8. Nevertheless foraging areas, even of conspecific colonies, frequently overlap, but aggressive interactions there are usually less intense than at the core areas (trunk trails plus nest yards), which normally do not overlap and are vigorously defended.