Chiricahua Mountains Research Articles

Evidence for a Late Cretaceous to Paleogene basement-involved retroarc wedge in the southern U.S. Cordillera: A case study from the northern Chiricahua Mountains, Arizona

Late Cretaceous to Paleogene contractional deformation in the southern U.S. Cordillera is commonly attributed to the Laramide Orogeny, in part because of the prevalence of moderate- to high-angle, basement-involved reverse faults. However, it is unclear if the tectonic models developed for the archetypal Laramide foreland belt in the U.S. Rocky Mountain region are applicable to the southern U.S. Cordillera. New geologic mapping of the northern Chiricahua Mountains in southeast Arizona, USA, indicates the presence of an originally sub-horizontal thrust fault, the Fort Bowie fault, and a thin-skinned ramp-flat thrust system that is offset by a younger thrust fault, the Apache Pass fault, that carries basement rocks. Cross-cutting relationships and new geochronologic data indicate deformation on both faults occurred between 60 Ma and 35 Ma. A biotite 40Ar/39Ar plateau age of 48 Ma from the hanging wall of the basement-involved Apache Pass fault is interpreted to record erosion related to reverse fault movement and rock uplift. The presence of thrust faults in southeast Arizona raises the possibility of a latest Cretaceous−Eocene retroarc orogenic wedge that linked the Sevier and Mexican thrust belts to the north and south, respectively. Basement-involved deformation does not rule out the presence of a retroarc wedge, and many Cordilleran orogenic systems include basement-involved thrusting.

Discovery of a new tarantula species from the Madrean Sky Islands and the first documented instance of syntopy between two montane endemics (Araneae, Theraphosidae, Aphonopelma): a case of prior mistaken identity.

The Chiricahua Mountains in southeastern Arizona are renowned for their exceptional biodiversity and high levels of endemism. Morphological, genomic, behavioral, and distributional data were used to report the discovery of a remarkable new tarantula species from this range. Aphonopelmajacobii sp. nov. inhabits high-elevation mixed conifer forests in these mountains, but also co-occurs and shares its breeding period with A.chiricahua-a related member of the Marxi species group-in mid-elevation Madrean evergreen oak and pine-oak woodlands. This marks the first documented case of syntopy between two montane endemics in the Madrean Archipelago and adds to our knowledge of this threatened region's unmatched tarantula diversity in the United States. An emended diagnosis and redescription for A.chiricahua are also provided based on several newly acquired and accurately identified specimens. Phylogenetic analyses of mitochondrial and genomic-scale data reveal that A.jacobii sp. nov. is more closely related to A.marxi, a species primarily distributed on the Colorado Plateau, than to A.chiricahua or the other Madrean Sky Island taxa. These data provide the evolutionary framework for better understanding the region's complex biogeographic history (e.g., biotic assembly of the Chiricahua Mountains) and conservation of these spiders.

Phenotypic diversity facilitates niche partitioning in a sky island assemblage of spiny lizards

Abstract If closely related species should be more similar and therefore more likely to compete for resources, why do we see so many examples of species-rich congeneric communities in nature? To avoid competition, many species possess suites of traits associated with differential resource use – or ecomorphologies – that promote niche differentiation with co-occurring species. Yet, the axes through which niche partitioning evolves and the traits involved are still poorly understood in most systems. Island systems, in which species interactions can form strong forces of selection due to limited resources, provide valuable insights into how ecomorphological diversity contributes to coexistence. Here, we examined axes of resource use and morphological traits that facilitate niche partitioning in a community of spiny lizards (genus Sceloporus) in a sky island system, the Chiricahua Mountains of southeastern Arizona, USA. By quantifying structural, temporal and thermal niche use for over 300 co-occurring lizards from four species over three field seasons, we show that sympatric species diverge primarily in perch height and type, but also in thermal and temporal resource use. Our results further demonstrate interspecific divergence in a suite of phenotypic traits known to covary with ecology in other lizard radiations, including body size, scale size, hindlimb length, foot length and dorsal coloration. Studies of niche partitioning and ecomorphology, especially of closely related species, deepen our understanding of how diverse communities assemble and how morphological diversity accumulates across the tree of life, and our findings highlight the importance of examining multiple axes of resource use to better understand these processes.

Insect collecting bias in Arizona with a preliminary checklist of the beetles from the Sand Tank Mountains.

The State of Arizona in the south-western United States supports a high diversity of insects. Digitised occurrence records, especially from preserved specimens in natural history collections, are an important and growing resource to understand biodiversity and biogeography. Underlying bias in how insects are collected and what that means for interpreting patterns of insect diversity is largely untested. To explore the effects of insect collecting bias in Arizona, the State was regionalised into specific areas. First, the entire State was divided into broad biogeographic areas by ecoregion. Second, the 81 tallest mountain ranges were mapped on to the State. The distribution of digitised records across these areas were then examined.A case study of surveying the beetles (Insecta, Coleoptera) of the Sand Tank Mountains is presented. The Sand Tanks are a low-elevation range in the Lower Colorado River Basin subregion of the Sonoran Desert from which a single beetle record was published before this study. The number of occurrence records and collecting events are very unevenly distributed throughout Arizona and do not strongly correlate with the geographic size of areas. Species richness is estimated for regions in Arizona using rarefaction and extrapolation. Digitised records from the disproportionately highly collected areas in Arizona represent at best 70% the total insect diversity within them. We report a total of 141 species of Coleoptera from the Sand Tank Mountains, based on 914 digitised voucher specimens. These specimens add important new records for taxa that were previously unavailable in digitised data and highlight important biogeographic ranges.Possible underlying mechanisms causing bias are discussed and recommendations are made for future targeted collecting of under-sampled regions. Insect species diversity is apparently at best 70% documented for the State of Arizona with many thousands of species not yet recorded. The Chiricahua Mountains are the most densely sampled region of Arizona and likely contain at least 2,000 species not yet vouchered in online data. Preliminary estimates for species richness of Arizona are at least 21,000 and likely much higher. Limitations to analyses are discussed which highlight the strong need for more insect occurrence data.

Hammer Test

Hammer Test Renata Golden (bio) Imagine a spectrum of living creatures. At one end are viruses, bacteria, paramecia. Add invertebrates like worms, snails, octopuses, and shrimp. In the middle, find spiders, crabs, and small animals like frogs, snakes, and songbirds. Somewhere toward the opposite end stand the bigger creatures like prairie dogs, house cats, wolves, alligators, and whales. Holding down the far end are humans—not because of their size or evolutionary superiority, but because of their claim to a moral code. Now picture yourself holding a very large metaphoric hammer that can take many shapes—revulsion, fear, hunger, defense, medical research, vivisection, euthanasia, capital punishment. That hammer represents your willingness to kill. How far along that continuum will you bring your hammer down? Squashing a bug is probably okay, especially if it is a spider or a cockroach or other creepy crawly that freaks you out. And you might be willing to catch a mouse in a snap trap if it’s in your kitchen, eating the crumbs in your dark corners. If you’re an omnivore, you let others butcher your dinner, unless you fish or hunt your own food. Where do you draw the line about killing living things, whether you actually do the deed or support others doing the killing in your name? According to national Gallup and Pew polls, fifty to sixty percent of American adults go all the way to support the death penalty. Where do you stop? [End Page 7] I was unsure of my own answer to that question, especially when I considered threatened species and their preservation. In a natural world made unnatural by human intervention, my ethical responsibilities have grown murky. In my view, a species doesn’t need to provide an obvious benefit to mankind—or even to the rest of the natural world—to be worth saving. Its value lies in the mere fact of its existence. I have heard it said that allowing a species to go extinct is like ripping pages out of a book that you are still reading. What do we lose when a species disappears? What do we suffer when we are the cause of that extinction? And what am I willing to do, either actively or passively, to affect the outcome one way or another? The first good look I had at an American bullfrog in the Chiricahua Mountains was in the sights of a .22 rifle. I had accompanied a biologist and his field technician—let’s call them John and Bob—to a pond that had potential to be a safe harbor for Chiricahua leopard frogs. John and Bob had been monitoring this pond in the flatlands east of Cave Creek Canyon for months. This morning, the two men started at the bottom of a pond and counted eyes as they circled to the top. They estimated more than 500 bullfrogs. They knew the frogs were bullfrogs and not leopard frogs because their size and the chirp they made when they jumped into the water were dead giveaways. John and Bob were on a mission to eradicate some bullfrogs. I found it ironic that they needed to kill a frog to save a frog. With hundreds of bullfrogs living in this flatlands pond, it was obviously not yet ready to receive the leopard frog tadpoles or egg masses that were ready for release. Tasked by U.S. Fish and Wildlife to eradicate the bullfrogs that make life impossible for Chiricahua leopard frogs, John and Bob intended not to kill every American bullfrog in southeastern Arizona, but to establish a buffer zone around Cave Creek where the leopard frogs could thrive. If Chiricahua leopard frogs can’t be returned to their entire previous range, they can at least be saved from extinction. The first step was to give them a suitable home. Before I came to the Southwest Research Station in the Chiricahua Mountains in 2016 to learn about the reintroduction of Chiricahua leopard frogs to their homeland, I had read that Chiricahua leopard frogs and [End Page 8] American bullfrogs are incompatible. Perhaps that’s not the right word—“incompatible” makes it seem like they argue a lot or have...

Diverse DNA virus genomes identified in fecal samples of Mexican free-tailed bats (Tadarida brasiliensis) captured in Chiricahua Mountains of southeast Arizona (USA)

Bats (order Chiroptera) are some of the most abundant mammals on earth and their species ecology strongly influences zoonotic potential. While substantial research has been conducted on bat-associated viruses, particularly on those that can cause disease in humans and/or livestock, globally, limited research has focused on endemic bats in the USA. The southwest region of the US is of particular interest because of its high diversity of bat species. We identified 39 single-stranded DNA virus genomes in the feces of Mexican free-tailed bats (Tadarida brasiliensis) sampled in the Rucker Canyon (Chiricahua Mountains) of southeast Arizona (USA). Twenty-eight of these belong to the virus families Circoviridae (n = 6), Genomoviridae (n = 17), and Microviridae (n = 5). Eleven viruses cluster with other unclassified cressdnaviruses. Most of the viruses identified represent new species. Further research on identification of novel bat-associated cressdnaviruses and microviruses is needed to provide greater insights regarding their co-evolution and ecology relative to bats.

Detecting patterns of post-fire pine regeneration in a Madrean Sky Island with field surveys and remote sensing

The American Southwest is experiencing drastic increases in aridity and wildfire incidence, triggering conversion of some frequent surface forests to non-forest. Extensive research has focused on these dynamics in regional ponderosa pine forests, but we know much less about Madrean pine-oak forests, which are broadly distributed from the Sierra Madre in Mexico to the Sky Island mountain ranges in the U.S. Increased fire incidence and drought in these forests are limiting pine regeneration and driving conversion of biodiverse forests to oak shrublands. We investigated regeneration patterns in Pinus engelmannii and P. leiophylla during severe drought 10 years after the Horseshoe Two Megafire in the Chiricahua Mountains, Arizona—a follow-up to an assessment five years post-fire. In long-term plots, we examined changes in pine seedling and resprout recruitment. Past research demonstrated that topography and fire severity influenced pine recruitment across environmental gradients. We investigated here whether Landsat-8 normalized difference vegetation index (NDVI) and evapotranspiration estimated by the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) added explanatory value to our understanding of these patterns. Conversion of Madrean pine-oak forest to oak shrublands continued 6–10 years post-fire. A dense, low oak canopy continued to coalesce in sites subject to severe fire. The importance of resprouts in P. leiophylla regeneration accelerated because these plants outgrew competing oak resprouts. Topography and fire severity (dNBR) were important predictors of 2021 patterns of pine recruitment. NDVI added explanatory value to these models, suggesting its potential in tracking forest dynamics. Evapotranspiration did not add value, likely because ECOSTRESS' larger pixel sizes and moving pixel locations created excessive subpixel heterogeneity in this highly dissected landscape. These models suggest that P. engelmannii is more drought sensitive, was more negatively affected by drought and fire, and is more at risk to shifts in climate and wildfires than P. leiophylla.

Shallow torpor keeps hummingbirds on their toes when conserving energy

Keeping warm is costly, especially when paired with one of the world's fastest lifestyles. During the day, hummingbirds zip about feeding on sugar-rich nectar to fuel their high-octane existence, but at night, the aeronautic acrobats must conserve energy, slipping into a miniature form of hibernation, known as torpor; many drop their body temperature to around 10°C and some get even chillier. But animals that use torpor are in danger from predators, so some minimise the risk by entering a shallower version from which they can emerge more rapidly. However, it wasn't clear to Anusha Shankar (Cornell University, USA), Catherine Graham (Swiss Federal Research Institute) and Donald Powers (George Fox University, USA) whether birds are also capable of using both shallow and deep types of torpor, either to avoid incurring the costs of deep torpor or as an intermediate step along the way. To find out, Shankar with Powers, Isabelle Cisneros and Sarah Thompson, also from George Fox University, headed to the Chiricahua Mountains of Arizona, USA – home to many migrating hummingbirds during spring and summer – to find out how the energetic birds deal with cold nights.‘We studied three species of hummingbird: tiny black-chinned hummingbirds [3 g], the blue-throated mountain-gem [8 g] and Rivoli's hummingbird [7 g]’, says Shankar, who trapped the wild birds by carefully dropping a net over them as they feasted at a feeder during the hour before sunset. Then, the team gently placed each hummingbird in a chamber positioned outside on a table next to a window, allowing the bird to settle before recording the temperature of its eye every 10 min using an infrared camera located in the window to find out how the animal's body temperature varied as it conserved energy overnight.Monitoring the air temperature, which ranged from 3 to 23°C, the team even recorded one particularly cold night when there was frost and the mercury fell to −1°C. They then analysed the body temperature of the birds and could see that they were quite warm as they settled down for the evening, with eye temperatures stabilising between 29 and 31°C. However, as the night progressed and the air temperature fell, the birds’ body temperature began to decline also, with all of the tiny black-chinned hummingbirds (Archilochus alexandri) dropping into deep torpor for approximately half of the night, with body temperatures below 20°C. However, the larger blue-throated mountain-gems (Lampornis clemenciae) maintained their warm evening body temperature for two-thirds of the night, only allowing their bodies to decline slightly below 30°C as they fell into shallow torpor for a quarter of the night; they rarely fell into deep torpor. Meanwhile, the Rivoli's hummingbirds (Eugenes fulgens) seemed to take an equally nonchalant approach to conserving energy. Although half of the birds resorted to deep torpor, with body temperature around 10°C for ∼20% of the night, 10 of the 12 birds dipped into shallow torpor for about a third of the night.So, hummingbirds are capable of selecting how torpid they become, suggesting that the costs associated with falling into deep torpor may sometimes outweigh the energy conservation benefits. ‘For example, torpid birds in trees might be more conspicuous than a mammal concealed in a burrow that can use deep torpor all the time’, says Shankar, explaining that hummingbirds in shallow torpor can warm up and become fully alert within a matter of seconds to evade predators, in contrast with hummingbirds that have descended into deep torpor, which may take up to half an hour to recover. ‘This makes shallow torpor more effective than deep torpor in some situations’, Shankar concludes.

Mixed-Severity Wildfire as a Driver of Vegetation Change in an Arizona Madrean Sky Island System, USA

Fire is a powerful natural disturbance influencing vegetation patterns across landscapes. Recent transitions from mixed-species forests to post-fire shrublands after severe wildfire is an increasingly prevalent phenomenon in pine-oak and conifer forest ecosystems in southwestern North America. However, we know little about how variation in fire severity influences other common forest types in the region. In this study, we evaluated fire-induced changes in woody plant community composition and forest structure in Chiricahua Mountains in southeastern Arizona in the United States that hosts a diverse set of vegetation types. Cluster analysis of the pre-fire vegetation data identified three dominant pre-fire vegetation types including juniper woodland, piñon forest, and pine-oak forest. All vegetation types experienced significant tree mortality across a wide range of size classes and species, from forests to shrublands. The magnitude of change within sample plots varied with fire severity, which was mediated by topography. Significant shifts in dominance away from coniferous obligate seeder trees to resprouting hardwoods and other shrubs occurred across all vegetation types in response to the fire. Regeneration from seed can be episodic, but projected increases in aridity and fire frequency may promote continued dominance by hardwoods and fire- and drought-resistant shrub communities, which is a regional forest management concern as wildfire size and severity continue to increase throughout the southwestern USA.

Thermochronological transect across the Basin and Range/Rio Grande rift transition: Contrasting cooling histories in contiguous extensional provinces

AbstractThe Basin and Range and Rio Grande rift (RGR) are regions of crustal extension in southwestern North America that developed after Laramide-age shortening, but it has not been clear whether onset and duration of extension in these contiguous extensional provinces were the same. We conducted a study of exhumation of fault blocks along a transect from the southeastern Basin and Range to across the RGR in southern New Mexico. A suite of 128 apatite and 63 zircon (U-Th)/He dates (AHe and ZHe), as well as 27 apatite fission-track (AFT) dates, was collected to investigate the cooling and exhumation histories of this region. Collectively, AHe dates range from 3 to 46 Ma, ZHe dates range from 2 to 288 Ma, and AFT dates range from 10 to 34 Ma with average track lengths of 10.8–14.1 µm. First-order spatiotemporal trends in the combined data set suggest that Basin and Range extension was either contemporaneous with Eocene–Oligocene Mogollon-Datil volcanism or occurred before volcanism ended ca. 28 Ma, as shown by trends in ZHe data that suggest reheating to above 240 °C at that time. AHe and ZHe dates from the southern RGR represent a wider range in dates that suggest the main phase of cooling occurred after 25 Ma, and these blocks were not reheated after exhumation. Time-temperature models created by combining AHe, AFT, and ZHe data in the modeling software HeFTy were used to interpret patterns in cooling rate across the study area and further constrain magmatic and/or volcanic versus faulting related cooling. The Chiricahua Mountains and Burro Mountains have an onset of rapid extension, defined as cooling rates in excess of >15 °C/m.y., at ca. 29–17 Ma. In the Cookes Range, a period of rapid extension occurred at ca. 19–7 Ma. In the San Andres Mountains, Franklin Mountains, Caballo Mountains, and Fra Cristobal range, rapid extension occurred from ca. 23 to 9 Ma. Measured average track lengths are longer in Rio Grande rift samples, and ZHe dates of >40 Ma are mostly present east of the Cookes Range, suggesting different levels of exhumation for the zircon partial retention zone and the AFT partial annealing zone. The main phase of fault-block uplift in the southern RGR occurred ca. 25–7 Ma, similar to what has been documented in the northern and central sections of the rift. Although rapid cooling occurred throughout southern New Mexico, thermochronological data from this study with magmatic and volcanic ages suggest rapid cooling was coeval with magmatism in the Basin and Range, whereas in the Rio Grande rift cooling occurred during an amagmatic gap. These observations support a model where an early phase of extension was facilitated by widespread ignimbrite magmatism in the southeastern Basin and Range, whereas in the southern Rio Grande rift, extension started later and continues today and may have occurred between local episodes of basaltic magmatism. These differences in cooling history make the Rio Grande rift tectonically distinct from the Basin and Range. We infer based on geologic and thermochronological evidence that the onset of extension in the southern Rio Grande rift occurred at ca. 27–25 Ma, significantly later than earlier estimates of ca. 35 Ma.

Wildfire and topography drive woody plant diversity in a Sky Island mountain range in the Southwest USA.

AimDrastic changes in fire regimes are altering plant communities, inspiring ecologists to better understand the relationship between fire and plant species diversity. We examined the impact of a 90,000‐ha wildfire on woody plant species diversity in an arid mountain range in southern Arizona, USA. We tested recent fire‐diversity hypotheses by addressing the impacts on diversity of fire severity, fire variability, historical fire regimes, and topography.LocationChiricahua National Monument, Chiricahua Mountains, Arizona, USA, part of the Sky Islands of the US–Mexico borderlands.TaxonWoody plant species.MethodsWe sampled woody plant diversity in 138 plots before (2002–2003) and after (2017–2018) the 2011 Horseshoe Two Fire in three vegetation types and across fire severity and topographic gradients. We calculated gamma, alpha, and beta diversity and examined changes over time in burned versus unburned plots and the shapes of the relationships of diversity with fire severity and topography.ResultsAlpha species richness declined, and beta and gamma diversity increased in burned but not unburned plots. Fire‐induced enhancement of gamma diversity was confined to low fire severity plots. Alpha diversity did not exhibit a clear continuous relationship with fire severity. Beta diversity was enhanced by variation in fire severity among plots and increased with fire severity up to very high severity, where it declined slightly.Main ConclusionsThe results reject the intermediate disturbance hypothesis for alpha diversity but weakly support it for gamma diversity. Spatial variation in fire severity promoted variation among plant assemblages, supporting the pyrodiversity hypothesis. Long‐term drought probably amplified fire‐driven diversity changes. Despite the apparent benign impact of the fire on diversity, the replacement of two large conifer species with a suite of drought‐tolerant shrubs signals the potential loss of functional diversity, a pattern that may warrant restoration efforts to retain these important compositional elements.

Oceanic Influence on Chiricahua Mountains Drought Observed in a 383-Year Douglas-Fir Reconstruction

Drought in the North American Southwest is a recurring phenomenon. The knowledge of drought recurrence and severity is crucial for sustainable water resource management in the region. Tree-ring reconstructions of climate variables provide valuable indirect evidence of climate variability and elucidate the relationship between large-scale circulation anomalies and the climate in the region. Here we have developed a May–July Palmer Drought Severity Index (PDSI) reconstruction from tree-ring chronologies of Pseudotsuga menziesii from the Chiricahua Mountains (southeastern Arizona) for the period 1634–2017 CE. The driest period occurred at the beginning of the 21st Century (2000–2005), followed by 1666–1670, 1952–1956, and 1729–1734. Reconstructed PDSI of the Chiricahua Mountains shows a weak correlation with the El Niño-Southern Oscillation, with intermittent influence as previous studies have reported. The Pacific Decadal Oscillation accounts for the majority of the variability in the Chiricahua hydroclimate, except for the period from 1860–1950 when the predominant driver was the North Atlantic Oscillation.

Wildfire as a natural stressor and its effect on female phenotype and ornament development.

Controlled low‐intensity fires are commonly used in ecosystem management for both habitat restoration and wildfire management. Animals in those ecosystems may respond to fire by shifting energy allocation away from reproduction and growth, and toward maintenance. Stress‐induced shifts in energy allocation may affect the expression of condition‐dependent sexual signals, which are sensitive to energetic and physiological trade‐offs mediated by glucocorticoids. Here, we examine the effect of fire on ornament expression, corticosterone, and other phenotypic traits in a population of striped plateau lizards, Sceloporus virgatus, affected by the Horseshoe 2 Fire in the Chiricahua Mountains, Arizona, USA. The condition‐dependent female ornament was significantly smaller the month following the fire than 2 years prior and was both smaller and less orange on the burned site relative to a nearby unburned site. These patterns are similar to those found in a previous experimental study examining the response of the ornament to corticosterone manipulations. Yet, in the current study, corticosterone levels were not different in lizards on the burned and unburned sites. Perhaps glucocorticoid levels already returned to baseline, or do not adequately track environmental change. Females tended to be smaller and lighter on the burned site than the unburned site; however, the year after the fire, body condition was higher for females on the burned site, indicating a rapid recovery and potential long‐term benefits in response to low‐intensity fires in this fire‐adapted ecosystem. We found that the lizards adjusted energy allocation away from sexual signaling and growth in response to low‐intensity fires. As fires and fire management are likely to increase in response to changing fire regimes across the globe, it will be important to consider behavioral and physiological responses of impacted species, as well as population‐, community‐, and ecosystem‐level responses.

Niche Partitioning between Two Sympatric Lizards in the Chiricahua Mountains of Arizona

Competition for resources between sympatric species can result in reduced fitness. Resource partitioning allows the minimization of competitive pressures, consequently promoting the coexistence of a diversity of species. We tested the hypothesis that the Striped Plateau Lizard (Sceloporus virgatus) and the Ornate Tree Lizard (Urosaurus ornatus) that occur in sympatry in the Chiricahua mountains of Arizona, USA have distinct ecological niches to minimize interspecific competition. We compared the activity times, perch microhabitat characteristics, and diet of these insectivorous lizards to test the prediction that they partition resources. Although we found no difference between the two species in the time at which lizards become active in the morning nor in the composition of their diets, the two species used different structural perch microhabitats. The Ornate Tree Lizard selected higher and narrower perches with more closed canopy than the Striped Plateau Lizard, and males generally occupied higher perches than females. These differences in perch microhabitat use may reduce interspecific competition and allow these two sympatric species to cohabitate.

Persistence of remnant boreal plants in the Chiricahua Mountains, southern Arizona

Boreal plants growing along the southern edge of their range on isolated mountains in a hot desert matrix live near the extreme of their physiological tolerance. Such plants are considered sensitive to small changes in climate. We coupled field observations (1974, 1993, 2019) about the abundance and vigor of small populations of ten remnant boreal plant species persisting in the uppermost elevations of spruce-fir forests of the Chiricahua Mountains, together with modeling of the species sensitivities to three stress factors associated with climatic change: warming, drought, and forest fire, in order to explore the persistence of frontier boreal plant species during climate change. We hypothesize that populations of these cryophilic plants have declined or become locally extinct during an adverse warming period since 1993, enforced by two large forest fires (1994, 2011). We used plant traits and principal component analysis to evaluate sensitivities of the studied plants to the combined actions of warming, drought, and forest fires. Our model predicted selective sensitivity to warming for two species: Vaccinium myrtillus and Rubus parviflorus. Other cryophilic species could be more sensitive to drought and fire. We surveyed the study area in 2019 and found eight of the ten previously investigated species still occur in the area. Five species occurred in wet canyons at lower elevations, but three species persisted in low vigor at the uppermost elevation, which was highly affected by fires. Neither warming-sensitive species showed signs of decline: populations of R. parviflorus increased in abundance and vigor, while V. myrtillus persists without significant changes since 1993. Despite the recorded increase in temperature in the study area >1 °C between years 1975–1993 and 1994–2019, our study did not find direct evidence of warming effects on the observed species. We conclude that severe wildfires and the multi-decadal decrease in precipitation rather than warming are the main limiting factors of remarkable but limited persistence of the remnant boreal species in the Chiricahua Mountains. Our study demonstrates how field observations can be combined with modeling to evaluate species selective responses to different environmental stress factors to make better environmental management decisions, particularly in light of climate change.

First natural history observations of the canyon pygmy mole cricket, Ellipes monticolus (Orthoptera: Tridactylidae)

The first live photos of the canyon pygmy mole cricket, Ellipes monticolus Günther, are presented, with preliminary observations on the habitat and behavior of populations in the Chiricahua Mountains of southeastern Arizona. The species was previously known solely from the original description in 1977, which included only drawings of the structure of the genitalia and almost no natural history information. This paper provides the first look at this species’ biology and provides a framework for future studies on Tridactylidae of the southwestern United States.

Differences in leaf physiology among juvenile pines and oaks following high-severity wildfire in an Arizona Sky Island Mountain range

Recent increases in wildfire severity are converting pine-oak (Pinus-Quercus) woodland to oak shrubland in many sites in the southwestern United States. A key mechanism underlying this transition is the vigorous resprouting capacity of oaks compared to low regeneration rates in pines following wildfire. Differences among species in leaf physiological characteristics may also contribute to such vegetation type conversions, especially in the context of recent increased regional aridity. To that end, we evaluated variation in leaf functional traits in post-fire recruits five years after the 2011 Horseshoe Two in the Chiricahua Mountains, Arizona, USA. We measured a suite of functional traits in two pines (Pinus engelmannii and P. leiophylla) and two oaks (Quercus hypoleucoides and Q. arizonica), including leaf gas exchange, leaf pigment concentrations, leaf spectral reflectance, and wood xylem δ13C, δ18O isotopes, and integrated water use efficiency (iWUE). The four study species displayed a range of plant functional traits tied to desiccation tolerance. P. engelmannii seedling recruits presented invariably low maximum photosynthetic rate (Amax), stomatal conductance (gs), and transpiration (E), and high relative leaf water content during the peak of the May-June drought, a response strongly indicative of a desiccation-avoidant leaf that prioritizes water conservation over carbon fixation in arid conditions. In contrast, resprouts of both oaks displayed leaf desiccation tolerance, with high levels of gs and E and low relative leaf water content. Gas exchange in P. leiophylla resprouts was more similar to the oaks, except for relative water content, which was similar to that of P. engelmannii. Compared to the other two species, P. engelmannii and Q. hypoleucoides exhibited significantly higher δ13C, δ18O and iWUE values—a pattern that appears to have arisen from different mechanisms in the two species. In desiccation-avoidant P. engelmannii, low instantaneous gs and high δ18O suggested that low stomatal conductance rather than high photosynthetic rates led to high iWUE, whereas lower δ18O and very high pigment concentrations in Q. hypoleucoides suggest a more important role for Amax in this species. Neither fire severity nor physiography influenced the physiological responses in any of the four species, suggesting that the expression of resprout and seedling functional traits is fixed. These results raise the possibility that differences in leaf physiological characteristics contribute to the regeneration success of some oak species and the poor seedling establishment of obligate seeder pines, such as P. engelmannii, after high-severity wildfire in the American Southwest.

Early Nesting Biology of the Bee Caupolicana yarrowi (Cresson) (Colletidae: Diphaglossinae) and Its Cleptoparasite Triepeolus grandis (Friese) (Apidae: Nomadinae)

The first part of this publication, written by a group of participants in Bee Course 2018, results from the discovery of three nests of Caupolicana yarrowi (Cresson, 1875) at the base of the Chiricahua Mountains in southeastern Arizona. The nests are deep with branching laterals that usually connect to large vertical brood cells by an upward turn before curving downward and attaching to the top of the chambers. This loop of the lateral thus seems to serve as a “sink trap,” excluding rainwater from reaching open cells during provisioning. Although mature larvae had not yet developed, an egg of C. yarrowi was discovered floating on the provisions allowing an SEM examination of its chorion, the first such study for any egg of the Diphaglos-sinae. Larval food for this species at this site came from Solanum elaeagnifolium Cav. (Solanaceae). Nests were parasitized by Triepeolus grandis (Friese, 1917) (Epeolini), which previously was known to attack only Ptiloglossa (Diphaglossinae: Caupolicanini).The subterranean nest cells of the desert bee Caupolicana yarrowi (Colletidae), which are enveloped by a casing of hardened soil that easily separates from the surrounding matrix, are discussed in a separate appendix. Chemical analysis revealed the casing to be rich in reducing sugars, indicating that the mother bee had regurgitated floral nectar onto the rough interior walls of the cell cavity before smoothing and waterproofing them. This novel use of nectar in nest construction is compared with that of other bee species that bring water to a nest site to soften soil for excavation.

Distant neighbors: recent wildfire patterns of the Madrean Sky Islands of southwestern United States and northwestern Mexico

BackgroundInformation about contemporary fire regimes across the Sky Island mountain ranges of the Madrean Archipelago Ecoregion in the southwestern United States and northern Mexico can provide insight into how historical fire management and land use have influenced fire regimes, and can be used to guide fuels management, ecological restoration, and habitat conservation. To contribute to a better understanding of spatial and temporal patterns of fires in the region relative to environmental and anthropogenic influences, we augmented existing fire perimeter data for the US by mapping wildfires that occurred in the Mexican Sky Islands from 1985 to 2011.ResultsA total of 254 fires were identified across the region: 99 fires in Mexico (μ = 3901 ha, σ = 5066 ha) and 155 in the US (μ = 3808 ha, σ = 8368 ha). The Animas, Chiricahua, Huachuca-Patagonia, and Santa Catalina mountains in the US, and El Pinito in Mexico had the highest proportion of total area burned (>50%) relative to Sky Island size. Sky Islands adjacent to the border had the greatest number of fires, and many of these fires were large with complex shapes. Wildfire occurred more often in remote biomes, characterized by evergreen woodlands and conifer forests with cooler, wetter conditions. The five largest fires (>25 000 ha) all occurred during twenty-first century droughts (2002 to 2003 and 2011); four of these were in the US and one in Mexico. Overall, high variation in fire shape and size were observed in both wetter and drier years, contributing to landscape heterogeneity across the region.ConclusionsFuture research on regional fire patterns, including fire severity, will enhance opportunities for collaborative efforts between countries, improve knowledge about ecological patterns and processes in the borderlands, and support long-term planning and restoration efforts.

Intraspecific variation in colony founding behavior and social organization in the honey ant Myrmecocystus mendax

Persistent cooperation between unrelated reproductives occurs rarely in mature eusocial insect societies, and when present, is frequently geographically constrained. Here we present genetic and behavioral evidence showing that primary polygyny occurs in some, but not all populations of the honey ant Myrmecocystus mendax. Specifically, we found that all mature colonies sampled in a population in the Sierra Ancha Mountains of central Arizona (USA) were polygynous with a relatively high number of queens (average = 6.27), while the majority of mature colonies sampled in the Chiricahua Mountains of southeastern Arizona were monogynous. Field and laboratory observations showed that Chiricahua foundresses are primarily haplometrotic, whereas Sierra Ancha foundresses can be either haplometrotic or facultatively pleometrotic. Nestmate relatedness of mature Sierra Ancha field colonies suggests that the reproductive individuals within these colonies are unrelated, consistent with primary polygyny. In the laboratory, Sierra Ancha foundresses cooperatively established incipient colonies without queen reduction, and colonies with multiple queens produced more minims and workers that may serve the role of repletes (honeypots) than haplometrotic colonies. This was in stark contrast to foundresses from the Chiricahua population, which showed strong aggression when forced to found colonies together in the laboratory. When brood raiding was experimentally induced between laboratory Sierra Ancha colonies, queens from colonies with more workers had a higher survival probability, although in some cases the competing colonies fused and queens from both colonies continued to reproduce. Fusion between incipient ant colonies is a rare phenomenon, but could contribute to the high frequency of polygyny and high queen number in mature colonies in the Sierra Ancha population.