Structure and standing crop of EgyptianThymelaea hirsuta populations

The population structure and standing crop of the desert shrubThymelaea hirsuta (L.) Endl. were evaluated in six different habitats in the western Mediterranean desert of Egypt. Under favourable conditions, populations ofT. hirsuta are denser and the size structure has a strong bias towards small, juvenile individuals, whereas the reverse tendency is found under adverse conditions with size structure biased towards big individuals. These results are discussed in the light of hypothesis of intraspecific competition. The standing crop is strongly affected by soil salinity and nature of soil surface (amount of exposed rocks).     

Quantitative PCR method for detection of mycoplasma spp. DNA in nasal lavage samples from the desert tortoise (Gopherus agassizii)

Mycoplasma agassizii and M. testudineum have been associated with upper respiratory tract disease (URTD) in the threatened desert tortoise (Gopherus agassizii). Because microbiological culture methods have proven difficult to employ in wild desert tortoises, our goal was to develop a sensitive and specific qPCR method for detecting and quantifying mycoplasma DNA in nasal lavage fluid collected in the field. Primers for 16S ribosomal RNA gene sequences specific for M. agassizii and M. testudineum were designed, together with primers that recognize conserved sequences of both microorganisms. Standard curves generated with DNA extracted from known numbers of mycoplasma cells revealed a lower detection limit of approximately 5 fg. The qPCR method did not recognize normal flora DNA, and nasal lavage fluid contained no interfering substances. Nasal lavage samples collected from 20 captive desert tortoises housed at the Desert Tortoise Conservation Center (Clark County, Nevada, USA) revealed the presence of M. agassizii DNA in 100% of the tortoises. Concentrations ranged from a low of 6 pg ml^− 1 to a high of 72,962 pg ml^− 1. Only one of the tortoises was positive for M. testudineum. Interestingly, not all of the qPCR positive tortoises showed evidence of seroconversion, suggesting that they were colonized but not infected. This new quantitative method will provide a critical tool for managing threatened populations of the desert tortoise.     

Reductions in daily soil temperature variability increase soil microbial biomass C and decrease soil N availability in the Chihuahuan Desert: potential implications for ecosystem C and N fluxes

Maximum and minimum soil temperatures affect belowground processes. In the past 50 years in arid regions, measured reductions in the daily temperature range of air (DTR_air) most likely generated similar reductions in the unmeasured daily temperature range of soil (DTR_soil). However, the role of DTR_soil in regulating microbial and plant processes has not been well described. We experimentally reduced DTR_soil in the Chihuahuan Desert at Big Bend National Park over 3 years. We used shade cloth that effectively decreased DTR_soil by decreasing daily maximum temperature and increasing nighttime minimum temperature. A reduction in DTR_soil generated on average a twofold increase in soil microbial biomass carbon, a 42% increase in soil CO₂ efflux and a 16% reduction in soil NO₃^?–N availability; soil available NH₄⁺–N was reduced by 18% in the third year only. Reductions in DTR_soil increased soil moisture up to 15% a few days after a substantial rainfall. Increased soil moisture contributed to higher soil CO₂ efflux, but not microbial biomass carbon, which was significantly correlated with DTR_soil. Net photosynthetic rates at saturating light (A_sat) in Larrea tridentata were not affected by reductions in DTR_soil over the 3 year period. Arid ecosystems may become greater sources of C to the atmosphere with reduced DTR_soil, resulting in a positive feedback to rising global temperatures, if increased C loss is not eventually balanced by increased C uptake. Ultimately, ecosystem models of N and C fluxes will need to account for these temperature‐driven processes.     

Reintroductions and controlling feral predators: Interview with Per Christensen

From tracking Antelope and other species in Kenya as a child, Per Christensen went on to train in ecology and participate in many of the key small mammal reintroduction programs in Western Australia. What lessons can be gleaned from these experiences for current and future restoration ecology?     

Effects of seed storage on germination of two succulent desert halophytes with little dormancy and transient seed bank

Seeds of both Salsola imbricata and Haloxylon salicornicum have high germination level and germination speed, and form a transient seed bank in nature. The impacts of storage period and condition on germination level and speed were assessed in the two species. Storage for three months significantly increased both germination level and speed of seeds stored under the different conditions, compared to that of fresh seeds. In both species, nine months storage did not affect germination percentage in cold storage seeds, but completely inhibited it in field seeds. Storage for longer time in room and warm temperatures resulted in significant reduction or complete inhibition in the germination of the two species, so this was more pronounced in H. salicornicum. Storage significantly increased germinate rate index of seeds stored in all conditions till 17 months in S. imbricata and till 12 months in H. salicornicum. In both species, fridge storage had little effects on final germination and germination speed of seeds incubated at the different temperatures, compared to fresh seeds. However, room temperature and warm storages significantly reduced final germination and germination speed at the different temperatures, so the reduction was more pronounced at 35 °C, especially in H. salicornicum.     

Life‐history traits predict perennial species response to fire in a desert ecosystem

The Mojave Desert of North America has become fire‐prone in recent decades due to invasive annual grasses that fuel wildfires following years of high rainfall. Perennial species are poorly adapted to fire in this system, and post‐fire shifts in species composition have been substantial but variable across community types. To generalize across a range of conditions, we investigated whether simple life‐history traits could predict how species responded to fire. Further, we classified species into plant functional types (PFTs) based on combinations of life‐history traits and evaluated whether these groups exhibited a consistent fire‐response. Six life‐history traits varied significantly between burned and unburned areas in short (up to 4 years) or long‐term (up to 52 years) post‐fire datasets, including growth form, lifespan, seed size, seed dispersal, height, and leaf longevity. Forbs and grasses consistently increased in abundance after fire, while cacti were reduced and woody species exhibited a variable response. Woody species were classified into three PFTs based on combinations of life‐history traits. Species in Group 1 increased in abundance after fire and were characterized by short lifespans, small, wind‐dispersed seeds, low height, and deciduous leaves. Species in Group 2 were reduced by fire and distinguished from Group 1 by longer lifespans and evergreen leaves. Group 3 species, which also decreased after fire, were characterized by long lifespans, large non‐wind dispersed seeds, and taller heights. Our results show that PFTs based on life‐history traits can reliably predict the responses of most species to fire in the Mojave Desert. Dominant, long‐lived species of this region possess a combination of traits limiting their ability to recover, presenting a clear example of how a novel disturbance regime may shift selective environmental pressures to favor alternative life‐history strategies.     

Carbon flux dynamics and its environmental controlling factors in a desert steppe

Net ecosystem carbon dioxide exchange (NEE) above a desert steppe in Inner Mongolia was measured with eddy covariance technique in growing season of 2008. Environmental factors were also observed during the same period. Our results show that the minimum of growing season daily cumulative NEE appeared on August 26 (?1.6 g Cm^?2), while the maximum appeared on June 11 (0.9 g Cm^?2). Monthly cumulative NEE distributed in the growing season unevenly. The minimum of monthly cumulative NEE appeared in June (0.74 g Cm^?2); the maximum appeared in September (?14.94 g Cm^?2). The sum of the growing season NEE was ?45.5 g Cm^?2. The most important environmental factor affecting the half-hour average NEE was photosynthetically active radiation. The most important environmental factor affecting the daily cumulative NEE was 20–30 cm soil water content.     

古尔班通古特沙漠南部短命植物群落物种多样性及空间分异

短命植物是早春多雨、夏季干热环境而形成的特殊植物类型,古尔班通古特沙漠南部是短命植物集中分布区,对保持沙漠稳定、防风固沙起到重要作用.目前对短命植物群落多样性、生态功能以及空间分布等研究较少.本研究采用分层抽样方法,调查分析了古尔班通古特沙漠南部35个样点3.86×104m2的短命植物多样性特征.共发现93个物种,分属...     

Dung beetle (Scarabaeus (Pachysoma)) biology and immature stages: reversal to ancestral states under desert conditions (Coleoptera: Scarabaeidae)?

The unique feeding biology of the unusual flightless Namib Desert dung beetle species belonging to Scarabaeus ( Pachysoma ) MacLeay (Scarabaeidae: Scarabaeinae) has been studied in the past but in this report we document breeding biology, larval feeding and immature morphology for the first time. Females provision burrows with fragments of dry herbivore dung and detritus, in which the larvae develop and on which they feed. This is a novel deviation, and a probable reversal to the ancestral state, from the obligatory brood ball constructed from wet dung in which scarab larvae usually develop. The free-living larvae and pupae have several unique attributes that distinguish them from relatives that develop within the confines of a brood ball and provide additional support for monophyly of the group. Many of these also appear as reversals to a probable ancestral condition. Unique larval characters include a left mandible with two teeth, the absence of a 'coprine' hump, small spiracles, and two- or indistinctly three-segmented antennae. Those unique to the pupa are the presence of peculiar prothoracic projections, the absence of lateral tergal supporting projections on the abdomen, and the perpendicular elytra and wings relative to the median bodyline.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 453–460.