Utilization of food resources by small and medium‐sized mammals in the Monte Desert biome,Argentina

Theoretical models of species coexistence between desert mammals have generally been based on a combination of food and microhabitat selection by granivorous rodents. Although these models are applicable in various deserts of the world, they cannot explain resource use by mammals in Neotropical deserts. The present study examines diet composition in a mammal assemblage in the Monte desert, Argentina. The results show that two main strategies are used by these mammals: medium‐sized species (hystricognath rodents: Dolichotis patagonum, Lagostomus maximus, Microcavia australis and Galea musteloides; and an exotic lagomorph: Lepus europaeus) are herbivores, whereas small‐sized species (a marsupial: Thylamys pusillus; and sigmodontine rodents: Graomys griseoflavus, Akodon molinae, Calomys musculinus, Eligmodontia typus) are omnivorous. Small mammals also show a tendency towards granivory (C. musculinus), insectivory (A. molinae and T. pusillus) and folivory (G. griseoflavus).     

Thermal responses and temperature tolerance of a dessert ant-lion larva

1. 1.Cueta trivirgata larvae construct pits in the dry Kuiseb River bed in the Namib Desert.

2. 2.An art, Ocymyrmex robustior comprises 65.4% of the biomass of prey consumed by the ant-lions.

3. 3.O. robustior is active between surface temperatures of 27–68°C.

4. 4.Ant-lions tolerate high body temperatures (LD₅₀ = 53.4°C).

5. 5.By exploiting the pit microclimate and by digging below the surface during extreme thermal loads, ant-lions can capture prey at surface temperatures of 13–63°C.

6. 6.These behavioural and physiological adaptations enable ant-lions to maximize the duration of vigilance and hence prey capture success.

Ecological resources for conservation and development in Wadi Allaqi,Egypt*

PULFORD, I. D., MURPHY, K. J., DICKINSON, G., BRIGGS, J. A. & SPRINGUEL, I., 1992. Ecological resources for conservation and development in Wadi Allaqi, Egypt. The creation of Lake Nasser behind the Aswan High Dam on the River Nile has brought about significant environmental changes in Upper Egypt. A multidisciplinary project was started in 1987 to assess the environmental changes associated with periodic inundation in desert ecosystems. The data presented here provide a baseline for studies aimed at assessing the potential for, and ecological impacts of, sustainable development in the target area, and may act as a blueprint for wider-scale development. Soil, water, vegetation, animal and human resources are being monitored. There has been a major increase in plant communities dominated by riverain species, at the expense of the original desert wadi vegetation. The water has attracted human settlement, with some 200–250 people now living in the wadi. The inherent high fertility of the soil has allowed them to grow a range of crops in small plots, using a system of shifting cultivation dictated by the lake water level. While this degree of development may be sustainable, larger-scale development of the fragile wadi ecosystem demands a full assessment of appropriate management techniques.     

Solitary male chacma baboons in a desert canyon

Solitary and paired adult (nine) and subadult (one) male chacma baboons, Papio ursinus, were observed over a period of years living in part of a wooded desert canyon not used by adjacent troops. These extratroop males were silent when alone and gave only one alarm vocalization, the “wa-hoo” call, when paired. The space occupied by them is unsuitable for use by troops according to criteria for adequate sleeping sites and access to water. But the foods available to them, especially figs, but also other fruits and fresh acacia seeds, were abundant. These foods are more highly preferred by baboons than those foods available to troop members. Troop members deplete these resources and shift to less preferred foods with lower water content and longer processing times. All of the adult members of the troop adjacent to these isolated males were infected with a skin disease. Isolated males were not so afflicted and so cannot have originated from, or ever been a part of, this troop. They probably moved to the space where they were observed from other inland troops, traveling to their current home range along the narrow canyon river course.     

Timing of precipitation in an arid environment: Effects on population performance of a large herbivore

Climate models predict that shifts in temperature and precipitation patterns are likely to occur across the globe. Changing climate will likely have strong effects on arid environments as a result of increased temperatures, increasing frequency and intensity of droughts, and less consistent pulses of rainfall. Therefore, understanding the link between patterns of precipitation, temperature, and population performance of species occupying these environments will continue to increase in importance as climatic shifts occur within these natural ecosystems. We sought to evaluate how individual, maternal, population, and environmental, particularly temperature and precipitation, level factors influence population performance of a large herbivore in an arid environment. We used mule deer (Odocoileus hemionus) as a representative species and quantified juvenile survival to test hypotheses about effects of environmental factors on population performance. Precipitation events occurring in mid‐ to late‐pregnancy (January–April) leading to spring green‐up, as indexed by normalized difference in vegetation index, had the strongest positive effect on juvenile survival and recruitment. In addition, larger neonates had an increased probability of survival. Our findings indicate that timing and amount of precipitation prior to parturition have strong influences on maternal nutritional condition, which was passed on to young. These results have important implications for understanding how animal populations may benefit from timing of precipitation during spring and prior to parturition, especially in arid environments.     

Molecular diversity and allergenic profiles of Alternaria spp. from desert environments in Arizona

This study examined the genetic diversity of small-spored Alternaria species in the southwest desert of the USA by sampling 552 isolates from different habitats (soil and plant debris) in different locations (urban and an undisturbed desert). To estimate the genetic diversity, Amplified Fragment Length Polymorphism (AFLP) fingerprinting analysis was performed for all isolates. Strains representative of the sampled genotypic diversity (n = 125) were further characterized according their sporulation pattern and the capability to produce allergens. Morphological characterization assigned the majority of the strains to the Alternaria alternata and Alternaria tenuissima morpho-groups with only two isolates assigned to the Alternaria arborescens morpho-group. AFLP fingerprinting differentiated the A. arborescens morpho-groups, but could not distinguish between the A. alternata and A. tenuissima morpho-groups. Western blot analysis showed that a large number of allergenic proteins were produced by strains. These proteins were not specific for any morpho-group nor source of isolation. A hierarchical analysis of molecular variance was performed on the AFLP data to quantify molecular variation and partition this variation among sampled locations and habitat. No statistically significant differentiation among locations and habitat was detected indicating a lack of population structure across environments.     

Characterization of Microbial Mats from a Desert Wadi Ecosystem in the Sultanate of Oman

Desert wadis are widespread in the Arabian Peninsula and play a vital role in the ecology of the region; nevertheless, these ecosystems are among the least studied. Various types of microbial mats are predominant in wadis, but information on their bacterial diversity and spatial distribution is very scarce. We investigated bacterial diversity, pigments and lipid composition of ten mats located at the down-, mid- and upstream of a desert wadi in Oman. Direct microscopy revealed the existence of different unicellular and filamentous cyanobacteria, with the dominance of the heterocystous genera Calothrix and Scytonema. The majority of MiSeq 16S rRNA sequences (44-76%) were affiliated to Cyanobacteria and Proteobacteria. While Alphaproteobacteria was the most dominant proteobacterial class (10 to 48% of total sequences), Gamma- and Deltaproteobacteria were subdominant. Cluster analysis showed that the mats’ bacterial communities at the different locations along the wadi were different and shared less than 60% of their operational taxonomic units (OTUs). Chlorophyll a and scytonemin were the most predominant pigments in all mats. Different saturated, branched and mono- and poly-unsaturated fatty acids were detected in all mats, with C₁₆ and C₁₈ compounds as most dominant. The detected pigments and fatty acids indicate a major role of cyanobacteria in the wadi mats and the adaptation of microorganisms therein to the harsh wadi environment. Detection of diadinoxanthin and fucoxanthin confirmed the presence of diatoms. We conclude that microbial mats are important elements in wadi ecosystems and exist in a great variety of structure and community composition.     

Mechanisms for the keystone status of kangaroo rats: graminivory rather than granivory?

Graminivory by kangaroo rats (Dipodomys spp.) was investigated as a potential mechanism for the keystone role of these rodents in the dynamics of desert grasslands. Experiments confirmed that Ord's kangaroo rats (Dipodomys ordii) cut and consumed a large proportion of the tillers of three Chihuahuan Desert tussock-forming grass species. Field observations indicated that the characteristically cut grass tillers were absent from all-rodent and medium-sized kangaroo rat exclosures, but were frequent in large-sized kangaroo rat and rabbit exclosures, indicating that the medium-sized kangaroo rats (D. ordii, D. merriami) were responsible for grass cutting. Tiller waste as a percentage of peak standing crop ranged from 7% in grassland habitats to 0.7% in Flourensia cernua shrubland. Of the 13 species of perennial, tussock-forming grasses measured, only one, Muhlenbergia porteri, had no tillers cut by kangaroo rats. This study demonstrates that the keystone role of kangaroo rats in Chihuahuan Desert grassland ecosystems is probably the result of their graminivory. Received: 28 October 1996 / Accepted: 26 February 1997     

Translocation of paclobutrazol and gibberellic acid in Sturt's Desert Pea (Swainsona formosa)

The translocation patterns of paclobutrazol and gibberellic acid were studied by applying these plant growth regulators locally to the main or lateral shoots of Sturt's Desert Pea. Paclobutrazol only reduced the growth of shoots to which it was directly applied indicating that it was readily translocated acropetally within a shoot (via xylem) but not basipetally (via phloem), although some phloem translocation has been reported. Gibberellic acid elongated the main shoot and enhanced apical dominance irrespective of the place of application suggesting it is readily translocated both through xylem and phloem. The translocation patterns did not vary between the main or lateral shoots.