共查询到20条相似文献，搜索用时 125 毫秒
1.
In this study, we provide the first evidence of scavenging behaviour in the spiny-tailed agamid lizard (Uromastyx aegyptia microlepis), a species which heretofore has been considered a strict desert herbivore. We examined 294 faecal samples collected in the desert of Qatar and found that 84% of the faeces (n = 247) contained exclusively plant material. Grains of barley (Hordeum vulgare) were present, suggesting that Uromastyx can benefit from the food provided to livestock when wild plants are scarce. We also found remains of invertebrates, vertebrates and stones in the lizard faeces. The type of vertebrate remains found suggests scavenging behaviour and some flexibility in feeding behaviour where food resources are scarce. Overgrazing by camels and goats in the area may affect food availability for Uromastyx populations, suggesting the need for conservation measurements in the Qatar desert. 相似文献
2.
Biological soil crusts of the arid Southwest US are habitat for a greater diversity of microfauna than soils with absent or physically disturbed crusts. The cyanobacteria of desert soil crusts fix nitrogen biologically, but it is not known whether these cyanobacteria are consumed by microfauna and are a significant component of the soil food web. We suspect that stylet-bearing nematodes and tardigrades are the most likely microfauna to graze on cyanobacteria, so we used natural abundance stable isotopes to test whether cyanobacteria are indeed a significant component of their diet in the field. We found that stable isotope composition of microinvertebrate biomass supports the hypothesis that cyanobacteria are a potential prey item in the food chain leading up to tardigrades and dorylaim-type nematodes in desert soils, but does not support the same hypothesis for Tylenchidae in these communities. Continued development of stable isotope methods may help to refine our understanding of feeding behaviors in belowground desert soil food webs. 相似文献
3.
Fire in shrub-dominated portions of the Great Basin, largely fueled by non-native annuals such as Bromus tectorum, has become an important structuring force altering vegetation composition and soil characteristics. The extent to which fire affects native species in drier portions of the Great Basin, termed salt desert, is poorly documented. We conducted a survey of grazed salt desert habitat in northwestern Nevada 5 years after wildfires burned 650,000 ha, with the goal of investigating community response to fire and factors correlating with post-fire recovery. We found that recruitment of a dominant shrub, Artemisia spinescens, is severely restricted following fire: it occurred in only 2 of the 24 burned sites. The co-dominant shrub, Atriplex confertifolia, occurred in most burned sites although on average its percent cover was one-third lower than adjacent unburned sites. Biotic soil crust cover was four times lower, and non-native species cover 5 times higher, in burned sites compared to unburned. Ordination analyses confirmed differences among plant communities in burned versus unburned sites, with environmental variables soil conductivity, plant litter, soil potassium (K+) and pH explaining 38% of the variance in community composition. However, we found no environmental predictors of recovery for native species in burned sites. Future recruitment is likely to be further limited, as fire frequency in the salt desert is expected to increase with invasion by non-native annual grasses and with global climate change. 相似文献
4.
In arid lands, food resources and predation risk become major decision factors in mule deer habitat use. We examined variables related to these two factors that might determine mule deer (Odocoileus hemionus) habitat use in a warm desert at two spatial scales: the macro-habitat scale, which relates to home range decisions, and the micro-habitat scale, which relates to decisions made during foraging. Our prediction was that habitat use should primarily be explained by food variables and, to a lesser degree, by variables related to predation risk by pumas (Puma concolor). We mapped all deer pellet groups in 72, 1 ha quadrats in the Mapimí Biosphere Reserve and measured food and habitat variables over two years with different precipitation amounts. The area was used more intensively during the dry year. Under drier conditions, deer habitat use was explained primarily by food resource variables and secondarily by variables related with predation risk. During the wetter year, food resources became unimportant while cover and visibility explained deer habitat use. The data suggest that the tradeoffs deer are willing to make between food resources and predation risk in an arid environment are strongly affected by food resource levels, as influenced by precipitation. 相似文献
5.
Grey brocket deer diet selection was studied during a period of water scarcity in the arid Chaco of Córdoba province, Argentina. Sampling took place during the dry season in and around Chancaní Provincial Reserve (Pocho department). Forty-eight fresh fecal samples were collected from 85 sampling plots located at random. Plant cover and abundance were used to estimate food availability. Diet composition was determined using microscopic analysis of brocket feces and resource selection was calculated using Ivlev’s Selectivity Index. Thirty-three plant species were identified in the diet. Fruits were found in high proportion (12.4%). Woody plants made up 67.7% of the diet; the most consumed species were Castela coccinea (23.1%), Maytenus spinosa (10.2%), Condalia microphylla (9.5%), Schinus fasciculatus (8.5%) and Ximena americana (7.4%). Mazama gouazoubira selects woody and succulent plants, while herbs are consumed according to availability and grasses in a proportion that is below what is available. 相似文献
6.
We studied the distribution in time and in space of desert arthropods as a food resource in order to gain insight into the relationship between foraging activity, foraging microhabitat use, and temporal changes in these parameters, and resource availability. We focused on two primarily insectivorous congeneric species of spiny mice, the common spiny mouse (Acomys cahirinus) and the golden spiny mouse (Acomys russatus), that overlap in their ecology, but differ in their diel activity patterns. Arthropod availability was higher during the night, suggesting that in terms of resource availability, night should be the preferred activity time for spiny mice. Different taxa were active during day and night, suggesting that temporal partitioning could indeed be a mechanism of coexistence between the two species. Seasonal variation in arthropod availability is reflected in spiny mouse diets, with more arthropods taken during summer, allowing temporal partitioning to be a viable mechanism of coexistence. In winter when arthropod availability drops, the two species exhibit trade-offs in foraging microhabitat use. Seasonal and spatial variability in arthropod availability between habitats conforms to habitat choice. Thus resource availability appears to be a significant factor structuring this rocky desert rodent community. 相似文献
7.
The ability of small canids to consume a variety of resources in an opportunistic manner has been cited as a reason for their wide distribution across many habitats. Black-backed jackals Canis mesomelas have varied diets that reflect changes in food availability as a result of seasonal fluctuations in resources. Seasonal fluctuations can include variations in food type availability, as well as variations in the phenology of food resources (i.e. ungulate birth peaks). Additionally, the presence of apex predators can affect opportunistic predator diets through the provision of carrion. We investigated the diet of black-backed jackals on a reserve in the semi-arid Karoo, South Africa. Ungulates (>5 kg) were the dominant prey item across all seasons, reflecting either active predation or scavenging. Most seasonal comparisons in percent occurrence of prey groups revealed significant seasonal fluctuations in black-backed jackal diet. However, in terms of biomass consumed, the diet remained stable, dominated by small ungulates across all seasons with no clear seasonal change in ungulate composition. These results suggest that in this study black-backed jackals, although being opportunistic in terms of diet composition, had a seasonally stable food resource, most likely facilitated by the presence of cheetahs Acinonyx jubatus providing scavenging opportunities. 相似文献
8.
We studied the small scale distribution pattern of Chorizanthe rigida, a serotinous desert annual, in a shrub-mound-to-desert-pavement gradient. Two sites were established in the Mojave Desert and two sites where established in the Sonoran Desert. We placed transects along a soil surface gradient from shrub mounds to desert pavements, and measured land surface properties, soil characteristics, and C. rigida's small scale distribution. A Principal Components Analysis was done on the resulting site × soil variables matrix. C. rigida established preferentially in desert pavements outside shrub canopies. Pavements showed finer soil textures and higher electrical conductivities, while shrub mounds had sandy textures, low surface rockiness, higher nitrogen, and higher cover of annuals. We discuss a probable relationship between seed retention and the establishment on desert pavements: timing seed release allows this species to avoid wind- or animal-induced seed dispersal into shrub mounds and establish outside the nurse mounds, where most annual plants concentrate. The seeds encased in the serotinous involucres, released after rains, are dispersed by run-off into the desert pavements and transition zones where, once developed, the dead seed-retaining structures of adult C. rigida plants persist for years releasing seeds to subsequent rain events. 相似文献
9.
In this study, we examined the reproductive tracts of preserved specimens of the Great Basin rattlesnake (Crotalus lutosus) to investigate the reproductive strategies used by the only species of rattlesnakes widely occurring in a cold desert. The vitellogenic cycle of female rattlesnakes spanned over two consecutive years: females started vitellogenesis in late spring/early summer, and ovulated in the summer of the next year. This contrasts with the female reproductive cycle of other rattlesnake species from warmer regions of North America, which typically initiate vitellogenesis in summer/fall, and ovulate in late spring of the next year. On the other hand, the reproductive cycle of male C. lutosus conformed well to those described for other rattlesnakes; that is, testes were active (i.e., sperm formation) in summer. The sexual segments of the kidneys of males were hypertrophied in summer, suggesting an unimodal summer mating season. Our findings suggests that the relatively short active season (i.e., 4–5 months) experienced by these snakes in the Great Basin of North America has implications for the timing of female reproductive events, such as an early onset of vitellogenesis, a late time of ovulation, and possibly a restricted period for giving birth. 相似文献
10.
M.I. Rosi S. Puig M.I. Cona F. Videla E. Méndez V.G. Roig 《Journal of Arid Environments》2009,73(3):273-279
Overgrazing by livestock has caused desertification in the Monte, where ctenomyids and livestock share grasses as main food items. The diet of Ctenomys eremophilus, above-ground food availability and changes related to cattle grazing are analyzed in the arid plain of Mendoza, Argentina. The most available categories were grasses, followed by low shrubs and tall shrubs. Tuco-tucos showed dietary generalism, ate mainly above-ground plant parts, preferred grasses and avoided shrubs at both grazed and ungrazed sites. Plant cover, grass diversity and availability decreased under livestock grazing, which was reflected in the diet by a lower percentage of grasses, a shift toward low shrubs and higher number of frequently used resources. Tuco-tucos in the grazed paddock compensated for lower consumption of vegetative plant parts by increasing the use of Prosopis flexuosa pods stored inside burrows. Moreover, greater dietary variation among individuals suggests foraging restricted to the items closest to burrow holes. These feeding tactics would allow them to reduce above-ground foraging as a response to high raptor predation risk due to increased bare soil. The plant recovery detected during the rest period, favoured by moderate stocking rate and rotational grazing system, would allow coexistence of tuco-tucos and cattle. 相似文献
11.
The saguaro (Carnegiea gigantea) is a keystone resource for Sonoran desert consumers of nectar, pollen, fruit, and cactus tissues. Saguaro tissue contains oxalic acid and is unavailable to most consumers. The white-throated woodrat (Neotoma albigula) is, however, able to consume foods with high oxalate content, and is strongly associated with desert succulents, primarily cacti of the genus Opuntia. N. albigula forages secondarily on saguaro tissues, reducing photosynthetic surface area and eliciting an energetically-demanding wound response that reduces energy stores available to fuel reproduction. We observed and quantified Neotoma herbivory on saguaros in a low desert environment. Evidence of Neotoma grazing was found on 44% of all saguaros surveyed, and 13% of all saguaros had >20% of their surface area affected by Neotoma grazing. Neotoma herbivory on saguaros was predicted by the number of nearby succulents, presence of Neotoma middens, and saguaro age. When comparing similarly sized plants, saguaros with high levels (>20% of surface) of herbivory produced fewer flowers and fruits than plants with no Neotoma herbivory. These findings suggest that periodic use of saguaros by N. albigula, such as during extended droughts with conditions unfavorable for Opuntia growth and establishment, may reduce long-term reproductive capacities in low-density saguaro populations. 相似文献
12.
Recent drought across the desert Southwest US may strongly affect the physiological functioning of evergreen desert species that maintain leaves through these dry periods. In July 2002 we compared the ecophysiological performance of the open-canopied, small-leaved creosotebush (Larrea tridentata) to the dense-canopied, more broad-leaved jojoba (Simmondsia chinensis) growing on a ridge-top, east- and west-facing slopes to assess how differences in leaf habit and exposure affect these species' ability to withstand severe drought. Standardized precipitation index (SPI) from 100 years precipitation data showed July 2002 rainfall was normal, but the 12-month period ending July 2002 was of extreme aridity (SPI = ?2.71). Predawn water potentials were extremely low, and lower in jojoba (?8.1 to ?9.5 MPa) than in Larrea (?6.6 to ?9.4 MPa). Chlorophyll fluorescence showed jojoba had more consistent photochemical performance than Larrea across three exposures, having higher optimal photosystem II (PSII) efficiency (Fv/Fm), lower light-adapted PSII yield, and better ability to thermally dissipate light energy (i.e. higher NPQ), especially in inner-canopy jojoba leaves. These findings suggest jojoba may better cope with high light under drought conditions, and that canopy shading in jojoba may reduce high-light stress. Moreover, lower Fv/Fm, NPQ and high PSII yields in Larrea was similar between east-facing and ridge-top locations, but achieved levels similar to jojoba on west-facing exposures. These findings suggest these drought-tolerant evergreens rely on different physiological mechanisms to cope with high light under extreme drought conditions. 相似文献
13.
Creosote bushes (Larrea tridentata) form islands of fertility that influence annual plant abundances in desert ecosystems, and the distribution of native and non-native annuals with respect to creosote may differ. We established plots on the north and south facing sides of L. tridentata in the Mojave and Sonoran Deserts within four different microhabitats spanning from under the shrub canopy into the open. We counted native and non-native annuals twice during the winter growing season to determine the effects of L. tridentata on the spatial distribution of native and non-native annuals. In both deserts, annual plant abundances were higher on the north side of L. tridentata and in open areas. Native annuals in the Mojave were most abundant near the edge of the shrub canopy, whereas native annuals in the Sonoran were most abundant in open areas. The effects of L. tridentata fertility islands on annual abundances were not consistent between the two deserts we studied. Our study emphasizes the importance of research on native and non-native annuals in multiple regions before generalizations can be made about the effects of L. tridentata on annual plant abundances in desert scrub ecosystems. 相似文献
14.
Arbuscular mycorrhizal (AM) fungi convey well documented benefits to plant growth in domesticated species. We investigated AM in Solanum centrale, a desert shrub of central Australia and traditional food for Indigenous Australians. AM were observed in roots of S. centrale from wild and cultivated stands of different ages and management regimes. Greenhouse seedlings grown in sterilised sand were provided with no or minor additions of phosphorus, with or without AM fungi. Inoculated seedlings not fertilised with phosphorus exhibited moderate AM formation. Added phosphorus resulted in an absence of AM. Inoculation did not significantly affect dry weight, root length and plant height of seedlings fertilised with phosphorus but significantly increased the size of unfertilised seedlings. Inoculation significantly increased root phosphorus content, decreased root to shoot ratio and decreased root biomass at all phosphorus additions, despite the absence of observable AM. Thus it appears AM fungi in the root zone influenced certain plant characteristics, regardless of phosphorus nutrition. Overall, S. centrale benefited from the presence of AM through increased phosphorus uptake, but only when the seedlings were growing in soil with extremely low available phosphorus. The response was immediate in our experimental system and is likely to be important in the wild. 相似文献
15.
Biological invasions are a major threat for natural ecosystems. Deserts are characterized by their scarce, highly variable rainfall and thus considerably susceptible to invasions, especially by annual plants that can quickly capitalize sporadic rainfall events. In this study we evaluated the potential of an invasive winter-annual species native to the Mediterranean region (Schismus barbatus) to invade a summer-rainfall desert in the Central-Northern Monte Phytogeographical Province, Argentina, where the native annual flora is mainly composed of summer species. We recorded the number of germinated seeds from soil samples collected in four seasons (during one year) coinciding with four important life-stages of Schismus (pre-germination, post-germination I and II and post-dispersal), and contrasted our results with data obtained from the literature. Almost 33,000 Schismus seeds were estimated to germinate per m2, and about 90% percent of them germinated from samples collected in the pre-germination stage. Compared to deserts in USA and Australia, where Schismus has been a successful invader, the density of germinated seeds we observed was especially high even though the amount of rainfall for the vegetative period of Schismus was considerable lower. Our results suggest that S. barbatus has a great invasive potential in the Central-Northern Monte. The low number of annual plant populations that are able to compete for highly variable cool-season rains may be a key feature determining the invasibility of these deserts during the winter. 相似文献
16.
Tecomella undulata is an important indigenous tree species found in the hot desert areas of Rajasthan State in India. Data from 22 sample plots were used to model the dominant height growth of T. undulata. Four algebraic difference form equations were compared to select the best model. Autocorrelation was modeled as a first-order autoregressive process. The models were evaluated based on qualitative and quantitative criteria. The Payandeh and Wang's model, which is a base-age invariant polymorphic equation derived as a constrained version of the Chapman–Richards function, produced the best results. With this model, site index can be explicitly determined through direct evaluation of the functions and there is no need for iterative numerical evaluation methods. The model is applicable regardless of the choice of rotation age. The Payandeh and Wang's model is recommended for site classification and dominant height prediction in T. undulata stands in the hot desert of Rajasthan State in India. 相似文献
17.
18.
Carbon and oxygen isotope ratios of bone apatite were measured in 14 endothermic and ectothermic vertebrates native to the Chihuahuan Desert and collected in June and July of 1999 and 2000. The δ8O values of most reptiles were very high, up to 44‰ (standard mean ocean water (SMOW), some of the highestδ18 O values ever measured for an animal. The δ18O values of rodents and birds were lower (32±5‰ vSMOW), and the earless lizard Holbrookia maculata were the lowest of all species analysed (25‰). Omnivorous grasshopper mice (Onychomys torridus) had lower δ18O values than granivorous rodents. Results from oxygen analysis likely reflect variation in diet and body water flux differences between endotherms and ectotherms. Carbon isotope analysis revealed a dramatic shift in diet from C3 plants in 1999 to C4 plants in 2000 in most rodents and birds. Kangaroo rats and reptiles did not change, having a constantδ13 C value indicative of a C3-based diet in both years. This suggests reliance on winter annual plant seed caches for kangaroo rats, but not other rodents. The carbon isotope data can be explained in terms of seasonal differences within and between years in the timing and intensity of the seasonal rainfall events, and the productivity of summer and winter annual plants. This study illustrates that stable isotope analysis is a powerful method for tracking dietary change and feeding behavior in desert vertebrates. 相似文献
19.
In arid environments, soil fertility exhibits a high degree of spatial and temporal heterogeneity, which results from high climatic variability seasonally and heterogeneous plant distribution. However, because most desert areas have been altered by human activities, heterogeneous fertility would originate from grazing or logging activities. We evaluated spatial and temporal heterogeneity of soil fertility in cattle-excluded sites under and outside woody plant cover (Prosopis flexuosa and Larrea divaricata), and in sites disturbed by tree removal during wet and dry season in Ñacuñán Biosphere Reserve (Central Monte desert of Argentina). Soil organic matter, fulvic acids, bioavailable organic matter, and nitrate were lower outside plant canopy (8.9 mg g?1, 0.03 mg g?1, 8.2 mg g?1, and 4.17 mg kg?1, respectively). Total N, humic acids, and abundance of microbial functional groups did not show differences among sites. Most parameters differed between seasons, tending to be higher in the wet season. Overall soils of Ñacuñán Reserve are characterized by: a) more homogenous spatial pattern than expected from woody plant presence; b) very heterogeneous temporal pattern; and c) after two years, tree removal does not seem to induce infertile soil formation. 相似文献
20.
A large body of studies have linked sexual segregation in dimorphic ungulates with differential resource selection and nutritional requirements of the sexes. However, detailed patterns of sexual dietary preferences have rarely been assessed as keystone mechanisms of sexual segregation. We compared diet and nutritional selection by 3 sex-age classes in the Iberian red deer (Cervus elaphus hispanicus Hilzheimer) across reproductive states and according to seasonal fluctuations in resource availability in a Mediterranean environment. Foraging segregation between sexes was found during rut when female/juvenile selection of shrubs was higher than that of males. Observed foraging patterns relate to a stronger selection of nitrogen, tannins and lignin by females and juveniles, and fibres by males. Our findings are associated to the Mediterranean climate, where rut and lactation concur with a shortage period, the particularly dry summer. Foraging segregation between sexes during the rut could be shaped by a conjunction of factors such as the low quality of resources and different fitness enhancement strategies. We highlight both the importance of including the dietary component and providing a temporal framework when documenting ungulate sexual segregation, and the interest of considering regional conditions when addressing management of ungulates with a wide distribution. 相似文献