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61.
Understanding the interactions between terrestrial and aquatic ecosystems remains an important research focus in ecology.
In arid landscapes, catchments are drained by a channel continuum that represents a potentially important driver of ecological
pattern and process in the surrounding terrestrial environment. To better understand the role of drainage networks in arid
landscapes, we determined how stream size influences the structure and productivity of riparian vegetation, and the accumulation
of organic matter (OM) in soils beneath plants in an upper Sonoran Desert basin. Canopy volume of velvet mesquite (Prosopis velutina), as well as overall plant cover, increased along lateral upland–riparian gradients, and among riparian zones adjacent to
increasingly larger streams. Foliar δ13C signatures for P. velutina suggested that landscape patterns in vegetation structure reflect increases in water availability along this arid stream
continuum. Leaf litter and annual grass biomass production both increased with canopy volume, and total aboveground litter
production ranged from 137 g m−2 y−1 in upland habitat to 446 g m−2 y−1 in the riparian zone of the perennial stream. OM accumulation in soils beneath P. velutina increased with canopy volume across a broad range of drainage sizes; however, in the riparian zone of larger streams, flooding
further modified patterns of OM storage. Drainage networks represent important determinants of vegetation structure and function
in upper Sonoran Desert basins, and the extent to which streams act as sources of plant-available water and/or agents of fluvial
disturbance has implications for material storage in arid soils. 相似文献
62.
Clark Tapia Ricardo Cecilia Alfonso Corrado María C. Mandujano Francisco Molina-Freaner 《Evolutionary ecology》2006,20(2):131-142
Stenocereus eruca is a prostrated, self-incompatible cactus endemic to the Sonoran Desert that regenerates primarily through clonal propagation.
Clonal growth is expected to affect mate availability by influencing the number and spatial distribution of mating types.
In this paper we examine the role of clonal growth on female fecundity through a series of pollination experiments in a population
of S. eruca. We set up a pollen supplementation experiment using five distance treatments with pollen collected at 1, 10, 100, 1000 and
25000 m from receptor flowers during the years 2001 and 2002 and evaluated genetic sifmilarities between pairs of receptor-donor
ramets through RAPD markers. Our data on fruit set, number of seeds/fruit, germination and overall fecundity revealed that
S. eruca show a significant reduction in female fecundity when pollination occurs between ramets located at short distances (1 and
10 m), while genetic data showed high levels of similarity at those distances. The reduction in female fecundity is apparently
a consequence of geitonogamy and inbreeding depression. Our data suggest that clonal growth and geitonogamy are likely to
be partially responsible for the low levels of sexual reproduction and seedling recruitment observed in populations of S. eruca.
Co-ordinating editor: H. Kudoh 相似文献
63.
Camille A. Holmgren Julio L. Betancourt Kate A. Rylander 《Palaeogeography, Palaeoclimatology, Palaeoecology》2006,240(3-4):405-422
A 36,200 cal yr B.P. vegetation history was developed from macrofossils and pollen from 55 packrat middens from 1287 to 1442 m elevation in the Peloncillo Mountains of southeasternmost Arizona, USA. Today, these elevations are dominated by semidesert grassland with a mixture of Chihuahuan and Sonoran Desert shrubs, including an eastern disjunct population of jojoba (Simmondsia chinensis). From 36,200 to 15,410 cal yr B.P., rocky areas just above large, pluvial lakes that occupied what are now dry playas supported Pinus edulis, Juniperus osteosperma, Juniperus cf. coahuilensis, Quercus cf. turbinella and a rich understory of summer-flowering C4 annuals and grasses, indicating abundant summer rains and mild winters. After 15,410 cal yr B.P., P. edulis declined in abundance and disappeared briefly at 13,925 cal yr B.P., coincident with expansion of more xeric species and paleohydrological evidence for regional aridity during the Bølling–Allerød warm interval. P. edulis rebounded briefly during the Younger Dryas at 12,405 cal yr B.P. before disappearing along with other mesic woodland species sometime after 12,100 cal yr B.P. The few middens dating from the early to middle Holocene (10,000–4000 yr B.P.) indicate wetter conditions than today at 7790 cal yr B.P. followed by a general drying trend. The 35 middens from the late Holocene detail the sequential arrival of desertscrub species as vegetation became more modern in character. 相似文献
64.
Path integration in insects 总被引:6,自引:0,他引:6
The most notable advance in our knowledge of path integration in insects is a new understanding of how the honeybee measures the distance that it travels during its foraging trips. Data from two groups show that the bee's odometer records distance in terms of the net amount of image motion over the retina that is accumulated during a flight. Progress has also been made in clarifying the relation between path integration and other navigational strategies. On unfamiliar ground, path integration is the only available means of navigation. In familiar surroundings, however, guidance by landmarks may override guidance by path integration. Path integration then becomes a back-up strategy that is used primarily when landmarks fail. 相似文献
65.
We studied the thermal tolerances of Rhinella arenarum during the dry and wet seasons of the Monte Desert in San Juan Province, Argentina. This toad had differences in CTmax between dry and wet seasons, and the CTmax values were higher in the wet season (Austral summer). Operative temperature, body temperature, environmental maximal temperature, and relative humidity were related to CTmax, suggesting seasonal acclimatization of R. arenarum. Additionally, the CTmax recorded for R. arenarum was 36.2 °C, and the maximum ambient temperature recorded during the toads' activity time was 37 °C. Also, the CTmin recorded for R. arenarum was 5.3 °C and the minimum environmental temperature recorded was 7.2 °C. The wide thermal tolerance range recorded and the relationship between tolerance limits and the environmental extremes indicate that seasonal acclimatization is an effective mechanism by which toads can raise their thermal tolerance, allowing them to survive in the challenging conditions of the Monte Desert. Additional studies are needed to understand the relationship between the thermal tolerance of this desert amphibian and the environmental parameters that influence its thermal physiology. 相似文献
66.
David J. Germano Galen B. Rathbun Lawrence R. Saslaw 《The Journal of wildlife management》2012,76(4):670-682
Much of California's San Joaquin Valley is a desert and, like portions of other North American deserts, is experiencing an ecological shift from being dominated by ephemeral native forbs, with widely spaced shrubs, to fire-prone non-native annual grasses. Small terrestrial vertebrates, many of which are adapted to open desert habitats, are declining. One hypothesis is that the invasive plants contribute to the decline by altering vegetative structure. Although cattle may have originally been a factor in the establishment of these non-native plants, their grazing may benefit the terrestrial vertebrates by maintaining an open structure, especially during average or wet winters when the exotic grasses grow especially dense. We experimentally tested the effect of cattle grazing on invasive plants and a community of small vertebrates at a site in the southwestern San Joaquin Desert. We established and monitored 4 treatment (grazed) and 4 control (ungrazed) plots from 1997 to 2006, and assessed the abundances of blunt-nosed leopard lizards (Gambelia sila), giant kangaroo rats (Dipodomys ingens), short-nosed kangaroo rats (Dipodomys nitratoides nitratoides), and San Joaquin antelope squirrels (Ammospermophilus nelsoni), all of which are listed as threatened or endangered by state or federal agencies. We also recorded abundances of the non-protected western whiptail lizards (Aspidoscelis tigris), side-blotched lizards (Uta stansburiana), San Joaquin pocket mice (Perognathus inornatus inornatus), and Heermann's kangaroo rats (Dipdomys heermanni). Based on repeated measures analysis of variance (ANOVA) and a 0.05 alpha level, only Heermann's kangaroo rats showed a treatment effect; they were more abundant on the control plots. However, this effect could be accounted for by the natural re-establishment of saltbush (Atriplex spp.) on part of the study site. Saltbush return also favored western whiptail lizards and San Joaquin antelope squirrels. A regression analysis indicated that populations of blunt-nosed leopard lizard and giant kangaroo rat increased significantly faster in grazed plots than the ungrazed controls, and abundances of 6 of 8 species were negatively correlated with increased residual dry matter. With relaxed alpha values to decrease Type II error, populations of blunt-nosed leopard lizards (500% greater), San Joaquin antelope squirrels (85% greater), and short-nosed kangaroo rats (73% greater) increased significantly on grazed plots over the course of the study compared to ungrazed plots. We did not find grazing to negatively affect abundance of any species we studied. When herbaceous cover is low during years of below average rainfall in deserts and other arid areas, grazing may not be necessary to maintain populations of small vertebrates. However, if cattle grazing is closely monitored in space and time to minimize adverse effects on the habitat, it could be an effective tool to control dense stands of non-native grasses and benefit native wildlife. © 2011 The Wildlife Society. 相似文献
67.
68.
Extreme climatic events, such as flooding rains, extended decadal droughts and heat waves have been identified increasingly as important regulators of natural populations. Climate models predict that global warming will drive changes in rainfall and increase the frequency and severity of extreme events. Consequently, to anticipate how organisms will respond we need to document how changes in extremes of temperature and rainfall compare to trends in the mean values of these variables and over what spatial scales the patterns are consistent. Using the longest historical weather records available for central Australia – 100 years – and quantile regression methods, we investigate if extreme climate events have changed at similar rates to median events, if annual rainfall has increased in variability, and if the frequency of large rainfall events has increased over this period. Specifically, we compared local (individual weather stations) and regional (Simpson Desert) spatial scales, and quantified trends in median (50th quantile) and extreme weather values (5th, 10th, 90th, and 95th quantiles). We found that median and extreme annual minimum and maximum temperatures have increased at both spatial scales over the past century. Rainfall changes have been inconsistent across the Simpson Desert; individual weather stations showed increases in annual rainfall, increased frequency of large rainfall events or more prolonged droughts, depending on the location. In contrast to our prediction, we found no evidence that intra‐annual rainfall had become more variable over time. Using long‐term live‐trapping records (22 years) of desert small mammals as a case study, we demonstrate that irruptive events are driven by extreme rainfalls (>95th quantile) and that increases in the magnitude and frequency of extreme rainfall events are likely to drive changes in the populations of these species through direct and indirect changes in predation pressure and wildfires. 相似文献
69.
R. C. Garrick C. A. Meadows A. N. Nicolas J. D. Nason R. J. Dyer 《Conservation Genetics》2008,9(6):1673-1676
We developed seven nuclear intron markers for Euphorbia lomelii. New exon-primed intron-crossing (EPIC) oligonucleotides were used for initial amplification and sequencing, then locus-specific
primers and restriction-fragment-length polymorphism genotyping assays were designed. Loci showed no significant deviation
from Hardy–Weinberg and linkage equilibrium, and they cross-amplify in at least three congeneric species.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
70.