Evapotranspiration at the land/water interface in a semi-arid drainage basin

1. Evapotranspiration (ET) is a major source of water depletion from riverine systems in arid and semiarid climates. Water budgets have produced estimates of total depletions from riparian vegetation ET for a 320‐km reach of the Middle Rio Grande, New Mexico, U.S.A., that have ranged from 20 to 50% of total depletions from the river. 2. Tower‐based micrometeorological measurements of riparian zone ET throughout the growing season using three‐dimensional eddy covariance provided high quality estimates of ET at the stand scale. 3. A dense stand of salt cedar (111–122 cm year^–1) and a mature cottonwood (Populus deltoides ssp. wislizenia Eckenwelder) stand with an extensive understory of salt cedar (Tamaria ramosissima Ledeb) and Russian olive (Eleagnus angustifolia L.) (123 cm year^–1) had the highest rates of annual ET. A mature cottonwood stand with a closed canopy had intermediate rates of ET (98 cm year^–1). A less dense salt cedar stand had the lowest rates of ET (74–76 cm year^–1). 4. Summer leaf area index (LAI) measurements within the four stands were positively correlated with daily ET rates. LAI measurements throughout the growing season coupled to riparian vegetation classification is a promising method for improving riverine corridor estimates of total annual riparian zone ET along a reach of river. 5. Combining recent estimates of the extent of riparian vegetation along the 320 km length of the Middle Rio Grande, from Landsat 7 imagery with annual growing season measurements of ET at the four riparian stands yields a first‐order riverine corridor estimate of total riparian zone ET of 150–250 × 10⁶ m³ year^–1. This is approximately 20–33% of total estimated depletions along this reach of river.     

The effects of multiple stressors on wetland communities: pesticides,pathogens and competing amphibians

1. Anthropogenic effects have propelled us into what many have described as the sixth mass extinction, and amphibians are among the most affected groups. The causes of global amphibian population declines and extinctions are varied, complex and context‐dependent and may involve multiple stressors. However, experimental studies examining multiple factors contributing to amphibian population declines are rare. 2. Using outdoor mesocosms containing zooplankton, phytoplankton, periphyton and tadpoles, we conducted a 2 × 2 × 3 factorial experiment that examined the separate and combined effects of an insecticide and the fungal pathogen Batrachochytrium dendrobatidis (Bd) on three different assemblages of larval pacific treefrogs (Pseudacris regilla) and Cascades frogs (Rana cascadae). 3. Larval amphibian growth and development were affected by carbaryl and the amphibian assemblage treatment, but only minimally by Bd. Carbaryl delayed metamorphosis in both amphibian species and increased the growth rate of P. regilla. Carbaryl also reduced cladoceran abundance, which, in turn, had positive effects on phytoplankton abundance but no effect on periphyton biomass. Substituting 20 intraspecific competitors with 20 interspecific competitors decreased the larval period but not the growth rate of P. regilla. In contrast, substituting 20 intraspecific competitors with 20 interspecific competitors had no effect on R. cascadae. Results of real‐time quantitative polymerase chain reaction (qPCR) analysis confirmed infection of Bd‐exposed animals, but exposure to Bd had no effects on either species in univariate analyses, although it had significant or nearly significant effects in several multivariate analyses. In short, we found no interactive effects among the treatments on amphibian growth and development. 4. We encourage future research on the interactive effects of pesticides and pathogens on amphibian communities.     

中国香港淡水鱼类的生物多样性与保护

Hong Kong Special Administrative Region,China,has an area of1095km2and is located at the edge of thenorthern tropical zone.The landscape is dominated byhills and ravines withflat landrestrictedtothe lowflood-plains and coastal regions.Inthis hilly domain,the smallrocky streams are typically fast flowing at their uplandsources,and graduallyreduceinspeed asthey wind alonghill cuttings to reach the lowlands.While streams arecommonlyfound,rivers are very limited in number.Thefewlong and meanderi…     

Development and assessment of a coupled crop–climate model

It is well established that crop production is inherently vulnerable to variations in the weather and climate. More recently the influence of vegetation on the state of the atmosphere has been recognized. The seasonal growth of crops can influence the atmosphere and have local impacts on the weather, which in turn affects the rate of seasonal crop growth and development. Considering the coupled nature of the crop–climate system, and the fact that a significant proportion of land is devoted to the cultivation of crops, important interactions may be missed when studying crops and the climate system in isolation, particularly in the context of land use and climate change.
To represent the two-way interactions between seasonal crop growth and atmospheric variability, we integrate a crop model developed specifically to operate at large spatial scales (General Large Area Model for annual crops) into the land surface component of a global climate model (GCM; HadAM3). In the new coupled crop–climate model, the simulated environment (atmosphere and soil states) influences growth and development of the crop, while simultaneously the temporal variations in crop leaf area and height across its growing season alter the characteristics of the land surface that are important determinants of surface fluxes of heat and moisture, as well as other aspects of the land-surface hydrological cycle. The coupled model realistically simulates the seasonal growth of a summer annual crop in response to the GCM's simulated weather and climate. The model also reproduces the observed relationship between seasonal rainfall and crop yield. The integration of a large-scale single crop model into a GCM, as described here, represents a first step towards the development of fully coupled crop and climate models. Future development priorities and challenges related to coupling crop and climate models are discussed.     

A STUDY OF THE DIFFUSIBLE FACTOR RELEASED BY THE JELLY OF THE EGG OF THE TOAD, BUFO ARENARUM

Some properties of an essential factor for fertilization released from the oocyte strings of the toad, Bufo arenarum were studied. All the experiments were carried out with a partially purified preparation of this diffusible factor, and the general procedure consisted in assaying under different conditions its capacity to recover the fertilizability of oocytes previously deprived of this active substance. Using this procedure, a test was devised for estimating the diffusible factor activity.
As regards the mechanism of action of this fertilization factor the data reported here are not consistent with the previous assumption that the factor plays its role in fertilization through a simple pH rise of the inseminating medium.
Treatment of the gametes with the diffusible factor before insemination proved to be ineffective to promote fertilization; the factor must be present at the very moment of insemination.     

The trackmaker of Apatopus (Late Triassic, North America): implications for the evolution of archosaur stance and gait

Abstract:  For some decades, a major focus of research has been on how locomotor modes changed in some archosaurian reptiles from a more or less 'sprawling' to an 'erect' posture, whether there were discrete intermediate stages, and how many times 'erect' posture evolved. The classic paradigm for the evolution of stance and gait in archosaurs, a three-stage transition from sprawling to 'semi-erect' to erect posture, has been replaced by a subtler understanding of a continuum of changing limb joint angles. We suggest a further separation of terminology related to stance vs. gait so as not to entail different processes: 'sprawling' and 'erect' should refer to continua of stance; 'rotatory' and 'parasagittal' are more appropriate ends of a continuum that describes the motions of gait. We show that the Triassic trackway Apatopus best fits the anatomy and proportions of phytosaurs, based on a new reconstruction of their foot skeleton; it is less likely to have been made by another pseudosuchian or non-archosaurian archosauromorph. Moreover, the trackmaker was performing the high walk. A phytosaurian trackmaker would imply that the common ancestor of pseudosuchians, and therefore archosaurs could approximate the high walk (depending on phylogeny), and if so, erect stance and parasagittal gait did not evolve independently in pseudosuchians and ornithosuchians, although the kinematic mechanisms differed in the two groups. It remains to be seen how far outside Archosauria, if at all, more or less erect posture and parasagittal gait may have evolved.     

Existing in plenty: abundance, biomass and diversity of ciliates and meiofauna in small streams

1. The ciliate and metazoan meiofaunal assemblages of two contrasting lowland streams in south‐east England were examined over the period of a year, using a high taxonomic resolution. Monthly samples were taken from an oligotrophic, acid stream (Lone Oak) and a circumneutral, nutrient‐rich stream (Pant) between March 2003 and February 2004. 2. We assessed the relative importance of ciliates and rotifers within the small‐sized benthic assemblage with respect to their abundance, biomass and species richness. In addition, we examined the influence of abiotic and biotic parameters and season on the assemblage composition at two levels of taxonomic resolution (species and groups). 3. Ciliates dominated the assemblages numerically, with maximum densities of over 900 000 and 6 000 000 ind. m^?2 in Lone Oak and Pant respectively. Rotifers and nematodes dominated meiofaunal densities, although their contribution to total meiofaunal biomass (maxima of 71.9 mgC m^?2 in Lone Oak and of 646.8 mgC m^?2 in the Pant) was low and rotifer biomass equalled that of ciliates. 4. Although the two streams differed in terms of total abundance of ciliates and meiofauna and shared only 7% of species, the relative proportion of groups was similar. Sediment grain size distribution (the percentile representing the 0.5–1 mm fraction) was correlated with assemblage structure at the species level, revealing the tight coupling between these small organisms and their physical environment. Seasonal changes in the relative abundance of groups followed similar patterns in both streams, and were correlated with the abundance of cyclopoid copepods and temperature. 5. Information on these highly abundant but often overlooked faunal groups is essential for estimates of overall abundance, biomass, species richness and productivity in the benthos, and as such has important implications for several areas of aquatic research, e.g. for those dealing with trophic dynamics.     

Enhancing litter retention in streams

1. Dobson & Hildrew (1992) enhanced leaf litter retention in four streams by placing small plastic leaf traps in manipulated stretches. Litter standing crop and the local abundance of shredders was increased, relative to control stretches, in all sites save one which was naturally highly retentive. These results could indicate food limitation in these detritivores, but might have occurred in response to an altered hydraulic regime or increased habitat availability. 2. Shear stress was characterized in the four streams manipulated by Dobson & Hildrew (1992). This was carried out on three occasions in both the manipulated and control stretches of each stream. While there was evidence that the manipulation of retention did influence near-bed flows, these changes were not consistent enough to explain the response of shredding invertebrates to experimental manipulation. 3. In a further experiment, we exposed real and artificial leaves to colonization by invertebrates. Shredders, collectors and predators all colonized real leaves in preference to plastic substitutes. 4. These results support the hypothesis that detritivorous macroinvertebrates exploit aggregations of leaf litter primarily as sources of food, rather than as habitat or habitat modifier.     

Grain aphid clones vary in frost resistance,but this trait is not influenced by facultative endosymbionts

1. Facultative endosymbiotic bacteria of insects are known to affect life‐history traits of their hosts, and can provide important fitness benefits under certain environmental conditions. While several distinct endosymbiont‐induced effects have been reported, there is no data on whether heritable facultative endosymbionts in any species affect their hosts' performance at low temperatures, something that could have a major effect on insect physiology and survival, and thus population structure and distribution. 2. The original facultative endosymbionts were experimentally removed from five clonal genotypes of the grain aphid, Sitobion avenae Fab., which were then exposed to frost. 3. Aphid genotypes differed considerably in survival following the exposure and in fecundity of the survivors. However, the presence of the facultative symbionts had no overall effect on the studied traits. 4. The results suggest that the facultative symbionts have limited effects on the cold hardiness of their grain aphid hosts.