Oxides of nitrogen and ozone: can our plants survive?

The authoritative talk by Professor Fowler (Fowler et al ., 1998), emphasized the huge increase in the rate of NO_x (NO and NO₂) emissions into the atmosphere due to fossil fuel combustion, from 1 Tg N y⁻¹ to over 20 Tg N y⁻¹ during the 100 yr between 1880 and 1980. He went on to predict that this rate of emission from anthropogenic sources would increase to 46 Tg N y⁻¹ by the year 2025. In addition, NO can also be released from the soil following microbial action, a process that is very dependent upon soil temperature, nitrogen availability and water content. Later in the meeting, Professor Raven (Raven & Yin, 1998) pointed out that terrestrial plants, though not necessarily each individual species, have over the past 450 million yr coped with large changes in nitrogenous compounds in the environment. Nevertheless, this is no basis for complacency about the current situation because the rates of change caused by man's activities are probably unprecedented. Furthermore, the fact that terrestrial plant life in some form can continue, despite massive changes in environmental chemistry, does not necessarily indicate that the systems on which we ourselves are dependent will be conserved.     

The hummingbird community of a lowland Amazonian rainforest

Between October 1987 and September 1989, the British Ornithologists' Union Colombia Expedition recorded 16 species of hummingbird at Matamatá in the Amacayacu National Park, Amazonas, Colombia. Most of these species were resident breeders at the study site although two appeared to be local migrants. Six species of hermit hummingbirds (subfamily Phaethornithinae) occurred at Matamatá; although very similar in general morphology and behaviour, they showed different preferences for habitat, food plants and foraging technique. Hermits were predominant in the forest, but in areas of secondary vegetation and along riverine borders, "typical" hummingbirds (subfamily Trochilinae) were more common. The study site consisted of terra firme and várzea forest and an area of riverine secondary vegetation and contained around 60 species of flowering plants visited by hummingbirds. In contrast with most groups of organisms, hummingbirds and hummingbird-pollinated plants had similar species diversity in primary forest and secondary habitats. The overall abundance of hummingbirds and flowers was significantly higher in areas of riverine secondary growth. The hummingbird community at Matamatá is remarkably species rich when compared with study sites elsewhere in North and South America. However, random null model comparisons among Amazonian hummingbird communities reveal that they share many characteristics in their structure and show a high degree of species overlap.     

Identification of a Microsporidian Polar Tube Protein Reactive Monoclonal Antibody

ABSTRACT. The microsporidia are characterized by spores containing a single polar tube that coils around the sporoplasm. When triggered by appropriate stimuli, the polar tube rapidly discharges out of the spore forming a hollow tube. The sporoplasm passes out of the spore through this tube serving as a unique vehicle of infection. Due to the unusual functional and solubility properties of the polar tube, the proteins comprising it are likely to be members of a protein family with a highly conserved amino acid composition among the various microsporidia. Polar tube proteins were separated from the majority of other proteins in glass bead disrupted spores of Glugea americanus using sequential 1% sodium dodecyl sulfate (SDS) and 9M urea extractions. The resultant spore pellet demonstrated broken, empty spore coats and numerous polar tubes in straight and twisted formations by negative stain transmission electron microscopy. After subsequent incubation of the pellet with 2% dithiothreitol (DTT), empty spore coats were still observed but the polar tubes were no longer present in the pellet. The DTT supernatant demonstrated four major protein bands by SDS-PAGE: 23, 27, 34 and 43 kDa. Monoclonal antibodies were produced to these proteins using Hunter's Titermax adjuvant. Mab 3C8.23.1 which cross-reacted with a 43-kDa antigen by immunoblot analyis, demonstrated strong reactivity with the polar tube of G. americanus spores by immunogold electron microscopy. This antibody will be useful in further characterization of polar tube proteins and may lead to novel diagnostic and therapeutic reagents.     

A feasible Global Carbon Cycle Observing System: a plan to decipher today's carbon cycle based on observations

A design is presented to continuously monitor the transfers of carbon between the atmosphere and the terrestrial biosphere and oceans on large spatial scales. A consideration of the expected signal-to-noise suggests that a very cost effective method is to perform repeated measurements of the mixing ratios of trace gases in the atmospheric column at an increased number of sites compared to the present geographical coverage. This can be accomplished with existing technology, provided that more automation is applied to the sampling process as well as to the analytical procedures. The resulting data will be crucial to test extrapolations based on direct flux measurements to regional and global scales.     

Coral reef bleaching: facts, hypotheses and implications

Coral reef bleaching, the temporary or permanent loss of photosynthetic microalgae (zooxanthellae) and/or their pigments by a variety of reef taxa, is a stress response usually associated with anthropogenic and natural disturbances. Degrees of bleaching, within and among coral colonies and across reef communities, are highly variable and difficult to quantify, thus complicating comparisons of different bleaching events. Small-scale bleaching events can often be correlated with specific disturbances (e.g. extreme low/high temperatures, low/high solar irradiance, subaerial exposure, sedimentation, freshwater dilution, contaminants, and diseases), whereas large scale (mass) bleaching occurs over 100s to 1000s of km², which is more difficult to explain. Debilitating effects of bleaching include reduced/no skeletal growth and reproductive activity, and a lowered capacity to shed sediments, resist invasion of competing species and diseases. Severe and prolonged bleaching can cause partial to total colony death, resulting in diminished reef growth, the transformation of reef-building communities to alternate, non-reef building community types, bioerosion and ultimately the disappearance of reef structures. Present evidence suggests that the leading factors responsible for large-scale coral reef bleaching are elevated sea temperatures and high solar irradiance (especially ultraviolet wavelengths), which may frequently act jointly.     

Plant coexistence in coastal heaths: Habitat segregation in the post-fire environment

Abstract Previous studies of heaths on Pleistocene coastal sands showed consistent variation in patterns of floristic composition between areas on ridges and slopes but not within them. A large wild-fire that swept this system provided an opportunity to observe temporal processes in habitat segregation of species. Ridges and slopes were found to differ in species richness of seedlings in 0.0625 m2 quadrats and there was no evidence that the species richness in the two habitats was converging over 3 years. This suggests that initially these processes differ in space between the two habitats with more species in the wet heath being packed into a smaller area than in the dry heath. Seed-banks of species did not saturate available space for recruitment in either habitat, but seedling densities differed asymmetrically between habitats across two pairs of species studied. Experimental manipulation of seeds among habitats also showed distinct differences in establishment and survival among representative species from different habitats. The presence of seed-banks of wet-heath species in dry heath suggested that recruitment of their seedlings may occur there, but experiments showed that seedlings that arise from them do not survive there. Conversely, although no seed-bank of either dry-heath species studied was found in wet heath, our manipulations showed that their seedlings could grow there. Thus, superficially, physiological tolerance appeared to limit regeneration of wet-heath species in dry heath. However, there appeared to be no physiological limit for dry-heath plants to survive in wet heath. This paper shows that segregation of species may operate at either of two stages of the life cycle: at dispersal when safe sites for establishment are required, and at recruitment after seedlings have established. These findings highlight the importance of the regeneration niche in structuring community composition in coastal heaths, and contrast with traditional explanations of species segregation invoking physiological tolerance and competition at later life-history stages.     

Risk-Sensitive Foraging, Fitness, and Life Histories: Where Does Reproduction Fit into the Big Picture?

Risk-sensitive foraging may occur whenever feeding success hasnon-linear effects on fitness. Models of sensitivity to variationin amount of food obtained have concentrated on foraging inorder to survive even though feeding during growth, migration,or reproduction can have strong and non-linear effects on fitness.I illustrate how risk-sensitive foraging for reproduction coulddiffer from risk-sensitive foraging for survival using two simplemodels. Each model assumes that organisms must accumulate somethreshold amount of resources before they can reproduce. Inthe first model, additional resources above the threshold leadto increased reproductive success. Here variance in feedingsuccess can be advantageous even when the mean gain would alloworganisms to reproduce. In the second model, early breedingis superior to late breeding because recruitment rate declinesover time. Here a symmetrical distribution in foraging ratesresults in a skewed distribution of breeding times. Despitethis, variance in feeding success may be advantageous even whenthe seasonal decline in recruitment is linear. The advantageof risk is much larger if foragers can switch freely betweenfeeding options. These two models are united by "the bankruptcyeffect" because all failures to reproduce carry the same consequences.These simple models suggest that risk-prone foraging may belikely when factors other than survival are important for fitness.Finally, I advocate using a mix of modelling techniques, notethe implicitly risk-sensitive nature of stochastic dynamic programming,and speculate on potential connections between risk-sensitiveforaging and theories of life histories in variable environments.INTRODUCTION visit restaurants that provided twice     

A new species of Phylloscopus warbler from central China

A new species of leaf warbler (Sylviidae: Phylloscopus) is described from the mountains of central China. Morphologically it is slightly, yet significantly, different from the partly sympatric P. (proregulus) chloronotus. However, both song and calls are very different, and playback tests elicited no response from either species to the other's song. There are also differences in habitat preference and breeding biology of the two species.