Monitoring and modelling of biosphere/atmosphere exchange of gases and aerosols in Europe

Monitoring and modelling of deposition of air pollutants is essential to develop and evaluate policies to abate the effects related to air pollution and to determine the losses of pollutants from the atmosphere. Techniques for monitoring wet deposition fluxes are widely applied. A recent intercomparison experiment, however, showed that the uncertainty in wet deposition is relatively high, up to 40%, apart from the fact that most samplers are biased because of a dry deposition contribution. Wet deposition amounts to about 80% of the total deposition in Europe with a range of 10-90% and uncertainty should therefore be decreased. During recent years the monitoring of dry deposition has become possible. Three sites have been operational for 5 years. The data are useful for model development, but also for model evaluation and monitoring of progress in policy. Data show a decline in SO(2) dry deposition, whereas nitrogen deposition remained constant. Furthermore, surface affinities for pollutants changed leading to changes in deposition. Deposition models have been further developed and tested with dry deposition measurements and total deposition measurements on forests as derived from throughfall data. The comparison is reasonable given the measurement uncertainties. Progress in ozone surface exchange modelling and monitoring shows that stomatal uptake can be quantified with reasonable accuracy, but external surface uptake yields highest uncertainty.     

Part IV: Fitness for Aquatic Systems Long-term Forecast: Key to groundwater protection

Groundwater resources are at risk from pollution, climate change and land-management practices. Long-term forecast is a tool to demonstrate future development and to support decisions on measures which can be implemented, controlled and eventually corrected. As the basis for preventive action, a forecast can be viewed as a key to groundwater protection. The soil zone plays a vital role in groundwater protection. Research on soil and groundwater trends, as affected by change of climate and/or land-management practices, is on the agenda. Integrated research is necessary to develop numerical soil-water system models reflecting all relevant transport processes at various scales. Even relatively simple problems like forecasting pollutant release from contaminated materials are difficult to resolve. Batch tests may be sufficient in low-risk cases. At higher risk when contaminated substrates are chosen for deposition on a large scale, a thorough characterization of the materials is necessary covering all aspects of stability and possible changes of the environment.     

The migrating herdsman Dolichoderus (Diabolus) cuspidatus: an ant with a novel mode of life

Summary The Malayan ant Dolichoderus cuspidatus lives in obligatory symbiosis with the pseudococcid Malaicoccus formicarii and other species of the same genus. The assemblies, which may be encountered up to 25 m away from the nest, are constantly covered with a great number of worker ants who protect them and receive honeydew. In the event of heavy rain the workers from a dense protective cluster, clinging to each other on top of the mealybugs. Neither hunting behavior nor active search for protein sources was observed in D. cuspidatus, although dead insects were accepted as food. When not searching for new plants, the activity of the ants outside the colony is limited to visiting the mealybugs. During the night and parts of the day the ants stay in their nest. Ant colonies deprived of their mealybugs are not viable due to their dependence on the symbiosis and because of the competition of other ants. Antless M. formicarii are likewise not viable. The mealybugs are extremely polyphagous and feed on many different monocotylous and dicotylous angiosperms. They feed exclusively on the phloem sap of young plant parts which are rich in amino acids. Dolichoderus cuspidatus workers carry the mealybugs to such locations. During the picking up and carrying process both partners display typical behavioral patterns. The colonization of new feeding sites takes place in well organized mass processions. During the foundation or disintegration of large feeding complexes, provisional depots with waiting mealybugs and ants are set up. The pseudococcids are carried not only while shifting the feeding sites, but also whenever the colony leaves its former nesting site and especially when any kind of disturbance occurs. They are even carried about without any apparent external cause, which leads to the fact that, at all times of trail activity, on average more than 10% of all ants using the trails carry mealybugs. Mealybugs are also present within the nest, especially adult females which are viviparous and give birth to their offspring there. Censused colonies each consisted of over 10 000 workers, about 4000 larvae and pupae, more than 5000 mealybugs and one ergatoid queen. Male winged ants were observed in large numbers during the dry season (January–February) and during the rainy season (September–October). The colonies form typical clumplike bivouac nests consisting of clusters of workers clinging to each other, thereby covering the brood and the mealybugs. The nesting site is in no way altered by constructive measures and is mostly found close to the ground. The preferred nesting sites are clusters of leaves, and cavities in wood or soil, although a freely hanging bivouac between a few branches may be set up as well. As soon as the distance between the nest and the feeding site is too great the colony moves to the feeding site, whereby the brood and the mealybugs are carried along in a well organized manner. During such nest-moving the establishment of intermediate depots can be observed. A shift of nest sites can also be induced by disturbances or by a change in the microclimate in the vicinity of the nest. Colonies multiply by budding. The tropical rain forest continuously offers different sprouting plants, the utilization of which requires extreme mobility on the part of the consumer. The unique behavioral strategy of D. cuspidatus, to carry constantly their polyphagous mealybug partners to new feeding sites and to take the whole colony there has enabled this ant and its symbiont to occupy this rich food niche. Dolichoderus cuspidatus is the first true nomad found in ants.     

Cyanobacterial Tintenstrich Communities and their Ecology

Tintenstrich   communities receive their name from the black strips on rocks, which are particularly spectacular on the background of white limestone and dolomite. They are dominated by cyanobacteria, green photosynthesizing procaryotes. However, cyanobacterial crusts are ubiquitous and much more widespread. On bare substratum on walls and rocks in temperate, arid, and tropical zones they are subject to severe stress by insolation, heat, and either too little or too much water. An array of ecophysiological traits allow them to endure this multifactorial stress. Particular features of their photosynthetic membranes may facilitate dissipation of surplus photosynthetically active radiation; special sun-screen pigments protect them from UV radiation, they are desiccation tolerant, concentrate inorganic carbon for photosynthetic fixation, and assimilate atmospheric dinitrogen. With their own success on bare substratum they become pioneers for other organisms.     

Walking on insect paths? Early ommatidial development in the compound eye of the ancestral crustacean, Triops cancriformis

 Ommatidia (the compound eye's functional units) in insects are formed by the recruitment of undifferentiated cells under the control of signalling factors. During this process, a sequence of "preclusters" composed of specifically arranged precursor cells is followed. In the growth zone of the eye of Triops, an ancestral crustacean, we observed a patterning process that corresponds well with that of insects. In both taxa, clusters with arc-like, five-cell and eight-cell patterns are found, and the sequence in which the photoreceptor or R-cells of each ommatidium become identifiable is basically the same. The first to appear are R8-like and R2/5-like cells, second are R3/4-like, and third are R1/6- and R7-like cells (if the fly's cell-numbering system is used). Thus, the morphogenetic steps during which the cell identities and the cellular architecture of the ommatidia develop appear to be conserved between these arthropod groups. Furthermore, the individual cells and cell pairs which build an insect ommatidium seem to have their homologues in crustaceans. In the evolution of developmental processes, intercellular recruitment seems to be a mechanism operating on the level of single cells even in distantly related species. Received: 12 May 2000 / Accepted in revised form: 17 May 2000