Biological Soil Crusts (BSCs), composed of lichens, mosses, green algae, microfungi and cyanobacteria are an ecological important part of the perennial landcover of many arid and semiarid regions (Belnap et al. 2001a), (Büdel 2002). In many arid and hyperarid areas BSCs form the only perennial "vegetation cover" largely due to their extensive resistance to drought (Lange et al. 1975). For the Central Namib Desert (Namibia), BSCs consisting of extraordinary vast lichen communities were recently mapped and classified into six morphological classes for a coastal area of 350 km x 60 km. Embedded into the project "BIOTA" (www.biota-africa.org) financed by the German Federal Ministry of Education and Research the study was undertaken in the framework of the PhD thesis by Christoph Schultz. Some of these lichen communities grouped together in so called "lichen fields" have already been studied concerning their ecology and diversity in the past (Lange et al. 1994), (Loris & Schieferstein 1992), (Loris et al. 2004), (Ullmann & Büdel 2001a), (Wessels 1989). Multispectral LANDSAT 7 ETM+ and LANDSAT 5 TM satellite imagery was utilized for an unitemporal supervised classification as well as for the establishment of a monitoring based on a combined retrospective supervised classification and change detection approach (Bock 2003), (Weiers et al. 2003). Results comprise the analysis of the mapped distribution of lichen communities for the Central Namib Desert as of 2003 as well as reconstructed distributions for the years 2000, 1999, 1992 and 1991 derived from retrospective supervised classification. This allows a first monitoring of the disturbance, destruction and recovery of the lichen communities in these arid environments including the analysis of the major abiotic processes involved. Further analysis of these abiotic processes is key for understanding the influence of Namib lichen communities on overall aeolian and water induced erosion rates, nutrient cycles, water balance and pedogenic processes (Belnap & Gillette 1998), (Belnap et al. 2001b), (Belnap 2001c), (Evans & Lange 2001), (McKenna Neumann & Maxwell 1999). In order to aid the understanding of these processes SRTM digital elevation model data as well as climate data sets were used as reference. Good correlation between geomorphological form elements as well as hydrological drainage system and the disturbance patterns derived from individual post classification change comparisons between the timeframes could be observed. Conjoined with the climate data sets sporadic foehn-like windstorms as well as extraordinary precipitation events were identified to largely affect the distribution patterns of lichen communities. Therefore the analysis and monitoring of the diversity, distribution and spatiotemporal change of Central Namib BSCs with the means of Remote Sensing and GIS applications proof to be important tools to create further understanding of desertification and degradation processes in these arid regions.
The study provides insights into the dynamic processes of vascular epiphyte vegetation in two host tree species of lowland forest in Panama. Further, a novel approach is presented to examine the possible role of host tree identity in the structuring of vascular epiphyte communities: For three locally common host tree species (Socratea exorrhiza, Marila laxiflora, Perebea xanthochyma) we created null models of the expected epiphyte assemblages assuming that epiphyte colonization reflected random distribution of epiphytes in the forest. In all three tree species, abundances of the majority of epiphyte species (69 – 81 %) were indistinguishable from random, while the remaining species were about equally over- or underrepresented compared to their occurrence in the entire forest plot. Permutations based on the number of colonized trees (reflecting observed spatial patchiness) yielded similar results. Finally, a Canonical Correspondence Analysis also confirmed host-specific differences in epiphyte assemblages. In spite of pronounced preferences of some epiphytes for particular host trees, no epiphyte species was restricted to a single host. We conclude that the epiphytes on a given tree species are not simply a random sample of the local species pool, but there are no indications of host specificity either. To determine the qualitative and quantitative long-term changes in the vascular epiphyte assemblage of the host tree Socratea exorrhiza, in the lowland forest of the San Lorenzo Crane Plot, we followed the fate of the vascular epiphyte assemblage on 99 individuals of this palm species, in three censuses over the course of five years. The composition of the epiphyte assemblage changed little during the course of the study. While the similarity of epiphyte vegetation decreased on single palm individuals through time, the similarity analyzed over all palms increased. Even well-established epiphyte individuals experienced high mortality with only 46 % of the originally mapped individuals surviving the following five years. We found a positive correlation between host tree size and epiphyte richness and detected higher colonization rates of epiphytes per surface area on larger trees. Epiphyte assemblages on single Socratea exorrhiza trees were highly dynamic while the overall composition of the epiphyte vegetation on the host tree species in the study plot was rather stable. We suggest that higher recruitment rates due to localized seed dispersal by already established epiphytes on larger palms promote the colonization of epiphytes on larger palms. Given the known growth rates and mortality rates of the host tree species, the maximum time available for colonization and reproduction of epiphytes on a given Socratea exorrhiza tree is estimated to be about 60 years. Changes in the epiphyte vegetation of c. 1000 individuals of the host tree species Annona glabra at Barro Colorado Island over the course of eight year were documented by means of repeated censuses. Considerable increase in the abundance of the dominating epiphyte species and ongoing colonization of the host tree species suggests that the epiphyte vegetation has not reached a steady state in the maximal 80 years since the establishment of the host tree. Epiphyte species composition as a whole was rather stable. We disentangled the relationship between epiphyte colonization and tree size/available time for colonization with the finding that tree size explained only a low proportion of colonization while other factors like connectivity to dispersal source and time explain may explain a larger part. Epiphyte populations are patchily distributed and examined species exhibit properties of a metapopulation with asynchronous local population growth, high local population turnover, a positive relationship between regional occurrence and patch population size, and negatively correlated relationship between extinction and patch occupancy. The documented metapopulation processes highlight the importance of not colonized suitable habitat for the conservation of epiphytes.
In this study, 27 marine bacteria were screened for production of bioactive metabolites. Two strains from the surface of the soft coral Sinularia polydactyla, collected from the Red Sea, and three strains from different habitats in the North Sea were selected as a promising candidates for isolation of antimicrobial substances. A total of 50 compounds were isolated from the selected bacterial strains. From these metabolites 25 substances were known from natural sources, 10 substances were known as synthetic chemical and herein are reported as new natural products, and 13 metabolites are new. Two substances are still under elucidation. All new compounds were chemically and biologically characterized. Pseudoalteromonas sp. T268 produced simple phenol and oxindole derivatives. Production of homogentisic acid and WZ 268S-6 from this bacteria was affected by the salinity stress. WZ 268S-6 shows antimicrobial and cytotoxic activities. Its target is still unclear. Isolation of isatin from this strain points out for the possibility of using this substance as a chemotaxonomical marker for Alteromonas-like bacteria. A large number of nitro-substituted aromatic compounds were isolated from both Salegentibacter sp. T436 and Vibrio sp. WMBA1-4. They may be derived from metabolism of phenylalanine or tyrosine. From Salegentibacter sp. T436, 24 compounds were isolated, of which four compounds are new and six compounds were known as synthetic chemicals. WZ 436S-16 (dinitro-β-styrene) is the most potent antimicrobial and cytotoxic compound. It inhibits the oxygen uptake by N. coryli and causes apoptosis in the human promyelocytic leukaemia (HL-60 cells). From Vibrio sp. WMBA1-4, 13 new alkaloids were isolated, of which four were known as synthetic products and herein are reported as new substances from natural sources. The majority of these compounds show antimicrobial and cytotoxic activities. The cytotoxic activity of WMB4S-11 against the mouse lymphocytic leukaemia (L1210 cells) is due to the inhibition in the protein biosynthesis, while the remaining cytotoxic alkaloids have no effect on the synthesis of macromolecules in this cell line. The antibacterial activity of WMB4S-2, -11, -12, -13 and the antifungal activity of WMB4S-9 are not due to the inhibition in the macromolecules biosynthesis or in the oxygen uptake by the microorganisms. The biological activity of these nitro-aromatic compounds from Salegentibacter sp. T436 and Vibrio sp. WMBA1-4 is influenced by the presence of a nitro group and its position in respect to the hydroxyl group, number of the nitro groups, and the type of substitutions on the side chain. In diaryl-maleimide derivatives, types and position of substitution on the aryl rings, on the maleimide moity, and the hydrophobicity of the aryl ring itself lead to variations in the extent of the bioactivity of these derivatives. This is the first time that vibrindole (WMB4S-14) and turbomycin B or its noncationic form (WMB4S-15), isolated from Vibrio sp., are reported as cytotoxic compounds. WMB4S-15 inhibits the biosynthesis of macromolecules in L1210 cells. The structural similarity between some of the metabolites in this study and previously reported compounds from sponges, ascidians, and bryozoan indicates that the microbial origin of these compounds must be considered.