Background: DNA barcoding, i.e. the use of a 648 bp section of the mitochondrial gene cytochrome c oxidase I, has recently been promoted as useful for the rapid identification and discovery of species. Its success is dependent either on the strength of the claim that interspecific variation exceeds intraspecific variation by one order of magnitude, thus establishing a "barcoding gap", or on the reciprocal monophyly of species.

For diverse communities of omnivorous insects such as ants, the extent of direct consumption of plant-derived resources vs. predation is largely unknown. However, determination of the extent of "herbivory" among ants may be crucial to understand the hyper-dominance of ants in tropical tree crowns, where prey organisms tend to occur scarcely and unpredictably. We therefore examined N and C stable isotope ratios (delta(15)N and delta(13)C) in 50 ant species and associated insects and plants from a tropical rainforest in North Queensland, Australia. Variation between ant species was pronounced (range of species means: 7.1 per thousand in delta(15)N and 6.8 per thousand in delta(13)C). Isotope signatures of the entire ant community overlapped with those of several herbivorous as well as predacious arthropods. Variability in delta(15)N between ants was not correlated with plant delta(15)N from which they were collected. Ant species spread out in a continuum between largely herbivorous and purely predacious taxa, with a high degree of omnivory. Ant species' delta(15)N were consistent with the trophic level predicted by natural feeding observations, but not their delta(13)C. Low delta(15)N levels were recorded for ant species that commonly forage for nectar on understorey or canopy plants, intermediate levels for species with large colonies that were highly abundant on nectar and honeydew sources and were predacious, and the highest levels for predominantly predatory ground-foraging species. Colonies of the dominant weaver-ants (Oecophylla smaragdina) had significantly lower delta(15)N in mature forests (where preferred honeydew and nectar sources are abundant) than in open secondary vegetation. N concentration of ant dry mass showed only very limited variability across species and no correlation with trophic levels. This study demonstrates that stable isotopes provide a powerful tool for quantitative analyses of trophic niche partitioning and plasticity in complex and diverse tropical omnivore communities.

Blü thgen, N., Stork, N. E. and Fiedler, K. 2004. Bottom-up control and co-occurrence in complex communities: honeydew and nectar determine a rainforest ant mosaic. Á/ Oikos 106: 344 Á/358Complex distribution patterns of species-rich insect communities in tropical rainforests have been intensively studied, and yet we know very little about processes that generate these patterns. We provide evidence for the key role of homopteran honeydew and plant nectar in structuring ant communities in an Australian tropical rainforest canopy and understorey. We also test the ant visitation of these resources against predictions derived from the 'ant-mosaic' hypothesis. Two ant species were highly dominant in terms of territorial behaviour and abundance: Oecophylla smaragdina and Anonychomyrma gilberti . Both dominant ant species monopolised large aggregations of honeydew-producing homopterans. Attended homopteran species were highly segregated between these two ant species. For the use of extrafloral and floral nectar (involving 43 ant species on 48 plant species), partitioning of ant species among plant species and between canopy and understorey was also significant, but less pronounced. In contrast to trophobioses, simultaneous co-occurrence of different nectar foraging ant species on the same plant individuals was frequent (23% of all surveys). While both dominant ant species were mutually exclusive on honeydew and nectar sources, cooccurrence with non-dominant ant species on nectaries was common. The proportion of visits with co-occurrences was low for dominant ants and high for many subordinate species. These findings support the ant mosaic theory. The differential role of honeydew (as a specialised resource for dominant ants) and nectar (as an opportunistic resource for all ants including the co-occurring non-dominant species) provides a plausible structuring mechanism for the Australian canopy ant community studied.

Environmental gradients have been postulated to generate patterns of diversity and diet specialization, in which more stable environments, such as tropical regions, should promote higher diversity and specialization. Using field sampling and phylogenetic analyses of butterfly fauna over an entire alpine region, we show that butterfly specialization (measured as the mean phylogenetic distance between utilized host plants) decreases at higher elevations, alongside a decreasing gradient of plant diversity. Consistent with current hypotheses on the relationship between biodiversity and the strength of species interactions, we experimentally show that a higher level of generalization at high elevations is associated with lower levels of plant resistance: across 16 pairs of plant species, low-elevation plants were more resistant vis-à-vis their congeneric alpine relatives. Thus, the links between diversity, herbivore diet specialization, and plant resistance along an elevation gradient suggest a causal relationship analogous to that hypothesized along latitudinal gradients.

Summary1. Feeding preferences of nectarivorous ants for sugars and amino acids were studied in an Australian tropical rain forest using artificial nectar solutions. Fifty-one ant species were recorded feeding on the solutions. 2. Preferences among carbohydrates were principally concordant between ant species. In paired tests, sucrose was often preferred over fructose, glucose, maltose, melezitose, raffinose and xylose, respectively. Attractiveness of sucrose baits increased with concentration. 3. Many ant species preferred sugar solutions containing mixtures of amino acids over pure sugar solutions. However, preferences among seven pairs of single amino acids in sugar solutions differed substantially between ant species, including several cases where different ant species displayed significant opposite choices. 4. Ant selectivity between solutions was significantly reduced when different ant species co-occurred on the same bait. Preferences for single amino acids were also reduced when colonies fed extensively on the same compound prior to the experiment for 2 days. 5. Our results indicate that both interspecific variability in gustatory preferences and conditional effects such as competition and colony requirements affect resource selection in multispecies communities. These processes may be crucial in niche partitioning of species-rich nectarivore assemblages.

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K. 2003. Unique elevation diversity patterns of geometrid moths in an Andean montane rainforest. -Ecography 26: 456-466.Alpha-diversity of geometrid moths was investigated along an elevational gradient in a tropical montane rainforest in southern Ecuador. Diversity was measured using 1) species number, 2) extrapolated species number (Chao 1 estimator), 3) rarefied species number, and 4) Fisher's alpha. When applied to the empirical data set, 1 and 2 strongly depended on the sample size, whereas 3 and 4 were suitable and reliable measures of local diversity. At single sites, up to 292 species were observed, and extrapolation estimates range from 244 to 445 species. Values for Fisher's alpha are among the highest ever measured for this moth family, and range from 69 to 131 per site. In contrast to theoretical assumptions and empirical studies in other regions of the world, the diversity of geometrid moths remained consistently high along the entire gradient studied. Diversity measures correlated with neither altitude nor ambient temperature. The large subfamily Ennominae has previously been assumed to be a group that occurs mainly at low and medium elevations. However, no decline in diversity was found in the study area. The diversity of the other large subfamily, Larentiinae, even increased from the lowest elevations and was highest at elevations above 1800 m. The roles of a decreasing diversity of potential host-plants, decreasing structural complexity of the vegetation, increasingly unfavourable climatic conditions and possible physiological adaptations in determining herbivore species richness are discussed. A relatively low predation pressure might be an advantage of high-altitude habitats. The physiognomy of the Andes (folded mountains, large areas at high altitudes) might also have allowed speciation events and the development of a species-rich high-altitude fauna. There is evidence that the species-richness of other groups of herbivorous insects in the same area declines as altitude increases. This emphasises difficulties that are associated with biodiversity indicator groups, and calls for caution when making generalisations from case studies. G. Brehm

Ants (Hymenoptera: Formicidae) consume a broad spectrum of liquid food sources including nectar and honeydew, which play a key role in their diet especially in tropical forests. This study compares carbohydrates and amino acids from a representative spectrum of liquid sources used by ants in the canopy and understorey of a tropical rainforest in northern Queensland, Australia. Eighteen floral nectars, 16 extrafloral nectars, two wound sap and four homopteran honeydew sources were analysed using high performance liquid chromatography. Wounds comprised flower abscission scars on Normanbya normanbyi L. H. Bailey and bitemarks on Cardwellia sublimis F. Muell. where ants were actively involved in wounding. Discriminant analysis was performed to model differences between food sources in sugar and amino acid concentration and composition. All characteristics varied significantly among plant species. Honeydew contained a broader spectrum of sugars (including melezitose, raffinose, melibiose, lactose and maltose) than nectar (sucrose, glucose, fructose), but certain extrafloral nectars had similar amino acid profiles and, like honeydew sources, were often monopolized by ants. Most common amino acids across the sources were proline, alanine and threonine among 17 ␣ -amino acids identified. Interspecific variability concealed characteristic differences in sugar and amino acid parameters between nectar, honeydew and wound sap across all plants, but these types differed significantly when found on the same plant. Among all sources studied, only a few flower nectars were naturally not consumed by ants and they were significantly less attended than sugar controls in feeding trials. These nectars did not differ in sugars and amino acids from ant-attended flower nectars, suggesting the activity of repellents. Apart from these exceptions, variability in amino acids and carbohydrates is proposed to play a key role in ant preferences and nutrition.