Karl Eduard Linsenmair

FRAGRANCE COLLECTION, STORAGE, AND ACCUMULATION BY INDIVIDUAL MALE ORCHID BEES

Individually marked males of two species of Euglossa were sighted repeatedly and over considerable periods of time (up to 44 days) at artificial fragrance baits exposed on Barro Colorado Island (BCI), Panama. Individuals switched between different bait chemicals that are attractive for the respective species, and no bait preferences or individual bait constancy was observed. GC-MS analyses of 153 males of three species showed that individual hind tibiae contain highly variable quantities of a complex and species-specific blend of fragrance compounds, mainly terpenoids and aromatics. In all three species, frequency distributions of individual quantities were strongly skewed towards individuals with small amounts, and individual amount and complexity were positively correlated. Tibial contents of male Euglossa imperialis that were kept alive in a flight cage for 0, 5, 10, or 15 days showed no qualitative or quantitative change over time, suggesting that the fragrances are very efficiently stored in the hind legs. In Euglossa cognata wing wear, an established age correlate of the species, was positively correlated with individual fragrance quantity. Our results suggest that male euglossines forage continuously for a variety of volatiles, store them, and finally acquire large quantities of a complex and specific fragrance bouquet. Both qualitative and quantitative aspects of individual contents are likely to contain information on male phenotypic and genotypic quality.

The effects of temperature on the architecture and distribution of Macrotermes bellicosus (Isoptera, Macrotermitinae) mounds in different habitats of a West African Guinea savanna

Summary: We determined density and distribution of the mounds of the fungus-cultivating termite Macrotermes bellicosus (Smeathman) in two habitats (shrub savanna and gallery forest) of the Comoé National Park (Ivory Coast, West Africa). We measured height, basal width, and interior and exterior temperatures of mounds in both habitats, and established a new method to measure the surface area of mounds.¶ In the shrub savanna, M. bellicosus mounds reached high densities (up to 22.7 live mounds/ha), whereas in the gallery forest mounds could only be found in open stands and at comparatively low densities (up to 6.5 live mounds/ha).¶ Ambient temperature had an important influence on the architecture of the mounds. Mounds in the warmer, but thermally more fluctuating shrub savanna were more structured with many ridges and turrets than the dome-like, compact mounds in the cooler, more equable gallery forest. The surface complexity was quantified as the ratio of surface (= rsf), which is the quotient of the real surface to the minimal possible surface of an ideal cone of the same height and basal width as the measured mound. By manipulating ambient temperatures, we were able to demonstrate causal relationships between temperature and mound shape. In the gallery forest, where shade was reduced surface complexity increased on mounds.¶Despite their different architecture in the gallery forest, the M. bellicosus colonies could not completely compensate for the cooler environment and had a lower than optimal nest temperature. We speculate that this might be caused by the need for a sufficient surface for gas exchange. The gallery forest is a suboptimal habitat for M. bellicosus, because of lower than optimal nest temperatures. This might limit M. bellicosus to open stands in the gallery forest and may explain its surprisingly low abundance in this habitat.

Interannual variation in land-use intensity enhances grassland multidiversity

Significance Land-use intensification is a major threat to biodiversity. So far, however, studies on biodiversity impacts of land-use intensity (LUI) have been limited to a single or few groups of organisms and have not considered temporal variation in LUI. Therefore, we examined total ecosystem biodiversity in grasslands varying in LUI with a newly developed index called multidiversity, which integrates the species richness of 49 different organism groups ranging from bacteria to birds. Multidiversity declined strongly with increasing LUI, but changing LUI across years increased multidiversity, particularly of rarer species. We conclude that encouraging farmers to change the intensity of their land use over time could be an important strategy to maintain high biodiversity in grasslands. Although temporal heterogeneity is a well-accepted driver of biodiversity, effects of interannual variation in land-use intensity (LUI) have not been addressed yet. Additionally, responses to land use can differ greatly among different organisms; therefore, overall effects of land-use on total local biodiversity are hardly known. To test for effects of LUI (quantified as the combined intensity of fertilization, grazing, and mowing) and interannual variation in LUI (SD in LUI across time), we introduce a unique measure of whole-ecosystem biodiversity, multidiversity. This synthesizes individual diversity measures across up to 49 taxonomic groups of plants, animals, fungi, and bacteria from 150 grasslands. Multidiversity declined with increasing LUI among grasslands, particularly for rarer species and aboveground organisms, whereas common species and belowground groups were less sensitive. However, a high level of interannual variation in LUI increased overall multidiversity at low LUI and was even more beneficial for rarer species because it slowed the rate at which the multidiversity of rare species declined with increasing LUI. In more intensively managed grasslands, the diversity of rarer species was, on average, 18% of the maximum diversity across all grasslands when LUI was static over time but increased to 31% of the maximum when LUI changed maximally over time. In addition to decreasing overall LUI, we suggest varying LUI across years as a complementary strategy to promote biodiversity conservation.

Phytomass and fire occurrence along forest–savanna transects in the Comoé National Park, Ivory Coast

In tropical West Africa, distribution patterns of forest islands in savannas are influenced by fires which occur regularly in the grass stratum. Along continuous forest-savanna transects in the Comoe National Park, the change in the amount and composition of non-woody phytomass was investigated from savanna to forest interior. This was correlated with the cover of vegetation strata above, soil depth, and the occurrence of seasonal surface fires. Phytomass mainly consisted of leaf litter in the forests (about 400 g m -2 at the end of the rainy season, and about 600 g m -2 at the end of the dry season) and of grasses in the savanna (about 900 g m -2 ). Low grass biomass appeared to be primarily the result of suppression by competing woody species and not of shallow soil. The occurrence of early dry-season fires seemed to be determined mainly by the amount of grass biomass as fuel because fires occurred in almost all savanna plots while forest sites remained unaffected. However, late dry-season fires will encounter higher amounts of leaf litter raising fire probability in forests. Due to the importance of the amount of combustible phytomass, fire probability and intensity might increase with annual precipitation in both savanna and forest.

Pollen amino acids and flower specialisation in solitary bees.

Pollen nutrient composition could be important in host-plant selection of oligolectic bees. In this study, pollen samples from 142 plant species were analysed separately for water-soluble and protein-bound amino acids. The composition of amino acids varied strongly among plant species, but taxonomically related species had similar compositions. All plant species contained the entire set of essential amino acids, although some in small quantities. Total concentration of freeand protein-bound amino acids was significantly lower in pollen sources used by oligoleges than in other pollen sources. Pollen sources of oligoleges showed a lower concentration of essential amino acids and deviated more strongly from the ideal composition of essential amino acids as determined for honey bees than plants not hosting oligoleges. However, this trend was not confirmed on a cruder phylogenetic plant family level, where pollen chosen by oligolectic bees was similar to other pollen.ZusammenfassungDie meisten Bienen ernähren sich ausschließlich von Pollen und Nektar, wobei Pollen die primäre Proteinquelle ihrer Larven darstellt. Während oligolektische Bienen auf den Pollen einer oder mehrerer nah verwandter Pflanzenarten spezialisiert sind, ist das Blütenspektrum polylektischer Bienen breiter. Der Vorteil der Oligolektie ist bisher weitgehend unbekannt, wobei eine Vielzahl von Hypothesen diskutiert wird. Dazu gehören eine höhere Effizienz der Pollenspezialisten beim Sammeln und bei der Verdauung des Pollens, sowie eine Spezialisierung auf Pollen mit höherem Stickstoffgehalt. Unser Ziel war, herauszufinden, ob die Pollenqualität, insbesondere der Anteil der essentiellen Aminosäuren (Abb. 1), für die Wahl bestimmter Pflanzenarten durch oligolektische Bienen verantwortlich sein könnte. Die Aminosäurezusammensetzung der Pollen von 142 Pflanzenarten (Tab. I) zeigte signifikante Unterschiede zwischen Pflanzenfamilien (Abb. 2). Von oligolektischen Bienen genutzter Pollen unterschied sich jedoch in der Komposition nicht signifikant von anderen Pollenarten. Allerdings enthielt der von oligolektischen Bienen genutzte Pollen eine signifikant geringere Konzentration an Aminosäuren (Abb. 3). Zudem zeigte sich eine verminderte Nahrungsqualität bei Pollenquellen oligolektischer Bienen: Die Komposition essentieller Aminosäuren zeigte eine signifikant größere Diskrepanz zu der für Honigbienen als ideal beschriebenen Komposition als die übrigen Pollenarten. Daher könnte spekuliert werden, dass oligolektische Bienen nährstoffärmeren Pollen nutzen, um interspezifische Konkurrenz mit anderen Pollenkonsumenten zu verringern. Hinweise auf tatsächlich verminderte Konkurrenz gibt es jedoch bislang nicht. Der Befund, dass oligolektische Bienen auf qualitativ minderwertigen Pollen spezialisiert sind, ist zudem stark geprägt durch die in der Analyse überrepräsentierten Asteraceen und Lamiaceen. Diese weisen ähnlich geringe Aminosäurekonzentrationen auf. Auf Familienniveau zeigte der von oligolektischen Bienen genutzte Pollen keine signifikant geringere Qualität.

Ant-hemipteran trophobioses in a Bornean rainforest - : diversity, specificity and monopolisation

Abstract.Trophobiotic interactions between ants, hemipterans and plants play an important role for all three partners. This study compared a broad spectrum of trophobiotic associations in a tropical rainforest in Sabah, Borneo. We studied partner specificity, ant recruitment, temporal continuity and monopolisation in 218 trophobioses, comprising 58 ant species, 62 hemipteran and over 31 plant species. The most common associations involved Dinochloa trichogona (Poaceae) with coreids and delphacids in the forest understorey, and the invasive weed Chromolaena odorata (Asteraceae) with Aphis gossypii and A. spiraeola in the open vegetation; both associations were attended by a broad spectrum of ant species. In general, associations between hemipterans and plants were highly and significantly specialised, while ants were more opportunistic in their choices of partners, although partitioning was also significant between ant versus hemipteran species and consequently between ant versus plant species. The number of ant workers increased significantly, but at a declining rate, with the number of hemipterans at a trophobiosis. Most trophobioses (96%) were only tended by a single ant species at a time and thus effectively monopolised. Occasionally these guards were replaced by another ant species after a few weeks (11%) or during the night (34%). In order to test whether other sugar-seeking ants as potential competitors occurred in the vicinity of trophobioses, sugar baits were placed next to the trophobioses, on a different branch of the same plant, and on a neighbouring plant. While the hemipteran-tending ant colony mostly monopolised the nearest sugar bait, the number of ant species on more distant baits was significantly higher. Our results show that ant associations with honeydew-producing hemipterans may be relatively opportunistic at the community level, but highly predictable on a smaller spatio-temporal scale in respect to recruitment to, and long term securing of this important resource.

Pollen foraging and resource partitioning of stingless bees in relation to flowering dynamics in a Southeast Asian tropical rainforest

Summary: We used microscopic pollen analysis to investigate the diversity and similarity of pollen diets of six colonies of stingless bees (Apidae; Meliponini) located within one monospecific (three colonies of Trigona collina) and one mixed nesting aggregation (one colony of T. collina, and one colony of each of the close relatives T. melina and T. melanocephala) in lowland tropical rain forest in Sabah, Malaysia. Samples of 20 corbicular loads, collected six times over a period of three months from each colony, contained a total of 74 different morphotypes of pollen grains with an average between 4.7 to 8.5 per sample for the different colonies. In an analysis on total diet composition intraspecific similarity was much greater than interspecific similarity. The focal colony of Trigona collina from the mixed aggregation distinctly clustered according to species rather than nest location, suggesting that some interspecific resource partitioning occurs. The sampling period was accompanied by a drastic increase in flowering activity as evidenced by data from a flower phenology transect. At times of limited flowering similarity of pollen diets was generally low, both within and between species. It is hypothesized that this is so because bees are forced to forage from scattered subsets of flower patches spread out over a large foraging range. In times of increased flowering pollen diet similarity significantly increased between colonies of the monospecific aggregation, presumably because colonies concentrated on more profitable sources in closer proximity. In contrast, similarity remained low within the mixed aggregation, suggesting that innate differences in foraging preferences precluded any effect of diet convergence.

Main nutrient compounds in food bodies of Mexican Acacia ant-plants

Summary.Myrmecophytic plants use obligate ant mutualists as a constitutive indirect defence mechanism. These plants often produce cellular food bodies (FBs) to nourish their resident ants. Lipids, proteins, and even highly specialised compounds such as glycogen have been reported from FBs, but detailed chemical analyses of FB composition have so far been presented only for Southeast Asian Macaranga and Central American Piper myrmecophytes. Here we report the chemical composition of FBs of five myrmecophytic Acacia (Fabaceae) species from Mexico using HPLC (carbohydrates and proteins) and GC-MS (lipids). Feeding experiments revealed no hints on any use of external food sources by the inhabiting Pseudomyrmex ants. These ants obviously rely completely on FBs and extrafloral nectar provided by their hosts. The total content of nutrients in Acacia FBs was 15-25% of FB dry mass, being much lower than in Macaranga or Piper FBs. Proteins were dominating (8-14 % dm) in Acacia FBs and thus were present in higher amounts than in Macaranga FBs, yet in lower amounts than in Piper. Lipids contributed 1-9 % of dry mass, showing a lower proportion than in FBs of Macaranga or Piper. Carbohydrates made up 3-11 % dm, reaching in most Acacia species the same range as observed in Macaranga and in Piper FBs. Water content was 18-24 % of FB fresh mass, and structural tissue obviously made up a much higher proportion in Acacia FBs than in Macaranga or Piper FBs. Both characters might represent an adaptation to producing FBs unprotected at the leaf tips under dry conditions. Acacia FBs contain all amino acids and all fatty acids that are considered essential for insects, and their contents of lipids and proteins are higher than in the leaves from which they are ontogenetically derived. This indicates a putatively adaptive enrichment of nutritionally valuable compounds in structures functioning as ant-food.

Foraging of a hypogaeic army ant: a long neglected majority

Summary: Army ants have been studied thoroughly for more than a century. The conduction of column and swarm mass raids, featured by epigaeicly active species, is believed to be a central characteristic of army ant behavior. Most army ant species, however, lead a hypogaeic life. Due to the difficulties to observe them, nothing is known about their hypogaeic behavior in the field. Using palm oil baits, trail excavations, and laboratory observations, the hypogaeic foraging of Dorylus (Dichthadia) laevigatus was observed in Malaysia. D. laevigatus was found to construct stable hypogaeic trunk trail systems providing quick and easy access to all parts of its foraging area. Small column raids were conducted throughout the ground stratum and above the ground surface. These raids were caste specific, with the smallest workers predominantly following existing cracks and tunnels in the soil. In case of food location, larger workers were recruited from nearby trunk trails. Exploratory trails leading to prey had to be widened before larger workers could gain access and help to process the food. Bulky food sources such as baits or termite mounds could be exploited over several weeks to months. Besides raiding in columns, D. laevigatus came occasionally to the ground surface at night to conduct swarm raids. This combination of swarm and column raids with the use of trunk trails has never been demonstrated for a classical army ant species. The omnipresence of D. laevigatus within its foraging area stands in sharp contrast to epigaeicly active species, characterized by a very localized and temporary presence at foraging sites. D. laevigatus stayed in the same foraging area for several weeks to months. Having a broad diet and the ability to exploit bulky food sources over long periods of time, D. laevigatus seems to follow a sustainable use of the soil fauna. Summing up these particularities demonstrates a remarkable divergence of the hypogaeic foraging of D. laevigatus from that of epigaeicly foraging army ant species.

Trade-off between chemical and biotic antiherbivore defense in the South East Asian plant genus Macaranga

The plant genus Macaranga is known for its manifold mutualistic associations with ants. The plants provide food for the ants and in turn get protection from herbivores. Depending on the strength of the plant–ant interaction, the plants investment in ants and the biotic defense derived from them is more or less effective. We conducted a comparative study on tannin content in 12 Macaranga species that were selected based on their associations with ants (three nonmyrmecophytes and nine myrmecophytes, three of which start their ontogeny as nonmyrmecophytes). Different developmental stages were investigated in three Macaranga species. Extracts of every individual plant analyzed for tannins were also tested for their effects on larval growth employing larvae of the common cutworm (Spodoptera littoralis). The studied Macaranga species differed significantly in their tannin contents as well as in the effects of their leaf extracts on the growth of S. littoralis larvae. A correlation analysis shows a connection between tannin contents and larval growth. High tannin contents and, thus more effective chemical defense, were observed in nonmyrmecophytic Macaranga species associated only facultatively with ants as compared to obligate myrmecophytes. Our study supports the hypothesis of a trade-off between chemical and biotic defense in the genus Macaranga.