Manfred Verhaagh

How plants shape the ant community in the Amazonian rainforest canopy: the key role of extrafloral nectaries and homopteran honeydew

Abstract. Ant-plant interactions in the canopy of a lowland Amazonian rainforest of the upper Orinoco, Venezuela, were studied using a modified commercial crane on rails (Surumoni project). Our observations show a strong correlation between plant sap exudates and both abundance of ants and co-occurrence of ant species in tree canopies. Two types of plant sap sources were compared: extrafloral nectaries (EFNs) and honeydew secretions by homopterans. EFNs were a frequent food source for ants on epiphytes (Philodendron spp., Araceae) and lianas (Dioclea, Fabaceae), but rare on canopy trees in the study area, whereas the majority of trees were host to aggregations of homopterans tended by honeydew-seeking ants (on 62% of the trees examined). These aggregations rarely occurred on epiphytes. Baited ant traps were installed on plants with EFNs and in the crowns of trees from three common genera, including trees with and without ant-tended homopterans: Goupia glabra (Celastraceae), Vochysia spp. (Vochysiaceae), and Xylopia spp. (Annonaceae). The number of ant workers per trap was significantly higher on plants offering one of the two plant sap sources than on trees without such resources. Extrafloral nectaries were used by a much broader spectrum of ant species and genera than honeydew, and co-occurrence of ant species (in traps) was significantly higher on plants bearing EFNs than on trees. Homopteran honeydew (Coccidae and Membracidae), on the other hand, was mostly monopolised by a single ant colony per tree. Homopteran-tending ants were generally among the most dominant ants in the canopy. The most prominent genera were Azteca, Dolichoderus (both Dolichoderinae), Cephalotes, Pheidole, Crematogaster (all Myrmicinae), and Ectatomma (Ponerinae). Potential preferences were recorded between ant and homopteran species, and also between ant-homopteran associations and tree genera. We hypothesize that the high availability of homopteran honeydew provides a key resource for ant mosaics, where dominant ant colonies and species maintain mutually exclusive territories on trees. In turn, we propose that for nourishment of numerous ants of lower competitive capacity, Philodendron and other sources of EFNs might be particularly important.

Ant nests in tank bromeliads - an example of non-specific interaction

Summary: Four species of epiphytic tank bromeliads on an island in the Orinoco river in Venezuelan Amazonia were inhabited by 13 ant species from four subfamilies. None of these ant species are known as specialised plant-ants. A Monte Carlo randomisation test showed that ants were randomly distributed among host plants: (1) there was no association between particular ant species and bromeliad species, and (2) there was no vertical stratification of the ant community between bromeliads sampled on the ground and at two height classes in trees. This contrasts with the few published data on the distribution of ants on terrestrial myrmecophytes and epiphytes, respectively, to which we applied the same analytical method.

Comparative study of nest architecture and colony structure of the fungus-growing ants, Mycocepurus goeldii and M. smithii.

Abstract Nest architecture and demography of the non leaf-cutting fungus-growing ant species Mycocepurus goeldii and M. smithii (Attini: Formicidae) were studied in an agroforest habitat near Manaus, Brazil during the excavation of 13 nests. Both species built their nests in two different ways. The first type possessed a “tree-like” architecture, in which a vertical tunnel led downwards and lateral tunnels branched off at 90° angles from the main tunnel, with a chamber at the end of each side branch. Alternatively, other nests displayed a “necklace-like” architecture, where the main tunnel also led down vertically, but entered each chamber from the top and exited it at the bottom, resulting in an architecture where chambers appeared like pearls on a necklace. The nest systems of M. goeldii and M. smithii consisted of 1–21 or 1–15 chambers, respectively. Of 199 excavated chambers, 57 % contained fungus-gardens. Chambers not containing fungus gardens were filled with organic matter from decaying fungus gardens or earthworm feces. Only M. smithii workers deposited loose soil in abandoned chambers during the construction of new nest chambers. Workers of M. smithii constructed significantly smaller chambers than those of M. goeldii. In both species, fungus garden-containing chambers were larger than non-garden chambers and were homogenously distributed in the soil between 17 cm and 105 cm depth. Neither fungus gardens nor abandoned chambers were encountered more frequently in deeper or shallower soil strata indicating that ants of both species did not abandon shallower versus deeper chambers, or move the colony to deeper soil layers with increasing colony age. Fungus gardens were suspended from the ceiling of the subterranean chambers and originated as small mycelial tufts. Through continual addition of organic debris, the tufts first grew vertically to strands before they expanded laterally until most of the chamber volume was filled with fungus garden curtains. New garden chambers were found at depths ranging from 17 to 83 cm, suggesting that new garden chambers were not constructed in deeper soil strata with increasing colony age. The size of M. goeldii and M. smithii colonies was dependent on their age. Worker counts varied between a few individuals in recently founded colonies and 1352 workers in an adult M. goeldii colony. The ratio of worker number per fungus garden chamber was higher in M. goeldii colonies than M. smithii colonies; the M. goeldii colonies were more populous. Both species were oligogynous with a maximum of four and three queens observed in a single chamber of M. goeldii and M. smithii, respectively. The reproductive status of each queen was unknown. In both species the ratio of brood to workers was approximately 2:3. Larvae and pupae were unequally distributed throughout the nest, but were only located in chambers containing a garden. Their location in the chamber was dependent upon the developmental state of the fungus garden.

Spectrum of Ants Associated with Araucaria angustifolia Trees and Their Relations to Hemipteran Trophobionts

The community of ants inhabiting Araucaria angustifolia trees or foraging on this conifer was studied in the rain forest reserve Pró-Mata on the Serra Geral of Rio Grande do Sul, southern Brazil. Ants of 44 species were recorded of which 23 were nesting on Araucaria trees. Data on their abundance and relationships to trophobionts are presented. Amongst the latter, Planococcus citri was by far the most common species. It was associated with ants of the genera Crematogaster, Solenopsis (Diplorhoptrum), Linepithema, Myrmelachista and Camponotus. The results are discussed under ecological and biogeographical aspects.

KARLSRUHE: The Zoological Collections of the State Museum of Natural History Karlsruhe

The State Museum of Natural History Karlsruhe is an institution of the state of Baden-Wurttemberg, with a staff of currently 57 permanent employees. It has emerged from the cabinet of natural history of Karoline Luise, Margravine of Baden and is open to the public since 1785. Permanent and temporary exhibitions extending to 5000 m2 provide the basis for manifold educational activities. Living animals are integrated into the permanent exhibition, a 240,000 l seawater tank with a living coral reef and reef sharks being a major attraction for the public. Zoological research at the museum mainly deals with biodiversity, i.e., taxonomy, faunistics, biogeography, natural history, and ecology. It is strongly based on museum collections but also on field sampling in soil ecological studies. The zoological collections incorporate about 8.5 million specimens, mostly terrestrial, but also a mollusk collection (Conchylia) of historical importance and the Kiefer collection of fresh water Copepoda. Important collections are on Arachnida, Lepidoptera, Coleoptera, Hymenoptera, Mantodea, as well as small mammals from Baden-Wurttemberg and large series of mammal skulls from West Africa. Biogeographic emphases are on the fauna of Southwestern Germany, the Middle East (Iran, Afghanistan), the Indo-Australian region and the Neotropics.