Three myrmecochorous rain forest herbs (Globba, Zingiberaceae)
Martin Pfeiffer (a), Jamili Nais (b) and K. Eduard Linsenmair (c)
(a) University of Ulm, Department of Experimental Ecology (Bio III), Albert-Einstein Allee 11, 89069 Ulm, Germany
(b) Sabah Parks Board, Malaysia, Kinabalu Conservation Centre, P O Box 10626, 88806 Kota Kinabalu, Sabah, Malaysia
(c) University of Würzburg, Department of Animal Ecology and Tropical Biology, Am Hubland, 97074 Würzburg, Germany
Introduction
The old-world tropics encompass one of the richest floral zones of the world and some of the hot spots of ant diversity. This results in a large variety of ecological interactions between both groups. One of them is the phenomenon of "myrmecochory", the seed dispersal of plants by ants which is also well known from temperate forests, where the part of ant dispersed species is up to 30 percent. At least 67 plant families on earth comprise myrmecochorous species. Beattie (1), who reviewed the distribution of ant dispersed plants in 1983 proposed that species richness and abundance of myrmecochores and diaspore-dispersing ants increase with decreasing latitude and predicted a greater variety of ant-dispersal systems in the tropics, in particular favoured by poor soils. However, up to now, only few tropical myrmecochores have been described (2), especially few in the paleotropics (3). In the Journal of Tropical Ecology we report about myrmecochory in a Malaysian forest-floor herb (4) (PDF). Here we present a short summary and additional material, especially photographs of ants, plants and seeds.Material and Methods
Globba species are plants of the shady primary forest that grow at moist places along streams and waterfalls. The slender herbs are up to 0.5-1 m high, with the delicate small, yellow, white or violet inflorescence on the top of the leafy shoots. In many cases the inflorescence points downwards or is pendulous (5). In several species bulbils replace the flowers (e.g. Globba marantina), in others bulbils or vegetative miniature ginger plantlets are additionally produced at the lower end of the inflorescence. Among the Zingiberaceae of the Peninsular Malaysia the Globbeae are a less diverse tribe with only 15 species (6).We studied three species: Globba franciscii, G. propinqua and G. pendula. Seeds (< ca. in G. propinqua, ca. 33 in G. franciscii) are inside a seed capsule. Several such capsules may hang at one shoot while the plant is still flowering, so fruiting is more or less continuously. When fruits are ripe the capsule will burst open and present the fruits. As common in the Zingiberaceae the examined seeds of the Globbeae have an aril, a fleshy appendage that encloses the seed partially and that connects to the seed coat at the micropylar region (7). Aril cells are usually rich in lipids and also contain proteins, starch grains and polysaccharides6. In the case of the Globbeae the fleshy aril forms a large, lacerate elaiosome (ant fruit) that serves for ants as food and allows them to handle the seed easily.
Field work took place in Kinabalu National Park and in Tawau Hills Park, both in Sabah, Malaysia. During the experiments always 10 seeds of the examined Globbae were presented on a small wooden tray (10 x 10 cm) that was placed randomly on the forest floor. To test arboreal ant species the tray was placed near the trunk roads of these ants. The behaviour of the ants towards the seeds was observed, and we noted dispersal distances and the number of seeds removed within one hour.
Results
In our preliminary study we found 23 species of ants of 12 genera and 4 subfamilies that fed on the seed arils of the examined Globbeae (see 4). Ant species included carnivore groups such as Ponerinae, but also Formicinae, Dolichoderinae, and Myrmicinae. Only one species, Polyrhachis sp., a widely distributed arboreal ant, was observed to remove seeds directly from the burst open fruit cap-sules.Dispersal distances achieved by this ant are especially long and may reach to more than 800 cm. Other Formicinae species observed were Camponotus and Oecophylla.Discussion
Here we show for the first time that myrmecochory is one of the mechanisms in seed dispersal of the Zingiberaceae. These results are confirmed by numerous observations of dispersal of other ginger species (Pfeiffer, unpublished data). Thus we confirm the thesis that ant-dispersal is a potential mechanism of seed distribution in the old world tropics. However, many of the ant species that we observed feeding at arils are also granivorous and will possibly fed also on the seeds. Kaspari (8) found more than 40 species of harvester ants in forests of Costa Rica and our unpublished results (9) show 50 granivorous species in the leaf litter of Borneo's rain forests. Thus the strong impact of harvester ants may work against the wide spread use of myrmecochory as a dispersal mechanism in tropical forests.Acknowledgements
We thank the Economic Planning Unit (EPU, Malaysia) for research permission and Sabah Parks for providing of logistic help. We are grateful to Alim Biun, Sabah Parks for the determination of the plants.Literature
- Beattie AJ Distribution of ant-dispersed plants in Sonderbände naturwissenschaftlicher Verhandlungen, Vol. 7, 249-270 (Hamburg, 1983)
- Horvitz CC (1981) Analysis of how ant behaviors affect germination in a tropical myrmecochore Calathea microcephala (P. & E) Koernicke (Marantaceae): microsite selection and aril removal by neotropical ants, Odontomachus, Pachycondyla, and Solenopsis (Formicidae). Oecologia 51, 47-52
- Kaufmann E, Weissflog A, Hashim R & Maschwitz U (2001) Ant-Gardens on the giant bamboo Gigantochloa scortechinii (Poaceae) in West-Malaysia. Insectes Sociaux 48, 125-133
- Pfeiffer M, Nais J, Linsenmair K (2004) Myrmecochory in the Zingiberaceae:
Seed dispersal of Globba franciscii and G. propinqua by ants (Hymenoptera - Formicidae) in rain forests on Borneo. Journal of Tropical Ecology 20: 705-708 PDF - Weber, A (1995) The Malayan species of Globba. Nature Malaysiana December 1995, 114-121
- Larsen K, Ibrahim H, Khaw SH & Saw LG (1999) Gingers of Peninsular Malaysia and Singapore (ed. Wong, K. M.) (Natural History Publications (Borneo), Kota Kinabalu
- Liao, JP & Wu QG (2000) A preliminary study of the seed anatomy of Zingiberaceae. Botanical-Journal-of-the-Linnean-Society. Sept.-Oct., 2000; 134, 287-300
- Kaspari M (1996) Worker size and seed size selection by harvester ants in a neotropical forest. Oecologia 105, 397-404
- Pfeiffer M and Linsenmair K.E. (submitted) Seed harvesting ant ensembles (Hymenoptera: Formicinae) in three primary rain forests on Borneo: diversity patterns, community organisation and seed size selection. Insectes Sociaux.
Figures
Fig. 1 Globba franciscii, a plant of the shady rain forests of BorneoFig. 2 A ripe fruit of Globba franciscii.
Fig. 3 A burst open fruit capsule of G. propinqua. Mind the large elaiosomes.
Fig. 4 A worker of Polyrhachis sp. is harvesting a seed of Globba propinqua directly from the plant.
Fig. 5 Workers of Colobopsis sp. 1 feeding at arils of seeds of G. pendula.
Fig. 6 Workers of Oecophylla smaragdina are carrying a seed of G. franciscii.
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