Abstract
Dispersal of 11 dominant grass species in the savanna of southern Botswana was investigated. The dispersal is autochorous, anemochorous and epizoochorous independent of the life-cycle (annuals, perennials). Dispersal distances were estimated experimentally. Anemochorous species with a plume-like spikelet such as Chloris virgata and Enneapogon cenchroides have a low rate of descent (<1 m s-1) and a low Reynold number (100–110). Nevertheless they can only be transported up to 13 m from the originating infructescence at a wind velocity of 10 m s-1. Therefore, the majority of the disseminules remained near the parent plant. By analysing the seed pool under the canopy of trees of Dichrostachys cinerea epizoochorous species such as Tragus berteronianus were dominant at the cattle resting sites under trees. The results are discussed in relation to the three seed dispersal hypotheses and the model of selective interaction of dispersal, dormancy, and seed site as adaptions to variable environments.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Agnew, A. D. Q. & Flux, J. E. C. 1969. Plant dispersal by hares (Lepus capensis L.) in Kenya. Ecology 51: 753–737.
Andersen, M. 1991. Mechanistic models for the seed shadows of wind-dispersed plants. Am. Nat. 137: 476–497.
Andrew, M. H. 1986. Granivory of the annual grass Sorghum intrans by the harvester ant Meranoplus sp. in tropical Australia. Biotropica 18: 344–349.
A.P.R.U. — Animal Production Research Unit, 1980. Ten Years of Animal Production and Range Research in Botswana. Ministry of Agriculture, Gaborone, Botswana.
Baker, H. G. 1972. Seed weight in relation to environmental conditions in California. Ecology 53: 997–1010.
Baker, H. G. 1974. The evolution of weeds. Ann. Rev. Ecol. Syst. 5: 1–24.
Bille, J. C. & Poupon, H. 1974. Recherches écologiques sur une savanne sahelienne du Ferlo septentrional Senegal: La régénération de la strate herbacée. Terre et la Vie 28: 21–48.
Bullock, S. H. & Primack, R. B. 1977. Comparative experimental study of seed dispersal on animals. Ecology 58: 681–686.
Burrows, F. M. 1973. Calculations of the primary trajectories of plumed seeds in steady winds with variable convection. New Phytol. 72: 647–664.
Burrows, F. M. 1975. Wind-borne seed and fruit movement. New Phytol. 75: 405–418.
Coffin, D. P. & Lanenroth, W. K. 1989. Spatial and temporal variation in the seed bank of a semi arid grassland. Am. J. Bot. 76: 53–58.
Cremer, K. W. 1977. Distance of seed dispersal in eucalypts estimated from seed weight. Aust. For. Res. 7: 255–258.
Davidson, D. W. & Morton, S. 1981. Myrmecochory in some plants (F. Chenopodiaceae) of the Australian arid zone. Oecologia 50: 357–366.
Ernst, W. H. O. 1981. Ecological implications of fruit variability in Phleum arenarium L., an annual dune grass. Flora 171: 387–398.
Ernst, W. H. O. 1991. Fire, dry heat and germination of savanna grasses in Botswana. In: Modern Ecology: basic and applied aspects, G.Esser & D.Overdieck (eds.), Elsevier Publ., Amsterdam: 349–362.
Ernst, W. H. O. & Tolsma, D. J. 1988. Dormancy and germination of semi-arid annual plant species, Tragus berteronianus and Tribulus terrestris. Flora 18: 243–251.
Ernst, W. H. O. & Tolsma, D. J. 1989. Mineral nutrients in some Botswana savanna types. In: Nutrients in Tropical Forests and Savannas, J.Proctor (ed.), Blackwell Scientific Publ., Oxford: 97–120.
Ernst, W. H. O. & Tolsma, D. J. 1990. Dispersal of fruits and seeds in woody savanna plants in southern Botswana. Beitr. Biol. Pflanz. 65: 325–342.
Ernst, W. H. O., Kuiters, A. T. & Tolsma, D. J. 1991. Dormancy of annual and perennial grasses from a savanna of southeastern Botswana. Acta Oecol. 12: 727–739.
Field, D. I. 1976. A Handbook of Common Grasses in Botswana. Ministry of Agriculture, Gaborone.
Green, D. F. & Johnson, E. A. 1989. A model of wind dispersal of winged or plumed seeds. Ecology 70: 339–347.
Green, D. S. 1980. The terminal velocity and dispersal of spinning samaras. Am. J. Bot. 67: 1218–1224.
Hilger, H. H. & Schultka, W. 1988. Plant dispersal in a semiarid thornbush savanna in Northern Kenya. Bot. Jahrb. Syst. 108: 385–406.
Howe, H. F. & Smallwood, J. 1982. Ecology of seed dispersal. Annu. Rev. Ecol. Syst. 13: 201–228.
Janzen, D. H. 1970. Herbivores and the number of tree species in tropical forests. Am. Nat. 104: 501–528.
Janzen, D. H. 1984. Dispersal of small seeds by big herbivores: Foliage is the fruit. Am. Nat. 123: 338–353.
Joubert, D. C. 1984. The soil seed bank under nasella tussock infestation at Boschberg. S. Afr. J. Plant Soil 1: 1–3.
Keay, R. W. 1957. Wind-dispersal species in a Nigerian forest. J. Ecol. 45: 471–478.
Marsh, A.C. 1987. The foraging ecology of two Namib Desert (Southwest Africa) harvester ant species. S. Afr. J. Zool. 22: 130–136.
Miller, S. & Veenendaal, E. M. 1991. The quantification of runoff and factors influencing its production in South Eastern Botswana. — Proceed. 1 st Land and Water Management Research Programme, ODA-SACCAR, Gaborone, Botswana (in press).
Milton, S. J., Siegfried, W. R. & Dean, W. R. J. 1990. The distribution of epizoochoric plant species: a clue to the prehistoric use of arid karoo rangeland by large herbivores. J. Biogeogr. 17: 25–34.
Morse, D. H. & Schmidt, J. 1985. Propagule size, dispersal ability, and seedling performance in Asclepias syriaca. Oecologia 67: 372–379.
Mott, J. J. & McKeon, G. M. 1977. A note on the selection of seed types by harvester ants in northern Australia. Aust. J. Ecol. 2: 231–235.
Okubo, A. & Levin, S. A. 1989. A theoretical frame work for data analysis of wind dispersal of seeds and pollen. Ecology 70: 329–338.
Pohl, R. W. 1955. Mechanik, Akustik und Wärmelehre. 13rd ed. Springer Verlag Berlin.
Sorensen, A. E. 1986. Seed dispersal by adhesion. Ann. Rev. Ecol. Syst. 17: 443–463.
Tevis, L. 1958. Interrelations between the harvester ant Veromessor pergandei (Mayr) and some desert ephemerals. Ecology 39: 695–704.
Tolsma, D. J. 1989. On the ecology of savanna ecosystems in southeastern Botswana. Doctoral Thesis Vrije Universiteit, Amsterdam.
Tolsma, D. J., Ernst, W. H. O. & Verweij, R. A. 1987. Nutrients in soil and vegetation around to artificial waterpoints in eastern Botswana. J. Appl. Ecol. 24: 991–1000.
Tomich, P. Q., Wilson, N. & Lamoureux, C. H. 1968. Ecological factors on Manana Island, Hawaii. Pacific Sci. 22: 352–368.
Van derPijl, L. 1982. Principles of Dispersal in Higher Plants. 3rd ed., Springer Verlag, Berlin.
Veenendaal, E. M. 1991. Adaptive strategies of grasses in a semi-arid savanna in Botswana. Doctoral Thesis Vrije Universiteit, Amsterdam.
Veenendaal, E. M. & Ernst, W. H. O. 1991. Dormancy patterns in accessions of caryopses from savanna grass species in southeastern Botswana. Acta Bot. Neerl. 40: 297–309.
Venabe, D. L. & Brown, J. L. 1988. The selective interaction of dispersal, dormancy, and seed size as adaptations for reducing risk in variable environments. Am. Nat. 131: 360–384.
Verkaar, H. J., Schenkeveld, A. H. & van deKlashorst, M. P. 1983. The ecology of short-lived forbs in chalk grasslands: Dispersal of seeds. New Phytol. 95: 335–344.
Whitford, S. C. 1978. Foraging in seed-harvester ants Pogonomyrmex spp. Ecology 59: 185–189.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Ernst, W.H.O., Veenendaal, E.M. & Kebakile, M.M. Possibilities for dispersal in annual and perennial grasses in a savanna in Botswana. Vegetatio 102, 1–11 (1992). https://doi.org/10.1007/BF00031700
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00031700