Advertisement

Why are there so many myrmecochorous species in the Cape fynbos?

  • R. M. Cowling
  • S. M. Pierce
  • W. D. Stock
  • M. Cocks
Part of the Tasks for vegetation science book series (TAVS, volume 31)

Abstract

The exceptionally high incidence of myrmecochory (ant-dispersed species) in Cape fynbos and similarly fire-prone vegetation on nutrient-poor soils in Australia has aroused much interest. An ecological advantage of myrmecochory on both continents is the removal of seeds to sites safe from seed predation. By failing to address evolutionary questions, ecological hypotheses do not explain the very high numbers of myrmecochorous species in fynbos. We show that myrmecochores are seldom dominant in fynbos communities although species numbers are invariably high. We also show that myrmecochores are not a random assemblage with regard to biological traits. Most myrmecochores are dwarf to low shrubs, obligately reseeding from relatively large seeds. Limited data suggest that myrmecochores have small, transient seed banks and are vulnerable to fire-induced local extinction. Myrmecochores were also significantly over-represented amongst a lowland neoendemic flora, suggesting that lineages possessing this trait are associated with recent diversification. Finally, in a general survey of the fynbos flora, we found that myrmecochorous genera were significantly more speciose than genera with other dispersal modes.

We conclude that the major ecological advantage of myrmecochory is the removal of large, precious seeds to sites safe from predators. Large seed size ensures seedling establishment in the nutrient-poor summer dry fynbos environment. Myrmecochores produce fewer seeds, however, and have smaller, less persistent seed banks than species with other dispersal modes. These traits, in combination with obligate reseeding and short dispersal distances, result in myrmecochore lineages being vulnerable to fire-induced population reduction and fragmentation. These processes also, and incidentally, promote diversification.

Key words

ant dispersal diversification 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Andersen, A.N. 1988. Dispersal distance as a benefit of myrmecochory. Oecologia 75: 507–511.CrossRefGoogle Scholar
  2. Beadle, N.C.W. 1966. Soil phosphate and its role in molding segments of the Australian flora and vegetation, with special reference to xeromorphy and sclerophylly. Ecology 47: 992–1007.CrossRefGoogle Scholar
  3. Berg, R.Y. 1975. Myrmecochorous plants in Australia and their dispersal by ants. Aust. J. Bot. 23: 475–508.CrossRefGoogle Scholar
  4. Bond, P. & Goldblatt, P. 1984. Plants of the Cape Flora. A Descriptive Catalogue. J. S. Afr. Bot. Supplementary 13: 1–455.Google Scholar
  5. Bond, W.J. & Breytenbach, G.J. 1985. Ants, rodents, and seed predation in Proteaceae. S. Afr. J. Zoo. 20: 150–154.Google Scholar
  6. Bond, W.J. & Slingsby, P. 1983. Seed dispersal by ants in shrublands of the Cape Province and its evolutionary implications. S. Afr. J. Sci. 79: 231–233.Google Scholar
  7. Bond, W.J., Yeaton, R. & Stock, W.D. 1991. Myrmecochory in Cape fynbos. In: Huxley, C.R. & Cutler, D.F. (eds.). Ant-Plant Interactions. Oxford University Press, pp. 448-462.Google Scholar
  8. Bond, W.J. & Slingsby, P. 1983. Seed dispersal by ants in shrublands of the Cape Province and its evolutionary implications. S. Afr. J. Sci. 79: 231–233.Google Scholar
  9. Boucher, C. & Moll, E.J. 1981. South African Mediterranean Shrublands. In: di Castri, F., Goodall, D.W. & Specht, R.L. (eds.). Ecosystems of the World 11. Mediterra neantype Shrublands. Elsevier, Amsterdam, pp. 233–248.Google Scholar
  10. Breytenbach, G.J. 1988. Why are myrmecochorous plants limited to fynbos (macchia) vegetation types? S. Afr. For. J. 144: 3–5.Google Scholar
  11. Campbell, B.M. 1985. A classification of the mountain vegetation of the fynbos biome. Mem. Bot. Surv. S. Afr. 50: 1–121.Google Scholar
  12. Cowling, R.M. 1984. A syntaxonomic and synecological study in the Humansdorp region of the fynbos biome. Bothalia 15: 175–227.Google Scholar
  13. Cowling, R.M. 1987. Fire and its role in coexistence and speciation in Gondwanan shrublands. S. Afr. J. Sci. 83: 106–112.Google Scholar
  14. Cowling, R.M. & Bond, W.J. 1991. How small can reserves be? An empirical approach in Cape Fynbos. Biol. Cons. 58: 243–256.CrossRefGoogle Scholar
  15. Cowling, R.M. & Campbell, B.M. 1980. Convergence in vegetation structure in the Mediterranean communities of California, Chile and South Africa. Vegetatio 43: 191–197.CrossRefGoogle Scholar
  16. Cowling, R.M. & Holmes, P.M. 1992. Endemism and speciation in a lowland flora from the Cape Floristic Region. Biol J. Linn. Soc. 47: 367–383.CrossRefGoogle Scholar
  17. Cowling, R.M., Pierce, S.M. & Moll, E.J. 1986. Conservation and utilization of South Coast Renosterveld, an endangered South African vegetation type. Biol. Cons. 37: 363–377.CrossRefGoogle Scholar
  18. Cowling, R.M., Straker, C.J. & Deignan, M.T. 1990. Does microsymbiont-host specificity determine plant species turnover and speciation in Gondwanan shrublands? A hypothesis. S. Afr. J. Sci. 86: 118–120.Google Scholar
  19. Davidson, D.W. & Morton, S.R. 1981. Myrmecochory in some plants (F. Chenopodiaceae) of the Australian arid zone. Oecologia 50: 357–366.CrossRefGoogle Scholar
  20. Fowler, C.W. & MacMahon, J.A. 1982. Selective extinction and speciation: their influence on the structure and functioning of communities and ecosystems. Am. Nat. 119: 480–498.CrossRefGoogle Scholar
  21. Givnish, T.J. 1987. Comparative studies of leaf form: assessing the relative roles of selective pressures and phylogenetic constraints. New Phytol. 106: 31–60.Google Scholar
  22. Grubb, P.J. & Hopkins, A.J.M. 1986. Resilience at the level of the plant community. In: Dell, B., Hopkins, A.J.M. & Lamont, B.B. (eds.). Resilience in Mediterranean-Type Ecosystems. W. Junk, The Hague, pp. 21–38.CrossRefGoogle Scholar
  23. Hall, A.V. & Veldhuis, H.A. 1985. South African Red Data Book: Plants — fynbos and karoo biomes. S. Afr. Nat. Sci. Prog. Rep. 117. CSIR, Pretoria.Google Scholar
  24. Harper, J.L. 1977. Population Biology of Plants. Academic Press, London.Google Scholar
  25. Hartmann, H.E.K. 1991. Mesembryanthema. Contrib. Bol. Herb. 13: 75–157.Google Scholar
  26. Hoffman, M.T. & Cowling, R.M. 1987. Plant physiognomy, phenology and demography. In: Cowling, R.M. & Roux, P.W. (eds.). The Karoo Biome: a preliminary synthesis. Part 2. Vegetation and History. S. A. Nat. Sci. Prog. Rep. 142. CSIR, Pretoria, pp. 1–34.Google Scholar
  27. James, S. 1984. Lignotubers and burls — their structure, function and ecological significance in Mediterranean ecosystems. Bot. Rev. 50: 225–266.CrossRefGoogle Scholar
  28. Kilian, D. 1991. Seed and seedling ecology of two co-occurring ericoid fynbos shrub species. M.Sc. Thesis. University of Cape Town.Google Scholar
  29. Knight, R.S. 1988. Aspects of plant dispersal in the southwestern Cape with particular reference to the roles of birds as dispersal agents. Ph.D. Thesis, University of Cape Town.Google Scholar
  30. Kruger, F.J. 1979. South African Heathlands. In: Specht, R. L. (ed.). Ecosystems of the World 9A. Heathlands and Shrublands Descriptive Studies. Elsevier, Amsterdam, pp. 19–80.Google Scholar
  31. Le Maitre, D. & Midgley, J.J. 1992. Reproductive ecology of fynbos plants. In: Cowling, R.M. (ed.). The Ecology of Fynbos — Nutrients, Fire and Diversity. Oxford University Press, Cape Town, pp. 135–174.Google Scholar
  32. Levyns, M.R. 1929. Veld-burning experiments at Ida’s Valley, Stellenbosch. Trans. Roy. Soc. S. Afr. 17: 61–92.CrossRefGoogle Scholar
  33. Levyns, M.R. 1935. Veld burning experiments at Oakdale, Riversdale. Trans. Roy. Soc. S. Afr. 23: 231–243.CrossRefGoogle Scholar
  34. Lewis, H. 1962. Catastrophic selection as a factor in speciation. Evolution 16: 257–271.CrossRefGoogle Scholar
  35. Linder, H.P. 1985. Gene flow, speciation and species diversity patterns in a species-rich area: the Cape Flora. In: Vrba, E.S. (ed.). Species and Speciation. Transvaal Museum, Pretoria, pp. 53–57.Google Scholar
  36. Linder, H.P. & Ellis, R.P. 1990. Vegetative morphology and inter-fire survival strategies in the Cape fynbos grasses. Bothalia 20: 91–103.Google Scholar
  37. Linder, H.P. & Vlok, J. 1991. The morphology, taxonomy and evolution of Rhodocoma (Restionaceae). Plant Syst. Evol. 175: 139–160.CrossRefGoogle Scholar
  38. Major, J. 1988. Endemism: a botanical perspective. In: Myers, A.A. & Giller, P.S. (eds.). Analytical Biogeography. An Integrated Study of Animal and Plant Distributions. Chapman and Hall, New York, pp. 117–146.Google Scholar
  39. Manders, P.T. 1990. Fire and other variables as determinants of forest/fynbos boundaries in the Cape Province. J. Veg. Sci. 1: 483–490.CrossRefGoogle Scholar
  40. Manders, P.T. & Richardson, D.M. 1992. Colonization of Cape fynbos communities by forest communities. For. Ecol. & Mgmt. 48: 277–293.CrossRefGoogle Scholar
  41. Midgley, J.J. 1987. Aspects of the evolutionary biology of the Proteaceae, with emphasis on the genus Leucadendron and its phylogeny. Ph.D. Thesis, University of Cape Town.Google Scholar
  42. Midgley, J.J. & Bond, W.J. 1989. Leaf size and inflorescence size may be allometrically related traits. Oecologia 78: 427–429.CrossRefGoogle Scholar
  43. Milewski, A.V. & Bond, W.J. 1982. Convergence of myrmecochory in Mediterranean Australia and South Africa. In: Buckley, R.C. (ed.). Ant-plant interactions in Australia. Dr W. Junk, The Hague, pp. 89–98.CrossRefGoogle Scholar
  44. Mossop, M.K. 1989. Comparison of seed removal by ants in vegetation on fertile and infertile soils. Aust. J. Ecol. 14: 367–373.CrossRefGoogle Scholar
  45. Musil, C.F. 1991. Seed bank dynamics in sand plain lowland fynbos. S. Afr. J. Bot. 57: 131–142.Google Scholar
  46. Phillips, J.F.V. 1931. Forest succession and ecology in the Knysna region. Bot. Surv. Mem. 14: 1–327.Google Scholar
  47. Pierce, S.M. 1990. Pattern and process in South Coast Dune Fynbos: Population, community and landscape level studies. Ph.D. Thesis, University of Cape Town.Google Scholar
  48. Pierce, S.M. & Cowling, R.M. 1991. Dynamics of soil-stored seed banks of six shrubs in fire-prone dune fynbos. J. Ecol. 79: 731–747.CrossRefGoogle Scholar
  49. Primack, R.B. 1987. Relationships among flowers, fruits and seeds. Ann. Rev. Ecol. Syst. 18: 409–430.CrossRefGoogle Scholar
  50. Raven, P.H. 1964. Catastrophic selection and edaphic endemism. Evolution 18: 336–338.CrossRefGoogle Scholar
  51. Rice, B.L.& Westoby, M. 1981. Myrmecochory in sclerophyll vegetation of the West Head, New South Wales. Aust. J. Ecol. 6: 291–298.CrossRefGoogle Scholar
  52. Slingsby, P. & Bond, W.J. 1981. Ants — friends of the fynbos. Veld & Flora 67: 39–45.Google Scholar
  53. Slingsby, P. & Bond, W.J. 1985. The influence of ants on the dispersal distance and seedling recruitment of Leucospermum conocarpodendron (L.) Buek (Proteaceae). S. Afr. J. Bolt. 5: 30–34.Google Scholar
  54. Stebbins, G.L. & Major, J. 1965. Endemism and speciation in the Californian flora. Ecol. Monogr. 35: 1–31.CrossRefGoogle Scholar
  55. Stock, W.D. & Bond, W.J. 1992. On the costs of ant, bird and wind-dispersal in fynbos Asteraceae. Presented paper of the 18th Annual Conference of the South African Association of Botanists, Durban.Google Scholar
  56. Stock, W.D., Pate, J.S. & Delfs, J. 1990. Influence of seed size and quality on seedling development under low nutrient conditions in five Australian and South African members of the Proteaceae. J. Ecol. 78: 1005–1020.CrossRefGoogle Scholar
  57. Thompson, K. & Rabinowitz, D. 1989. Do big plants have big seeds? Am. Nat. 133: 722–728.CrossRefGoogle Scholar
  58. Thwaites, R.N. & Cowling, R.M. 1988. Soil-vegetation relationships on the Agulhas Plain, South Africa. Catena 15: 333–345.CrossRefGoogle Scholar
  59. Van Wilgen, B.W., Higgins, K.B. & Bellstedt, D.U. (1990). The role of vegetation structure and fuel chemistry in excluding fire from forest patches in the fire-prone fynbos shrublands of South Africa. J. Ecol. 78: 210–222.CrossRefGoogle Scholar
  60. Vrba, E.S. 1980. Evolution, species and fossils: how does life evolve? S. Afr. J. Sci. 76: 61–84.Google Scholar
  61. Westoby, M., Hughes, L. & Rice, B.L. 1991. Seed dispersal by ants; comparing infertile with fertile soils. In: Huxley, C.R. & Cutler, D.F. (eds.). Ant-Plant Interactions. Oxford University Press, Oxford, pp. 434–447.Google Scholar
  62. Westoby, M., Rice, B. & Howell, J. 1990. Seed size and plant growth form as factors in dispersal spectra. Ecology 71: 1307–1315.CrossRefGoogle Scholar
  63. Williams, I. 1982. Studies in the genera of the Diosmeae (Rutaceae): 14. A review of the genus Diosma L. J. S. Afr. Bot. 48: 329–407.Google Scholar
  64. Willson, M.F., Rice, W.L. & Westoby, M. 1990. Seed dispersal spectra: a comparison of temperate plant communities. J. Veg. Sci. 1: 547–562.CrossRefGoogle Scholar
  65. Yeaton, R.I. & Bond, W.J. 1991. Competition between two shrub species: dispersal differences and fire promote coexistence. Am. Nat. 138: 328–341.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 1994

Authors and Affiliations

  • R. M. Cowling
    • 1
  • S. M. Pierce
    • 2
  • W. D. Stock
    • 1
  • M. Cocks
    • 1
  1. 1.Department of BotanyUniversity of Cape TownRondeboschSouth Africa
  2. 2.Bolus HerbariumUniversity of Cape TownRondeboschSouth Africa

Personalised recommendations