, Volume 103, Issue 3, pp 365–370 | Cite as

Effect of density on magnitude of directional selection on seed mass and emergence time in Plantago wrightiana Dcne. (Plantaginaceae)

  • A. A. Winn
  • T. E. Miller
Original Paper


Although population density is believed to be an important factor influencing evolutionary processes, surprisingly few studies have documented the existence or nature of density-dependent selection. We quantified the effects of density on directional selection on seed mass (the mass of a sown seed) and emergence time in the greenhouse and field for the annual plant Plantago wrightiana. In the greenhouse, we quantified selection on seed mass and emergence time at each of five planting densities (1 m−2 to 10,000 m−2) using the relationship between final plant mass and each trait at each density. We observed no significant selection on either seed mass or emergence time when plants were grown alone. At all higher densities, there was significant selection favoring early emergence and large seed mass, but there were no significant differences among the selection gradients determined at densities greater than individually grown plants. In the field, we detected no relationship between the magnitude of selection for early emergence and density. Our results suggest that selection on seed mass and time of emergence is density dependent, but the relationship between density and the magnitude of directional selection on these traits is not continuously increasing. Over broad ranges of density in the greenhouse and in the field, there was no detectable relationship between density and the magnitude of directional selection.

Key words

Density dependence Selection Competition Seed mass Emergence time 


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  1. Anderson WW (1971) Genetic equilibrium and population growth under density-regulated selection. Am Nat 105:489–498Google Scholar
  2. Biere A (1991) Parental effects in Lychnis flos-cuculi. II. Selection on time of emergence and seedling performance in the field. J Evol Biol 3:467–486Google Scholar
  3. Black JN (1958) Competition between plants of different initial seed sizes in swards of subterranean clover (Trifolium subterraneum L.) with particular reference to leaf area and the light microclimate. Aust J Agric Res 9:299–318Google Scholar
  4. Boyce MS (1984) Restitution of r- and K-selection as a model of density-dependent natural selection. Annu Rev Ecol Syst 15: 427–447Google Scholar
  5. Charlesworth B (1971) Selection in density-regulated populations. Ecology 52:469–474Google Scholar
  6. Crawley MJ, Nachapong M (1985) The establishment of seedlings from primary and regrowth seeds of ragwort (Senecio jacobaea). J Ecol 73:255–261Google Scholar
  7. Efron B (1982) The jackknife, the bootstrap, and other resampling plans. Society for Industrial and Applied Mathematics. PhiladelphiaGoogle Scholar
  8. Efron B, Gong G (1983) A leisurely look at the bootstrap, the jackknife, and cross-validation. Am Statist 37:36–48Google Scholar
  9. Howell N (1981) The effect of seed size and relative emergence time on fitness in a natural population of Impatiens capensis Meerb. (Balsaminaceae). Am Midl Nat 105:312–320Google Scholar
  10. Kalisz S (1986) Variable selection on the timing of germination in Collinsia verna (Scrophulariaceae). Evolution 40:479–491Google Scholar
  11. Lande R, Arnold SJ (1983) The measurement of selection on correlated characters. Evolution 37:1210–1226Google Scholar
  12. MacArthur RH, Wilson EO (1967) The theory of island biogeography. Princeton University Press, PrincetonGoogle Scholar
  13. Marshall DL (1986) Effect of seed size on seedling success in three species of Sesbania (Fabaceae). Am J Bot 73:457–464Google Scholar
  14. Miller TE, Winn AA, Schemske DW (1994) The effects of density and spatial distribution on selection for emergence time in Prunella vulgaris (Lamiaceae). Am J Bot 81:1–6Google Scholar
  15. Mueller LD (1988a) Density-dependent population growth and natural selection in food-limited environments: the Drosophila model. Am Nat 132:786–809Google Scholar
  16. Mueller LD (1988b) Evolution of competitive ability in Drosophila by density-dependent natural selection. Proc Natl Acad Sci USA 85:4383–4386Google Scholar
  17. Ross MA, Harper JL (1972) Occupation of biological space during seedling establishment. J Ecol 60:77–88Google Scholar
  18. Schaal BA (1980) Reproductive capacity and seed size in Lupinus texensis. Am J Bot 67:703–709Google Scholar
  19. Schmitt J, Ehrhardt DW (1990) Enhancement of inbreeding depression by dominance and suppression in Impatiens capensis. Evolution 44:269–278Google Scholar
  20. Stanton ML (1984) Seed variation in wild radish: effect of seed size on components of seedling and adult fitness. Ecology 65: 1105–1112Google Scholar
  21. Stanton ML (1985) Seed size and emergence time within a stand of wild radish (Raphanus raphanistrum L.): the establishment of a fitness hierarchy. Oecologia 67:524–531Google Scholar
  22. Stratton DA (1992) Life-cycle components of selection in Erigeron annuus: I. Phenotypic selection. Evolution 46:92–106Google Scholar
  23. Van der Toorn J, Pons TL (1988) Establishment of Plantago lanceolata L. and Plantago major L. among grass. II. Shade tolerance of seedlings and selection on time of germination. Oecologia 76:341–347Google Scholar
  24. Waller DM (1984) Differences in fitness between seedlings derived from cleistogamous and chasmogamous flowers in Impatiens capensis. Evolution 38:427–440Google Scholar
  25. Watkinson AR, Lonsdale WM, Firbank LG (1983) A neighborhood approach to self-thinning. Oecologia 56:381–384Google Scholar
  26. Weis IM (1982) The effects of propagule size on germination and seedling growth in Mirabilis hirsuta. Can J Bot 60:1868–1874Google Scholar
  27. Winn AA (1985) Effects of seed size and microsite on seedling emergence of Prunella vulgaris in four habitats. J Ecol 73: 831–840Google Scholar

Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • A. A. Winn
    • 1
  • T. E. Miller
    • 1
  1. 1.Department of Biological ScienceFlorida State UniversityTallahasseeUSA

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