, Volume 105, Issue 4, pp 509–516

Effects of flower size and number on pollinator visitation to wild radish, Raphanus raphanistrum

  • Jeffrey K. Conner
  • Scott Rush
Plant Animal Interactions Original Paper


Plant traits that increase pollinator visitation should be under strong selection. However, few studies have demonstrated a causal link between natural variation in attractive traits and natural variation in visitation to whole plants. Here we examine the effects of flower number and size on visitation to wild radish by two taxa of pollinators over 3 years, using a combination of multiple regression and experimental reductions in both traits. We found strong, consistent evidence that increases in both flower number and size cause increased visitation by syrphid flies. The results for small bees were harder to interpret, because the multiple regression and experimental manipulation results did not agree. It is likely that increased flower size causes a weak increase in small-bee visitation, but strong relationships between flower number and small-bee visitation seen in 2 years of observational studies were not corroborated by experimental manipulation of this trait. Small bees may actually have responded to an unmeasured trait correlated with flower number, or lower small-bee abundances when the flower number manipulation was conducted may have reduced our ability to detect a causal relationship. We conclude that studies using only 1 year, one method, or measuring only one trait may not provide an adequate understanding of the effects of plant traits on pollinator attraction.

Key words

Pollinator attraction Raphanus raphanistrum Corolla size Flower number Experimental manipulation 


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  1. Augspurger CK (1980) Mass-flowering of a tropical shrub (Hybanthus prunifolius): influence on pollinator attraction and movement. Evolution 34:475–488Google Scholar
  2. Bell G (1985) On the function of flowers. Proc R Soc Lond B 224:223–265Google Scholar
  3. Buchmann SL, Cane JH (1989) Bees assess pollen returns while sonicating Solanum flowers. Oecologia 81:289–294Google Scholar
  4. Campbell DR, Waser NM, Price MV, Lynch EA, Mitchell RJ (1991) Components of phenotypic selection: pollen export and flower corolla width in Ipomopsis aggregata. Evolution 45:1458–1467Google Scholar
  5. Clements FE, Long FL (1923) Experimental pollination: an outline of the ecology of flowers and insects. Carnegie Institution of Washington, Washington, DCGoogle Scholar
  6. Conner J, Via S (1993) Patterns of phenotypic and genetic correlations among morphological and life-history traits in wild radish, Raphanus raphanistrum. Evolution 47:704–711Google Scholar
  7. Conner JK, Davis R, Rush S (1995) The effect of wild radish floral morphology on pollination efficiency by four taxa of pollinators. Oecologia 104:234–245Google Scholar
  8. Conner JK, Rush S, Jennetten P (1996) Measurements of natural selection on floral traits in wild radish (Raphanus raphanistrum). I. Selection through lifetime female fitness. Evolution, in pressGoogle Scholar
  9. Cruzan MB, Neal PR, Willson MF (1988) Floral display in Phyla incisa: consequences for male and female reproductive success. Evolution 42:505–515Google Scholar
  10. Darwin C (1877) The different forms of flowers on plants of the same species. University of Chicago Press, ChicagoGoogle Scholar
  11. Eckhart VM (1991) The effects of floral display on pollinator visitation vary among populations of Phacelia linearis (Hydrophyllaceae). Evol Ecol 5:370–384Google Scholar
  12. Eckhart VM (1992) Spatio-temporal variation in abundance and variation in foraging behavior of the pollinators of gynodioecious Phacelia linearis (Hydrophyllaceae). Oikos 64:573–586Google Scholar
  13. Galen C (1989) Measuring pollinator-mediated selection on morphometric traits: bumblebees and the alpine sky pilot, Polemonium viscosum. Evolution 43:882–890Google Scholar
  14. Galen C, Newport MEA (1987) Bumble bee behavior and selection on flower size in the sky pilot, Polemonium viscosum. Oecologia 74:20–23Google Scholar
  15. Geber MA (1985) The relationship of plant size to self-pollination in Mertensia ciliata. Ecology 66:762–772Google Scholar
  16. Harder LD, Thomson JD, Cruzan MB, Unnasch RS (1985) Sexual reproduction and variation in floral morphology in an ephemeral vernal lily, Erythronium americanum. Oecologia 67:286–291Google Scholar
  17. Hodges CM, Miller RB (1981) Pollinator flight directionality and the assessment of pollen returns. Oecologia 50:376–379Google Scholar
  18. Kay QON (1976) Preferential pollination of yellow-flowered morphs of Raphanus raphanistrum by Pieris and Eristalis spp. Nature 261:230–232Google Scholar
  19. Kearns CA, Inouye DW (1993) Techniques for pollination biologists. University Press of Colorado, NiwotGoogle Scholar
  20. Lande R, Arnold SJ (1983) The measurement of selection on correlated characters. Evolution 37:1210–1226Google Scholar
  21. Mitchell RJ (1993) Path analysis: pollination. In: Scheiner SM, Gurevitch J (eds) Design and analysis of ecological experiments. Chapman and Hall, New York, pp 211–231Google Scholar
  22. Neter J, Wasserman W, Kutner MH (1985) Applied linear statistical models, 2nd edn. Irwin, HomewoodGoogle Scholar
  23. Rush S, Conner J, Jennetten P (1995) The effects of natural variation in pollinator visitation on rates of pollen removal in wild radish, Raphanus raphanistrum (Brassicaceae). Am J Bot 82:1522–1526Google Scholar
  24. Sampson DR (1964) A one-locus self-incompatibility system in Raphanus raphanistrum. Can J Genet Cytol 6:435–445Google Scholar
  25. SAS Institute (1994) JMP, version 3. SAS Institute, CaryGoogle Scholar
  26. Schmid-Hempel P, Speiser B (1988) Effects of inflorescence size on pollination in Epilobium angustifolium. Oikos 53:98–104Google Scholar
  27. Stanton ML, Preston RE (1988) Ecological consequences and phenotypic correlates of petal size variation in wild radish, Raphanus sativus (Brassicaceae) Am J Bot 75:528–539Google Scholar
  28. Stanton ML, Snow AA, Handel SN (1986) Floral evolution: attractiveness to pollinators increases male fitness. Science 232:1625–1627Google Scholar
  29. Stanton ML, Snow AA, Handel SN, Bereczky J (1989) The impact of a flower-color polymorphism on mating patterns in experimental populations of wild radish (Raphanus raphanistrum L.). Evolution 43:335–346Google Scholar
  30. Stanton ML, Young HJ, Ellstrand NC, Clegg JM (1991) Consequences of floral variation for male and female reproduction in experimental populations of wild radish, Raphanus sativus L. Evolution 45:268–280Google Scholar
  31. Thomson JD (1988) Effects of variation in inflorescence size and floral rewards on the visitation rates of traplining pollinators of Aralia hispida. Evol Ecol 2:65–76Google Scholar
  32. Thomson JD, Maddison WP, Plowright RC (1982) Behavior of bumble bee pollinators of Aralia hispida Vent. (Araliaceae). Oecologia 54:326–336Google Scholar
  33. Waser NM (1983) The adaptive nature of floral traits: ideas and evidence. In: Real L (eds) Pollination biology. Academic Press, Orlando, pp 241–285Google Scholar
  34. Willson MF, Bertin RI (1979) Flower-visitors, nectar production, and inflorescence size of Asclepias syriaca. Can J Bot 57:1380–1388Google Scholar
  35. Willson MF, Rathcke BJ (1974) Adaptive design of the floral display in Asclepias syriaca L. Am Midl Nat 92:47–57Google Scholar
  36. Young HJ, Stanton ML (1990) Influences of floral variation on pollen removal and seed production in wild radish. Ecology 71:536–547Google Scholar

Copyright information

© Springer-Verlag 1996

Authors and Affiliations

  • Jeffrey K. Conner
    • 1
  • Scott Rush
    • 1
  1. 1.Department of Ecology, Ethology, and EvolutionUniversity of IllinoisChampaignUSA

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