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Effects of floral display size and plant density on pollinator visitation rate in a natural population of Digitalis purpurea

  1. J. M. GRINDELAND†,
  2. N. SLETVOLD‡,*,
  3. R. A. IMS§

Article first published online: 13 JUN 2005

DOI: 10.1111/j.1365-2435.2005.00988.x

Issue

Functional Ecology

Functional Ecology

Volume 19, Issue 3, pages 383–390, June 2005

Additional Information

How to Cite

GRINDELAND, J. M., SLETVOLD, N. and IMS, R. A. (2005), Effects of floral display size and plant density on pollinator visitation rate in a natural population of Digitalis purpurea. Functional Ecology, 19: 383–390. doi: 10.1111/j.1365-2435.2005.00988.x

Author Information

  1. Department of Biology, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway

  1. †

    Present address: Sør-Trøndelag University College, Rotvoll Allé 1, N-7004 Trondheim, Norway.

  2. ‡

    Present address: Natural History Museum, University of Oslo, PO Box 1172 Blindern, N-0318 Oslo, Norway.

  3. §

    Present address: Department of Biology, University of Tromsø, N-9037 Tromsø, Norway.

* †Author to whom correspondence should be addressed. E-mail: nina.sletvold@nhm.uio.no

Publication History

  1. Issue published online: 24 JUN 2005
  2. Article first published online: 13 JUN 2005
  3. Received 1 November 2004; revised 2 February 2005; accepted 17 February 2005

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Keywords:

  • Bombus;
  • flower visitation rate;
  • plant density effects;
  • plant–pollinator interactions;
  • pollinator foraging behaviour

Summary

  • 1
    Pollinator visitation patterns in relation to variation in floral display size may be modified both quantitatively and qualitatively by local plant density. In this study four measures of pollinator response by Bombus spp. (plant visitation rate, bout length, proportion of flowers visited, flower visitation rate) were investigated under two or three different plant densities in two consecutive years in a natural population of Digitalis purpurea L.
  • 2
    Plant visitation rate increased with floral display size in both years, and was higher in dense patches compared with sparse ones in 1999. Bout lengths increased with display size in 1999, and bouts were longer in sparse patches. However, the actual rate of increase with display size was independent of plant density for both response measures.
  • 3
    The proportion of flowers visited decreased with floral display size in both years, and in 1999 the decline was faster in high-density patches. As a result, the proportion visited was higher in dense patches for the smallest display sizes, and higher in sparse patches for larger display sizes.
  • 4
    Flower visitation rate decreased with floral display size in both years. This is inconsistent with the idea that bees achieve an ideal free distribution across flowers. There was no significant effect of plant density.
  • 5
    These results demonstrate that local plant density variation may modify the functional relationship between floral display size and pollinator visitation rate, and potentially influence plant mating patterns.
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