Abstract Detail



Ecology

Anderson , Steven Richard [1], Ford, Bruce [2], Worley, Anne [3].

Changes in the floral community contribute to increased fruiting success in southern populations of a rewardless orchid, Cypripedium candidum.

Plants that do not offer a food reward for pollinators rely on co-flowering rewarding species to sustain pollinator populations and maintain insect foraging in an area. However, rewarding flowers may compete with rewardless species for insect visits. Extended growing seasons at equatorial latitudes may allow rewardless plants to avoid co-flowering competitors by flowering earlier than most species. The resulting decrease in early-season diversity and abundance of rewarding taxa may increase reproductive success of rewardless species in regions with long growing seasons. In addition to changes in the plant community, insect diversity and body size may also vary with latitude. Therefore, reproductive success in plants with restrictive flowers may also depend on latitudinal variation in the abundance and size of pollinators.
Cypripedium candidum is a globally threatened rewardless orchid that is endemic to tall grass prairies in North America. The flowers in this species have restrictive openings, creating a one-way semi-trap for pollinators. We conducted a survey of 21 populations in four study regions (northern Iowa, southern and northern Minnesota and southern Manitoba) in the western part of this species range. In each region, we quantified the composition of the co-flowering and insect communities, and recorded the fruiting success of up to 50 orchid plants per site.  
Consistent with predictions, insect and co-flowering species diversity was highest in Manitoba and lowest in southern regions. Regression analyses of site variation determined that increased fruiting success in C. candidum was associated with more southern latitudes. This increase in fruiting success was most closely associated with a decrease in the diversity of the co-flowering community, as well as an increase in the abundance of the potential facilitators, Packera and Zizia. Large-bodied insects, which were too large to fit the restrictive openings in C. candidum, were most abundant at higher latitudes whereas appropriately sized pollinators were most abundant in southern study regions. To our knowledge, this study was the first to survey reproductive success across the latitudinal range of a rewardless species. Our research provides evidence that extended growing seasons benefit reproduction in rewardless taxa, as predicted in the literature.


1 - University of Manitoba, Biological Sciences, 50 Sifton Road, 212B Biological Sciences Building, Winnipeg, MB, R3T2N2, Canada
2 - University Of Manitoba, Department Of Biological Sciences, 50 Sifton Road, Winnipeg, MB, R3T 2N2, Canada
3 - University of Manitoba, Biological Sciences, 50 Sifton Road, Winnipeg, MB, R3T2N2, Canada

Keywords:
pollination
Cypripedium candidum
rewardless orchid
phenology
plant-plant interactions
plant-insect interactions
Conservation
Endangered Species
latitude
tallgrass prairie.

Presentation Type: Oral Paper
Number:
Abstract ID:748
Candidate for Awards:Cinq Mars Award


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