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here, where none of the plants provide any incentive in the form of a significant food
source for pollinators, the size of bumblebees. Firmage and Cole (
1988
) found that
the level of fruit set in
C. tuberosus
at their Maine study site, where none of the
proposed orchid models occur, was greater than the level that Thien and Marcks
(
1972
) reported for their Wisconsin population, where such a model was present
(Table
8.2
).
If mimicry is involved, it seems more likely that the orchids have converged upon
other more common taxa in the same biotype that offer a more bountiful reward.
Pollinators preconditioned to other pink flowers might visit the similar flowers of
the orchids by mistake (Mosquin
1970
). Seeking the possible identities of these
other species in northern Wisconsin and Maine bogs, Thien and Marcks (
1972
),
Heinrich (
1975
), and Firmage and Cole (
1988
) have found bumblebees actively pol-
linating many pink flowered ericaceous shrubs, as well as
Sarracenia purpurea
L.,
Epilobium
L. species, and
Polygala paucifolia
Willd. The latter is thought to be a
particularly good model as one of its pink-magenta petals also has a brush-like
structure that absorbs light in the ultraviolet range, and it flowers when the three
orchids are in bloom (Thien and Marcks
1972
7AL5PTONIN
van der Cingle 2001
)
reports that Douglas H. Goldman has also observed mimicry of
Rhexia virginica
L.
in eastern Texas. Of course, unless the deception is very good, the presence of sym-
patric models that offer a reward might actually reduce rather than increase the
frequency of pollinator visits to
C. tuberosus.
Moreover, the thing mimicked may
not be another flower at all, but rather the pollen food source purportedly simulated
by the anther-like brushes on the lip, the so-called pseudopollen of Dafni (
1984
).
On the other hand, it cannot be excluded that the flowers of
Pogonia
or
Arethusa
do contain sufficient nectar to serve as a basis for convergence (e.g., Thien and
Marcks
1972
; Heinrich
1975
). Heinrich (
1975
) reported frequent movement of
bumblebees among simultaneously blooming plants of
Calopogon
and
Pogonia
in
Maine, and considered that this activity might be prolonged by food rewards col-
lected from
Pogonia
. Given the effectiveness of the pollination mechanism, succes-
sive visits of a single pollinator to nonrewarding flowers could lead to the production
of abundant seed (Heinrich and Raven
1972
). However, such movement implies the
chance transfer of pollen between
Pogonia
and
Calopogon
or, at other sites, between
Pogonia
and
Arethusa
with the possible production of sterile hybrids or seeds. Such
hybridization would reduce the reproductive success of both species and would tend
to remove one from mixed populations (Lewis
1961
; Heinrich
1975
) or lead to
selection for character displacement or changes in phenology or habitat (Levin and
Kerster
1967
; Levin and Schaal
1970
; Heinrich
1975
).
Gregg's (
1991
) report of a carpenter bee (
Xylocopa virgincia
L.) possibly col-
lecting pollen from
Calopogon pallidus
Chapman in North Carolina suggests a dif-
ferent basis for mimicry. Carpenter bees have not as yet been implicated in the
pollination of either
Pogonia
or
Arethusa
; however, Thien and Marcks (
1972
) noted
that some pollinators were probably overlooked and that those identified in
Wisconsin are absent from the southern range of all three orchids.
Convincing evidence for mimicry remains to be established. The flowers, which,
after all, possess a suite of characters usually associated with bumblebee pollina-
tion, may not need to mimic those of any other species, and pollen transfer may
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