Biology Reference
In-Depth Information
In C. tuberosus , male and female reproductive success at the Maine site increased
with increasing inflorescence size (Firmage and Cole 1988 ). The number of open
flowers (typically 2-4) was independent of inflorescence size, and larger inflores-
cences did not attract more pollinators at any one time; however, the overall proba-
bility of pollinator visits was increased by a longer period of sequential flowering.
A larger inflorescence and longer display time might represent one response to a
competition for scarce pollinators (Willson and Price 1977, 1980 ; Wyatt 1982 ;
Firmage and Cole 1988 ). Yet, both the Maine and Wisconsin study sites were located
in sphagnum bogs, an environment commonly considered to be low in nutrient
resources. Nutrient limitation might be expected to produce the opposite trend in
inflorescence evolution (Firmage and Cole 1988 ). Where both factors are signifi-
cant, inflorescence size and display time should reflect some level of compromise
between the need to attract scarce pollinators and the limited resources available to
produce the inflorescence (Firmage and Cole 1988 ). In addition to a reduction in
inflorescence size and display time, the savings realized by allocating limited
resources to purposes other than a pollinator reward must likewise be balanced
against a resulting reduction in the attractiveness of the flowers and a contingent
decrease in annual reproductive success (Firmage and Cole 1988 ).
Additional Species of Calopogon
The four other species of Calopogon native to North America resemble C. tuberosus
in flower morphology, color, and ultraviolet reflectance. Calopogon multiflorus
Lindley, C. barbatus (Walter) Ames, and C. pallidus Chapman are found in pine
SAVANNASANDGRASSLANDSOFTHESOUTHEASTERN5NITED3TATES4HIEN 1971 ; Luer 1972 ;
Goldman et al. 2002b ). They have 2 n = 40 or 42 chromosomes, as does C. tuberosus
in this area, and all are self-compatible and interfertile with each other and with
C. tuberosus (Thien 1973 ; Goldman et al. 2002b, 2004 ). However, C. tuberosus has
larger flowers, about 4 cm across compared with about 2.5-3 cm in the other three
(Tables 8.1 and 8.5 ). According to van der Pijl and Dodson ( 1966 ) and Thien ( 1973 ),
a resulting difference in “fit” discriminates among prospective pollinators and pre-
vents gene flow between C. tuberosus and these species.
Flower size does not separate the more recently discovered midwestern species,
C. oklahomensis G. H. Goldman, from C. tuberosus (Tables 8.1 and 8.5 ). However,
C. oklahomensis is a hexaploid with 120 or 114 chromosomes and it blooms earlier
than C. tuberosus over the principal part of their remaining sympatric range. It is not
known to hybridize with either C. tuberosus or the other species of Calopogon
(Goldman 1995 ; Goldman et al. 2004 ).
Thien ( 1973 ) considers reproductive isolation among the small-flowered species
to be maintained primarily by differences in phenology and habitat. Although the
ranges and flowering dates of C. barbatus and C. multiflorus often overlap, C. mul-
tiflorus is different in its ecological preferences from C. barbatus and C. tuberosus
and is usually found in dryer situations (Goldman et al. 2004 ). The blooming seasons
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