Tribe Calypsoeae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 121

pollinated individuals, were more likely to flower the following year than those with
many fruits: 23% did so compared to only 3% of those with over 10 fruits (Snow
and Whigham 1989 ). Plants that produced less than 10 fruits also showed a reduc-
tion in leaf area and corm size the following season compared to nonfruiting plants,
and naturally pollinated plants flowered on average only every 2.5 years. The per-
centage of plants blooming varied from 8.9% to 23% (Whigham and McWethy
1980 ), but the number of flowers produced per inflorescence remained more or less
constant (Whigham and O'Neill 1991 ). Further studies of seasonal allocation pat-
terns and photosynthetic characteristics of Tipularia have verified the importance of
carbohydrate storage in the corm for future growth and reproduction (Zimmerman
and Whigham 1992 ; Tissue et al. 1995 ).
Other researchers have reported that in addition to plant size, environmental con-
ditions, such as variation in the availability of soil water or protective snow cover,
affect flowering (Firmage and Cole 1988 ; Wells and Cox 1989 ). Whigham and
O'Neill ( 1991 ), however, found no clear association between flowering and any
climatological factor. They believe that differences in flowering and fruiting are
related chiefly to costs associated with sexual reproduction. Recovery from repro-
ductive costs may, however, have been prolonged by other factors (Snow and
Whigham 1989 ; Whigham 1990 ).
Reproductive success was, for example, affected by herbivory. Whigham and
O'Neill ( 1988 ) reported that white-tailed deer ( Odocoileus virginianus Zimmerman)
are important predators in Maryland and commonly remove the whole leaf. Most
plants usually had their single leaf eaten once every 2 or 3 years. Although mainte-
nance of a large part of the nutrient stores below ground may allow the plants to
withstand relatively high levels of herbivory, complete and partial experimental
defoliations resulted in a reduction in future growth and sexual reproduction; even
higher costs were associated with the combined effects of simulated herbivory and
fruit production (Whigham 1990 ,).
Immediate reproductive gains in species that are subject to heavy predation like
Tipularia may be more important than future fitness (Whigham and O'Neill 1988
and references therein). The production of 6-8 fruits per year probably represents a
compromise between the chances of immediate and future reproductive success.
However, additional data on survivorship and age-specific fecundity of both parents
and clonal descendents are needed to evaluate the possible advantages of reproduc-
tion early in the life cycle and the trade off in fitness between the numbers of fruits
produced per season and the number of reproductive seasons (Cole 1954 ; Schaffer
and Gadgil 1975 ; Snow and Whigham 1989 ).
In addition to sexual reproduction, fruit set had an effect on asexual reproduc-
tion, which, in turn, could affect fitness by attracting pollinators to neighboring
inflorescences of the same genet (e.g., Firmage and Cole 1988 ) and by dispersing
the risk of mortality over a larger area (e.g., Cook 1979 ). Plants frequently gener-
ated one leaf each year. Those that branched produced two leaves with the subse-
quent degeneration of connecting corms (Snow and Whigham 1989 ). Branching
was correlated with the supply of available resources and was observed in 75% of
the plants with no fruit, 50% of those with less than 10 fruits, and 34% of those with