 | Shefferson, R.P. 2002. Dormancy and survival in rare terrestrial orchids. Pp. | |
| 53-64 in P. Kindlmann, J.H. Willems, and D.F. Whigham, editors. Trends and fluctuations and underlying mechanisms in terrestrial orchid populations. Backhuys Publishers, Leiden, the Netherlands |
Abstract Seemingly high variability in orchid populations is often due to a
phenomenon called 'dormancy', in which no photosynthetic material sprouts in a
year. Dormancy can cause underestimation of survival through its superficial
resemblance to mortality. A probabilistic demographic model, such as that used in
mark-recapture studies, may be best able to estimate survival in the face of this
confounding life history phenomenon. We tested the effects of dormancy on
estimation of survival using data on 263 small yellow lady's slippers, Cypripedium
calceolus var. parviflorum (Salisb.) Fernald, in Lake Co., Illinois, USA, monitored
from 1994 to 2000. Resighting histories were created of two-, three-, four-, five-, six-,
and seven-year lengths starting from 1994, to test the effects of inclusion of extra
years of data on survival estimation. Conventional demographic estimation
approaches, involving correcting for dormancy where it must exist but not where it
might, were then compared to the results of mark-recapture analyses conducted on
the same datasets. The results suggest that conventional approaches
underestimate survival, at times greatly. Conventional approaches yielded highly
variable estimates for the same years in all dataset lengths, ranging from 0.383 to
0.882 for 1994, while mark-recapture methods yielded consistent estimates for all
dataset lengths, ranging from 0.796 to 0.844 in 1994. Mean survival was consistently
lower for conventional than for mark-recapture methods (0.765 vs. 0.845 in the seven-
year dataset). Mark-recapture methods were also consistent in estimation of
dormancy, with a low estimate of 0.370 for the three-year dataset and a high
estimate of 0.402 for the seven-year dataset. The mark-recapture approach appears
preferable to conventional demographic estimation approaches, as it yields
consistent, relatively unbiased estimates of survival. This may increase accuracy in
population viability studies, which may suggest higher extinction likelihoods with
more variable data.
Book copyright notice: © 2002 by Backhuys Publishers, Leiden, the Netherlands
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Copyright 2009 Richard P. Shefferson. All rights reserved.
Shefferson 2002
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