Appendix S1: Simulation of Pradel model with low probability of initial detection
Methods.
We used hypothetical capture histories to test the effect of low probabilities of initial
detection on the projections of λ from the Pradel (1996) model. Our simulations
spanned 15 years with an initial population of 300 individuals. We used a constant
probability of survival (0.85) for all simulations. We added individuals to the
population in each year equal to the expected number of individuals that were
removed from the population (i.e., λ=1). Resighting probability (p) was modeled
either as constant (p = 0.75) or temporally variable (mean = 0.75; var = 0.01).
Probability of initial detection was modeled as low (0.3) or equal to resighting
probability. We created our capture histories by generating a matrix of random
numbers in MATLAB and used these numbers to create our capture histories in
EXCEL.
Simulated capture histories were analyzed in MARK using the Pradel model to
estimate survival and λ (White & Burnham, 1999). Models were run that
incorporated both constant and time-dependent survival, resighting probability, and λ.
We used AIC to select the most parsimonious models and recorded the projected
value of λ for the selected model. We calculated the sample mean and standard error
of λ for each combination of initial and resighting probabilities.
Results
The most parsimonious model for each simulation was a model with constant
survival, time-dependent resighting probability and a single value of λ. Projections of
λ were relatively consistent among our models (Fig. 1). Models with decreased
probabilities of initial detection were slightly negatively biased, on average the
estimates of λ were 0.003 lower than models that had equal probabilities of initial and
subsequent detection were equal. However, all estimates were within one standard
error and paired t-tests that compared projections from models with the same
resighting probabilities were not significant (P > 0.25). From these results we can
conclude that reduced probability of initial detection had little impact on estimated
growth rate.
Supplemental References
Pradel, R. (1996) Utilization of capture-mark-recapture for the study of recruitment
and population growth rate. Biometrics, 52, 703-709.
White, G.C. & Burnham, K.P. (1999) Program MARK: survival estimation from
populations of marked animals. Bird Study, 46, 120-139.
Figure S1 Sample mean and (± 1SE) of projected λ from 10 replications of the Pradel
(1996) model. Hypothetical capture histories were generated with both equal or low
probabilities of initial detection and constant or variable resighting probabilities.
1.02
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