ESTIMATION OF TEMPORAL VARIABILITY OF SURVIVAL IN ANIMAL POPULATIONS

Temporal variation of demographic characteristics for animal populatio ns is of interest to both ecologists and biological modelers. The stan dard deviation of a series of estimated parameter values (e.g., estima ted population size) or some function thereof (e.g., log of the estima ted parameters) is commonly used as a measure of temporal variability. These measures of temporal variation overestimate the true temporal v ariation by not accounting for sampling variability inherent to the es timation of unknown population parameters. Using a variance-components approach to partitioning the total variability of an estimated parame ter, we demonstrate the ease with which sampling variation can be remo ved from the observed total variation of parameter estimates. Estimate s of temporal variability of survival are given after removal of sampl ing variation for three bird species: the federally listed Roseate Ter n (Sterna dougallii), Black-capped Chickadees (Parus atricapillus), an d Mallard ducks (Anas platyrhynchos). Sampling variation accounted for the majority of the total variation in the survival estimates for nea rly all of the populations studied. Substantial differences in observe d significance levels were observed when testing for demographic diffe rences in temporal variation using temporal variance estimates adjuste d and unadjusted for sampling variance.