A central goal in ecology is to predict population dynamics from demographic information. Based on the asymptotic population growth rate , calculated from a projection matrix model as a descriptor of the population dynamics, we analyze published data of 49 species of birds to determine how is influenced by variation in different demographic traits. Across species, the mean elasticity of the adult survival rate was significantly larger than the mean elasticity of the fecundity rate. The contribution of the fecundity rate to the population growth rate increased with increasing clutch size and decreasing adult survival rate, while the greatest contribution of adult survival rate occurred among long-lived species that matured late and laid few eggs. This represents a continuum from ''highly reproductive species'' at one end to ''survivor species'' at the other end. In addition, a high contribution of adult survival rate was found in some relatively long-lived species with early age at maturity (and a large clutch size) which was assumed to represent a bet-hedging strategy, i.e., producing a large number of offspring in some occasional good years. In a retrospective analysis, interspecific differences in the effects of actual temporal variation in adult survival rate and fecundity rate on the variability of were analyzed. These effects are expected to be large when the variance or the sensitivity of the trait is large. Because there was a negative relationship among species, both for the adult survival rate and the fecundity rate between the variability and the sensitivity of the trait, contribution of a trait to the variance in decreased with sensitivity. Similarly, within species, less temporal variation was found in traits with high elasticities than in traits with less contribution to . In some species, covariance among matrix elements also influenced the contribution of a demographic trait to . Monitoring schemes of bird demography should be designed in such a way that temporal variances and covariances among demographic traits can be estimated. Furthermore, it is important in such schemes to include data from a combination of traits that either have large sensitivities or high temporal variation.
A central goal in ecology is to predict population dynamics from demographic information. Based on the asymptotic population growth rate λ, calculated from a projection matrix model as a descriptor of the population dynamics, we analyze published data of 49 species of birds to determine how λ is influenced by variation in different demographic traits. Across species, the mean elasticity of the adult survival rate was significantly larger than the mean elasticity of the fecundity rate. The contribution of the fecundity rate to the population growth rate increased with increasing clutch size and decreasing adult survival rate, while the greatest contribution of adult survival rate occurred among long‐lived species that matured late and laid few eggs. This represents a continuum from “highly reproductive species” at one end to “survivor species” at the other end. In addition, a high contribution of adult survival rate was found in some relatively long‐lived species with early age at maturity (and a large clutch size) which was assumed to represent a bet‐hedging strategy, i.e., producing a large number of offspring in some occasional good years. In a retrospective analysis, interspecific differences in the effects of actual temporal variation in adult survival rate and fecundity rate on the variability of λ were analyzed. These effects are expected to be large when the variance or the sensitivity of the trait is large. Because there was a negative relationship among species, both for the adult survival rate and the fecundity rate between the variability and the sensitivity of the trait, contribution of a trait to the variance in λ decreased with sensitivity. Similarly, within species, less temporal variation was found in traits with high elasticities than in traits with less contribution to λ. In some species, covariance among matrix elements also influenced the contribution of a demographic trait to λ. Monitoring schemes of bird demography should be designed in such a way that temporal variances and covariances among demographic traits can be estimated. Furthermore, it is important in such schemes to include data from a combination of traits that either have large sensitivities or high temporal variation.
Summary 0[ In order to compare spatial and temporal variation in the demography of a meta! population of house sparrows living on four islands o} the coast of Northern Norway\ we computed the asymptotic population growth rate "l# for three transitions between years\ using a projection matrix model[ 1[ The mean growth rate of the metapopulation was positive "l 0=94#[ 2[ Large variation was found in space and time in the asymptotic growth rate[ Even though the standard deviations of the estimates were large\ l was signi_cantly greater than 0 on one island in 1 out of 2 years[ In contrast\ l signi_cantly less than 0 occurred on an island on _ve occasions[ 3[ Decomposition of the magnitude of the spatial and temporal components of l showed that one year "0884# had a particularly negative impact on l[ In contrast\ one island had a great positive e}ect[ 4[ These di}erences in l were most closely related to variation in the juvenile survival rate and in the fecundity rate\ which\ in turn\ was closely related to variation both in space and time in the proportion of the eggs that produced a~edgling[ 5[ As expected from the large spatio!temporal variation in l\ the sensitivities and the elasticities of l to variation in the di}erent elements in the projection!matrix also di}ered both in space and time[ When l was small\ it was most in~uenced by variation in adult survival rate[ In contrast\ for large l\ it was most sensitive to variation in the recruitment rate[ 6[ We suggest that conditions during the breeding season determine whether a popu! lation acts as a source or sink in this temperate small passerine metapopulation\ and that the ratio of juveniles to adults can be used to characterize populations as sources or sinks[ 7[ These results demonstrate large variation in space and time in the demography of a small passerine metapopulation[ These di}erences result from a combination of regional e}ects on the whole metapopulation\ and factors that occur at one particular island in a single year[ Key!words] demography\ elasticity\ house sparrow\ metapopulation\ population growth rate\ sensitivity[ Journal of Animal Ecology "0888# 57\ 517Ð526
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