Avian Life History Variation and Contribution of Demographic Traits to the Population Growth Rate

Abstract

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.

Adélie penguin (Pygoscelis adeliae) survival rates and their relationship to environmental indices in the South Shetland Islands, Antarctica

“…Consequently, seabirds typically exhibit low variability in adult survival rates (Saether and Bakke 2000). During a period of population decline among Adélie penguins in the South Shetland Islands (Lynch et al 2008;Trivelpiece et al 2011), survival rates of banded Adélie penguins declined among juveniles, while both juvenile and adult age classes were characterized by strong variability, ranging from survival rates from\30 to[70 %.…”

Biologia reprodutiva de Tyrannus savana (Aves, Tyrannidae) em cerrado do Brasil Central

“…Calculamos a taxa de fecundidade (Tf) anual das fêmeas para cada ano de 2003 a 2007 através da fórmula: nº de filhotes eclodidos de todas as ninhadas de cada ano/nº de fêmeas presentes ( Aguilar et al 1999, Saether & Bakke 2000. Calculamos a média ± EP de todas as estações reprodutivas.…”

“…Esta baixa taxa de eclosão pode ser devida à predação de ninhos na fase de incubação ou infertilidade dos ovos, mas não devido ao abandono dos ninhos, o qual foi raro. A taxa de fecundidade anual representa a capacidade fisiológi-ca e individual de cada fêmea da espécie em deixar descendentes (Saether & Bakke 2000). A taxa de fecundidade encontrada para T. savana (1,5 filhotes/fêmea) foi superior à média encontrada para E. chiriquensis (1,1) (Medeiros & Marini 2007) e E. cristata (0,9) (Marini et al 2009), e muito maior que a de N. fasciata (0,31) (Duca, 2007) na mesma área.…”

Two decades of cumulative impacts to survivorship of endangered California condors in California

“…Lead accounted for 14% (5/35) of deaths with known cause in immature condors (b 6 years old) and the majority of deaths in the adult age class (≥ 6 years; 70%, 7/10). Because mortality factors leading to the greatest numbers of adult deaths generally have the largest influence on overall rates of avian population change (Saether and Bakke, 2000), lead poisoning ranks highest among threats to the population. Since initiation of the reintroduction program in 1992 through 2009, lead poisoning was also the most important mortality factor for immature and adult condors in the combined free-ranging populations with 26% of juveniles and 67% of adults dying as a result of lead toxicosis (Rideout et al, 2012).…”