Conclusions
This study highlights the importance of integrating different approaches
used to study life-history variation in order to gain a better
understanding of the ecological causes and ultimately the evolutionary
consequences of variation in the tempo of life-history strategies (i.e.
pace-of-life). By combining an analysis of individual variation in
life-histories based upon individual projection matrices, along with
age- and density-dependent survival and reproduction models, we were
able to understand the genetic and demographic sources of individual
variation in generation time within a metapopulation of house sparrows.
Furthermore, we show how competitive regimes can affect the mean age at
reproduction, supporting predictions from classic life-history theory
predicting that density dependence is a key determinant in shaping the
pace-of-life. Because generation time determines the speed of
evolutionary responses to selection, detailed understanding of how
ecological dynamics affect the mean age at reproduction is therefore a
key to predicting evolutionary adaptations to environmental change.