Decomposing the variation in population growth into contributions from multiple demographic rates

Abstract

Summary1. The decomposition of variation in population growth into the relative contributions from different demographic rates has multiple uses in population, conservation and evolutionary biology. Recent research has favoured methods based on matrix models termed 'life-table-response experiments' or more generally 'the retrospective matrix method', which provide an approximation of a complete demographic decomposition. The performance of the approximation has not been assessed. 2.We compare the performance of the retrospective matrix method to a complete decomposition for two bighorn sheep populations and one red deer population. 3. Different demographic rates make markedly different contributions to variation in growth rate between populations, because each population is subject to different types of environmental variation. 4. The most influential demographic rates identified from decomposing observed variation in population growth are often not those showing the highest elasticity. Consequently, those demographic rates most strongly associated with deterministic population growth are not necessarily strongly associated with temporal variation in population growth. 5. The retrospective matrix method provides a good approximation of the demographic rate associated most strongly with variation in population growth. However, failure to incorporate the contribution of covariation between demographic rates when decomposing variation in population growth can lead to spurious conclusions.

Metapopulation viability of a globally endangered gazelle on the Northeast Qinghai–Tibetan Plateau

“…Additionally, covariation between vital rates may have substantial effects on the outcome of demographic models, and it is necessary to account for (Evans and Holsinger, 2012;Morris and Doak, 2002). Roughly one third of all variation in population growth rate in three ungulate populations could be attributed to covariation between demographic rates (Coulson et al, 2005). In this study, vital rates accounted for much more of the variation in subpopulation growth rates than covariation between these rates.…”

“…Several methods have been used to identify these demographic contributions in ungulates (Coulson et al, 2005;Gaillard et al, 2000). Our estimates suggest that OFY accounts for more of the variation in population size than other demographic rates.…”

“…However, in the case of Przewalski's gazelle, there is incomplete demographic information on the fate of each individual, meaning that we could not include ideal covariation among vital rates in our models. Failure to take into account the contribution of covariation between vital rates to population dynamics can yield misleading conclusions which holds important implications for conservation (Coulson et al, 2005;Morris and Doak, 2002). Therefore, one goal is to collect more detailed census data in future and use other methods, such as structured demographic accounting and the retrospective matrix method, to decompose the variation in population growth rate into contributions from multiple demographic rates (Coulson et al, 2005).…”

Natural selection and population dynamics

“…Elasticity analysis [14] is an effective tool for evaluating the relative importance of different phenotypic traits on population growth rate through their effects on survival and reproduction. Some generalisations that are relevant to particular taxa should emerge from such analyses, bearing in mind that dissimilar ecological circumstances can alter the influence of particular traits even within a single species [15].…”

Consecutive cohort effects driven by density-dependence and climate influence early-life survival in a long-lived bird

“…Environmentally induced responses are often complex and lead to covariance processes within demographic traits [51,52]. For instance, a decrease in density dependence during rearing increased not only survival rates of gulls (our study), but also the reproductive performance of breeders [22].…”