‘How to…’ paper
Quantifying individual variation in behaviour: mixed-effect modelling approaches
- Growing interest in proximate and ultimate causes and consequences of between- and within-individual variation in labile components of the phenotype – such as behaviour or physiology – characterizes current research in evolutionary ecology.
- The study of individual variation requires tools for quantification and decomposition of phenotypic variation into between- and within-individual components. This is essential as variance components differ in their ecological and evolutionary implications.
- We provide an overview of how mixed-effect models can be used to partition variation in, and correlations among, phenotypic attributes into between- and within-individual variance components.
- Optimal sampling schemes to accurately estimate (with sufficient power) a wide range of repeatabilities and key (co)variance components, such as between- and within-individual correlations, are detailed.
- Mixed-effect models enable the usage of unambiguous terminology for patterns of biological variation that currently lack a formal statistical definition (e.g. ‘animal personality’ or ‘behavioural syndromes’), and facilitate cross-fertilisation between disciplines such as behavioural ecology, ecological physiology and quantitative genetics.