Table 1 .

Characteristics of population-based and individual-based approaches

Approach
	Population based	Individual based
Lifetime fitness	Only possible for semelparous species	Iteroparous and semelparous species
Age	Often impossible or poorly accurate. Where possible, estimated indirectly from biomarkers	Directly estimated in all cases
Social network	Not possible	Measurable
Resource distribution and allocation	Partially possible if different genotypes can be associated to different allocation strategies	Measurable
Phenotypic plasticity	Changes in population means and variances. Individual plasticity not measurable (often lower than the population range)	Changes in population and individual means and variances
Repeatability	Only for population averages	Measurable
Interstage effects	Population level effects. Prone to ecological fallacy	Measurable
Intergenerational effects	Population level effects. Prone to ecological fallacy	Measurable
Behaviour	General patterns. Prone to ecological fallacy	Animal personalities and behavioural syndromes
Physiology	General patterns. Prone to ecological fallacy	Within-individual dynamics
Cost and workload	Relatively low	High
Versatility	Low	High

Comparison of measurable traits and effects between population-based and individual-based approaches on parasite-related research