Demographic rates are shaped by the interaction of past and current environments that individuals in a population experience. Past environments shape individual states via selection and plasticity, and fitness-related traits (e.g. individual size) are commonly used in demographic analyses to represent the effect of past environments on demographic rates. We quantified how well the size of individuals captures the effects of a population's past and current environments on demographic rates in a well-studied experimental system of soil mites. We decomposed these interrelated sources of variation with a novel method of multiple regression that is useful for understanding nonlinear relationships between responses and multicollinear explanatory variables. We graphically present the results using area-proportional Venn diagrams. Our novel method was developed by combining existing methods and expanding upon them. We showed that the strength of size as a proxy for the past environment varied widely among vital rates. For instance, in this organism with an income breeding life history, the environment had more effect on reproduction than individual size, but with substantial overlap indicating that size encompassed some of the effects of the past environment on fecundity. This demonstrates that the strength of size as a proxy for the past environment can vary widely among life-history processes within a species, and this variation should be taken into consideration in trait-based demographic or individual-based approaches that focus on phenotypic traits as state variables. Furthermore, the strength of a proxy will depend on what state variable(s) and what demographic rate is being examined; that is, different measures of body size (e.g. length, volume, mass, fat stores) will be better or worse proxies for various life-history processes.
Individual soil mite data
Indiv is a data frame stored in "Individual soil mite data.Rdata" which contains the following columns relevant to the sampling experiment.
*trt* has levels that represent the food treatment: T1 (constant), T2 (famine), T3 (declining), T4 (fluctuating)
*pop.ID* is a unique identifier for each of 2 replicate populations per treatment.
*date* is the date when a sampling event began
*stage* is the life stage of the individual at the beginning of the 24 hour sampling period.
*ind.ID* is a unique identifier of an individual observed for a sampling period.
*s24* is 1 if the individual was alive after 24 hours, 0 if it was dead, or NA if it was lost.
*t24* indicates transiton to either the same stage as the beginning of the sampling period (initial stage) the next, or in between stages (quiescent).
*f24* is the number of eggs laid in the 24 hour sampling period.
*l0* is the body length at the beginning of the sampling period (mm).
*l24* is the body length at the end of the sampling period (mm).
*density* is the approximate value of body lenghths summed over the population on the date of sampling (see apendix S2 from publication) (mm).
*supply* is food given divided by density on the date of sampling (mg/mm).
*food* is the amount of food given to the population on that date (mg).
*density.s* is the density scaled to have mean 0 and variance 1.
*supply.s* is the supply scaled to have mean 0 and variance 1.
*l0.s* is body length scaled to have mean 0 and variance 1.
*day* is the number of days since the start of the experiment.
Egg size from sampling
eggdat is a data frame stored in "Egg size from sampling.Rdata" contianing measurments of individual eggs from sampled females.
*egg.ID* is a unique identifier for an egg.
*pop.ID*, *date*, *trt*, *s24*, *f24*, *l0*, *l0.s*, *density*, *density.s*, *supply*, and *supply.s* are the same as in the individual data in another file.
*fem.ID* is the same as indiv.ID above for the mother of the eggs.
*esize* is the size of the sampled egg (mm).
Population Counts with Predictors
Pop.counts is a data frame stored in "Population Counts with Predictors.Rdata" containing stage specific counts from both sampling and counting populations.
*date*, *trt*, *pop.ID*, *density*, *supply*, *food*, *density.s*, *supply.s*, and *day* are the same as in the individual data in another file.
*pop.type* is the type of the population counting or sampling (see appendix S1 for details).
*eggtot*, *larvaetot*, *prottot*, and *trittot* are are *4 times* the number of soil mites in a given stage (egg, larvae, protonymph, tritoonymph) counted in a quarter of the tube where the population was living (see appendix S1 for details).
*maletot* and *femaletot* are the number of adult mites counted in the entire population (see appendix S1 for details).