DOI: 10.5061/dryad.kkwh70s58
title: Slower environmental cycles maintain greater life-history variation within populations

description: Populations in nature are comprised of individual life histories, whose
 variation underpins ecological and evolutionary processes. Yet the forces
 of environmental selection that shape intrapopulation life-history
 variation are still not well understood, and efforts have largely focused
 on random (stochastic) fluctuations of the environment. However, a
 ubiquitous mode of environmental fluctuation in nature is cyclical, whose
 periodicities can change independently of stochasticity. Here we test
 theoretically-based hypotheses for whether shortened (‘Fast’) or
 lengthened (‘Slow’) environmental cycles should generate higher
 intrapopulation variation of life history phenotypes. We show, through a
 combination of individual-based modelling and a multi-generational
 laboratory selection experiment using the tidepool copepod Tigriopus
 californicus, that slower environmental cycles maintain higher levels of
 intrapopulation variation. Surprisingly, the effect of environmental
 periodicity on variation was much stronger than that of stochasticity.
 Thus, our results show that periodicity is an important facet of
 fluctuating environments for life-history variation.
description: Two data files “EvolExp_xxxx_data.csv” contain life history trait
 measurements from Tigriopus californicus laboratory experiment. The two
 share the first four common columns: “Source_pop”, “Treatment”,
 “Treat_rep”, and “Ind_rep”. “Source_pop” denotes
 arbitrary incubator containers that were used for pre-experiment rearing
 of stock populations, but was not used for analyses.
 “Treatment” is categorial disturbance regime administered to
 replicate populations. During the data collection phase, “H” stood for
 High frequency but is subsequently indexed as “Fast” for a more intuitive
 term; “L” stood for Low frequency but is subsequently indexed as “Slow”
 for a more intuitive term; “S” is “Stochastic”. Treatments indexed with
 “_C” were arbitrary ‘controls’ but were irrelevant for analyses in this
 paper; they are included for completeness. “Treat_rep”
 is numerical replicate population index under Treatments.
 “Ind_rep” is numerical replicate individual index measured in a
 population. Subsequent columns, for both
 “EvolExp_xxxx_data.csv” files, contain event timing records.
 “EvolExp_fecundity_data.csv” contains Date+AM/PM records of productions of
 clutches of juveniles. “EvolExp_maturity_data.csv” contains Date records
 of appearances of gravid females in mating wells. See main text for
 detailed descriptions of measurement methods, and associated .R scripts
 for how analyses using event records were coded. R
 Code: “EvolExp_results_dataclean.R” reproduces how life
 history event record data were cleaned, processed, and
 summarized. “EvolExp_results_means.R” reproduces
 summary of intrapopulation means of life history traits. Dependent on
 “~/dataclean.R”. “EvolExp_results_variances.R”
 reproduces summary of intrapopulation variances of life history traits.
 Dependent on “~/dataclean.R”.
 “permutation_intrapopvar_pvals.R” reproduces Monte Carlo
 permutation method used to test for differences in intrapopulation
 variances of life history traits. Dependent on “~/dataclean.R”.
 “ABM_full_final.R” reproduces full Agent-Based Model simulations,
 including plots of mean and variance trajectories of realizations,
 statistical analyses on endpoints, and plots of demographic dynamics under
 the four environmental regime scenarios.