DOI: 10.5061/dryad.73n5tb31n
title: Data from: Causes and consequences of individual variation: Linking state-dependent life histories to population performance

description: The tradeoff between investment in current reproduction versus future
 survival is central to life-history theory, and long-lived, iteroparous
 mammals disproportionately favor their own survival. Previous work has
 demonstrated that adjustment of reproductive effort in long-lived mammals
 often occurs after parturition, owing to the greater cost of lactation
 relative to gestation. Under the right conditions, however, this
 difference in the relative costs of reproduction may also facilitate
 another, arguably less intuitive, strategy. Those conditions, which are
 relatively common among capital-breeding ungulates, include: (1) Females
 have the capacity to adjust gestation length; (2) Neonatal mortality
 occurs mostly during the first month of life and is inversely related to
 birth mass; and (3) The influence of birth mass on the probability of
 surviving the first month of life is stronger than the influence of autumn
 body mass on the probability of surviving the first winter of life. Under
 these circumstances, a female in poor condition in early spring could
 potentially increase fitness by delaying parturition and increasing
 investment in gestation, giving birth to a correspondingly larger neonate
 that has a higher probability of survival during its first month of life,
 and subsequently reducing investment in lactation to help rebuild somatic
 reserves. We developed and empirically parameterized a state-dependent
 model of maternal resource allocation that reflected this strategy. We
 tested the prediction that population growth would be faster when resource
 allocation was state-dependent than when gestation length was decoupled
 from dam condition and adjustment of reproductive investment was largely
 post-natal. Our results supported this prediction: state-dependent
 resource allocation by maternal females increased lambda by an average of
 4%, leading to larger population sizes after 30 years. Population growth
 was consistent across a range of winter severities, suggesting that
 state-dependent resource allocation could help buffer ungulate populations
 against climatic variation. Our results reveal a potentially general
 mechanism underpinning intraspecific variation in life-history strategies
 of long-lived, capital-breeding mammals, and suggest that such variation
 at the individual level can influence performance outcomes at the
 population level.
description: A detailed description of data-collection methods can be found in
 the following publications: Long, R.A., R.T. Bowyer, W.P.
 Porter, P. Mathewson, K.L. Monteith, S.L. Findholt, B.L. Dick, and J.G.
 Kie.  2016.  Linking habitat selection to fitness-related traits in
 herbivores: the role of the energy landscape.  Oecologia
 181:709-720. Long, R.A., R.T. Bowyer, W.P.
 Porter, P. Mathewson, K.L. Monteith, and J.G. Kie.  2014.  Behavior and
 nutritional condition buffer a large-bodied endotherm against direct and
 indirect effects of climate.  Ecological Monographs 84:513-532.
description: The two data files are in .txt format. The code is contained in
 .R files that require program R (or associated GUI like R Studio) to
 open.
description: # Data from: Causes and consequences of individual variation: Linking
 state-dependent life histories to population performance The file
 "Starkey_Elk_Data.txt" contains data for the subset of
 dam/juvenile pairs for which we had data on (1) birth mass of the neonate,
 (2) mass of the juvenile in the winter following birth, (3) nutritional
 condition of the dam both in the spring prior to parturition and the
 winter following. It was exploratory analyses of these data that suggested
 the bet-hedging strategy in the first place. The following meta-data
 pertain to columns in that dataset: * **Sex:** Sex of the neonate (female
 or male). * **Birth mass:** Birth mass of the neonate in kg. * **Birth
 date:** Birth date of the neonate. * **Julian birth date:** Julian date on
 which the neonate was born. * **Winter mass date:** Date on which mass of
 the neonate (now juvenile) was measured during capture operations in the
 winter following birth. * **Julian winter mass date:** Julian date on
 which the winter mass measurement was obtained. * **Winter mass:** Winter
 mass of the juvenile in kg. * **Rate of mass change:** Rate of mass change
 of the juvenile between birth and winter in kg/d. * **Change in BC:**
 Difference in nutritional condition (% ingesta-free body fat) of the dam
 between spring and winter. * **Spring BC:** Nutritional condition of the
 dam (% ingesta-free body fat) in spring. * **Add.** **To Gestation (kJ):**
 Estimated additional energy devoted to gestation by the dam (in kJ) based
 on the difference between actual birth mass of the neonate and the minimum
 birth mass of 12.6 kg. * **Invested in Lactation (kJ):** Estimated energy
 invested in lactation (in kJ) by the dam based on growth rate of the
 juvenile between spring and winter. * **Winter BC:** Nutritional condition
 of the dam (% ingesta-free body fat) in winter. The file
 "Calf-Survival.txt" is the encounter history file used to
 estimate survival of neonatal elk during the first four months of life as
 a function of their sex, birth mass, and growth rate. This encounter
 history was analyzed as presented using the known-fate model in Program
 MARK. The following meta-data pertain to columns in that dataset: *
 **ID:** Unique ID of each monitored elk calf. * **EncHist:** The encounter
 history for the calf, coded according to requirements for analysis using
 the known-fate model in Program MARK. * **Grp:** A required grouping
 variable, set to 1 in this dataset so that all calves were included as
 part of the same analysis. * **Sex:** Sex of each calf (1 = male, 0 =
 female). * **BM:** Birth mass of each calf in kg. * **Growth:** Estimated
 growth rate of each calf. The file "StateDependentModel_Code.R"
 contains annotated code for running the state-dependent bet-hedging model
 of maternal investment. The file "PostNatalModel_Code.R"
 contains annotated code for running the post-natal model of maternal
 investment.