Causes and consequences of individual variation: Linking state-dependent life histories to population performance

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 th..., 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., 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., # 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 t...