THE INFLUENCE OF FOOD AVAILABILITY ON LIFE-HISTORY TRAJECTORIES
Open Access
- Author:
- Dinsmore, Carli
- Graduate Program:
- Ecology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- September 23, 2019
- Committee Members:
- David Andrew Miller, Thesis Advisor/Co-Advisor
Julian D Avery, Thesis Advisor/Co-Advisor
Tracy Langkilde, Committee Member
Jason Philip Kaye, Program Head/Chair - Keywords:
- Cohort
condition
body size
growth
reptiles
von Bertalanffy
Thamnophis sirtalis
survival
reproduction
garter snake
climate change
environmental variation - Abstract:
- Variation in environments, particularly in food availability, can strongly influence life-history traits, and these effects may be immediate or delayed. In order to maximize fitness, organisms must differentially allocate energy among multiple life-history traits such as growth, survival and reproduction, and decisions regarding trade-offs may differ between males and females. Body size is a fundamental component of an organism’s life-history, and for indeterminately growing species, lifelong trade-offs may occur between increasing body size or nutrient storage, survival and reproduction. For most reptiles, little is known about actual demographic rates and life-history variation, despite geographically and taxonomically widespread declines in these species over recent decades. Using 17 years of capture-mark-recapture data, we investigate the relationship between demographic parameters and environmental variation to quantify patterns in life-history traits for multiple populations of garter snakes. We evaluated the effect of food availability on key traits including somatic growth, survival, reproduction and body condition, which ultimately drive population demography. We analyzed data on growth in snout-vent length (SVL) and body condition (measured as the residual of the regression of log-transformed mass on SVL) for two species: the western terrestrial garter snake, Thamnophis elegans, and the common garter snake, Thamnophis sirtalis from five sites surrounding Eagle Lake in Lassen County California. We found that the impact of food availability on structural growth and nutritional reserves is largely context dependent, and patterns of energy allocation may shift with resource availability. Crucially, we found that the influence of food availability early in life is a critical determinant of lifetime patterns of growth. For both T. elegans and T. sirtalis, individuals from nutritionally deficient early-life cohorts increased structural body size more rapidly than individuals from high nutrition cohorts when food was abundant later in life. The results of our study suggest that spatial and temporal variation in traits such as growth and body condition are a result of the complex integration of food availability throughout the lifetime of animals within wild populations. This study highlights the importance of assessing the long-term response in life-history traits to differing environmental conditions using multiple populations to ensure robust estimates for predicting future shifts in population demographic processes.