Biology ETDs


Zuo Wenyun

Publication Date



The laws of energy and material conservation are fundamental principles across various scales and systems. Based on the conservation laws, I derive several theoretical models to understand mechanisms behind the energy budget of ontogenetic growth and the pattern of the late Pleistocene extinction of megafauna in the Americas. First, I present a model, empirically grounded in data from birds and mammals, that correctly predicts how growing animals allocate food energy between synthesis of new biomass and maintenance of existing biomass. Previous energy budget models have typically been based on rates of either food consumption or metabolic energy expenditure. The model provides a framework that reconciles these two approaches and highlights the fundamental principles that determine rates of food assimilation and rates of energy allocation to maintenance, biosynthesis, activity, and storage. The model predicts that growth and assimilation rates for all animals should cluster closely around two canonical curves. Second, the previous model, which focuses on endotherms, has been extended to understand effects of temperature on the energy budget of ontogenetic growth of ectotherms. A tendency for ectotherms to develop faster but mature at smaller body sizes in warmer environments has been studied for decades, and is called the temperature size rule (TSR). It can be explained by a simple model in which the rate of growth or biomass accumulation and the rate of development or differentiation have different temperature dependence. The model accounts for both TSR and the less frequently observed reverse-TSR, predicts the fraction of energy allocated to maintenance and synthesis over the course of development, and the temperature independent growth efficiency. It also predicts that less total energy is expended when developing at warmer temperatures for TSR and vice versa for reverse-TSR. It has important implications for effects of climate change on ectothermic animals and also provides how selection may lead to the evolution of both TSR and reverse-TSR. Finally, based on mammalian life history and life history scaling relationships, an exploitation-extinction theory has been developed for the rate of human harvest in the disappearance of the Pleistocene megafauna in the Americas. The theory demonstrates that the added mortality of human harvest on populations need not be selective to produce a size-biased extinction. The variation in the adult natural instantaneous mortality rate and/or the maximum recruitment compensation at any body mass are main components determining the probability of extinction. The theory successfully predicts the shapes of the extinction probability curves for the late Pleistocene extinction in the Americas. It provides a theoretical basis to challenge a major criticism of the "overkill" theory that early Paleoindian hunters had to be extremely selective to have produced the highly size-biased pattern characteristic to the late Pleistocene extinction of megafauna in the Americas.

Project Sponsors

HHMI-NIBIB Interfaces grant and Scholarships from the Biology Department at UNM for their five years support on this work




energy budget, endotherm, ectotherm, late Pleistocene, the effect of temperature

Document Type


Degree Name


Level of Degree


Department Name

UNM Biology Department

First Committee Member (Chair)

West, Geoffrey B.

Second Committee Member

Moses, Melanie E.

Third Committee Member

Wearing, Helen