MAPPING THE FUNDAMENTAL NICHE: PHYSIOLOGY, CLIMATE, AND THE DISTRIBUTION OF A NOCTURNAL LIZARD

Abstract

The fundamental niche can be viewed as the set of conditions and resources that allow a given organism to survive and reproduce in the absence of biotic interactions. Quantitative descriptions of the environmental variables with which organisms are asso- ciated are becoming common with the advent of geographic information systems (GIS). Although such descriptive approaches to the niche are useful for interpolating species distributions, they implicitly incorporate biotic interactions and therefore do not represent the fundamental niche. A mechanistic understanding of the fundamental niche, when com- bined with GIS data, can provide us with greater insight into the causes of distribution and abundance, a solid foundation for exploring the role of biotic interactions, and greater confidence in extrapolating to novel circumstances such as climate change and species introductions. We apply such a mechanistic approach to study the climatic component of the fundamental niche of a nocturnal lizard, Heteronotia binoei, across an entire continent. We combine physiological measurements of this species (thermal requirements for egg development, thermal preferences and tolerances, metabolic and evaporative water loss rates), and high-resolution climatic data for the Australian continent (air temperature, cloud cover, wind speed, humidity, and radiation), with biophysical models to calculate the cli- matic component of the fundamental niche of this lizard and map it onto the Australian landscape at high resolution. We also use this approach to predict the effects of a mild global warming on the degree-days in the soil for egg development and the potential for aboveground activity of the study organism.