Physiological constraints on geographic distributions of species

Abstract

Understanding species’ geographic distributions constitutes a major priority in biodiversity science, biogeography, conservation biology, and evolutionary biology. Species’ geographic distribution are shaped by abiotic (climate) factors, biotic (e.g., resources for survival, competitors) factors, and dispersal factors. In this dissertation, I have used physiological parameters measured in the laboratory under controlled conditions to understand constraints on species’ distributions. In my first chapter, I explored how parameters documented in detailed physiological studies could be used to understand the constraints on the geographic distribution of Spansh moss (Tillandsia usneoides). I used four physiological parameters of Spanish moss that circumscribe optimal conditions for the species for survival and growth. Using high-temporal-resolution climate data, optimal and non-optimal areas in the species’ geographic distribution could be identified. My results indicated that Spanish moss survives under suboptimal conditions for few days in many parts of its geographic distribution, although numbers of days differed for various physiological parameters. Continuing from the first chapter’s results, I investigated whether optimal physiological parameters are available for Spanish moss populations specifically during the flowering/fruiting season. Flowering/fruiting season is an important life stage for plant species, as it is during this period that the plant produces new recruits for maintaining populations. Results in this chapter indicated that flowering/fruiting period of Spanish moss frequently is under suboptimal conditions, but that the flowering period tends to be tuned such that Spanish moss populations receive at least one optimal physiological parameter, and generally the parameter emphasized is that of minimum temperature. In the third and final chapter, I analyzed 33 anuran species for the critical maximum temperature parameter (CTmax). CTmax plays a crucial role in larval stages of anuran species. I evaluated whether any part of the species’ distribution experiences CTmax, and whether this CTmax is being experienced more often in recent years as a consequence of warming climates. My analysis supported the idea that 70% of the anuran species experienced CTmax at some point over a 22-year time period. However, only a single species saw CTmax being experienced across its distribution more often through time.