Wednesday, August 6, 2008: 2:50 PM
202 B, Midwest Airlines Center
Background/Question/Methods
In his influential 1967 paper, ‘Why mountain passes are higher in the tropics’ Janzen proposed that there is a larger difference in climate experienced between high and low elevation species in the tropics compared with those in temperate zones. An important assumption of this hypothesis is that range boundaries are maintained by differences in physiological tolerances between species. I test the hypothesis that species ranges are maintained by differences in physiology for three species of land snail (family Helicarionidae) endemic to rainforests in Northeastern Australia. These snails are commonly known as semi-slugs due to their greatly reduced shell, and thus are presumably sensitive to environmental conditions. I measured dessication resistance, critical thermal minimum (CTmin), and critical thermal maximum (CTmax) across elevational and latitudinal gradients for a species with a broad elevational range (Fastosarion brazieri, n=25), a high elevation species (Thularion semoni, n=20), and a low elevation species (Parmacochlea fisheri n=22). I then mapped where each species can potentially occur based on their ecophysiology presently, and considering future climate change. I compared these estimates with range maps generated using a species distribution model.
Results/Conclusions
There were significant differences in dessication rates between the three species. Desiccation was not signifcantly related to body size, elevation or latitude. There were significant differences in the CTmax for all three species, but not significant differences in CTmin. There was considerable overlap between the three species potential ranges based upon physiology. Ranges estimated with the species distribution model have significantly less overlap. When future warming is considered in the physiological model T. semoni may have its range truncated and be replaced by P. fisheri particularly in the far north. The species distribution model predicted considerable range contraction for all three species. This research demonstrates how ecophysiology can be combined with spatial environmental data to elucidate what factors determine species ranges, and how ranges may change in the future. These results highlight the importance of mechanistic models in estimating climate change impacts rather than relying on species distribution models alone.
In his influential 1967 paper, ‘Why mountain passes are higher in the tropics’ Janzen proposed that there is a larger difference in climate experienced between high and low elevation species in the tropics compared with those in temperate zones. An important assumption of this hypothesis is that range boundaries are maintained by differences in physiological tolerances between species. I test the hypothesis that species ranges are maintained by differences in physiology for three species of land snail (family Helicarionidae) endemic to rainforests in Northeastern Australia. These snails are commonly known as semi-slugs due to their greatly reduced shell, and thus are presumably sensitive to environmental conditions. I measured dessication resistance, critical thermal minimum (CTmin), and critical thermal maximum (CTmax) across elevational and latitudinal gradients for a species with a broad elevational range (Fastosarion brazieri, n=25), a high elevation species (Thularion semoni, n=20), and a low elevation species (Parmacochlea fisheri n=22). I then mapped where each species can potentially occur based on their ecophysiology presently, and considering future climate change. I compared these estimates with range maps generated using a species distribution model.
Results/Conclusions
There were significant differences in dessication rates between the three species. Desiccation was not signifcantly related to body size, elevation or latitude. There were significant differences in the CTmax for all three species, but not significant differences in CTmin. There was considerable overlap between the three species potential ranges based upon physiology. Ranges estimated with the species distribution model have significantly less overlap. When future warming is considered in the physiological model T. semoni may have its range truncated and be replaced by P. fisheri particularly in the far north. The species distribution model predicted considerable range contraction for all three species. This research demonstrates how ecophysiology can be combined with spatial environmental data to elucidate what factors determine species ranges, and how ranges may change in the future. These results highlight the importance of mechanistic models in estimating climate change impacts rather than relying on species distribution models alone.
