| Glacial - interglacial cycles have a pronounced impact on species distributions and genetic structure. Many species shift their distributions to lower latitudes and altitudes during the colder glacial periods and expand northwards and up the elevation during warmer interglacial periods. Some species however are capable of adapting to changing environment which allows them to persist in place despite climatic changes. I explored how climatic changes after the last glacial maximum (LGM) effected two species inhabiting the deserts of western North America: one mammal (Chisel-toothed Kangaroo Rat, Dipodomys microps) and one reptile (Desert Horned Lizard, Phrynosoma platyrhinos). I used a methodology of transferal modeling which is commonly used to predict species responses to future climatic changes. I approximated the species current and LGM distribution by modeling their current climatic niches, which I then projected onto the climatic conditions of the LGM. The accuracy of the transferal models, however, is dependent on several conceptual and algorithmic assumptions. Therefore, I compared the models with the phylogeographic structure of each species as phylogeographic signals imprinted in species genomes can inform us about species past geographic and demographic processes. The transferal models predicted that the northern parts of the species current ranges were unsuitable during the LGM and that both species could have persisted only within the more southern deserts where climatic conditions remained suitable. The phylogeographic analyses, however, suggested that D. microps did not experience large scale distributional changes in response to the warming climate after the LGM as suggested by the models and instead persisted in place throughout most of its current range. Phrynosoma platyrhinos expanded its range northwards after the LGM but was able to expand further than indicated by models, into colder and wetter areas than those experienced during the LGM. My results indicate that the two species responded to the warming climate after the LGM in an idiosyncratic fashion and that the transferal models did not correctly predict the species response to the climate change. These results motivated me to explore in the last chapter several high-priority challenges in transferal modeling through theoretical background and sets of experiments. I demonstrated how these challenges can affect resulting models and, when possible, offered suggestions on how uncertainties might be diminished. |
