Chasing the Dragon: the Resilience of a Species to Climate Change in the Wet Tropics, Australia
Total Page：16
File Type：pdf, Size：1020Kb
Chasing the Dragon: The Resilience of a Species to Climate Change in the Wet Tropics, Australia Author Bernays, Sofie Published 2015 Thesis Type Thesis (PhD Doctorate) School Griffith School of Environment DOI https://doi.org/10.25904/1912/126 Copyright Statement The author owns the copyright in this thesis, unless stated otherwise. Downloaded from http://hdl.handle.net/10072/367595 Griffith Research Online https://research-repository.griffith.edu.au Chasing the dragon: The resilience of a species to climate change in the Wet Tropics, Australia Sofie Bernays Bachelor of Environmental Management (Honours) Griffith School of Environment Griffith Sciences Griffith University Submitted in fulfilment of the requirements of the degree of Doctor of Philosophy June 2015 Summary Summary Throughout history, climatic changes have caused environmental systems to shift and have influenced biotic assemblages. Most of these changes have occurred slowly, over millions of years, enabling species to either adapt to new conditions, endure the changes, or shift distributions to maintain their habitat requirements. Due to the fast rate at which climate change is currently occurring, it is unknown if species will be able to use these mechanisms to successfully respond to this rapidly changing environment. Areas that have small geographical extents, elevated uplands and high numbers of endemic species, such as the Wet Tropics in north-eastern Queensland, are expected to be particularly vulnerable to climate change. The endemic species in this at-risk area are also expected to be more susceptible to climate change. The endemic Boyd’s forest dragon (Hypsilurus boydii, Macleay) is a highly camouflaged, large lizard that inhabits lowland and upland forests from the northern to the southern boundary of the Wet Tropics. Determining how H. boydii has responded to previous climate change may give insight into how the species may respond to future climatic changes. The main aims of this study were to understand how geographical features and climate have influenced the genetic makeup, morphology and distribution of H. boydii, and to use this information to determine how climate change may influence future populations. This study used genetic analyses to identify evolutionary and geographical relationships across the Wet Tropics (north vs. south of the Black Mountain corridor [BMC] and upland vs. lowland) and within each of these regions; explore morphological variation across the regions and examine conformity to three eco-geographical rules (Bergmann’s rule, Allen’s rule, and the isolation rule); and attempt to predict species distribution patterns of the species throughout the Wet Tropics during past, present and future climatic scenarios. Seventy- seven dragons were collected from nine sites across the Wet Tropics, with a blood sample (for genetic analyses) taken from each individual, 47 of these individuals, from eight of the sites, were sampled for morphological measurements. Due to the cryptic and ambush nature of the species, sample sizes were low and uneven. i Summary To understand the influence that geography and climate have had on the genetic makeup of H. boydii, genetic patterns were examined using one mitochondrial (ND4) and three nuclear genes (PTGER4, MKL1 and BZW1; N = 76). Genetic diversity and genetic structure were high across the Wet Tropics, with differences detected between northern and southern regions, although not between upland and lowland regions. The deep divergence between populations north and south of the BMC was suggested to have occurred 0.90 – 3.26 million years ago. There was variation in the detected levels of divergence between mitochondrial and nuclear genes, with the mitochondrial gene and one nuclear gene reflecting the highest genetic structure. The findings from this study suggest long-term isolation between northern and southern populations with no evidence of secondary contact or cryptic species. There was also evidence for significant genetic differentiation among sites within the regions. It is therefore suggested that H. boydii has experienced restrictions to dispersal across the BMC but also within the northern and southern regions. The dispersal ability of the species appears to quite be limited, and may become negligible if further fragmentation of forest habitat occurs. Influences of geography (latitude) and climate (altitude) on morphological variation were explored by testing three eco-geographical rules: Bergmann’s rule, Allen’s rule, and the isolation rule. The inverse of Bergmann’s rule and Allen’s rule suggest there may be evolutionary advantages for small reptiles in cool habitats, as small animals are expected to have a faster rate of heat absorption, whereas the isolation rule suggests different evolutionary pressures affect isolated populations differently. Due to warmer habits in lowlands and cooler habitats in the uplands, it was expected that H. boydii would: conform to the inverse of Bergmann’s rule (larger animals found in warmer lowlands than in cooler uplands); conform to Allen’s rule (larger limbed animals found in warmer lowlands than in cooler uplands); and show little effect from the isolation rule (no variation across the BMC). The morphological analysis found phenotypic differences between upland and lowland populations, with lowland individuals significantly larger than those found in the uplands, as well as slight evidence for male ‘limbs’ being larger in lowland regions compared with those ii Summary found in upland regions. There were no morphological differences detected between northern and southern regions across the BMC and no evidence for cryptic species. The results conformed to the inverse of Bergmann’s rule, showed weak support for Allen’s rule in males, and did not support the isolation rule. The homogeneous morphology across the BMC supported findings from previous studies on other reptile species. Relationships between environmental factors and species occurrences were detected which indicate how these features may have influenced past, present and future distributions of H. boydii. Species modelling was conducted on three climatic scenarios (HadGEM2-ES, ACCESS1-0, MIROC-ESM) using the RCP 8.5 emissions scenario (future atmospheric emissions release is ‘business as usual’). The species distribution modelling suggested the BMC latitudinal barrier may not have always been present, with suitable habitat predicted in the BMC approximately 22,000 years ago. Future modelling suggested that the BMC latitudinal barrier will become more pronounced as suitable habitat both sides of the BMC is reduced by 68 – 86 % by the year 2070. Overall, genetic analysis suggested that the BMC has maintained a barrier to north-south dispersal. In contrast, species modelling suggested the BMC has not remained a firm barrier to north-south dispersal. With numerous possible explanations for the discrepancy between these findings, the most likely explanations are: the model is over predicting suitable habitat; the limited dispersal ability of H. boydii does not enable movement into all suitable habitat; or suitable habitat does not guarantee inhabitance. The slight morphological variation across altitudes is not expected to influence the resilience of the species in the future. However, the limited dispersal ability of the species may reduce the likelihood of H. boydii moving into new habitat as the fragmentation effects of future climate change take place. iii Statement of originality "This work has not previously been submitted for a degree or diploma in any university. To the best of my knowledge and belief, the thesis contains no material previously published or written by another person except where due reference is made in the thesis itself." Sofie Bernays i Table of Contents Summary ................................................................................................................................ i Statement of originality.......................................................................................................... i Table of Contents .................................................................................................................. ii Table of Figures ..................................................................................................................... v List of Tables ........................................................................................................................ vii Acknowledgements ............................................................................................................... ix Chapter 1 General introduction ........................................................................................ 1 1.1 Climate change ....................................................................................................... 2 1.3 Contemporary climate change ................................................................................ 3 1.4 At-risk regions ......................................................................................................... 3 1.4.1 Elevated regions .............................................................................................. 3 1.4.2 Rainforests ....................................................................................................... 4 1.5 At-risk area – Wet Tropics ....................................................................................... 4 1.6 At-risk species ........................................................................................................