Macroecological relationships between primary productivity and ecological specialisation Hugh Munro Burley PhD thesis School of Biological Earth and Environmental Sciences University of New South Wales August 2017 iv Dedication For my Grandmother Alice Burley (1917-2011), who was a geographer all her life, but did not have the chance to attend university. v Acknowledgements There are many people who deserve a big thank you for all their help. Firstly, I cannot thank Shawn enough for his patience, encouragement and technical genius — to say nothing of his prompt editorials! One could not ask for a better supervisor. Similarly, I am very grateful to Karel for his invaluable conceptual and technical input. This project took much of Karel’s time, and would not have succeeded without his insight and commitment. I am very fortunate to have been affiliated with the CSIRO macroecological modelling team. Firstly, I am indebted to Kristen Williams for helping me apply for the CSIRO scholarship, bringing me into the team and supporting me throughout the process. Simon Ferrier has been very generous with his time, imparting much of his accumulated biogeographic wisdom. I thank him for entrusting me with these ideas, and hope this project has been useful for the team. Many thanks also to Tom Harwood, who has provided valuable technical and conceptual insights, spatial layers, and of course the chance to play the drums for the final ‘CES who’ gig. Many other people at CSIRO have also been very helpful. Randall Donohue provided the crucial response variable for this project — without which there would be nothing to explain (!) — and I am very grateful for his prompt and encouraging responses to all my enquiries. Helen Murphy, Dan Metcalfe and Andrew ford provided valuable insights into the floristic datasets for the Wet Tropics, improving the analyses substantially. Many thanks also to Dean Paini for his encouragement, and to Greg Forster, Peter Zaffina and Amar Singh for some much needed comradery whilst using the Black Mountain gym during my time in Canberra. vi I have also been lucky to have fantastic mentors during the PhD process. Will Cornwell has been a supportive friend and collaborator, while Rob Kooyman has provided valuable botanical insights. I am also indebted to Andrew Thornhill for his work on the Phylogeny of the Wet Tropics flora (for future collaboration), his biogeographic expertise and some classic Australian-isms while enjoying the Mexican cuisine in Berkeley. Many thanks also to Darren Crayn for kindly hosting Shawn and I at the Tropical Herbarium in Cairns, and to Brent Mishler for his academic guidance. Adrian Fisher has also been a great friend during my time at UNSW, and I look forward to many more trips together to the SFS and SCG (albeit likely frustrated by the outcome!). It has been a privilege to receive support from the Australian government, UNSW and CSIRO. The UNSW Graduate Research School provided funding through the Australian Postgraduate Award and the UNSW research excellence award, while CSIRO provided funding through the Office of Chief executive top up scholarship, for which I am very grateful. Many thanks must also go to all the UNSW staff who make the school of BEES work: Firoza, Jonathan, Chris and Penny, to mention but a few. Suffice to say we are so lucky to live in Australia with all this support! Throughout life I’ve relied on my family and friends. Without the support of Jane and Neil, university wouldn’t have been possible, and I can’t thank them enough for putting our education first. Meanwhile everyone at Kanangra deserves a long holiday (perhaps to the Kimberley?). This list is woefully inadequate. But nonetheless, huge thanks to: Bill, Camille (we can, will and did), Pat, Rowan, Chris, Greg, Kate, Vito, Delwyn — and everyone else (!) — for their friendship. Also I’m very grateful to Pete Kostic for teaching me the drums again, and to Molly and Parker for their love and friendship during the PhD. Finally I would like to thank Cameron Tonkinwise, formerly of the University of Technology in Sydney, who first introduced the idea of sustainability in 2003 to a bunch of graphic design students, beginning a rambling adventure. Long may it continue! vii Abstract A key debate in contemporary ecology concerns whether ecosystem functions such as productivity are distinctly influenced by biological diversity in natural environments. Recent work has emphasised the importance of links between ecosystem functions and measures of ecological specialisation as proxies of biodiversity. However, few studies have analysed these relationships at broad spatio-temporal scales. This research tests the empirical relationship between primary productivity and ecological specialisation at continental and bioregional scales, using two proxies of specialisation: taxonomic β-diversity and site-level environmental niche width. It also examines how the environmental niches of species vary across continental environmental gradients. Gross primary productivity (GPP) may be influenced not only by the biological diversity at each location (α-diversity) but also by the biological turnover between locations (β-diversity). Generalized additive models were used to test whether the magnitude or variability of GPP were distinctly influenced by either taxonomic α- or β-diversity across continental Australia, over and above environmental influences. Neither α- nor β-diversity improved the explanatory power of GPP models beyond that of environment-only models. The realised environmental niches of species are important indicators of ecological specialisation and biogeographic history. Bivariate regression models were used to test whether species niches vary across continental environmental gradients for 1771 vascular plants from the Australian Wet Tropics. The temperature niches of these species did not vary substantially. However, niches were narrower in drier and less fertile environments. The macroecological complementarity hypothesis predicts that locations with greater ecological specialisation —those with collectively narrower niches — should be more productive viii than locations with less ecological specialisation. For pairs of environmentally similar Wet Tropics sites, linear models were used to test the pairwise relationship between differences in site GPP (response) and differences in the median environmental niche width of all tree species present at each site (predictor). Sites with narrower temperature niche widths had higher productivity, whereas sites with narrower rainfall niche widths had lower productivity. These results will improve our understanding of the broad-scale interrelationships between ecosystem functions, environmental conditions and ecological specialisation in natural ecosystems, helping to assess utilitarian arguments for biodiversity conservation. ix Table of contents Dedication ........................................................................................................................................... v Acknowledgements ......................................................................................................................... vi Abstract .......................................................................................................................................... viii Table of contents ............................................................................................................................... x Publications and conference presentations (2013 – 2017) ........................................................... xiii 1 Introduction ............................................................................................................................... 1 1.1 Historical context and aims ...................................................................................................... 1 1.2 Geographic and biological scope of the thesis ....................................................................... 11 1.3 Structure of the thesis ............................................................................................................. 14 2 Macroecological relationships between ecosystem functions and biodiversity ............ 17 Abstract .......................................................................................................................................... 18 2.1 Introduction ............................................................................................................................ 19 2.2 Making MB-EF relationships applicable to real ecosystems ................................................. 23 2.3 A broader view of MB-EF relationships in natural ecosystems ............................................. 26 Macroecological complementarity ............................................................................................. 27 Macroecological spatio-temporal compensation ....................................................................... 30 2.4 A case study: potential MB-EF relationships for trees across an elevation gradient ............. 33 2.5 Potential avenues for testing MB—EF mechanisms in real ecosystems ............................... 38 2.6 Supporting information .......................................................................................................... 42 3 Primary productivity is weakly related to alpha and beta diversity across Australia 44 Abstract .........................................................................................................................................