Impacts of moisture availability on species interactions: a test from Western Australia’s York Gum woodlands.

Margaret  M    Mayfield (1),    Janneke    Hille    Ris    Lambers (2),    Claire    Wainwright (3),    Hao    Ran    Lai (4)

1    The    University    of    Queensland,    School    of    Biological    Sciences,    Brisbane,    Qld    4072,    m.mayfield@uq.edu.au,    @MayfieldLabUQ

2    The    University    of    Washington,    Department    of    Biology,    Seattle,    Washington,    USA,    jhrl@uw.edu

3    The    University    of    Queensland,    School    of    Biological    Sciences,    Brisbane,    Qld    4072,    claire.wainwright@uq.net.au

4    The    National    University    of    Singapore,    Department    of    Biological    Sciences,    Singapore    117543,    hrlai.ecology@gmail.com

Novel communities are common outcomes of climate and land use changes in ecosystems around the world. Though some novel communities are species poor and dominated by exotic invaders, others support high levels of native and exotic diversity. The York Gum woodlands of SW Western Australia commonly support diverse and species poor novel communities within remnants and thus make ideal systems in which to study factors driving patterns of diversity in novel communities.  Past studies of York gum woodlands have identified moisture availability and aridity as important drivers of diversity and suggest that increasing aridity may reduce the prevalence of exotic species in this system. These studies are based on patterns of community species and trait diversity, however, and it remains unclear how changes in moisture availability and aridity impact interactions among native and exotic species within communities. We report on two large field experiments testing the impacts of moisture availability on the competitive outcomes of native and exotic annual plants that commonly co-occur in novel York Gum communities.  In the first experiment we manipulated water availability and assessed the reproductive success of native and exotic species in a mesic and an arid site.  In the second experiment, we used shade to create protected microsites and compared the outcome of species interactions under shade and open situations in arid novel communities.  Results vary by species but provide insights into the ways that direct native and exotic plant interactions may shift in response to environmental changes likely to occur under climate change.