© 2018, The Authors. Functional Ecology © 2018 British Ecological Society. The attached document (embargoed until 16/12/2019) is an author produced version of a paper published in FUNCTIONAL ECOLOGY uploaded in accordance with the publisher’s self- archiving policy. The final published version (version of record) is available online at the link below. Some minor differences between this version and the final published version may remain. We suggest you refer to the final published version should you wish to cite from it.