Key points are not available for this paper at this time.
Click to increase image sizeClick to decrease image size Acknowledgements We are very grateful to the authors who contributed articles for this special issue, many of whom worked to tight timescales to submit and revise their work. We would also like to thank our team of reviewers, half from the UK and half from overseas, who also worked to tight deadlines to enable us to produce this special issue.
Murray et al. (2011) studied this question.