The proportion of positive, neutral and negative BEF relationships among studies with direct diversity manipulations vs. indirect diversity change through trophic cascades, increased habitat complexity and land use (a); among observational studies compared with manipulative experiments in field and micro- and mesocosms (b); depending on the dimensions of ecosystem functions (c) and ecosystem services and disservices (d), see Supplementary Table S6 for details. Numbers near bars show the number of assessed BEF relationships (n = 140).