02208nas a2200181   4500008004100000245006800041210006100109300001200170490000700182520162800189653001701817653001401834653002001848653002601868653002101894100002001915856009101935       2004                        eng d00aOn the statistical significance of functional diversity effects0 astatistical significance of functional diversity effects  a297-3030 v183 a1. Changes in biodiversity can affect ecosystem processes through a variety of pathways, such as changes in community structure, loss of a keystone or changes in resource use patterns among species. The latter, also known as resource use complementarity, is an established mechanistic link between species and ecosystems. 2. At present, functional group richness is the dominant measure of the extent of resource use complementarity and has been manipulated in several experiments. These groups are constructed a priori  using information about differences between species and a statistically significant effect is typically identified by standard parametric tests. These tests implicitly assume that the a priori  functional groups are correct. 3. Avoiding this assumption requires a randomization (bootstrap) test of statistical significance that accounts for the effects of grouping per se . This test compares the observed test statistic to the distribution of the test statistic resulting from random assignment of species to groups. 4. Re-analyses of experimental manipulations of plant functional diversity by boot- strapping the critical significance value changed the ecological interpretation of results in nearly half of the experiments. This occurred because random assignment of species to functional groups frequently creates a strong relationship between functional diver- sity and ecosystem functioning. 5. The significant bootstrapped results that were found perhaps represent some of the most convincing evidence that functional diversity is an important determinant of local-scale ecosystem functioning. 10abiodiversity10abootstrap10acomplementarity10aecosystem functioning10afunctional group1 aPetchey, O., L.  uhttps://scarabnet.myspecies.info/statistical-significance-functional-diversity-effects