Professor East China Normal University Shanghai, China (People's Republic)
Abstract: Intraspecific variability (IV) is crucial for understanding species coexistence because it can affect the competitiveness of species and ultimately determine species coexistence. Several models show that IV can promote coexistence only when the inferior species has a higher IV than the superior, which is referred to as the interspecific mean-variance trade-off. However, whether and when this trade-off exists remains unknown. Based on competitive responses of 10 key traits from 6750 seedlings of 10 tree species over a 3-year period, we found no significant difference (P = 0.32) in trait variability between inferior and superior species in a competition-free homogenous environment, indicating that the trade-off is not always present. Nevertheless, when seedlings were subjected to pairwise competition (P < 0.01), multispecies competition (P < 0.05), or heterogeneous environments (P < 0.05), the trade-off emerged. This was due to inferior species generally having a significantly (P < 0.05) larger increase in trait variability in response to competition or abiotic environment, with the largest increase seen in fine root traits. Our study provides the first experimental evidence of the interspecific mean-variance trade-off and the conditions under which it arises. The negative relationship between the increase in IV and competitive ability in our findings not only explains the emergence of the trade-off, but also provides a new avenue for refining competition models and better understanding the impact of IV on species coexistence.
