Hypothesis
With resources heterogeneously distributed, a species mixture should maximise productivity across a metacommunity and outperform every monoculture, while a balanced local resource supply should favour coexistence and higher evenness.
What failed
In an experiment with five freshwater algal species, mixtures did not outperform all monocultures at the metacommunity scale, so no general transgressive overyielding was observed; and contrary to the local-scale prediction, balanced resource supply did not generally produce higher evenness, though the lowest evenness was confined to the most imbalanced patches.
Broken assumption
Heterogeneous resource supply guarantees that diverse mixtures maximise productivity across a metacommunity.
Why
The authors note resource-use efficiency was nonetheless always higher in mixtures than monocultures predicted, suggesting resource partitioning or facilitation at high supply, and describe their support for the theory as mixed.
From the published paper: Gamfeldt et al. PLoS ONE, 2011. ↗CC BY