Partitioning of biodiversity effects
The net biodiversity effect (BE) of a polyculture mesocosm was measured
by the difference between the observed yield and its expected yield,
which was generated by a species proportional abundance multiplied by
biomass estimated in monoculture. CE was the average performance of
species above or below their expected performance. SE was measured by
the covariance between the monoculture yield of species and their change
in relative yield in the mixture. These various effects can be related
by an additive partition (Loreau & Hector 2001):
\begin{equation}
BE=CE+SE=N\ \overset{\overline{}}{{RY}_{i}}\ \overset{\overline{}}{M_{i}}+N\ cov({RY}_{i},M_{i})\nonumber \\
\end{equation}where i was the component species in the mixture, N was
the number of component species, ΔRYi was the
deviation from expected relative abundance of species i in the
mixture, and Mi was the yield of species iin its monoculture. Positive CE indicates that species yields in a
mixture are on average higher than expected values of the component
species (the weighted average monoculture yields), and positive SE
indicates that species with higher-than-average monoculture yields
dominate the mixture.