Measurement of species turnover rate
Species turnover rate is the rate of dissimilarity among species
composition across all possible plot pairs along the spatial or
environmental gradient. The slope of the relationship between the
species turnover and environmental divergence measures species turnover
rate. Jaccard’s index (βj; Jaccard et al., 1912) and
SØrenson’s index (βs; SØrenson et al., 1948) were used
to measure turnover rate of species composition. βj and
βs are two widely employed indices, which only consider
presence/non-presence of species, are independent of α-diversity (Jost
et al., 2007). βj and βs are calculated
following the equations:
\begin{equation}
\beta_{j}=1-c/(a+b+c)=(a+b)/(a+b+c)\nonumber \\
\end{equation}\begin{equation}
\beta_{s}=1-2c/(a+b+2c)=(a+b)/(a+b+2c)\nonumber \\
\end{equation}where a and b are the numbers of species only occurring in
the focal and neighboring plots, respectively, and c is the
number occurring in both.