Community contribution* |
Proportion of a given genus in the community,
based on the total number of rodent individuals. Calculated for each
rodent genus. See Appendix 1 Text A1 on calculation at location
level. |
Mean density |
Mean trapping index, calculated for each rodent
genus. |
Cycle amplitude |
Variability of the population abundance around the
mean. Calculated using the standard deviation of log-transformed (log
+0.01) time-series (i.e. the s-index, (Stenseth and Framstad 1980)).
Calculated for each rodent genus. |
Peak sharpness |
Based on skewness of the data, which is defined as
\(\gamma_{1}=\mu_{3}/\mu_{2}^{3/2}\) (µ2 and
µ3 are the second and third central moments of the
time-series). Skewness describes the degree of asymmetry of data.
Negative skewness relates to a few observations at very low density, but
most near the maximum density (i.e. round cycles), whereas zero skewness
relates to symmetric data and positive skewness to most observations at
low density and only few at high densities (i.e. sharp cycles) (Turchin
et al. 2000). Calculated for each rodent genus. |
Peak interval* |
Mean number of years between population peaks.
Calculated based on visual inspection of data, assigning year t as a
peak year when a population had a positive growth rate from t-1 and
negative to t+1. See Hanski et al. (1991) and Appendix 1 (Text A1).
Calculated for the entire rodent community, as different rodent species
at the same location usually have synchronous cycles, and at sampling
units with little data the signal of a cycle could be missed if
evaluated for one species only. |