Number of communities is the number we choose to plot and analyse. For elm-get, CRAN and PyPI, other numbers of communities also seemed reasonable. NRSS not reported because it did not contribute to analysis. Communities are considered to have declined if their activity at the end of the study period is substantially lower than their peak activity. All numbers are provided to two significant figures. k refers to the in and out degrees, σ is the standard deviation, and E is the arithmetic mean.