An R function to estimate population density using Morisita's spacing method
Morisita M. (1957) A new method for the estimation of density by spacing method
applicable to nonrandomly distributed populations. Physiology and Ecology 7:134-144
(in Japanese).
http://reference.morisita.or.jp/paper_pdf/29.pdf
English translation: Forest Service translation number 11116,
USDA Forest Service, Washington, D.C., USA.