Morisita

Morisita is a name used in various scientific contexts, most notably in ecology for two dispersion and similarity measures that bear the Morisita name. Morisita's index of dispersion, also known as Morisita's index, is a statistic used to describe how individuals of a species are distributed across sampling units. It helps assess whether counts are aggregated, randomly distributed, or regularly spaced. In practice, researchers calculate the index from frequency counts across quadrats or other sampling units; values greater than 1 indicate clumping, values near 1 indicate a random pattern, and values less than 1 suggest a more uniform distribution than expected under randomness. The method is valued for being relatively insensitive to small sample sizes and to differences in quadrat area.

Another related measure is the Morisita-Horn index, a similarity measure between two communities based on species abundances. It yields values from 0 to 1, where 1 indicates identical species composition and proportional abundances, and values near 0 indicate little similarity. The Morisita-Horn index is widely used in beta diversity studies and in comparing ecological communities across sites and times.

Beyond ecology, the Morisita name has appeared in other scientific contexts and literature, including as the nomenclature for methods developed by researchers bearing the surname. The term Morisita thus denotes both a family name and a set of statistical tools used to analyze distribution and similarity in ecological data.