| 释义 |
over-dispersion Ecology.|ˌəʊvədɪˈspɜːʃən|
[f. over- 29 b + dispersion.]
A greater unevenness in the distribution of individuals than would be the case if the existence and position of each were independent of the rest, so that there is an increased proportion of the area with a large or small concentration of individuals. Hence ˌover-diˈspersed a., distributed in this manner.
1936Jrnl. Ecol. XXIV. 234 If in a set of counts of numbers of individuals per sample area the relative variance is greater than unity, this indicates that the dispersion is greater than would be expected on the assumption of random (Poisson) distribution... [This] first condition, over-dispersion, implies that individuals are scattered less evenly than would be expected. Ibid. 250 Over-dispersion shows itself in an excess of quadrats containing no ‘individuals’ or a large number of ‘individuals’, there being a corresponding deficit in central classes. 1946Ecology XXVII. 329/2 The writer [sc. L. C. Cole] prefers the terms ‘contagious’ and ‘negatively contagious’ to ‘overdispersion’ and ‘underdispersion’ both of which have suffered reversals of meaning in the hands of different authors. 1948Bot. Rev. XIV. 226 The study of over⁓dispersion is of major importance in statistical ecology. Ibid., Over-dispersion is the rule rather than the exception among animals. Ibid. 227 Cole applied this technique to the analysis of various over-dispersed populations. 1957P. Greig-Smith Quantitative Plant Ecol. iii. 56 The former has been termed overdispersed (referring to the distribution curve obtained) and the latter underdispersed. Unfortunately these terms have sometimes been used in the reverse sense (referring to the pattern of individuals on the ground)..and are better avoided. 1964V. J. Chapman Coastal Vegetation ii. 24 The plants are over-dispersed or aggregated into clumps. |