A ratio of variance to mean > 1 indicates:
The variance-to-mean ratio, often called an index of dispersion, compares observed variation among equal sampling units with the Poisson expectation. Randomly and independently placed individuals yield a ratio near 1 because a Poisson distribution has equal mean and variance. A ratio greater than 1 indicates overdispersion: counts differ more among quadrats than chance alone predicts, with many low-count units and some high-count units. This is the statistical signature of clumping. Patchy resources, social attraction, restricted dispersal, and reproduction near parents can all generate it. Un
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 9
