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- Title
Measures of spatial heterogeneity for species occurrence or disease incidence with finite-counts.
- Authors
Shiyomi, Masae; Yoshimura, Jin
- Abstract
We propose two types of indices with finite-count correction to measure the spatial heterogeneity of binary characteristics of organisms, such as occurrence or non-occurrence of organisms and infected or non-infected plants. We consider the following two examples: plant occurrence in a grassland community, and yellow dwarf disease infection in a rice field. For the grassland community, N quadrats comprising n cells of equal area, were set at random sites in a grassland, and the occurrence of a given species A in each of n cells was recorded. For disease infection, N quadrats, each consisting of n rice plants, were set at random sites in a paddy field, and the number of plants infected with yellow dwarf virus in each quadrat were counted. In these examples, since the number of cells in a quadrat is finite, neither occurrence nor incidence increase infinitely, unlike the number of aphids on a maize leaf. The first category of index belongs to the mean: variance ratio type. The estimated index value for occurrence (or incidence) is the same as that for non-occurrence (or non-incidence). The second category belongs to the k-type of a negative binomial distribution. If some random plants die or recover from the disease then the expected value of the second type of index does not change. For n → ∞, the current indices approach the mean: variance ratio and the inverse of k in a negative binomial distribution, respectively. This indicates that these indices are suitable for binary data sets.
- Subjects
PLANT diseases; ENVIRONMENTAL indicators; ECOLOGICAL heterogeneity
- Publication
Ecological Research, 2000, Vol 15, Issue 1, p13
- ISSN
0912-3814
- Publication type
Article
- DOI
10.1046/j.1440-1703.2000.00326.x