Partitioning of diversity: the "within communities" component
It is routinely understood that the total diversity within a metacommunity (γ-diversity) can be partitioned into one component summarizing the diversity within communities (α-diversity) and a second component representing the contribution of diversity (or differences) between communities (β-...
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-10-01
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| Series: | Web Ecology |
| Online Access: | http://www.web-ecol.net/14/51/2014/we-14-51-2014.pdf |
| Summary: | It is routinely understood that the total diversity within a metacommunity
(γ-diversity) can be partitioned into one component
summarizing the diversity within communities (α-diversity) and
a second component representing the contribution of diversity (or
differences) between communities (β-diversity). The underlying
thought is that merging differentiated communities should raise the total
diversity above the average level of diversity within the communities. The
crucial point in this partitioning criterion is set by the notion of
"diversity within communities" (DWC) and its relation to the total
diversity. The common approach to summarizing DWC is in terms of
averages. Yet there are many different ways to average diversity, and not
all of these averages stay below the total diversity for every measure of
diversity, corrupting the partitioning criterion. This raises the question
of whether conceptual properties of diversity measures exist, the fulfillment
of which implies that all measures of DWC obey the partitioning
criterion. It is shown that the straightforward generalization of the plain
counting of types (richness) leads to a generic diversity measure that has
the desired properties and, together with its effective numbers, fulfills
the partitioning criterion for virtually all of the relevant diversity
measures in use. It turns out that the classical focus on DWC (α) and
its complement (β as derived from α and γ) in the
partitioning of total diversity captures only the apportionment perspective
of the distribution of trait diversity over communities (which implies
monomorphism within communities at the extreme). The other perspective,
differentiation, cannot be assessed appropriately unless an additional level
of diversity is introduced that accounts for differences between communities
(such as the joint "type-community diversity"). Indices of apportionment <i>I</i><sub>A</sub>
(among which is <i>G</i><sub>ST</sub> and specially normalized versions of β) and
differentiation <i>I</i><sub>D</sub> are inferred, and it is demonstrated that conclusions
derived from <i>I</i><sub>A</sub> depend considerably on the measure of diversity to which
it is applied, and that in most cases an assessment of the distribution of
diversity over communities requires additional computation of <i>I</i><sub>D</sub>. |
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| ISSN: | 2193-3081 1399-1183 |