From multi-criteria approach to simple protocol:: Assessing habitat patches for conservation value using species rarity

We investigated conservation value (CV) related to the quality of spider communities in different non-wooded habitat patches - ranging from arable land to natural grasslands. The study was conducted in two ecologically distinct regions of Hungary: the Hungarian Great Plain and the Buda Hills. We used seven variables to indicate CV which together formed a multi-criteria space of spider community characteristics. These variables were either related to species characters obtained from an extensive background database: abundance and frequency based rarity, specialist status, association to natural habitats; or were calculated for the community at the given patch: species richness, functional diversity and species evenness. Using the variables in an ordination analysis we could establish a gradient of the patches in the multi-criteria space of the spider community characteristics. Position of patches along the first axis of the ordination was taken as the multi-criteria measure of CV. CVs established this way were strongly and positively correlated with an independent botanical CV assessment. We also sought a simpler measure of spider CV by: (a) calculating only one variable out of the seven and using it as a surrogate for the multi-criteria CV measurement; by (b) calculating this variable only for a short time period or (c) for only one spider family. Average abundance based rarity value of the species proved to be the best surrogate of the multi-criteria CV measure for both regions, and it also performed very well when sample size was restricted to two sampling occasions per patch or to a single family. This adds further evidence to, what has been found in other studies, that species rarity is a sensitive and reliable measure of the ecological and conservational status of communities. (C) 2008 Elsevier Ltd. All rights reserved.