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Taxon 21:213–251. _______________________________ Ecology, 87(8), 2006, pp. 2128–2131 Ó 2006 by the Ecological Society of America RIPARIAN ZONES INCREASE REGIONAL RICHNESS BY SUPPORTING DIFFERENT, NOT MORE, SPECIES: REPLY John L. Sabo 1,2 and Candan U. Soykan 1 We thank Hylander (2006) for clarifying the interpretation of b-diversity in our paper, Riparian zones increase regional richness by supporting different, not more, species (Sabo et al. 2005). ‘‘Narrow-sense’’ turnover (sensu Koleff et al. 2003) between riparian and upland habitats is, indeed, overestimated by Jaccard’s index of similarity, or ‘‘broad-sense’’ turn- over. Nevertheless, in dispelling one myth, our original paper does not give rise to a new one. We will present new analyses of our data that clearly substantiate the claim that riparian zones harbor unique fauna and flora globally and increase regional species richness, albeit by an average 38% rather than the 50% we calculated in our previous paper. Further, our broad- sense turnover calculations (1  b J ; Sabo et al. 2005: Fig. 3) for riparian plants are some of the highest values in the published literature, yet occur across extremely small spatial scales (typically 1 km or less). Here we address Hylander’s two central critiques separately. Hylander’s first critique: 1  b J is not a good measure of (narrow-sense) turnover As Hylander points out, we used Jaccard’s index, b J , to estimate similarity in species composition between riparian and upland habitats. We then estimated dissimilarity as 1  b J . Dissimilarity is ‘‘broad-sense’’ turnover (Koleff et al. 2003), and can be estimated as the sum of the species unique to either habitat divided by the regional pool (Gaston et al. 2001), or 1  b J ¼ ða þ bÞ ða þ b þ cÞ : ð1Þ Hylander’s first critique of our paper is that the ‘‘dissimilarity’’ in species pools is not an accurate estimate of [narrow-sense] turnover (sensu Koleff et al. 2003), because the proportion of species not shared by riparian and upland habitats (a and b) includes species from both habitats. We thank Hylander for this clarification and here provide two new, complementary analyses of b-diversity. First, we estimated the propor- tion of unique riparian species as a R;u ¼ a ða þ b þ cÞ : ð2Þ This is similar to narrow-sense b-diversity measures described by Simpson (1943) and Lennon et al. (2001). Second, we estimate the proportional increase in the regional species pool due to riparian habitats as c R ¼ a ðb þ cÞ ð3Þ where b þ c is the regional pool excluding riparian species. The proportion of unique riparian species (i.e., narrow-sense turnover) is high (mean 0.24, range 0– 0.6) with a lower confidence bound of 0.18 for the mean of all studies (Fig. 1a). Thus, narrow-sense turnover is nearly half of broad-sense turnover (Sabo et al. 2005). This result is not surprising, given that we found no significant differences in either a- or cumulative richness between riparian and upland habitats (Sabo et al. 2005: Figs. 1 and 2). On average, riparian zones and upland habitats share half of the regional species pool and harbor half (each) of the remaining ‘‘unique’’ species. The proportional increase in regional species richness due to riparian habitats is similarly high (mean 0.38, range 0–1.5; Fig. 1b). Thus, our claim that riparian zones increase regional richness by 50% (Sabo et al. 2005:56) is inaccurate. A more accurate estimate of this parameter is 38% (99% CI: 0.258–0.499; Fig. 1b). This lower percentage is still surprisingly high, given that estimates of proportional riparian habitat coverage are small, on the order of 5% or less (e.g., for the entire land mass of the United States, NRC 2002). In both cases (Fig. 1a, b), we assess the significance of proportions using parametric confidence intervals, which brings us to Hylander’s second critique. Manuscript received 8 March 2006; accepted 9 March 2006. Corresponding Editor: T. J. Stohlgren. 1 School of Life Sciences, Arizona State University, P.O. Box 874501, Tempe, Arizona 85287-4501 USA. 2 E-mail: John.L.Sabo@asu.edu COMMENTS 2128 Ecology, Vol. 87, No. 8