Orchids of the West Indies: predictability of diversity and endemism

Abstract

Aim We examined phytogeographical patterns of West Indian orchids, and related island area and maximum elevation with orchid species richness and endemism. We expected strong species-area relationships, but that these would differ between low and montane island groups. In so far as maximum island elevation is a surrogate for habitat diversity, we anticipated a strong relationship with maximum elevation and both species richness and endemism for montane islands.Location The West Indies.Methods Our data included 49 islands and 728 species. Islands were classified as either montane ( ‡ 300 m elevation) or low (< 300 m). Linear and multivariate regression analyses were run to detect relationships between either area or maximum island elevation and species richness or the number of island endemic species.Results For all 49 islands, the species-area relationship was strong, producing a z-value of 0.47 (slope of the regression line) and explaining 46% of the variation. For 18 relatively homogeneous, low islands we found a non-significant slope of z ¼ )0.01 that explained only 0.1% of the variation. The 31 montane islands had a highly significant species-area relationship, with z ¼ 0.49 and accounting for 65% of the variation. Species numbers were also strongly related to maximum island elevation. For all islands < 750 km 2 , we found a small-island effect, which reduced the species-area relationship to a non-significant z ¼ 0.16, with only 5% of the variation explained by the model. Species-area relationships for montane islands of at least 750 km 2 were strong and significant, but maximum elevation was the best predictor of species richness and accounted for 79% of the variation. The frequency of single-island endemics was high (42%) but nearly all occurred on just nine montane islands (300 species). The taxonomic distribution of endemics was also skewed, suggesting that seed dispersability, while remarkable in some taxa, is very limited in others. Montane island endemics showed strong species-area and species-elevation relationships.Main conclusions Area and elevation are good predictors of orchid species diversity and endemism in the West Indies, but these associations are driven by the extraordinarily strong relationships of large, montane islands. The species richness of low islands showed no significant relationship with either variable. A smallisland effect exists, but the montane islands had a significant relationship between species diversity and maximum elevation. Thus, patterns of Caribbean orchid diversity are dependent on an interplay between area and topographic diversity.

Speciation Has a Spatial Scale That Depends on Levels of Gene Flow

“…In particular, isolation and elevation were also important and significant factors in the overall models and were important and significant in most of the individual-taxon models. The effect of elevation was always positive, as predicted if greater altitudinal variation increases the number of habitats and promotes greater ecological speciation (Ackerman et al 2007;Losos and Parent 2009). In all cases except birds, the probability of in situ speciation increased with increasing isolation, consistent with predictions that lower colonization rates of distant islands should leave more niches available for speciation (Gillespie and Baldwin 2009).…”

“…For both the individual-taxon models and the overall models considering all taxa together, we began with a maximal additive model including area, elevation as a proxy for habitat diversity in the absence of a direct measure (Ackerman et al 2007), isolation from other landmasses, and whether the unit of study was a single island or an archipelago. We then calculated the Akaike Information Criterion corrected for small sample sizes (AIC c ; Burnham and Anderson 2002) for each submodel of this full model.…”

Native plant species richness on Eastern Polynesia’s remote atolls

“…Ackerman et al, 2007;Chown et al, 1998;Diamond and Mayr, 1976;Price, 2004). Less important relationships were also observed between native species richness and coastal index, elevation and shoreline length.…”

Analysis of epiphytic orchid diversity and its host tree at three gradient of altitudes in Mount Lawu, Java

“…Kindlmann and Vergara (2009) highlight the importance of research in orchid especially in the topics of species diversity, such as species-area and species-abundance relationships. Two important factors for predicting orchid diversity and endemism in large and montane islands in West Indies are area and elevation (Ackerman et al 2007). Van Steenis (1972) mentioned that generally, orchids grow well in mountain areas with altitude ranging from 500 to1500 m asl, and their variation decreases in out site of this range (below 500 m asl.…”