Factors shaping diversity patterns in pelagic rotifer assemblages of high mountain lakes (Pyrenees)
Bartumeus, Frederic; Ventura, Marc; Catalan, Jordi
Factors shaping diversity patterns of pelagic rotifer assemblages were studied from data collected on 80 Pyrenean lakes during summer 2000. Different diversity aspects were investigated for the whole set of lakes (i. e. the metacommunity) and for a series of subsets (i. e. local communities): i) species incidences, rank abundance distribution and species richness per lake, ii) β-diversity spectra of species richness and Shannon index in relation to different environmental and ecological gradients, and iii) species abundance distributions (SADs). Our results show the basic patterns of rotifer diversity in the Pyrenees. We found that gradients of altitude, depth, macrozooplankton (MZP) abundance and especially the organic matter content (measured as the percentage of matter loss on ignition, LOI) were shaping rotifer β-diversity in the Pyrenees. In particular, the percentage of LOI has a relevant impact on plankton abundances in both rotifers and MZP. At the metacommunity level, the SAD showed a power law with an exponent β ≈ -1. Exactly the same behaviour was observed for randomly grouped local communities. However, local communities including lakes located at the lowest altitudes (1620-2210 m a. s. l.) or with low organic matter content (i. e. <17 % LOI) showed deviations from β ≈ -1. Based on these analyses our main conclusions are: (i) three main factors were shaping rotifer diversity patterns: the presence of littoral species in pelagic rotifer assemblages in shallow lakes, the carbon flux through the lake, and the existence of increasing environmental restrictions in altitude; (ii) assuming neutral theory to be an appropriate model, our results suggest that rotifer species are not strongly limited by dispersal in the Pyrenees; and (iii) differentiation between local communities and the metacommunity was only detectable on the basis of major environmental changes (e. g. altitude, LOI).