Local richness-species pool patio: A consequence of the species-area relationship

A constant ratio between species richnesses estimated at the local and regi onal scale is interpreted as a proof of quasi-neutral unsaturated communiti es. Based on Zobel's model of plant community we tested the methodology of the species-pool concept by comparing the saturated and unsaturated communi ties generated by spatially-explicit mechanistic simulations with known ass embly rules. Tests show that local-regional species plots can be applied to distinguish saturated vs. unsaturated communities, however. the outcome of tests, i.e. the relationship between local and regional richness depends o n the size of the areas compared, independently from the mechanisms control ling diversity, trivial saturation will appear if one of the scales is eith er too small or too broad because species-area curves are bound at these ex treme scales. Similarly, trivial unsaturation will appear if the two scales compared are close to each other. The application of species-area curves i s useful because they help to find scales for non-trivial relationships. Field tests reporting quasi-neutrality and unsaturated plant communities we re performed at the intermediate scales of the corresponding species-area c urves, and they were estimated from heterogeneous samples. Therefore. this field evidence might be biased by scaling artefacts. We propose to reanalyz e the field evidence with solid scaling conventions and to restrict the con cept of quasi-neutrality to subordinated functional groups based on the fol lowing hypotheses: (1) neutrality will appear within subordinated guilds as a consequence of the hierarchical structure of plant communities; (2) the lower a guild in the hierarchy the higher neutrality of within-layer proces ses detected; (3) quasi-neutrality found at the community level is not a pr oof of community-level neutrality but it is due to the higher number of sub ordinated species in the samples.