Identification of spatial patterns of species diversity is a central problem in conservation
biology, with the patterns having implications for the design of biodiversity monitoring
programs. Nonetheless, there are few field data with which to examine whether variation
in species richness represents consistent correlations among taxa in the richness of rare or
common species, or the relative importance of common and rare species in establishing
trends in species richness within taxa. We used field data on three higher taxa (birds, butterflies,
vascular plants) to examine the correlation of species richness among taxa and the
contribution of rare and common species to these correlations. We used graphical analysis
to compare the contributions to spatial variation in species richness by widely-distributed
('common') and sparsely-distributed ('rare') species. The data came from the Swiss Biodiversity
Monitoring Program, which is national in scope and based on a randomly located,
regular sampling grid of 1 km2 cells, a scale relevant to real-world monitoring and management.
We found that the correlation of species richness between groups of rare and common
species varies among higher taxa, with butterflies exhibiting the highest levels of
correlation. Species richness of common species is consistently positively correlated
among these three taxa, but in no case exceeded 0.69. Spatial patterns of species richness
are determined mainly by common species, in agreement with coarse resolution studies,
but the contribution of rare species to variation in species richness varies within the study
area in accordance with elevation. Our analyses suggest that spatial patterns in species
richness can be described by sampling widely distributed species alone. Butterflies differ
from the other two taxa in that the richness of red-listed species and other rare species
is correlated with overall butterfly species richness. Monitoring of butterfly species richness
may provide information on rare butterflies and on species richness of other taxa
as well.