Geography Reference
In-Depth Information
lands toward forest canopies, high latitudes, grasslands, deserts, caves,
and mountains. Taxon pulses take place when generalists (plesiotypes) ra-
diate into new habitats and become specialists (apotypes) and even su-
perspecialists (superapotypes). Plesiotypes generate several pulses, which
overtake previous pulses and replace them along the pathways. Taxa may
be categorized into sets that reflect how far they have departed from the
generalist basal stage.
Liebherr and Hajek (1990) tested the taxon pulse model using eight taxa
of New World Carabidae (Insecta: Coleoptera) for which both phylogenetic
hypotheses and habitat data were available. They compared cladistic trans-
formations of habitat preference with patterns generated randomly under a
nullhypothesis,findingthatonlyoneofthegroupsanalyzedexhibitedastat-
istically significant pattern supporting the taxon pulse. They suggested that
the failure of the model as a predictive hypothesis may result from historical
changes in climate that allow range expansions for species restricted pre-
viously to small habitats, and habitat shifts do not progress in linear trans-
formation series.
