T. Pavlicek et al., The niche-width variation hypothesis revisited: Microscale testing of the earthworm Bimastos syriacus (Rosa) and multispecies comparison, ZOOL ANZ, 239(1), 2000, pp. 21-26
The niche-width variation hypothesis, which predicts positive correlation b
etween niche width and genetic diversity, was tested in the earthworm Bimas
tos syriacus (Rosa). The earthworms were collected from the microclimatical
ly warmer, drier, and more stressful south-facing (SFS) and opposite dense
liveoak maquis north-facing (NFS) slopes at "Evolution Canyon", Lower Nahal
Oren, Mt. Carmel, Israel. The opposite slopes of "Evolution Canyon", which
are 100 m apart at the bottom, share the same geology and macroclimate but
differ drastically in microclimate, flora and fauna. We predicted higher g
enetic diversity in earthworms living on SFS because they are exposed to cl
imatically more heterogeneous and stressful conditions.
Eighty-four specimens of earthworms were examined from SFS, NFS, and the va
lley bottom, each tested for 16 allozyme putative loci. Genetic diversity i
ndices were higher on SFS as predicted. In a multispecies test involving 8
species (lichens, wild barley, earthworms, mollusks, diplopods and beetles)
studied earlier we showed that the subpopulations living on SFS display si
gnificantly higher gene diversity than subpopulations from NFS. Our results
indicate higher gene diversity in climatically more fluctuating and hetero
geneous conditions and thus corroborate the prediction of the niche-width v
ariation hypothesis.