Thesis

Niche relationships among rodents in a southern California chaparral community

Niche relationships and coexistence of ten species of rodents occurring in southern California chaparral were studied from October 1975 through September 1976. Habitat selection and utilization were investigated to determine the extent to which the fundamental niche of each species was reduced in size because of effective competitors. A 2.2 hectare study plot with 96 trap stations was used to census rodents regularly. Vegetation at each trap site was quantified using the profile board technique. Neotoma fuscipes selected habits of heavy chaparral cover and socially dominant to N. lepida, which was relegated by fuscipes to the chaparral edges. Peromyscus californicus also preferred dense chaparral and the presence of three congeners did not alter its selection of the preferred habitat. Distributions of P. truei and P. boylii were microparapatric within the chaparral and riparian woodland habitats. This distribution is maintained by direct interaction. Peromyscus maniculatus was found occasionally at the shrub-grassland interface but more often in the grassland habitat. It was excluded from the richer habitats by socially dominant congeners. It coexists in the grassland habitat with Microtus californicus and Reithrodontomys megalotis by being socially subordinate to M. californicus and dominant to R. megalotis. Dipodomys agilis was trapped at chaparral edges, open areas between chaparral shrubs and in grassland areas. Its negative pair-wise association with N. fuscipes represents fundamental differences in habitat requirements for these two species. Perognathus californicus coexists with the cricetids in the chaparral by being the most socially subordinate and by filling the interstices among species already present.

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