Determinants of the structural niches of columnar cacti in the Southwest

I evaluated whether morphological differences among populations of Carnegiea gigantea and Pachycereus pringlei actually represent evolutionary adaptation, different developmental responses to the environment, or simply differences in population age structure. Populations of Carnegiea running east to west across southern Arizona differ primarily in size structure, not in growth form. Where growth form differences do exist, they are correlated with variation in aridity. Carnegiea and Pachycereus in less xeric environments have more branches, greater total branch length, and earlier initiation of branching than those of equal height in more xeric environments. I found no evidence of evolutionary divergence among Carnegiea or Pachycereus populations. Natural experiments comparing adjacent stands support the hypothesis that the growth form variation is a developmental response to aridity, not evolutionary adaptation. The presence of a similar competitor was not associated with divergence of Carnegiea or Pachycereus populations from the growth form of populations without similar competitors.

Name thesis:degree_name

Master of Science (MS)

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Biological Science

Grantor dc:publisher

University of Nevada, Las Vegas

Year

1991

Author dc:creator

• Hentz, Joseph George

Contributors dc:contributor

• Joseph R. McAuliffe

Statement dc:rights

• IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

Language dc:language

English

Identifier

https://oasis.library.unlv.edu/rtds/146

OAI identifier oai:identifier

oai:oasis.library.unlv.edu:rtds-1145