Award Date


Degree Type


Degree Name

Master of Science (MS)


Biological Science

First Committee Member

Lawrence Walker

Number of Pages



Seed dynamics of Larrea tridentata and Ambrosia dumosa were measured for two consecutive years (2000--2001) in microhabitats under adult Larrea, under adult Ambrosia, under non-Larrea/Ambrosia shrubs, in barren open areas, and in open areas with >50% microphytic crust cover. Microhabitat measurements were replicated at four large-scale sites that differed in elevation and canyon. Both species produced equivalent numbers of seeds per shrub when both years were considered. Ambrosia had significantly more seeds in the soil seed bank than Larrea at two of the four large-scale sites. Microsite effects on the seed dispersal and subsequent distribution of these species were not significant beyond the parent shrub. Post-dispersal granivory experiments indicated that Larrea seeds were preferentially removed relative to Ambrosia on occasion. Microhabitat-specific granivory was not a consistent effect; The density of Ambrosia juveniles was ca. 60 times that of Larrea. This increase in the relative number of Ambrosia over Larrea could not be explained by large differences in their seed set or their seed bank size. Both species had more juveniles associated with adult Ambrosia shrubs than other microsite types and no juveniles of either species were found in association with microphytic crust. This evidence suggests adult Ambrosia may facilitate the recruitment of its conspecifics and Larrea, while soil crust may inhibit successful recruitment.


Ambrosia; Desert; Dumosa; Fecundity; Heterogeneous; Landscape; Larrea; Mojave; Spatially; Tridentata

Controlled Subject


File Format


File Size

3358.72 KB

Degree Grantor

University of Nevada, Las Vegas




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