Publication Date

Fall 2015

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Studies

Advisor

Rachel E. O'Malley

Keywords

Bay checkerspot butterfly, Endemic plants, Nitrogen deposition, Serpentine ecosystem

Subject Areas

Climate change; Ecology; Entomology

Abstract

Recent anthropogenic increases in atmospheric nitrogen due to urbanization and combustion have had many adverse effects on natural systems, including loss of biodiversity, especially in sensitive habitats. One such region is the serpentine ecosystem of Coyote Ridge in San Jose, CA, the last refuge for recurring populations of the federally threatened Bay Checkerspot Butterfly (BCB) (Euphydryas editha bayensis). Increases in non-native grass cover and decreases in native forb cover (including cover of the BCB’s native larval host plants) have been attributed to the fertilizing effects of increased atmospheric nitrogen deposition. To counteract this effect, grazing has been implemented as a grassland management strategy. However, the effects of nitrogen enhancement and grazing, and the combined effects on shoulder-season nectar resources, have not been previously studied. This research aimed to fill this gap by utilizing a split block experimental setting at Coyote Ridge with four treatments, comprising of fertilized, unfertilized, grazed and ungrazed plots. According to the study results, nitrogen enhancement tended to reduce the abundance of nectar resources in both grazed and ungrazed plots. It also tended to reduce native vegetation in the grazed plots, while potentially increasing its prevalence in the ungrazed plots. These findings suggest that the effects of grazing and nitrogen on serpentine ecosystems are complex, highlighting the need to reduce nitrogen deposition.

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