The structure and dynamics of arthropod communities in an old-field ecosystem

Graduation Date

2006

Document Type

Thesis

Program

Other

Program

Thesis (M.A.)--Humboldt State University, Biological Sciences, 2006

Committee Chair Name

Michael Mesler

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Nutrient addition, Insect community, Humboldt State University -- Theses -- Biology, Community ecology, Plant community

Abstract

Determining the factors that shape arthropod communities has a long history in ecology. I examined the direct and indirect effects of nitrogen availability on plant productivity and plant community composition to assess their effects on arthropod community structure in an old-field ecosystem. I sampled arthropods across the entire plant community, as well as on individual dominant plant species over two years. Both the addition and reduction of plant-available nitrogen had deleterious effects on arthropod richness and abundance. The negative effect of nitrogen was indirect: an increase in nitrogen increased early season cover of Bromus sp., which altered the microenvironment and reduced the availability of host plant diversity later in the season. Arthropod richness and abundance were not influenced by plant productivity or richness with or without the influence of nitrogen. Instead, particular plant species were better predictors of the arthropod community, although the pattern was complex and changed within and between years. Among the three dominant plant species, Verbesina occidentalis hosted fewer arthropods than V. virginica or Solidago canadensis in 2005. In both years V. virginica hosted more arthropod species than S. canadensis or V. occidentalis. At a broader scale, arthropod abundance in nitrogen plots decreased in 2004 but these relationships were only significant in mid-summer. These temporal changes in the arthropod community may be explained by changes in susceptibility of plants to herbivores, which in turn depends on leaf texture and trichome density. My results suggest that the overall attributes of a plant community are poor predictors of arthropod community structure. Instead, the direct and indirect effects of nitrogen on Bromus sp., and also the persistence of particular plant species throughout the summer, shape arthropod community structure in this old-field ecosystem.

https://scholarworks.calstate.edu/concern/theses/2f75rb520

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