Environmental Studies Program

 

Date of this Version

Fall 12-2010

Comments

AN UNDERGRADUATE THESIS Presented to the Faculty of The Environmental Studies Program at the University of Nebraska-Lincoln In Partial Fulfillment of Requirements For the Degree of Bachelor of Science, Major: Environmental Studies, Emphasis: Biological Sciences, Under the Supervision of Dr. Johannes Knops; Lincoln, Nebraska : December 2010
Copyright 2010 Caitlin Falcone

Abstract

The choice of a specific microhabitat represents a compromise among a number of different factors organisms use to monitor habitat suitability. Grassland vegetation structure can vary widely along environmental gradients over a relatively small area. This vegetation structure can have a large influence on habitat selection by grasshoppers (Orthoptera). However, it is not clear which vegetation characteristics are most important in determining grasshopper abundance. We found that plant biomass, plant species richness, and plant quality all have an effect on grasshopper abundance and distribution. We observe that these affects vary both within and among the two years of data collection. The timing of rainfall within a year strongly affects plant productivity and a large difference in plant productivity among years may lead to different outcomes. In a year of lower plant productivity, plant biomass and plant species richness determine grasshopper abundance. In a year of higher plant productivity, plant quality and plant biomass determine grasshopper abundance.

There has been little work to examine how increased nutrient loads in today's environment affect grassland plant communities and in turn, insect herbivore communities. Grasshopper choice between two vegetation treatments, control and nutrient addition, can affect the outcome of interactions of soil nutrients, plant biomass, and grasshopper biomass. By modeling the effects of grasshopper choice for plant quality and quantity, I was able to predict an effect multiple levels of nutrients can have on the overall vegetation biomass in nitrogen enriched and control plots. I found that there is a threshold level of nitrogen addition at which the nitrogen enriched plots have the same value of plant biomass as the control plots mediated by grasshopper response to plant quality and quantity. A comparison of two models, constant vs. variable (constant plant quality vs. variable plant quantity), revealed that the constant model predicts the biomass of grasshopper better.