Drivers of herbivore damage on tree seedlings at Powdermill Nature Reserve, PA, USA
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Evolution, Ecology, and Organismal Biology Undergraduate Research Theses; 2014
Herbivores can cause major damage and affect survival of tree seedlings. The factors that cause variation in herbivore damage rates among individual plants are not well known. Most prior studies have focused on single factors that affect herbivore damage rates on plants. The purpose of this study is to test which variables affect herbivore damage rates on tree seedlings. Specifically, I was interested in testing whether abiotic variables, such as elevation and moisture levels (as measured by distance from stream), and biotic variables (such as the density of conspecifics and plant species diversity), influence herbivore damage rates. I took data from thirty-seven 20×20 meter plots at Powdermill Nature Reserve (PNR) in southwestern Pennsylvania (40°09’S, 79°16’W). I took photos of tree seedling leaves and quantified percent herbivore damage in the photos using Image J software for 296 tree seedlings of 22 species. I ran Spearman rank correlations and a generalized linear regression model to test for effects of distance from stream, elevation, seedling diversity and conspecific neighbor density on percent herbivore damage. I found large variation in herbivore damage rates among species (0.373-10.8%) and among individuals (0-40.6%). The herbivore damage rate was particularly high for American basswood(Tilia americana) seedlings. From the multiple linear regression model, I found the biotic factors had significant, but minimal effects on herbivore damage rate, while the abiotic variables had no significant effects on herbivore damage rate. In related biotic factors, height had a positive relationship with herbivore damage and species richness had a negative relationship with herbivore damage. My results suggest that herbivore damage is not influenced by abiotic factors such as elevation and moisture level. It shows that biotic factors can affect the relationship between herbivores and tree seedlings, although the effects were small. This study helps eliminate some of the potential abiotic factors that could affect herbivore damage rates, and also indicates that further studies are needed to determine what other abiotic elements can drive variation in herbivore damage rates.
Academic Major: Biology
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