<b>Plant Leaf Nutrients and Insect Herbivory from Herbarium Specimens over 180 Years of Rising Atmospheric CO</b>_{<strong>2</strong>}

<p dir="ltr">Terrestrial plants and animals have been substantially impacted by human actions, from the movement of species to new locations to pollution and land use changes. Here I examine how ecosystem dynamics and species interactions are responding to global change. The first chapter considers the potential for theories of species invasions to be used in the context of climate change-induced range shifting. Both are forms of species spread, though populations undergoing invasion and range shifting differ in factors such as their genetic diversity, climatic tolerance, local adaptation, and coevolutionary history. I find that invasion theories may be useful in making management decisions for range shifting populations, as long as adjustments are made for these key differences. The second chapter investigates the effects of rising atmospheric CO₂ concentration on the nutritional quality of six plant species that are food sources for herbivorous insects. Using herbarium specimens that had been collected from 1880 to 2022, I analyzed the change in leaf nitrogen concentration as CO₂concentration increased since the Industrial Revolution. The rise in CO₂, in addition to other changing environmental factors, led to an 18% decrease in leaf nitrogen concentration over the 142-year period. In the third chapter, I quantify the amount of herbivore damage on the herbarium specimens used in chapter two. I find an increase in herbivore damage over time for some plant species that is explained by the age of the leaf and collection location, but is not correlated to leaf nitrogen concentration. Together, these chapters demonstrate how existing ecological frameworks and natural history collections can be leveraged to better understand how climate change and human actions have already affected ecosystem dynamics since the Industrial Revolution, and how to manage for future changes.</p>