Nutritional Ecology of a Generalist Herbivore Vanessa cardui Linnaeus (Lepidoptera: Nymphalidae) on Variable Larval and Adult Diets

This dissertation research examined whether generalist feeding Vanessa cardui larvae display dietary self-selection, what rules of compromise are followed when larvae are constrained to suboptimal diet, how larval and adult nutrition affect butterfly fitness, and whether adults are able to compensate for variations in larval nutrition with differential adult foraging. First, I examined dietary self-selection and rules of compromise for protein and digestible carbohydrate intake by 5th instar V. cardui larvae. Larvae regulated nutrient intake to a near equal-ratio protein:carbohydrate in choice trials, consistent with results found for other Lepidoptera. Larvae on no-choice diets had reduced fitness on protein-biased or carbohydrate-biased larval diets relative to equal-ratio, and the rule of compromise exhibited by V. cardui is consistent with that expected for a generalist herbivore. Second, I determined whether larval nutrition affects adult foraging behaviors. Females reared on carbohydrate-biased diet were more likely to probe towards nectar mimic containing sugars and amino acids than towards mimic containing sugars alone. Butterflies reared on protein-biased diet consumed more nectar than butterflies reared on carbohydrate-biased diet. Butterflies, however, did not exhibit preference between sugar and sugar plus amino acids solutions, regardless of larval nutrition.Third, I examined the relative importance of larval and adult dietary nutrient intake on V. cardui fitness. Adult nutrition played a greater role in realized fitness than larval nutrition, but was mediated by larval dietary history. The most important factor influencing female fitness was adult carbohydrate consumption. Nectar-derived amino acids did not appear to increase fitness, but appeared to negatively affect total egg production when butterflies were reared on equal-ratio larval diet.Lastly, I studied whether V. cardui exhibit mate choice based on the levels of proteins/amino acids and carbohydrates on which potential mates fed. Mate choice was not affected by larval diet, but was affected by the adult diet of potential mates. Overall, selecting butterflies were more likely to pair with animals provided sugar and amino acids than those given sugar alone. Those fed protein-biased diet as juveniles and sugars plus amino acids as adults were most preferred, while animals provided carbohydrate-biased diet and sugars were least preferred

Examining Decomposition and Nitrogen Mineralization in Five Common Urban Habitat Types across Southern California to Inform Sustainable Landscaping

Urban landscaping conversions can alter decomposition processes and soil respiration, making it difficult to forecast regional CO2 emissions. Here we explore rates of initial mass loss and net nitrogen (N) mineralization in natural and four common urban land covers (waterwise, waterwise with mulch, shrub, and lawn) from sites across seven colleges in southern California. We found that rates of decomposition and net N mineralization were faster for high-N leaf substrates, and natural habitats exhibited slower rates of decomposition and mineralization than managed urban landcovers, especially lawns and areas with added mulch. These results were consistent across college campuses, suggesting that our findings are robust and can predict decomposition rates across southern California. While mechanisms driving differences in decomposition rates among habitats in the cool-wet spring were difficult to identify, elevated decomposition in urban habitats highlights that conversion of natural areas to urban landscapes enhances greenhouse gas emissions. While perceived as sustainable, elevated decomposition rates in areas with added mulch mean that while these transformations may reduce water inputs, they increase soil carbon (C) flux. Mimicking natural landscapes by reducing water and nutrient (mulch) inputs and planting drought-tolerant native vegetation with recalcitrant litter can slow decomposition and reduce regional C emissions

Examining Decomposition and Nitrogen Mineralization in Five Common Urban Habitat Types across Southern California to Inform Sustainable Landscaping

Urban landscaping conversions can alter decomposition processes and soil respiration, making it difficult to forecast regional CO2 emissions. Here we explore rates of initial mass loss and net nitrogen (N) mineralization in natural and four common urban land covers (waterwise, waterwise with mulch, shrub, and lawn) from sites across seven colleges in southern California. We found that rates of decomposition and net N mineralization were faster for high-N leaf substrates, and natural habitats exhibited slower rates of decomposition and mineralization than managed urban landcovers, especially lawns and areas with added mulch. These results were consistent across college campuses, suggesting that our findings are robust and can predict decomposition rates across southern California. While mechanisms driving differences in decomposition rates among habitats in the cool-wet spring were difficult to identify, elevated decomposition in urban habitats highlights that conversion of natural areas to urban landscapes enhances greenhouse gas emissions. While perceived as sustainable, elevated decomposition rates in areas with added mulch mean that while these transformations may reduce water inputs, they increase soil carbon (C) flux. Mimicking natural landscapes by reducing water and nutrient (mulch) inputs and planting drought-tolerant native vegetation with recalcitrant litter can slow decomposition and reduce regional C emissions