While positive species interactions are increasingly recognized as playing a fundamental role in the ecology and evolution of most organisms, the dynamics of multi-species positive interactions remain poorly understood. My dissertation takes a community ecology approach to investigating positive species interactions among insects, plants, and microbes, asking how associations among one set of organisms affect mutualisms among others sets of interacting organisms. The first chapter experimentally demonstrates the positive effects of plant-rhizobia interactions on aphid growth and honeydew composition. I grew 180 soybean (Glycine max) plants belonging to two strains: a nodulating strain, the nodules of which are colonized by nutrient-fixing bacteria (rhizobia), and a non-nodulating strain that does not harbor rhizobia. Plants were inoculated with soybean aphids (Aphis glycines), and measurements of aphid colony growth and plant traits were taken over three weeks, after which aphid honeydew was collected and chemically analyzed. Aphid colonies grew slightly larger on nodulating plants and honeydew collected from aphids feeding on nodulating plants (i.e. plants that associate with rhizobia) were found to have significantly higher sugar content than aphids feeding on non-nodulating plants. The potential for this result to affect community properties (e.g. ant-aphid interactions) and ecosystem properties (e.g. microbial nitrogen mineralization in the soil) is discussed. Because honeydew is an important factor mediating aphids' interactions with ants, and because ant-aphid interactions are considered keystone interactions in many ecological communities, my second chapter provides an analysis of the arthropod community in the same experimental system. Using a classic community ecology approach, the abundance, diversity, richness, evenness, and community structure of herbivorous and predacious arthropods are compared between plant strains (nodulating and non-nodulating) and experimental treatments. Both the herbivorous and predacious arthropod communities were significantly influenced by the presence of aphids and ants, but results indicate that the additional treatments of aphids and ants negate previously demonstrated positive effects of plant-rhizobia interactions on arthropod community properties. My third chapter provides a taxonomic characterization of the microbiomes of lycaenid caterpillars, an insect group with diverse life histories, diets, and ant associations. Specimens belonging to three subfamilies were collected from the United States, Thailand, and Singapore, and included herbivorous species that facultatively associate with ants and wholly carnivorous taxa that eat homopterans (often under ant attendance). Using high throughput sequencing on an Illumina platform, I used comparative analysis of 16s rRNA gene sequences to characterize and contrast the microbiomes of each specimen. This work is the first to explore the microbial associations of lycaenid butterflies using high throughput culture-independent techniques. This research will be expanded in future work to address questions related to host-symbiont interactions and the possibility that the evolution of diet and ant- association may be microbially mediated in this group. Finally, in addition to my dissertation research, I completed a capstone project in biodiversity informatics and citizen science. In response to the growing popularity of citizen science and biodiversity monitoring projects and the importance of science outreach and education, I developed a mobile tool for natural history education and biodiversity informatics. The resulting iOS application--The Butterfly Guide: Butterflies of the Sacramento Valley, Delta, and San Francisco Bay Area--is both a mobile field guide and a data collection tool, allowing for the acquisition, synthesis, and dissemination of butterfly data by students, naturalists, and citizen scientists. Most importantly, all source code and development materials are freely available as a template for other developers interested in creating similar field guides. This project thereby serves as a prototype with the hope that it will increase opportunities for non-scientists to engage in the natural world, participate in the scientific process, and generate reliable biodiversity data.