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Anthropogenic stressors reshape communities worldwide, motivating research on predictions of future impacts as well as developing tools and approaches for promoting resilience. My research focuses on marine algal communities in two habitats, temperate rocky intertidal zones and tropical fringing reefs, that have undergone widespread shifts due to global and local stressors.For over four decades, ecologists have improved understanding of how plant communities shift in response to environmental drivers using a trait-based framework. In Chapter 1, I develop a quantitative method for determining traits that are critical to measure for understanding the performance of rocky intertidal macroalgae. I measured a wide suite of traits then used ordination and correlation to reduce to six traits that limit collinearities, maximize potential tradeoffs, and create a functionally diverse trait space. I discovered an axis of variation for maximizing resource acquisition that varies between being tall and strong versus maximizing surface area and being short and weak. This work provides a roadmap for trait selection that I test in Chapter 2 for macroalgae on a tropical fringing reef. By following this same quantitative approach, I determine a core set of traits important for understanding ecological strategies of tropical algae. I select five traits critical to understand this temperate fringing reef and discover two axes of variation for resource acquisition and resistance to herbivory. By comparing Chapter 1 and 2, we find three traits useful in describing these diverse communities, suggesting there is a set of universally important traits that will facilitate comparisons between algal-dominated communities across multiple scales. In Chapter 3, I test the effects of tropical storms on turf algae, a critical transition community on reefs that can facilitate coral recovery. Understanding the impacts of storms is important as their intensity is projected to increase with climate change. In a field experiment we simulate a storm with physical abrasion, sediment deposition, increased nutrients, and altered herbivore activity as stressors. We found that herbivores can reverse storm-generated transitions on coral reefs. In summary, my dissertation advances the development of novel approaches for understanding the shifting functions of algal communities and improves our ability to predict the responses of tropical algal communities to climate change.

Saprotrophic fungi perform the vital role of cycling nutrients and carbon back into the environment through the decomposition of organic matter. But in a rapidly changing global environment, we do not fully understand how these environmental changes will affect the process of decomposition by saprotrophic fungi. To understand decomposition and carbon cycling at a global scale, we must first begin to identify the life history strategies that saprotrophic fungi employ. For saprotrophic fungi, resources are arrayed in patches in the environment, much like an archipelago of islands. On these resource islands, interspecific competition is intense and available resources are continually depleted as a consequence of fungal metabolism. Here, airborne dispersal is a key factor that allows fungi to avoid being restricted to an island experiencing total resource patch collapse and to persist within the environment. In this thesis, I take an experimental approach and explore how living in finite resource patches shapes allocation to dispersal in fungi, and how a resource patch can alter the course of interspecific competition. In Chapters 2 and 3, I tracked allocation to dispersal in saprotrophic fungi using Phacidium lacerum, a novel model species. In Chapter 2, I ran a Petri-dish experiment varying resource island size (Petri-dish size) and nutrient concentration to test how environmental quality influenced allocation to dispersal. In Chapter 3, I included both interspecific and intraspecific competitors to see how negative interactions changed patterns of allocation to dispersal. In Chapters 4 and 5, I focused on competition between saprotrophic fungi. In Chapter 4, I explored how the strength of competition varied across simple and complex substrates, and in Chapter 5, I tracked how wood decay was influenced by interspecific competition in a paired wood block experiment. Altogether, these studies highlight the importance of considering dispersal and competition in saprotrophic fungi, especially in the context of finite resource patches as islands.