UC Berkeley

Island-like (“insular”) environments are hotspots of rare and threatened biodiversity. These patchy environments differ markedly from their surroundings in one or more key environmental factors. For example, cool north-facing hillslopes receive less energy from the sun than their surrounding landscapes, and wet montane meadows retain more water. Consequently, insular habitats often host unique assemblages of taxa that depend on these distinctive environmental conditions. Many taxa that depend on insular environments have been negatively impacted by human land use change, which has made their habitats even rarer. This conservation challenge is exacerbated by climate change, which may push conditions in some patches beyond the tolerance of their inhabitants (e.g., too warm, too dry, etc.) or bring in new competitors that could outcompete resident taxa. As climate change progresses, it will be crucial to improve our understanding of the factors shaping dynamics of populations, species, and communities in these insular environments. In this dissertation, I focus on responses of plants to spatiotemporal environmental variation among islands and other insular environments. In Chapter 1, I examine how climate change influences tree community composition in hypothesized climatic microrefugia on north-facing hillslopes in the contiguous western United States. Chapter 2 explores how spatial variation in multiple climate variables shapes ecophysiological adaptations to climate for Lemmon’s willow (Salix lemmonii) in island-like montane meadows of the Sierra Nevada. Chapter 3 shifts the focus to another facet of environmental variation, the biotic environment, and introduces a new method for observational studies of interspecific competition in metacommunities distributed across patches of suitable habitat. In sum, these three chapters provide complementary views on the question of how plant populations, species, and communities respond to spatial and temporal variation in conditions among insular environments.