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Drivers of Marine Biodiversity Along a Latitudinal Gradient


A major goal of community ecology is to understand how communities are formed and which abiotic and biotic conditions constrain biodiversity and community assembly. To accurately predict and understand how communities are likely to change in response to changes in environmental conditions, it is important to understand the associations between species, the geographic patterns of species associations, how changes in associations and interactions affect community structure, and the demographic characteristics of populations throughout a species’ geographic range. To determine if the geographic distribution of species affects site diversity and potential interactions at each site, I executed an observational study of eight sites along the California coast where I categorized species as either narrow-range endemics or widespread species. I found that species were more likely to co-occur with one another south of Point Conception than north of Point Conception indicating potentially positive interactions in a more thermally stressful environment. I also found that narrow-range endemic species were the major drivers of the latitudinal patterns (Chapter 1). To determine if the effect of rockweeds on mobile invertebrate diversity and abundance differed across latitudes and at sites with differing levels of seaweed diversity, I used field observations and experimental removals of two rockweed species at three sites along the California coast. I found that rockweeds tended to increase mobile invertebrate species richness and abundance, especially at sites where functional redundancy was low (Chapter 2). Lastly, I followed populations of rockweeds at four different sites and characterized growth, survival, and reproduction of individuals over a 12-month period to determine how population demographic patterns differed between leading and trailing edge populations. Using these data, I constructed an integral projection model of each population of rockweeds. I found that populations living in the leading edge and central part of their species’ range had similar demographic characteristics, while trailing edge populations had lower population growth estimates and fecundity estimates compared to central populations (Chapter 3). My results identify and highlight some of the important drivers of biodiversity along California rocky shores, especially with respect to changes across spatial gradients and species’ ranges.

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