Reconstructing animal-vectored nutrient fluxes in paleoenvironments: A case-study of Aotearoa New Zealand’s burrowing procellariiforms
The cross-ecosystem flux of nutrients resulting from animal activity (animal-vectored subsidies) can significantly impact the communities receiving them. However, these functions are threatened by the ongoing decline and loss of species driving them. To understand ecosystem response to the loss of these functions, we must quantify what we have lost and determine the resulting change. My thesis extends previous efforts to quantify nutrient fluxes in paleoenvironments via a framework that integrates model-based approaches, using burrowing procellariiformes in Aotearoa New Zealand as a case study. In Chapter Two, I demonstrate how merging historic and fossil records can help account for biases in these data sources and model the past ecological niche of burrowing procellariiform breeding grounds. Comparing past to contemporary distributions highlights dramatic range contractions, with most inland colonies being lost and seabird populations now restricted to the coast and predator-free islands. In Chapter Three, I present a novel method for estimating nutrient flux volume using Orderspecific stoichiometric measurements and allometric models of excreta production. Using this method to estimate global nitrogen and phosphorus flux for three seabird Orders suggests that these fluxes are potentially one to two orders of magnitude lower than previously thought. In Chapter Four, I describe an agent-based model of procellariiform metapopulation dynamics under environmental change. Analysis of this model demonstrates that the presence of predators in one population can suppress a linked predator-free population via source-sink dynamics and that ENSO-associated variability in mortality rate may tip the scale for population extirpation. In Chapter Five, I combine the methods outlined in my previous three chapters to estimate nitrogen and phosphorus fluxes in New Zealand by burrowing procellariiforms in the past and present and characterize their population declines since the arrival of Europeans. I estimate that over a 50-year window, the fluxes declined to ~16% of their previous volume and to 8% of their former area. Finally, in Chapter Six, I discuss how the methods I developed could be applied to other species and fluxes in paleoenvironments, highlighting how this framework could be further extended to help us better understand cross-ecosystem dynamics.
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