Date of Award

Spring 2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean/Earth/Atmos Sciences

Committee Director

Eileen E. Hofmann

Committee Member

Daniel L. Dickerson

Committee Member

William R. Fraser

Committee Member

Chester Grosch

Committee Member

John M. Klinck

Abstract

Coupled individual-based models that simulate Adélie penguin ( Pygoscelis adeliae) chick growth and adult foraging behavior during the chick growth period were developed and used to explore factors that influence chick fledging mass and adult foraging energetics off the western Antarctic Peninsula (WAP). Adélie penguin colonies in this region are undergoing changes in population size that have been correlated with climate-driven alteration of the marine and terrestrial environment. Simulations were selected to highlight possible mechanistic linkages between climate variability and chick growth and adult foraging processes. These processes were the focus of this study because chicks that fledge at a greater mass are more likely to recruit to the breeding population and Adélie penguin population dynamics can link directly with recruitment and fledging mass.

Simulations using the chick-growth model tested the influence on penguin chick fledging mass of variability in (1) timing of Antarctic krill ( Euphausia superba) spawning, (2) chick diet composition [Antarctic silverfish (Pleuragramma antarcticum) combined with Antarctic krill compared to an all-Antarctic krill diet], (3) provisioning rate, and (4) the extent to which chicks become wet (from rain or melting snow). Simulations coupling the adult-foraging and chick-growth models investigated the influence on adult mass, foraging energetics, and chick growth of variability in (1) prey-availability characteristics (prey ingestion rate and distance between colony and prey), (2) the extent to which adults prioritize self-maintenance over chick provisioning, (3) adult digestion rate while foraging (a poorly studied physiological rate), and (4) adult diet composition [Antarctic krill combined with Antarctic silverfish (50% female) compared to all-Antarctic krill (50% and 100% female)].

In the chick-growth model simulations, shifting peak Antarctic krill spawning from early December to early March reduced fledging mass by 12%, enough to reduce a chick's probability of recruitment. Introducing a minimal amount of third-year age class (AC3) Antarctic silverfish to an Antarctic krill diet increased Adélie penguin fledging mass by 5%. Environmental stress that results in more than a 4% reduction in provisioning rate or wetting of just 10% of the chick's surface area decreased fledging mass enough to reduce the chick's probability of recruitment. The negative effects of reduced provisioning and wetting on chick growth can be compensated by an increase in AC3 Antarctic silverfish in the chick diet. Results from the coupled models showed that increasing adult ingestion rate, decreasing distance to prey, increasing adult digestion rate, feeding only on female Antarctic krill, and including Antarctic silverfish in the diet increased the range in prey-availability characteristics over which adults can raise full-sized chicks.

Overall, results suggest future observational and modeling studies that focus on factors that influence the ability of foraging adult Adélie penguins to provide high-quality prey to their young. Furthermore, results indicate that future studies should be directed at improving our knowledge of the energetic and physiological constraints on adult Adélie penguin foraging and chick growth. Results suggest that factors that influence the timing and extent of lipid aquisition and spawning among Antarctic krill may have important consequences for Adélie penguin chick growth. Additionally, climate-driven alteration of processes that determine the availability of phytoplankton biomass may have important consequences for Adélie penguins and other top-predator species that time critical activities to coincide with dependable availability of prey with maximum energy density. Also, results suggest that the loss of Antarctic silverfish from the diets of Adélie penguins in some parts of the WAP may have limited the ability of adults to compensate for the negative effects of climate-related changes in the marine (reduced Antarctic krill abundance) and terrestrial (increased wetting of chicks) environment.

Comments

Additional dissertation committee members: Margaret R. Mulholland, Christine A. Ribic, and Thomas C. Royer

DOI

10.25777/hw25-3b31

ISBN

9781109217506

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