Fitness consequences of deviation from body size
Credit: The San Francisco Chronicle
Females must balance energy investment into non-essential processes such as growth and reproduction. However, attainment of large size can often facilitate greater reproductive success and increased survival. I explored the fitness consequences of deviating from age-expected body size for northern elephant seal females, as well as the associated trade-offs between growth, reproduction, and survival.
I found that larger female elephant seals reproduced more and skipped fewer breeding attempts. However, I found evidence of a trade-off between growth and longevity whereby seal pups that grew rapidly to attain large adult body size had shorter lifespans.
Manuscript has been submitted.
Energy investment into marine mammal growth
Growth of structural mass and energy reserves can influence individual survival and reproductive success. Metrics of structural growth and energy storage of individuals are often used to assess population health. Understanding energy allocation to growth with respect to both structural size and energy reserves can improve our use of body size as a proxy for individual and population health. However, the cost of growth in marine mammals is poorly documented. Here, I provide the first empirically estimated cost of growth in marine mammals and review the primary literature on growth trajectories and prioritization of growth in marine mammals.
Understanding trends in body condition
Body condition is a term used to describe the health of animals. It usually refers to the energy reserves (fat stores, usually blubber for marine mammal species) that can be readily mobilized when energy needs surpass energy intake. Understanding seasonal and life history-related trends in body condition can improve our understanding of when populations are experiencing energetic stress and may be more vulnerable to anthropogenic disturbance, and improved documentation of body condition can aid in bioenergetic modeling.
Constructing a morphologically accurate 3D model of marine mammals
Studying marine mammal morphology presents an interesting challenge. These animals live under water and are typically extremely large, making it difficult to study their size and shape without advanced technical equipment. The “truncated cones” method is traditionally used to examine marine mammal morphology, which divides the marine mammal body into a series of geometric shapes.
Using a series of pilot whale images and Blender, an open-source 3D modeling interface, I constructed a biologically accurate model of pilot whales that could then be scaled by individual girth and length measurements to determine surface area and volume. When comparing measurements from the 3D model with the traditional truncated cones method we found that the latter method tended did not accurately represent the nuanced morphology of pilot whales.
This research provided an easily accessible method and cost-effective way to examine the morphology of marine mammals.
Is bigger better? Exploring the benefits and energetic constraints on large body size
Harbor porpoises are one of the smallest marine mammals in a class of animals that trend towards gigantism. Their small size results in an energetic challenge where they must feed near continuously to maintain their energy reserves, which makes them vulnerable to periods of reduced energy intake via environmental or anthropogenic disturbance.
I explored the fitness benefits and energetic constraints of attaining a larger body size in harbor porpoises using Stochastic Dynamic Programming. I simulated three populations of harbor porpoises that differed in size class and examined individual and population vital rates, as well as resilience to disturbance.
Manuscript is in production.
Image from Adamczak et al. 2019
Do pilot whales follow ecogeographic rules?
Ecogeographic rules explain latitudinal variation in biological traits. Rules such as Bergmann’s rule and Allen’s rule describe latitudinal variation in body size and appendage size, respectively, driven by heat conservation in cold environments. However, these rules have predominantly been studied in terrestrial animals, disregarding the unique evolutionary pressures faced by marine mammals.
I found that pilot whales followed Bergmann’s rule, since long-finned pilot whales (the larger species with a more northern, cold-water distribution) were larger and have lower SA:V (surface area to volume; a metric of heat loss) ratios than the short-finned pilot whale. Long-finned pilot whales also had much larger pectoral flippers, therefore, pilot whales represented an exception to Allen’s rule. However, the most fascinating result was that larger long-finned pilot whales (e.g. mature males) had proportionally larger pectoral flippers than smaller long-finned pilot whales (e.g. immature females). This indicated that very large animals with low SA:V ratios (a heightened ability to keep heat within the body) needed to have larger appendages to rapidly offload heat.
Studying the impacts of the Adelaide Dolphin Sanctuary on a resident dolphin population
Marine sanctuaries are becoming increasingly popular for the conservation and protection of marine species. However, the success of these sanctuaries in protecting highly mobile marine mammal species needs to be studied in more detail. I examined the efficacy of management on the Adelaide Dolphin Sanctuary, where the resident bottlenose dolphin population had been previously impacted by anthropogenic (human-induced) disturbance such as vessel traffic and intentional killings. I found that the Adelaide Dolphin Sanctuary was successful in its mission to protect the dolphins from anthropogenic disturbance, as there was a decrease in deaths caused by humans (such as vessel strikes and entanglement in fishing gear). This research demonstrates that sanctuaries can be successful in protecting marine mammal species and are a useful management tool.
Photo from Stephanie Adamczak