Author ORCID Identifier
https://orcid.org/0000-0002-9449-3920 : Danielle Orrell
Date of Award
Acoustic telemetry, Ascension island, Behavioural ecology, Fine-scale tracking, Movement ecology, Vemco positioning system
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Our ability to identify and understand the relationships and distributions of organisms in nature is key to exploring the rich tapestry of life seen on Earth. The term "niche" describes how animals partition resources in space and time, shaped by behavioural choices and environmental conditions. Iterations of niche over time have focused on different aspects of a species' ecological characteristics, from Grinnell’s initial study of songbird distribution (‘spatial niche’) in 1917 to Elton’s description of functional attributes shaping trophic position (‘trophic niche’). The fusion of these niche definitions formed Hutchinson’s n-dimensional niche hypervolume. The coexistence of species that utilize the same niche has been explained by a concept called ‘niche partitioning’, whereby species will differ in how they utilize resources (spatially, temporally or by the resources they acquire). Examples of niche partitioning include the selection of differing size spectra prey items, and differences in space use across diel or seasonal periods. Acoustic telemetry has been used to track the movements of aquatic species across a range of spatial scales and offers a powerful tool to estimate spatial niche and the mechanisms which facilitate coexistence. Additionally, trophic ecology is an important tool for understanding species interactions and the mechanisms that support coexistence, often explored using stomach content analysis and chemical tracers.
In this thesis, I explored the applications of acoustic telemetry, a forerunner in technology used to estimate the Grinnellian (spatial) niche of aquatic animals. Positioning algorithms shift the resolution of acoustic telemetry and the application of electronic tags from identifying the location of an animal within hundreds of metres to sub-metre precision. Through a systematic review of a commercial positioning system, I identified that this technology has been used to investigate fine-scale aquatic animal movement across a range of habitats, taxa and development stages. Analytical approaches to handling high precision datasets are adopting complex models which can accommodate a large quantity of contextual data to investigate facets of ecology including home range, habitat selection, activity and animal behaviour. The factors that shape the success of this fine-scale acoustic telemetry system can be grouped under factors relating to the study system, species studied, and logistical and technological constraints. Describing the steps that guide experimental design in fine-scale studies, as well as process to derive animal positions, is central to robust hypothesis testing and the identification of constraining factors which limit ecological inference. I use acoustic telemetry and dietary techniques (stomach content analysis and chemical tracers) to investigate coexistence of two abundant mesopredators in a nearshore environment. My findings suggest that the versatility of rock hind (Epinephelus adscensionis) and spotted moray eel (Gymnothorax moringa), including generalist dietary choices and individual differences in space use, facilitate their coexistence in a competitive high-biomass environment. Coexistence, particularly of species that perform similar trophic roles, provides ecosystem resilience in the wake of change, e.g., anthropogenic stressors or climate fluctuations, and contributes to the maintenance of biodiversity.
Orrell, Danielle, "Utilizing an Integrated Approach to Explore Niche in a Complex Equatorial System" (2022). Electronic Theses and Dissertations. 9134.