- Title
- Studies of the Green and Golden Bell Frog (Litoria aurea) in a modified habitat: enabling technologies, impacts of fire and disturbance, and assessment of translocation outcome
- Creator
- Lenga, Dean Jacob
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2024
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Conservation Biology is the science of the management of the Earth’s biodiversity and has the objective of protecting common and threatened species, their habitats and ecosystems from extinction. The importance of the concept of conservation biology has only been acknowledged with its recognition as a discrete discipline in recent decades with increasing awareness of the requirement to preserve biodiversity across the community. It is understood that for management plans to be successful, the results of implemented action must prevent the decline of organisms from detrimental natural and anthropogenic factors. At a global level, species richness and resources (e.g. habitats) are rapidly declining to levels where recovery seems improbable. One of the major causes of reduction of biodiversity is the loss of habitats. This can range from small changes in environmental conditions to complete elimination of ecosystems arising from drastically impacted landscapes. Other major driving factors in degraded systems are habitat loss, habitat fragmentation, invasive species and diseases, as well as, increasingly, climate change. In order to mitigate and reverse these and other drivers of the decline in biodiversity, ecologists have attempted to devise paradigms and methodologies in conservation to manage the underlying causes. Habitat creation is defined as “creating a dynamic community of interacting plants and animals that should increase in diversity over time”. This method is implemented to remedy the damages caused by loss of habitat. Its advantage comes from the possibility to mitigate and reverse substantial, long-term effects of habitat degradation over large areas. As such, the approach of habitat creation has been used alongside habitat protection and monitoring programs to support the conservation of populations and habitats of endangered species and even prevent extinction. Implementation of habitat creation requires careful planning and the setting of clear goals for target species in conservation projects. This should be in combination with an ongoing post habitat construction monitoring program and, where necessary, the ongoing maintenance of habitats, if the highest chance of mitigating the damages caused by the original habitat loss are to be achieved. This thesis delves into the investigation of one such constructed habitat that was developed for the endangered endemic species the Green and Golden Bell Frog (Litoria aurea). The aim of this project was to monitor this habitat over the course of multiple breeding seasons 2017 to 2020 and evaluate the conditions of the habitat for the use of L. aurea as an ecosystem that can both be used to maintain as well as increase population numbers via the activity of breeding and recruitment events. The thesis is presented as four separate chapters, each of which is a manuscript in preparation that will be published with multiple authors. Chapter 2: Amphibians' calling activity is a key behavioural indicator of both frog presence in a habitat as well as the quality of the habitat for the frog’s ecological needs. The identification of calling males provides a powerful passive ecological insight into a habitat and thus is an important data point to collect when monitoring an ecosystem’s capacity for frog conservation. The aim of chapter 1 was to evaluate the use of a newer and more compact acoustic recording device against a historically established and used acoustic recording device in frog monitoring projects. Using two different PAR models, the AudioMoth and the Song Meter SM4 and human observers to assess their efficiency in detecting vocalizations of a wetland frog community. We found that the AudioMoth detected slightly more frog calls than the Song Meter, making it a cost-effective alternative for ecological monitoring of frogs. Further analysis of the results from the raters verifying audio files found that the agreement between four experienced observers (raters) was generally satisfactory, but variations exist, emphasising that consistent raters and observer training can help to avoid bias. After completing this comparative study of acoustic devices and observer (rater) outputs, it was intended to use this methodology as a part of the ecological surveys reported in the three field-oriented chapters below. However, constraints on time and resources meant that this was not feasible, so this chapter is a stand-alone study of recording devices used in amphibian field studies. Chapter 3: Understanding and separating the difference between preadaptation (exaptation) and adaptation in relation to an environmental change is an important problem in understanding a species ability to respond to global environmental change occurring because of climate change and linked environmental events such as increasing frequency and intensity of fire. Chapter 2 delves into this missing gap in our understanding with the use of the opportunistic events of two unplanned anthropogenic fire events that occurred on my field study site (Kooragang/Ash Island). Due to these events we aimed to take the opportunity to determine the ability of L. aurea to react to “unnatural” habitat disturbance events and determine the extent to which the species has the capacity to react to fire in their habitats. This chapter used both the wealth of historical survey data available that was collected prior to my PhD candidature as well as the resource of the Island wide data sets collected by fellow ecologists on other section of Kooragang Island including data collected on the NCIG site (my primary study site). In this study, we show that the adaptation of L. aurea that has resulted in natural drought resilience has pre-adapted the species to be resilient to fire in the landscape. Chapter 4: This chapter focussed on the effectiveness of an accepted management strategy for managing habitats of L. aurea i.e. the reduction of aquatic emergent vegetation (macrophytes) in wetland waterbodies to create a more open water aquatic environment. Focusing on the evaluation of habitat manipulation methods of Macrophyte clearance of water bodies on Kooragang Island, Chapter 3 aims to determine if L. aurea prefer habitats with recent successional disturbance and reduced amounts of vegetation. The question is whether providing disturbed habitats at earlier successional stages due to reduced vegetation cover would be more conducive for breeding and increase occupation and abundance of Litoria aurea in disturbed waterbodies. We hypothesise that ponds that had vegetation removed will show an increase in presence of L. aurea compared to survey results prior to the habitat manipulation event. The combined findings suggest that a significant portion (around 40%) of relocated frogs swiftly returned to their source pond, while about 60% of frogs that moved from disturbed ponds to other ponds, were still alive after a year post the disturbance event. However, the actual survival rate could be even higher due to survey limitations such as detectability limits. The data indicated no impact of disturbance on frog numbers at the treated ponds, with no decrease or increase observed. No breeding events were induced by disturbance in both disturbed and undisturbed ponds throughout the observation period from the time of the disturbance event to a year later. Chapter 5: The current wetland mosaic within the reconstructed Ash Island habitat (75 ha) was investigated over 3 years of breeding seasons (2017/18 to 2019/20) to assess the utilisation (and viability) of wetland habitats constructed in 2014 as L. aurea habitat. The patterns of occupancy and waterbody utilisation against existing paradigms of L. aurea ecology and expected behaviour, dispersal, breeding and occupancy in reconstructed systems intended as supplementary habitat for this species were assessed in Chapter 4. The occupancy of the constructed system on Ash Island (constructed wetland habitats produced by Newcastle Coal Infrastructure Group (NCIG) to meet environmental licencing requirements) was assessed against adjacent constructed habitats (approximately 1 km from the NCIG wetlands) constructed by BHP. The occupancy of the NCIG habitats was assessed against currently accepted criteria for constructed habitats considered to constitute ideal habitat conditions for colonisation and breeding by L. aurea. These include the presence of ephemeral ponds in a landscape mosaic of permanent and ephemeral water bodies. It was found that the population of L. aurea in the NCIG habitats bred successfully and continued to occupy constructed wetland habitats through to the end of the monitoring period, despite showing an overall negative trend in population numbers. In comparison, another adjacent constructed habitat system displayed higher population sizes and increased over time (before also decreasing towards the end of the study period). The extremely dry (drought) conditions may explain some aspects of these trends. Other factors (such as various measures of water quality) did not explain the population trends. Further work on the L. aurea population in the constructed NCIG habitat system is required to better understand the population and system dynamics driving outcomes in this constructed wetland landscape.
- Subject
- Green and Golden Bell Frog; Litoria aurea; conservation biology; habitat degradation; habitat creation
- Identifier
- http://hdl.handle.net/1959.13/1511415
- Identifier
- uon:56491
- Rights
- Copyright 2024 Dean Jacob Lenga
- Language
- eng
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