- Title
- Restoration ecology of the threatened green and golden bell frog (litoria aurea)
- Creator
- Beranek, Chad Thomas
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2021
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The decade encompassing 2021-2030 has been designated by the United Nations as the ‘Decade of Restoration’ where massive action is required to mitigate the threat of extinction for many species and ecosystems. Threatening processes that have greatly altered the Earth’s biomes generating a need for restoration on an unprecedented scale include habitat fragmentation and destruction, pollution, disease, introduced predators, disruption of nutrient cycles and climate change. Some of the main actions that can be taken to ameliorate these threats include protection of key habitat, managing disease, captive breeding for reintroduction, control of invasive species, and directly restoring degraded and destroyed habitat. All environmental actions and interventions fall under the paradigms of restoration ecology. Restoration ecology is a relatively new sub-discipline of conservation biology. Broadly, it is the study of ecological restoration, and involves research on the development of methods for recovering degraded or destroyed ecosystems, or re-establishing components of ecosystems through active intervention. Processes that come under its remit include habitat restoration, rehabilitation, enhancement, and reclamation and mitigation of threatening processes within restored systems. As a sub-discipline of conservation biology, restoration ecology draws on the practical and theoretical science within conservation biology to design and test restoration strategies and achieve outcomes. The large amount of prior research available for the threatened green and golden bell frog (Litoria aurea) makes this species an ideal a candidate to test principles and theory of restoration ecology and further refine restoration techniques for amphibians. The aim of this project was to investigate the response of a population of L. aurea within wetlands created in a disturbed landscape for the passive management of the fungal chytrid pathogen (Batrachochytrium dendrobatidis; Bd) and the invasive fish Gambusia holbrooki. The study aimed to determine if the wetland design was successful in achieving those objectives, with the intention of identifying components of the wetland design that added or detracted from the intended enhancement of the landscape habitat values. Ultimately, the intention was to illuminate approaches to improve the design of restored wetlands for this species and others with a similar ecology. The science behind the reasoning for particular aspects of the created wetland design is introduced and presented in Chapter 1 as a template that conservation managers can apply in other restoration projects for species like L. aurea that operate in and disperse through a complex habitat mosaic across multiple generations and breeding cycles. The key components of the design to enhance the habitat for L. aurea populations are; (1) passive management of Bd through permanent wetlands that interface with the ground-water table to promote a saline influence within waterbodies in the system, and through ephemeral wetlands that dry completely. (2) Earthen-bunding walls that surround each wetland to prevent or limit colonisation by Gambusia. (3) A habitat mosaic that provides variability in wetland structure in terms of aquatic vegetation, water quality, hydro-period and interpolated terrestrial habitats. The study found evidence to indicate the wetland design was a success, as the created wetlands had substantial numbers of breeding events associated with a rapid population increases (Chapter 2). Furthermore, there was support for the hypothesis that the passive management Gambusia contributed to enhanced breeding. However, there was less clear evidence that the design was successful in passive management Bd. These results highlight that future wetland creation for L. aurea should encompass measures to exclude Gambusia and further research is needed to optimise the design to passive mitigate Bd. Further examination of the rapid population response of L. aurea to the created wetlands revealed evidence of sex-specific population dynamics. It was found that females matured 1.5 times slower than males (Chapter 3); this produced a lag in adult female recruitment to the population compared to males, despite both sexes having comparable survival and detection probabilities. This finding has implications for future reintroduction and wetland creation targeted for amphibians that possess sex-specific maturation periods. Breeding and population turnover is limited by females in newly colonized habitats as they are the sex that will take longer to reach maturity from initial reproduction. Hence a strategy to overcome this is through either repeated yearly propagule releases or release gravid females from captivity into the newly colonized habitat when there is male chorusing but no reproductively mature females present. The reproductive ecology of L. aurea was explored through genetic pedigree analysis was provided in Chapter 4. This enabled the identification of several instances of multiple paternity which led to the conclusion that L. aurea is polyandrous, the only Pelodryadid species which has been confirmed as such. While this investigation into adaptive significance of amphibian behaviour was not directly related to restoration ecology, it is included as a chapter as it furthers our understanding of amphibian ecology, for which the applied ecological restoration for the created wetlands is based off. Furthermore, the intensive sampling and ease of access of the study site made these unique insights possible to obtain, where this might have been impossible in natural and more complex habitat. A novel means for genetic monitoring of the fecundity of L.aurea was produced in Chapter 5, which may be a valuable approach for other species with easily sampled aquatic larvae. The approach was to conduct pedigree analysis with high-resolution genetic markers on wild caught cohorts of tadpoles to estimate the number of mating pairs that reproduced in each breeding event within waterbodies. This allowed a more accurate estimation of the number of mating pairs that contributed to a cohort of tadpoles, which led to more accurate estimation of the total number of propagules that were produced. With the application of the population genetics methodology presented in Chapter 5, it was possible to account for the number of mating pairs in each ‘breeding event’ to estimate the rate of metamorph recruitment in different breeding habitats (Chapter 6). It was revealed in Chapter 6 that newly recharged ephemeral wetlands within the system produced 8.2 times as many metamorphs as permanent wetlands (or ephemeral wetlands that had remained filled for >170 days). There was evidence that the driver of this increased output was the absence of tadpole predators in newly recharged waterbodies. This finding supports the habitat mosaic approach, where the suitability of wetlands in terms of metamorph recruitment fluctuates temporally and spatially. The response of the population in the created wetlands to a drought was opportunistically examined in Chapter 7. It was found that there were large reductions in adult population size, where survival rate was negative influenced by an interaction between rainfall and maximum temperature. Despite this, late summer rain enabled the population to undergo large explosive breeding events, which resulted in large numbers of metamorphs being produced to replenish and restore the population numbers (following declines during the dry period). This finding demonstrates that L. aurea is somewhat resistant to drought and was able to persist in the created wetlands. However, it is unknown if this species can persist under more severe droughts. Global action to mitigate climate change is required to reduce the risk of severe drought to conserve this species into the future. Lastly, a preliminary investigation into factors permitting the co-occurrence of a threatened bat (Myotis macropus) and L. aurea is presented in Chapter 7. It was found that the co-occurrence of these species can be achieved in large permanent wetlands where there is low coverage within waterbodies from emergent vegetation. Hence, emergent vegetation management is recommended in large permanent wetlands to enhance co-occurrence of these species. This is a general principle that could be applied across multiple wetland restoration systems to achieve enhanced outcomes and greater returns on investment in restoration of such systems for multiple taxa. The new insights from the collective results presented in this thesis further our understanding of amphibian restoration ecology, not only for L. aurea, the focus species, but also for other landscape restoration projects that seek to restore and optimise resilience in species occupying wetland landscape mosaics. Future landscape design in those projects will be approached with greater confidence and understanding as a result of the findings in this study. This work will contribute to inform the global effort of ecosystem restoration in the 2021-2030 Decade of Restoration.
- Subject
- ecology; conservation biology; pedigree; polyandry; single-nucleotide polymorphisms; POPAN; capture-mark-recapture; growth; amphibians; predator-prey dynamics; thesis by publication; population dynamics; sex ratios; introduced species; batrachochytrium dendrobatidis; disease; wetlands; co-occurrence; population genetics
- Identifier
- http://hdl.handle.net/1959.13/1494279
- Identifier
- uon:53757
- Rights
- Copyright 2021 Chad Thomas Beranek
- Language
- eng
- Full Text
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