PhD Thesis
Islands and their biodiversity have high conservation value globally. Non-native species are largely responsible for island extinctions and island ecosystem disruption and are one of the major drivers of global biodiversity loss. Developing tools to effectively measure and understand island ecosystem change is therefore vital to future island conservation management, specifically island communities and the threatened species within them. One increasing utilised island conservation management tool is invasive mammal eradication. Such programs are increasing in number and success, with high biodiversity gains. Typically, it is assumed that the removal of target non-native species equates to management success and in some instances, recovery of a key threatened or charismatic species affected by the pest species are monitored. Yet to date, there are few published studies quantifying post-eradication ecosystem responses. Such monitoring helps to calculate return-on-investment, understand the conservation benefits of management and inform conservation decision-making associated with current and future restoration programs. Not only are there few studies providing empirical evidence of whole-of-ecosystem recovery following mammal eradications, but research that measures the responses of lower trophic organisms and communities is also scarce. In consequence, questions remain regarding how best to manage ecosystems following large-scale eradications. When should we intervene to actively restore habitats or species interactions? What biodiversity indicators do we use to measure and monitor ecosystem change? How do we compensate when data are scarce? And perhaps most importantly, how can we learn from previous management efforts to inform future conservation decisions? To investigate optimal monitoring strategies for changing ecosystems, it is vital to understand which sampling methods to use, which habitats to focus on, and which taxa to monitor that will reflect broader ecosystem change. Moreover, non-native plant and invertebrate species that are not targets of invasive mammal eradication, can persist in an ecosystem following an eradication. These organisms interact with native species, impact biodiversity and can even create novel ecosystems. To understand the implications of these changes and make informed decisions to act effectively, conservation managers require tools to efficiently measure ecosystem change.
My research focuses on World Heritage islands of the sub-Antarctic and I concentrate on a commonly overlooked group – terrestrial invertebrates. My thesis aims to address some of the questions raised above; first by reviewing the state of knowledge around non-native species iii impacts on invertebrates on in the sub-Antarctic region (Chapter 2), developing methods for effective and meaningful monitoring of invertebrates in changing ecosystems (Chapter 3), quantifying the invertebrate response to sub-Antarctic island mammal eradications (Chapter 4), understanding drivers of invertebrate richness and abundance in order to interpret these responses and develop indicators for effective long-term monitoring (Chapter 5), and using a traits-based analysis to identify non-native invertebrate taxa of biosecurity concern and future threat to the region (Chapter 6).