Roberts, M.

Island ecosystems are recognised as high priority for biodiversity conservation, with invasive species a significant threat. To investigate prioritisation invasive species control, we conducted cost-effectiveness analysis of donkey control on Bonaire, Caribbean Netherlands. Successful prioritisation must take account of ecological, economic and social aspects of conservation. Further improvements are possible where impacts are measured across ecosystem boundaries, and management is tied to funding. We modelled the expected ecological impacts of control options, estimated costs, and connected this to the willingness of beneficiaries to fund such projects. Finally we surveyed experts to understand the social acceptability of donkey control. Of the control options, eradication is predicted to have the highest ecological impacts across two ecosystems, and to be cost-effective over the long term. Costs of all control options were within user willingness to pay. Social acceptability was highest for fencing, and lowest for lethal control. Though eradication offers the highest ecological benefits, we suggest that lower initial costs and higher social acceptability make fencing the better choice for Bonaire in the immediate future. In this way we illustrate the importance of considering economic and social impacts alongside the ecological in environmental conservation, and present an integrated application for prioritising conservation choices.

Raw monitoring data on terrestrial bird abundance observations. A long list of species is recorded accompanied by date/time and location. The species are grouped and indicators (e.g. species richness, shannon diversity index, abundance per species group) are automatically calculated .

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A Thesis Submitted for the Degree of PhD at the University of St Andrews:

Abstract

Environmental degradation is accelerating worldwide, yet environmental conservation remains limited by funding. Tackling this limitation requires not only absolute increases in funding, but improved prioritisation of actions. On a global scale island ecosystems are of high priority, with invasive species one of their most significant threats. In this thesis I investigate prioritisation of invasive grazing species control, incorporating ecological, economic, and social concerns, on the island of Bonaire, Caribbean Netherlands. To enable the trade-off of potential grazer control options for their ecological impacts I modelled the relationship between of grazer density and vegetation, and watershed vegetation and the coral reef. I found negative relationships for goat and pig grazing with grass presence, and for donkey grazing with ground cover. Coral cover below 10m showed a positive relationship to ground cover, and, surprisingly, a negative relationship to tree biomass. Because conservation action is most likely to be sustainable when connected to funding, I conducted choice experiments with SCUBA divers, which estimated a positive willingness to pay for reef health improvements achieved using terrestrial grazer control. Through communication with local policy makers and practitioners I identified three options for grazer control, eradication, population reduction, or fencing, and estimated costs and social acceptability for each option. Though the ecological models predicted eradication to have the highest impacts on the terrestrial and marine ecosystem, lower costs and higher social acceptability identified fencing as the most suitable option for grazer control on Bonaire in the short term, with the potential to be funded through a fee on SCUBA divers. Through linking ecological, economic, and social considerations within a real world conservation context I illustrate the importance of looking beyond only ecological improvements when prioritising conservation action. This research is directly applicable to policy and practise on Bonaire.

Content:

Chapter 1 Literature Review 

Chapter 2 Impacts of introduced grazing species on terrestrial ecosystems 

Chapter 3 Impacts of vegetation cover on coral reef health 

Chapter 4 User fees across ecosystem boundaries: Are SCUBA divers willing to pay for terrestrial biodiversity conservation? 

Chapter 5 Prioritising conservation actions 

Chapter 6 Discussion

Long periods of isolation and small island size make island ecosystems highly vulnerable to degradation and invasive species are one of the most significant threats (Cronk, 1997). Due to their role as livestock, introduced species such as sheep, goats, pigs, cows and donkeys are some of the most common invasive species worldwide (Island conservation, 2015). Introduced grazing species consume island vegetation at a rate faster than it is able to regenerate, and islands with invasive grazers are characterised by few, small trees of limited species, and low grass, herb, and shrub cover (Dahlin et al., 2014).

Coral reefs are in decline worldwide. While coral reef managers are limited in their ability to tackle global challenges, such as ocean warming, managing local threats can increase the resilience of coral reefs to these global threats. One such local threat is high sediment inputs to coastal waters due to terrestrial over-grazing. Increases in terrestrial sediment input into coral reefs are associated with increased coral mortality, reduced growth rates, and changes in species composition, as well as alterations to fish communities. We used general linear models to investigate the link between vegetation ground cover and tree biomass index, within a dry-forest ecosystem, to coral cover, fish communities and visibility in the case study site of Bonaire, Caribbean Netherlands. We found a positive relationship between ground cover and coral cover below 10 m depth, and a negative relationship between tree biomass index and coral cover below 10 m. Greater ground cover is associated to sediment anchored through root systems, and higher surface complexity, slowing water flow, which would otherwise transport sediment. The negative relationship between tree biomass index and coral cover is unexpected, and may be a result of the deep roots associated with dry-forest trees, due to limited availability of water, which therefore do not anchor surface sediment, or contribute to surface complexity. Our analysis provides evidence that coral reef managers could improve reef health through engaging in terrestrial ecosystem protection, for example by taking steps to reduce grazing pressures, or in restoring degraded forest ecosystems.

Highlights​

• Ecosystems are intrinsically linked, but conservation across boundaries is limited.
• User fees applied across ecosystem boundaries may improve conservation funding.
• Divers will fund terrestrial conservation, if coral improvements are expected.
• On Bonaire these funds would be large enough to cover terrestrial grazer control.

While ecological links between ecosystems have been long recognised, management rarely crosses ecosystem boundaries. Coral reefs are susceptible to damage through terrestrial run-off, and failing to account for this within management threatens reef protection. In order to quantify the extent to that coral reef users are willing to support management actions to improve ecosystem quality, we conducted a choice experiment with SCUBA divers on the island of Bonaire, Caribbean Netherlands. Specifically, we estimated their willingness to pay to reduce terrestrial overgrazing as a means to improve reef health. Willingness to pay was estimated using the multinomial, random parameter and latent class logit models. Willingness to pay for improvements to reef quality was positive for the majority of respondents. Estimates from the latent class model determined willingness to pay for reef improvements of between $31.17 - $413.18/year, dependent on class membership. This represents a significant source of funding for terrestrial conservation, and illustrates the potential for user fees to be applied across ecosystem boundaries. We argue that such across-ecosystem-boundary funding mechanisms are an important avenue for future investigation in many connected systems.