The Use of Extant Non-Indigenous Tortoises as a Restoration Tool to Replace Extinct Ecosystem Engineers

Abstract

We argue that the introduction of non-native extant tortoises as ecological replacements for extinct giant tortoises is a realistic restoration management scheme, which is easy to implement. We discuss how the recent extinctions of endemic giant Cylindraspis tortoises on the Mascarene Islands have left a legacy of ecosystem dysfunction threatening the remnants of native biota, focusing on the island of Mauritius because this is where most has been inferred about plant-tortoise interactions. There is a pressing need to restore and preserve several Mauritian habitats and plant communities that suffer from ecosystem dysfunction. We discuss ongoing restoration efforts on the Mauritian offshore Round Island, which provide a case study highlighting how tortoise substitutes are being used in an experimental and hypothesis-driven conservation and restoration project. The immediate conservation concern was to prevent the extinction and further degradation of Round Island's threatened flora and fauna. In the long term, the introduction of tortoises to Round Island will lead to valuable management and restoration insights for subsequent larger-scale mainland restoration projects. This case study further highlights the feasibility, versatility and low-risk nature of using tortoises in restoration programs, with particular reference to their introduction to island ecosystems. Overall, the use of extant tortoises as replacements for extinct ones is a good example of how conservation and restoration biology concepts applied at a smaller scale can be microcosms for more grandiose schemes and addresses more immediate conservation priorities than large-scale ecosystem rewilding projects.

Introductions over introductions: the genomic adulteration of an early genetically valuable alien species in the United Kingdom

“…Nevertheless, the potential conservation value of non-natives has been recently highlighted. In some cases alien species can provide habitat, shelter and food to native ones, catalyze restoration of indigenous communities, recover ecological services by replacing the role of extinct taxa, and contribute to ecosystem resilience and stability through the increase of local species richness (Salm et al 2009;Griffiths et al 2010;Schlaepfer et al 2011Schlaepfer et al , 2012. Davis et al (2011) claimed for ad hoc assessment of the environmental impact of any given taxon rather than judging the same merely on whether it can be native or alien.…”

Turtles and Tortoises of the World During the Rise and Global Spread of Humanity: First Checklist and Review of Extinct Pleistocene and Holocene Chelonians.

“…Rewilding or assisted migration are potentially promising lines of conservation management strategies that may help restore vanished or threatened ecosystems to islands or continental regions that no longer harbor the tortoises that previously existed there, but were driven into extinction by human exploitation (Truett and Phillips 2009;Griffiths et al 2010Griffiths et al , 2011Griffiths et al , 2013aPedrono et al 2013). These strategies are particularly pertinent in the Mascarene Islands and on Madagascar, as well as in the Galápagos.…”

Biological invasions, ecological resilience and adaptive governance

“…Invasive species can replace ecological functions lost with species extinctions in ecosystems (Griffiths et al, 2010), and therefore could replace lost, or complement current, ecosystem services in a desired regime (Thijs et al, 2015). This conclusion should be viewed with caution, however, as there may be a time lag in the effects of invasions on the overall system.…”