1/16 Does the introduction of novel species to assist in ecosystem functioning have a place in modern #rewilding? In todays #rewildingscience paper @DennisMHansen puts forward his argument for non-native megaherbivores to combat island plant invasion 
2/16 Note: In the context of the paper ‘megaherbivore’ is used to refer to both the extinct giant tortoises and introduced counterparts due to their role as ecosystem engineers on island habitats
3/16 Island ecosystems are disproportionately impacted by invasive species (plant or animal). Removal of mammalian species have shown to assist in native plant recovery whilst loss of herbivores can lead to surges in invasive plants where they were previously held in check
4/16 This occurred on Round Island where to counter invasive plants, hundreds of giant tortoises were introduced to restore a native herbivory regime. This, alongside biological control agents, chemicals, and mechanical removal are tools used to control unrestrained plant growth
5/16 In place of such measures, Hansen suggests the use of vetted non-native megaherbivores (tortoises) to threatened islands with no history of native individuals. These could act as functionally important species by shifting competitive advantages towards endemic plants
6/16 This, the author states, can be viewed within the context of #rewilding due to the use of functionality without reliance on explicit historical baselines E.g. use of giant tortoises on Kaua’I island in place of the extinct giant flightless duck due to a similar feeding role
7/16 The benefits of using tortoises in this way include the ease of which they are reared in captivity, the natural distribution of taxa across climates, the ease of transport and in extreme cases the ease of removal…
8/16 Additionally, studies into rewilding projects have indicated feeding preferences of invasive rather than native plants due to moisture/nutritional content. From a neutral standpoint, likelihood of invasive plant selection is higher, giving native plants a competitive edge
9/16 These kind of adaptations in plants could indicate an anti-herbivory mechanism, again supporting the use of tortoises on these island ecosystems
10/16 The author acknowledges that this type of introduction veer towards the ‘unacceptable’ end of the translocation spectrum. This high to low scale starts with classic reintroductions towards ecological replacements. The use of completely novel species may seem undesirable…
11/16 However, Hansen writes, ‘ecosystem history is often a baseline that shifts with increasing knowledge’ e.g. on Efate island where few extinct herbivores were recorded, finds of meiolaniid tortoise bones meant tortoise translocations went from novel to ecological replacement
12/16 Use of novel species should not then be wholly ruled out on the basis of no previous extinct species when a) they could be providing beneficial functional roles, and b) evidence of past inhabitants is yet to be discovered
13/16 For endangered species, in situ conservation is priority, but even in these cases, translocations of captive bred individuals could provide animals for island projects elsewhere. This could offer species more routes from extinction alongside standard conservation practices
14/16 Thought experiments can be done using comparable islands with endemic species and those without. If control of invasive plants on islands with a history of tortoises is considered rewilding then, he argues, it may be transferrable to paired islands with no such history
15/16 He concludes saying that his proposal is based on ecological functioning rather than ecological history/species origin. In a changing world, multiple avenues need to be taken to build resilient habitats, where native plants can prosper under flexible regimes and new ideas
16/16 To read the paper in full please follow the link here! academic.oup.com/aobpla/article…
