4.1 Risks and considerations for whole-of-community rewilding
There are, however, risks associated with whole-of-community rewilding that need to be acknowledged and addressed. Land managers should be aware of the potentially detrimental effects on remnant sites that this form of rewilding may have if it were unregulated. For example, the repeated removal of habitat from remnant areas during the rewilding event might diminish source populations of invertebrates and microbes or degrade habitats. This is especially true if the microclimatic and biotic conditions of the new restoration site are unsuitable for the transplantees as they will likely perish, meaning the only outcome of the transplant is a diminishment in source populations as opposed to an increase in their range. This could be remedied by regulation of the harvesting in space and time, for example by spreading the collection event over various areas within the remnant sites, ensuring that: a) source populations are not depleted; b) transplanted populations capture the breadth of diversity and life history stages in natural communities; and c) interacting co-dependant taxa are introduced together.
Land managers will also need to be conscious of the potential to spread invasive invertebrates and microbes during the rewilding event as non-natives may be embedded within remnant sites. Even though remnants sites would ideally be “pristine”, thorough sampling of the source population pre-rewilding is needed to assess the risks of spreading invasive species into areas in which they may not be present. The introduction of invasive species or pathogens is a risk for all reintroduction projects, regardless of whether they are single species or whole-of-community reintroductions. Rewilding should therefore only occur when natural recolonisation seems to be impossible or exceedingly slow (Jourdan et al. , 2019) (Figure 2). Although both single species and whole-of-community reintroductions carry inherent risks, the latter may provide benefits that outweigh negatives. For example, Haase and Pilotto, (2019) argue that because single species freshwater macroinvertebrate reintroductions are unsuccessful 62.5% of the time (Jourdan et al. , 2019), whole community transfers may be the preferable method for stream restoration as they increase the likelihood of at least some species establishing.
Whole-of-community rewilding may also pose risks to the genetic integrity of species. For example, in a review of freshwater macroinvertebrate reintroduction projects, Jourdan et al., (2019) noted that the mixing of different evolutionary lines during reintroductions may diminish conservation goals. Flightless invertebrates (such as benthic freshwater macroinvertebrates and terrestrial mygalomorph spiders) are often dispersal constrained meaning genetic differentiation between populations is common. If a reintroduced population mixes with undetected individuals persisting in the restoration site, there could be hybridisation between the two populations, which jeopardises the integrity of the independent evolutionary lineages and their conservation. Jourdan et al.,(2019) recommend genetic assessment of intraspecies diversity pre-reintroductions, and if this is not possible, choosing to reintroduce populations from the nearest remnant population, as we have previously recommended in this review.