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.