‘Rewilding’ is a concept in conservation biology generally defined as the idea of restoring an ecosystem to more natural historical state. The concept is based on the surrender of human influence over an environment, as natural equilibriums and trophic interactions are left to run their course.
There are distinct schools of thought within this, which essentially differ on how far we should turn the ecological clock. The 3 main types of rewilding are, trophic, passive, and Pleistocene; the latter being the only form with a specified historical baseline.
Trophic rewilding focusses on top-down trophic interactions and promoting natural cascades which lead to self-regulating and balanced ecosystems, normally in the form of reintroduced predators. Passive rewilding simply relinquishes human control over wild areas, allowing nature to regain power over the land, leading to a modern equilibrium.
Pleistocene Rewilding is distinguishable because it is founded on the belief that due to the megafauna extinction event that occurred ~50,000 years ago, many ecosystems have lost core processes, which make an ecological equilibrium in the Holocene impossible. Therefore, through processes of back-breeding to ‘recreate’ extinct species, translocation of ecological replacement species, or reintroduction of locally extinct species, we would reinstate the natural order of the ecological systems in Europe.
This essay will discuss a hypothetical example of Pleistocene rewilding, and thus will not be constricted by real-world processes of reintroduction and human pushback from local communities, but instead focus on which selection of mammals would be most successful, and have the most significant impact in a project within modern Europe, rather than species that would be most logically possible in reality. The project of 8,000km2 in Europe will contain a rich and diverse vegetation structure, and the full variety of extant mammals from the last 10,000 years.
I will present a case for which mammals could be (re)introduced into Europe, from the selection that were lost locally, within the Last Pleistocene megafauna extinction, to reconstruct an ecologically functioning community.
This will be structured by first addressing native European mammals that could be reintroduced, followed by a discussion of non-native species which could be introduced as ecological replacements in certain niches, with the focus being on the ecological functionality of each species/family chosen.
Reintroduction of Native Pleistocene Mammals:
The reintroduction of animals is possible when species have only gone locally extinct, but persisted and remain successful in other geographic regions, enabling translocation of communities. In these cases, we have to assess whether the species went extinct for a ‘just’ reason, such as being outcompeted for resources or a trophic niche, rather than a stochastic event such as natural disaster, or human-driven extinction factors such as hunting and habitat-loss. Defining the cause of extinction can help us discern whether the species is likely to be successful in the long term, or whether it was ‘fated’ to go extinct in these conditions.
In this section I will be making arguments to reintroduce lost predatory megafauna.
Firstly, I believe the reintroduction of Wolves (Canis lupus) to this European ecosystem would be greatly beneficial. Depending on the specific location of the rewilding reserve, there might already be wolf populations in the area (Okarma, 1995), but otherwise, they have been proven to be not only successful in reintroductions, but also play an important ecological role in restoring trophic balance (Laundre, 2001). The most documented example of this is the Yellowstone National Park, where the reintroduction of Wolves initiated a trophic cascade, controlling prey communities which had become overpopulated, and impacting plant primary-production by influencing plant–herbivore interactions (Fortin, 2005). Their reintroduction to Scotland has been discussed to combat the overpopulation of Red Deer in the region, which are decimating plant-life at an unsustainable speed (Manning, 2009); although the diet of wolves is diverse, featuring many ungulates, they often specialise on cervids (Okarma, 1995), which makes them a prime predator to introduce with the aim of naturally reducing deer numbers, which are often unchecked in Europe and cause chaos to plant communities, which affects many other species (Boitani, 2000).
In addition to wolves, Brown Bears and Eurasian Lynx would also be good candidates for reintroduction. Each of these species have scattered and small populations which are isolated due to highly fragmented human-dominated habitats (Boitani, 2000), but given the full range of extant local flora and fauna within a protected reserve, I believe these species could restore the predator-prey balance within Europe. Having a canine, feline, and Ursidae selection of predators provides a balance of prey specialisation (Okarma, 1995).
Introduction of Non-native Pleistocene Mammals:
Cases where introduction of non-native species is appropriate involve species that were driven globally extinct but, where an organism that plays an ecologically similar role remains extant, and the niche that the extinct species filled is still vacant, causing trophic imbalance.
Multiple examples of this involve the extinction of primary predators in the Pleistocene mass extinction, which led to many ecosystems becoming herbivore-driven.
This form of rewilding is called ecological replacement and aims to reconstruct balanced mammal trophic interactions by identifying animals that fill a similar niche to extinct species, and translocating communities into new regions.
Firstly, as an example of predator replacement, the Iberian Lynx (Lynx pardinus), which is increasingly endangered in its home range, may be more successful in other European habitats, due to changing climate envelopes (Palomares, 2001). Many species are shifting their distribution in response to climate changes, but the environment is changing faster than animals can keep up with, especially in areas which are highly fragmented by human barriers which prevent mammal movement (Thomas, 2011). The Iberian Lynx is a prime example of this, as the critically endangered species is predicted to have just ~200 individuals left in the national parks of Spain (Gaona, 1998); a second contributing factor to their decline is the loss of rabbits due to Myxomatosis, which has affected their populations in Britain less so (Palomares, 2001). Therefore, although the Eurasian Lynx would be a native reintroduction to Britain (Hetherington, 2005), the Iberian Lynx may be more suitable, firstly because it would have a better prey population, and the climate would be more suitable (Richmond, 2010), but furthermore, this rewilding reserve could be used as a conservation method for this species, giving a two-fold benefit to its introduction: firstly as a predator to control herbivore populations such as rabbits and other rodents, but also to try and increase their worldwide numbers, and remove them from the brink of extinction.
Much of rewilding focusses on predators, but there was also herbivorous megafauna lost in the Pleistocene, which played important roles in habitat maintenance (Donlan, 2006). There is a distinct lack of megaherbivores (>1,000kg) in Europe, and the niche filled by these animals is currently vacant (Maroo, 2000); they can forage lower quality material due to a larger gastrointestinal tract, reach and utilise unique foraging opportunities to target different flora, so present a very different selection pressure upon native plant life, which creates different habitats.
Two species I would suggest introducing to replicate the effects of ancient megaherbivores are: Bison in the place of Aurochs, and Asian Elephants to replace Straight-Tusked Elephants, both of which were species present in the Last Interglacial period (Maroo, 2000). These species are clearly not direct replacements, but there is evidence suggesting that they could play ecologically similar roles (Thomas, 2011), and aide in the maintenance of habitats, as well as controlling smaller mammal populations, through indirect effects, such as emerging woodlands being kept at bay, at earlier successional stages, through herbivory on larger plants, which current native mammals cannot reach.
I believe that the species I have identified would make excellent additions to the current native ecosystems in a European rewilding reserve (Wolves, Bears, Lynx, Bison, Elephants). Each was chosen in response to identifying a vacant niche in European ecosystems, with the aim of encouraging natural equilibrium in the Holocene, with the range of mammals we have available, and as little human involvement as possible. My approach to this has been a combination of Trophic and Pleistocene rewilding, with a focus on predators, due to the range of evidence that supports successful trophic cascades caused by apex predators.
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