When is the right time for a species reintroduction?

Across the globe, species reintroductions and reinforcements (collectively termed translocations), have been taking place for decades. Humans have always manipulated our environments to better meet our needs, including moving individual species to where we can make best use of them.

From the first neolithic farmers planting seeds from one area to cultivate another, to early man domesticating the horse for manual tasks and transporting us further distances. Much later, as we became an increasingly globalised species, we started cultivating plants far away from their homelands where they evolved.

The Victorians placed tropical plants in great glasshouses for people to marvel at, with fantastic discoveries in the fields of medicine and food as a result. However, this movement of species by human activity has had, in some cases, many unintended consequences. Think of the rats which disembarked from the ships of explorers on many small island nations, decimating the populations of endemic species which had not evolved to cope with these new arrivals.

The UK itself was not immune to these “Invasive Non-Native Species” (INNS), Grey Squirrels (an American species) were introduced deliberately to the British Isles in the 1890’s and it was in fact, a conservationist called Herbrand Russell (former owner of the Woburn Estate) who is credited as being responsible for introducing them(Dunning, 2016). INNS can have a terrible impact on ecosystems. Grey squirrels were responsible for the crash in red squirrel populations in the UK, and cause around £37 million in damage to the UK’s timber industry each year (RDI associates, 2021).

Asking the wrong questions

Given the risk posed by Invasive Non-Native species, and how wrong some of these translocations have gone in the past, it would seem that choosing which species to move and for what reason would be both a highly important question and a difficult one to solve.

However, this seemingly obvious conclusion misses one fundamental point which makes the weighing up of deliberate translocations far simpler. That is, was this species (or its close ancestor) ever in this ecosystem before?

If it was, then it has co-evolved with the other species present and would naturally fit in this environment. If it wasn’t, then the other species present have never encountered this newcomer before (in evolutionary terms) and things may get out of balance. Simple.

Of course, this is in fact a massive oversimplification, but it is a useful central tenet to hold onto when discussing translocations. The major confounding factor with this simple idea is (once again) us.

Now, in the 21st century, we have changed the habitats around us so fundamentally, that whole ecosystems have broken down. Many of the relationships between species may have been lost and we have even shifted the climate around us - potentially making regions alien to species which were previously found there.

But rather than this presenting a problem to the understanding of “which species belongs where?” it may instead present an opportunity to consider, which species are now moving this way in response to climatic changes.

Once again, the answer may be surprisingly simple, requiring only a slight modification to the central tenet mentioned earlier, this being:  "how far away has this species come?” I.e. was it known from this ecosystem at the broadest scale (so in the case of the UK meaning Europe) and how long ago was it last seen in this location. Whilst climate change and human modification of habitats has shifted things a lot, chances are that if it’s anything more recent than the last ice age, then it’ll still have a place where it was last known.

However, whilst this central governing idea of - translocations needing to be relevant to their ecosystems to be successful - may seem simple. It is almost always forgotten when the risks are being weighed up in any given species reintroduction debate.

The question most quickly reached for by those who fear a species return is: “what does this species do to the environment?” which encapsulates a whole host of fears, from breeding out of control, to introducing disease, to attacking people. Often the people most strongly attached to these questions are themselves ecologists or naturalists with an interest in a given taxa.

The natural defense to these questions by any proponents of reintroduction is to justify the species on ecological grounds. For example, “it’s a keystone species”, “it will help solve flooding”, “it will help improve people’s connection to nature”. These responses (which are undoubtedly all true) fundamentally miss the point as to the reason for reintroducing species and result in inertia as ecologists are forced to study to death every possible interaction between a given species and every other species it might encounter with of course, inconclusive (and likely irrelevant) results.

A better way to consider species reintroductions

Instead, I would like to propose an alternative argument. The question of “what does this species do to the environment?” is fundamentally flawed. It is based on the idea that we humans know everything there is to know about the ecology of our planet. How can we? We don’t even understand our own biology fully let alone that of every other species and then how all those entities interact with each other.

Keystone species are usually the first species that are chosen for reintroduction, this is due to the outsized effects they cause on their surrounding habitats which are easily perceived by us. But species do not evolve in a vacuum, they all evolve together. An ecosystem is not a set of habitats which happens to have some bigger animals within them, they are all one and the same, animals evolve with plants and plants evolve with animals (not to mention fungi). In such an interconnected system, every species has a role to play. After all, evolution only acts to promote genetic traits which allow species to fill niches not otherwise occupied. As niches become occupied by the evolution of species, new niches are in turn created by those species. Thus, the term “keystone” may be deservedly applied to a much greater range of species than we currently do - it’s just that we do not yet perceive the benefits those species create.

So, instead of this anthropocentric view of nature, where we are in control of every species and determine by our own values where they belong. Why not consider ourselves as part of this ecosystem and realise that whilst we do have agency to move species around, we are far less in control than we might like to think?

When considering a translocation, why not keep it simple. Ask questions such as: “was this species here before?” “Was it us that wiped it out (either directly or indirectly)?” “Has that reason now gone or can be mitigated for?” In which case, do we not have a moral obligation to bring that species back?

In this way; we could undo much of the ecosystem breakdown that we have caused, let nature restore a state of balance by having the right species in the right places and reap the rewards of a thriving and complex ecosystem that is resilient to climate change.

By not trying (and failing) to understand every aspect of a species ecology to determine its value, we can instead concentrate on what’s really important. It’s place in our society. In our densely populated country, we do not interact with animals daily. To make reintroductions a success we should focus on people’s perceptions, look for ways to mitigate any negative impacts on people and their livelihoods and work towards coexistence.

Whilst we cannot hope to understand everything about the natural world, if we recognise our place within it and our interdependence on the species around us then we can reap its benefits and marvel at its wonders once more.

References

Hayley Dunning, 2016. Don't blame grey squirrels: their British invasion had much more to do with us. Imperial College London news. https://www.imperial.ac.uk/news/170448/dont-blame-grey-squirrels-their-british/

RDI associates, 2021. An Analysis of the Cost of Grey Squirrel Damage to Woodland. Royal Forestry Society. https://rfs.org.uk/wp-content/uploads/2021/03/analysis-of-the-cost-of-grey-squirrel-damage-to-woodland-publication-copy-180121.pdf