Another attempt to undo a human-induced intrinsic harm is the introduction of Aldabra giant tortoises to ile aux Aigrettes, near Mauritius, to replace an extinct local species that had been crucial to maintaining this island’s ebony forests.
Introductions are also sometimes made to reduce the risk of a localised species becoming extinct.
Pyne’s ground plum, native to a handful of sites in the central basins of Tennessee but now transplanted to others, falls into this category.
Relational values are the most esoteric, being experienced on an emotional rather than a practical level.
Lots of people feel good about native wildlife, which is generally the main motive for its conservation.
But that feel-good factor can extend to interlopers as well, especially if the interloping happened a while back.
Dingoes, for example, are the descendants of dogs brought to Australia more than 3,500 years ago, presumably by human agency, but which have lived free there ever since and have entered the mythologies of aboriginal Australians.
Similarly, the wild horses and asses (mustangs and burros) of North America, though not as long established as dingoes, have found places in the hearts of sufficient numbers of people to have active lobbies for their conservation.
Relational values can cut both ways, however.
For example, ring-necked parakeets, an Asian and African species, have been spreading through Britain for several decades.
Some find them a colourful addition to the local wildlife, others a gaudy, noisy competitor for native birds.
Having established their intellectual framework, Dr. Sax and his colleagues suggest future research might work within it and, in particular, be properly open-minded about the benefits as well as the costs of introductions.
Past attempts to do this for significant numbers of species at a time are rare, though they have come up with two.
One, published in 2020, examined 105 species.
It showed only benefits for 30, only costs for 31 and both for 44.
Another, from 2014, came to similar conclusions for 87 marine species introduced into European waters.
7 provided pure benefit, 17 pure cost and 63 both.
In light of their analysis Dr. Sax and his team therefore suggest that researchers studying introduced species should in future follow three principles.
First, they should create a clear distinction in their studies between changes that have happened and judgments about the value of those changes.
Second, when making those judgments, they should acknowledge all three types of values, rather than focusing narrowly on one or two of them.
Third, they should actively consider biases in previous research that might have led to unbalanced conclusions.
That done, many species will surely still end up on the debit side of the ledger.
But others, badly thought of in the past, may not.
Dingoes, for one, were originally despised by Australia’s more recent, European, settlers.
Now those, too, include partisans seeking the dogs’ preservation.