Reintroduction of extinct keystone species – which ecosystems should we restore?

Extinctions are a natural part of species history, but for example habitat fragmentation, habitat loss, alien species, hunting and competition with humans have accelerated the rate of extinctions. The extinction of some species is more crucial than that of others, because it may jolt the whole food web or ecosystem. In some cases the whole ecosystem has been maintained by an animal, the keystone species. Without reintroducing the keystone species the ecosystem’s structure and stability might not re-evolve at all or the ecosystem is not complete and self-managing.

How long is too long?

Quite often the main question when talking about restoration is which ecosystems should be restored. Ecosystems have fluctuated through time and so the target is not stationary. Replacing a current ecosystem may not result in the same pure historical ecosystem, but in a mixture from current and historic. Some researchers think that restoration should be aimed at ecosystems existing just after the last ice age before the extinction of big mammals. This was the time before humans greatly effected speciescompositions. With this base, some researchers have proposed the reintroduction of megafauna in the prairies of North America. Megafauna were lost about 13 000 years ago, but some have remained in Africa. Large carnivores and herbivores could work as keystone species and create rare temperate grasslands.

The question is what happens to the current fauna if the old fauna is restored, i.e. what is the value of these actions for the current fauna? In the USA a large share of current fauna is threatened and wildlife is fragmented. Megafauna would need large areas and even current environments are fragmented. Quite many African megafauna species are also endangered and every individual is needed for making the gene pool bigger. In this case restoration would be controversial, because there is a threat that the current African fauna will suffer because of shrinking gene pools and the current American fauna would suffer when losing space.

Megafauna was extinct from North America about 13 000 years ago due to humans. In Africa they survived.  African elephant in Basel zoo. © Sari Holopainen

Megafauna was extinct from North America long ago due to human actions. In Africa they survived. African elephant in Basel zoo. © Sari Holopainen

Good bad wolves

Top predators can be keystone species, but many areas are lacking them because hunting and persecution have driven them to local extinctions. Top carnivores have an important impact in controlling herbivore populations and as a result also vegetation. For example the wolf (Canis lupus) is a keystone species that was killed to extinction from Scotland almost three hundred years ago. There is now an attempt of woodland restoration in Scotland and it has been supposed that also wolves could be reintroduced. Woodlands are not regenerated in Scotland, because of strong herbivore pressure, mainly by sheep and red deer (Cervus elephus). The reintroduction of wolves could decrease deer populations in a natural way and allow forest regeneration.

Apart from ecological aspects, there are sociological aspects that must be considered before reintroductions. In the Scottish example, economic aspects associate with sociological aspects via costs to the sheep farmers. A study about public attitudes against wolf reintroductions revealed that the rural population was concerned about loss of livestock, but still had less negative views to the wolf reintroductions that was expected. Rural population saw deer control as a major benefit brought by wolf reintroductions. Farmers actually had less negative attitudes than the organizations representing them; this might be due to the low price of sheep. But tolerance might not depend on economic costs, and so also emotional consequences should be regarded. The urban population was more concerned about the harm wolves could cause to humans, but they also saw that tourism would be the major benefit. As a conclusion, the general attitude of the Scottish public had a positive idea of reintroducing wolves.

American beaver full fills the ecofunction of the extinct european beaver © Sari Holopainen

American beaver full fills the ecofunction of the extinct european beaver © Sari Holopainen

Restoration of ecofunction

The quality and number of wetlands is decreasing in all of Europe. One of the reasons is that beavers have been extinct from some parts of Europe for a long time and this has had a remarkable effect on wetland availability. In the Kabetogama peninsula of North America the recovery of beaver populations caused strikingly large changes in the landscape by flooding. It can be supposed than also in Europe the effect of beavers has historically been larger. Beavers have been reintroduced in some areas and in many cases they have been successful.

If species have only become extinct locally and remained elsewhere, the knowledge about population biology is available. Genetic evidence must be used reintroducing species, to ensure that the species is the same as the extinct one. This is critical, because usually the target of reintroductions is to restore the original ecosystem. Before advanced gene technology some mistakes were made. For example, in Finland the locally extinct European beaver (Castor fiber) was partly replaced with the American beaver (Castor canadensis). But sometimes the problem is to decide whether a genetic or functional relationship is more important, especially if the original species is extinct. This can concern especially keystone species, because the functioning of a keystone species is in the main role. The target of restoration might be to return the ecofunction instead of the actual original species. Ecofunction was returned although the species was changed with the case of beavers in Finland.

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