Problems in paradise: the destruction of Hawaiian species

A few months ago I wrote a post on invasive species in Finland, and in particular on the North American beaver (Castor canadensis). I received a comment on how it is bold (or maybe the commenter meant reckless) to say that almost all invasive species are threatening the native species of the region. I began thinking of this comment, and tried to find some studies that proved that invasive species are beneficial for the subject ecosystem. Unfortunately, I only came up with sad tales. One very devastating example of invasive species is the Hawaiian Islands.

The Hawaiian Islands in the center of the Pacific Ocean are one of the most isolated islands in the world. Their endemic terrestrial species originate from some hundred species that migrated thousands of kilometers over the Pacific Ocean during several millions of years. Because of the immigration bottleneck and isolated evolution, the Hawaiian Islands have become a place for numerous distinctive and fascinating species. But it has also made the fauna and flora of the islands very vulnerable to various disturbances, such as human invasion and human-mediated invasions.

Nowadays almost a quarter of Hawaiian terrestrial species are non-native. Birds have probably suffered the most. Previously there were 11 native goose species in the Hawaiian Islands, but nowadays only one species is left: the nene (Branta sandvicensis), also known as the Hawaiian goose. The same has also happened to the native duck species; just two duck species are left (the Hawaiian duck, Anas wyvilliana and the Laysan duck, Anas laysanensis).

The nene, also known as the Hawaiian goose (Branta sandvicensis), is the only endemic goose species left in the Hawaiian Islands. © Sari Holopainen

The nene, also known as the Hawaiian goose (Branta sandvicensis), is the only endemic goose species left in the Hawaiian Islands. © Sari Holopainen

The main reasons for these extinctions are introduced predators (e.g. the feral cat and mongoose), and feral and game species (e.g. the mouflon, Axis deer and feral pig). There are almost 60 studies on domestic ungulates, but none have demonstrated any positive effects of them on native species. Ungulates stimulate the growth of grass among other things, leading to more grasses and less forest. And all this changes the light regime and fire resistance of an ecosystem. Grazing is therefore destructive to Hawaiian forests and to every native organism living in them. It has also been proven that the invasive vertebrate species of Hawaii have facilitated at least 33 invasive plant species. In addition to damages caused by grazing, feral pigs alter nutrient cycling and accelerate soil erosion.

The main problems caused by feral pigs are alteration to nutrient cycling and acceleration of soil erosion. © Sari Holopainen

The main problems caused by feral pigs are alteration to nutrient cycling and acceleration of soil erosion. © Sari Holopainen

There is still some light at the end of the tunnel, although it might be rather dim. The public has come to aid in the eradication of many species. Scientists and wildlife managers have concurrently begun multi-scale population monitoring, which includes aerial and ground-based visual surveys as well as trail cameras. To intensify and simplify the eradications even further, several hundred kilometers of management fences have been constructed. As an outcome of this some success stories have emerged; the eradication of rabbits and feral goats. Furthermore, the midway islands of Hawaii are now rat and non-native mammal free!

Unfortunately, it has been too late for some Hawaiian ecosystems. A key threshold has been crossed in some regions, and recovery of certain ecosystems may not be possible any longer. The populations of illegally introduced axis deer (Axis axis) have been reduced to some dozens, but their eventual eradication has been problematic, because assessing the number of remaining deers on private properties has proved difficult. The axis deer was introduced to provide game, so private properties owned by hunters act as reservoirs for the deer, from where they can be disperse to clean areas.

The main feral goat eradication was performed in 1980s, and nowadays the Hawaiian Islands are goat free. © Sari Holopainen

The main feral goat eradication was performed in 1980s, and nowadays the Hawaiian Islands are goat free. © Sari Holopainen

To conclude, I still dare say that almost all invasive species threaten native species. Even though some invasive species don’t harm all native species, we are always looking at nature as a complex ecosystem consisting of several species and functions. When introducing an alien species, we will always alter the pristine ecosystem.

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Eradicating species – an occasional necessity

If Finland is to obey the EU strategy on Invasive Alien Species (IAS), 10 000 North American beavers (Castor Canadensis) are to come under the trigger. Why is this eradication necessary?

Although invasive alien species, e.g. the American mink (Neovison vison), the ruddy duck (Oxyura jamaicensis) and the Himalayan balsam (Impatiens glandulifera), may seem adorable and interesting novelties, they nearly always threaten the survival of native species. Invasive alien species are harmful to agriculture and forestry, and at their worst can even threaten human health. Sometimes we face the inevitable: the eradication of an animal or plant species.

The most efficient way to minimize the risks is to prevent it spreading to an area in the first place. Australia is probably the most famous example of preventing the spread of alien species, as they even clean the shoes of tourists at the airport before allowing them into the country. Unfortunately no nation has been successful in averting the spread of IAS.

Not that a tough fight isn’t being fought the new EU strategy on invasive alien species took effect earlier this year.

The main aim of the strategy is to aggregate a list of the most pernicious invasive alien species and to repulse them in different ways. Finland has 160 harmful IAS. Whether each of them will be on the EU’s black list remains unclear.

The North American beaver is first in line

The North American beaver is one of the most potential mammal alternatives for the list. The species was brought to Finland in the 1930s to save Finland’s beaver population. Back then the genetic differences between European and North American beavers were unknown, although we now know that the species differ even more than humans and chimpanzees.

The niches of both species are identical. They eat the same nutrition and their damming activities are the same. Both species have identical effects on ecosystems.

There are approximately 12 000 beavers in Finland. Most of them (10 000) are North American beavers, while European beavers comprise only a fifth of the North American beaver population. The North American beaver threatens the existence of the European beaver in Finland. It might eventually competitively exclude the European beaver. Adhering to the precautionary principle and seriously considering eradicating the North American beaver from Finland and Eurasia is essential. An eradication plan has nevertheless been conspicuously absent. An eradication plan for North American beavers would abide to the guidelines of both the IUCN’s and Finland’s National Strategy on Invasive Alien Species.

How to eradicate a species in practice?

A large scale eradication of the North American beaver is possible, at least in theory. Several possible methods could be used simultaneously, such as hunting, live capture, sterilization, reintroduction of the European beaver and population monitoring.

Beaver hunting is also financially tempting. Beaver furs have once again become popular in China, so their markets have a demand for beaver furs. After the sterilization or dead trapping of North American beavers, they should be replaced with European beavers.

But this is not a straightforward process. Although the two species differ genetically, they have a similar effect on the ecosystem. Beavers act as ecosystem engineers and benefit several other species in Finland and elsewhere. The present population size of the North American beaver ameliorates e.g. the green sandpiper (Tringa ochropus), the moor frog (Rana arvalis) and the Daubenton’s bat (Myotis daubentonii). However, if all North American beaver individuals were removed and replaced by European beavers, the eradication would be harmless to Finnish nature. Unfortunately, there is nothing to guarantee the success of the reintroductions.

Finland must begin eradication if the North American beaver is placed on the EU strategy plan on Invasive Alien Species. The activity of citizens and hunters will determine the eradication outcome. The Ministry of Agriculture and Forestry in concert with the Finnish Advisory Board for Invasive Alien Species are in charge of the decisions and eradication procedures.

Not so cute and cuddly – it’s time for the cat wars

Feral cats (Felis catus) have spread globally thanks to their reputation as cuddly house pets. Their habitat use is very diverse, ranging from urban areas to e.g. agricultural, woodland, and grassland landscapes. Feral cats also rapidly become semi-wild if given the chance to move freely in the great outdoors. Combining their ability to spread fast and wide with their ability to eat very varying diets (small mammals, birds, reptiles, amphibians, everything goes) is apt to spell major trouble for native wildlife. And though they are fairly small-sized mammals, they do not only go for small animals, but have been recorded to kill animals weighing up to four kg (nearly 9 lbs).

Feral cats have also been dubbed “compulsive killers”. That means that not only do semi-wild feral cats hunt food for their survival, but house cats momentarily let loose in back yards etc. will go after anything moving, despite having a meal waiting back home. They effectively conquer the niches of several native small or medium-sixed predators around the world, thus disrupting food webs and ecosystems. And to top it all of, feral cats can also spread toxoplasmosis, a parasitic disease that threatens humans and livestock (e.g. sheep in Australia).

Native and endemic island populations have been particularly hard struck by the spreading of feral cats, but the numbers behind this feline invasion are massive everywhere: an estimated 18 million native animals are eaten by feral cats every year in Australia alone, and a single cat is believed to kill five to 30 animals a day. This is no small-scale problem; the US alone has an estimated 100 million pet cats, each of which kills around 5 to 15 birds per year. That’s 1,500 000 000 birds. Feral cat-caused mortality rates of birds in Great Britain are estimated at 50 million a year.

The Australian government has reacted to feral cats with the strongest measures. They are not hard-pressed to find reason, as 100 native Australian species are in direct extinction threat caused by feral cats. Australia has issued a national threat abatement plan for predation by feral cats, aiming to eradicate them from three islands, with plans to evict the species from two more in the near future. New Zealand also has a zealous plan for lessening the damage caused by small mammals (including feral cats), with the aim of eradicating the species completely (except as an indoor pet) from the country.

Urban and rural feral cats can devastate native wildlife populations. ©Stella Thompson

Urban and rural feral cats can devastate native wildlife populations. ©Stella Thompson

Cat wars are being waged across the world with one common denominator: high-tech technology. Eradication measures include using thermal imaging, motion and remote sensing cameras, and GPS tracking collars along with more traditional baiting, trapping, and using tracking dogs. Several countries have also issued desexing programs and cat-free zones around particularly important areas (e.g. nesting sites). Fines can also be issued in some countries (including Finland) to cat owners whose cats have killed native animals. These fines can reach thousands of euros/dollars, depending on the species in question.

It seems unlikely that pet cats are going anywhere in the near future (and why should they); however, maybe what remains a question is whether their freedom in the great outdoors should be restricted or whether laws should be passed mandating cat owners to fasten little bells or colorful cat collars around their pets’ necks. Both have been shown to significantly lessen the numbers of birds, reptiles, and amphibians falling prey to this miniscule feline predator. It is important to remember that what people think is cute play when witnessed at home is actually stalking that will result in native species mortality when the cat is let loose. Attitudes must also change; all too often people believe it is okay to abandon their pet cats after caring for them for a while. Such cats can form populations of tens or hundreds of semi-wild individuals, living in abandoned buildings around the countryside and cities. Many may believe this to be a random occurrence, but e.g. 20 000 pet cats are abandoned yearly in Finland.

Community participation – a key to eradicating invasive alien species

Invasive alien species are a serious threat to both national and global biodiversity. New species might seem fascinating and interesting, but quite often they threaten the existence of native species. Invasive alien species also have impacts on livelihood and economies by damaging agriculture and forestry, as well as infrastructure and human health. They impede native species by one or several ways: eating them, competing with them for resources, interbreeding with them, disrupting or destroying their habitats and introducing new pathogens.

The key to avoid invasions is to shut off every possible entrance pathway. Australia is a known master at blocking the pathways of invaders. However, in reality no country has managed to escape from invasives. The battle against alien species is usually an extensive and long process, which requires a multitude of participants.

One efficient, but surely challenging way to eradicate alien species is community participation. Usually local people are easy to involve in eradication programs when the alien species threatens their livelihood. This was the case of the lionfish (Pterois) in the Caribbean. It has invaded the Caribbean Sea, putting local fish stocks at risk and filling in the catches of fishermen. At first the fishermen didn’t have any possibility of selling this new product, as the locals falsely believed the lionfish to be poisonous. After authorities released their eradication strategy with corrected information and the slogan “Let’s eat it to beat it”, the locals’ involvement in the eradication rose to a great extent. When people gained the correct knowledge, they began eating the lionfish to save the native fish species.

One main challenge in community participation is unawareness. Mostly people don’t even recognize alien species from native ones. So the key is to inform the public. In Finland the Finnish Association for Nature Conservation (FANC) encourages Finns to recognize, prevent and report alien plant species, such as the Himalayan balsam (Impatiens glandulifera) and Persian Hogweed (Heracleum persicum coll.). FANC has even established an internet page http://www.vieraslajit.fi, where the public can report their observations of alien species.

Persian Hogweed (Heracleum persicum) is a harmful alien species to both native species and humans. It causes burnlike damages. © Sari Holopainen

Persian Hogweed (Heracleum persicum) is a harmful alien species to both native species and humans. It causes burnlike damages. © Sari Holopainen

According to FANC the success of alien species eradication lies on the shoulders of every Finn. This statement has been greeted by getting down to business at the University of Helsinki. Each spring students attending the ‘Alien species’ course do their share and remove the very feisty alien species Ramanas Rose (Rosa rugosa) from a beach in eastern Helsinki. The dispersion of Ramanas rose is unpleasant also from the public view, because it is aggressively occupying the beaches of sunbathers.

Successful eradication needs everyone’s effort. Organizing a prevention event is easy. In Finland FANC provides detailed instruction on how, and you can always contact your local environmental authorities for further information and guidelines.

Common water hyacinth is native in Amazon, but it has successfully invated many areas around the world. This picture is from Borneo. Water hyacinth is very problematic alien species, as it covers all open water areas of lakes and ponds affecting dramatically to the function of ecosytems © Sari Holopainen

Common water hyacinth is native in Amazon, but it has successfully invated many areas around the world. This picture is from Borneo. Water hyacinth is very problematic alien species, as it covers all open water areas of lakes and ponds affecting dramatically to the function of ecosytems © Sari Holopainen