Invasive alien species: biggest threat to Pacific biodiversity

• So what is an invasive species anyway?
• Effects of invasive species
• How did they get here?
• What can we do about them?
• SPREP's work on invasives

The Pacific is biologically unique, because the isolated islands provide ideal conditions for the development of new species. Birds illustrate the outstanding biological uniqueness of the region – the Pacific has 15% (408 of 2700) of the world’s restricted range bird species in only 0.4% of its total land area.

Many of the unique plants and animals of this region are amongst the most endangered in the world, mainly because the tiny sizes of most of the islands also means the total world populations of many of these species are naturally very small, which makes them very vulnerable to any disturbance. Thus most extinct species came from islands – similar figures apply to other groups. Pacific currently has 24% of the world’s threatened bird species and has already lost many species.

One of the key threats to the remaining species globally and in the Pacific is land clearing. But on the islands, invasive species pose an even greater risk to living things.

So what is an invasive species anyway?

Invasive species are also known as introduced species or pest species, sometimes called invasive alien species. They are species living where they do not belong.

Invasive species are highly adaptable and usually widespread. They can live in a wide range of environments. They breed fast and spread easily. When they arrive in a new country, they have usually left the diseases and predators that would have kept their numbers under control back in their home country.

The brown tree snake was introduced to Guam accidentally in the late 1940s. Its introduction has resulted in ecological devastation, including the permanent loss of nine of the eleven original native bird species in Guam, along with five species of lizard. There are an estimated 80 million brown tree snakes on Guam today, and they cause damage to electrical infrastructure, causing power outages every 4 –5 days, damage to household electrical appliances, and research and control costs totalling over $US 5 million a year in Guam alone. This does not include the costs to Guam’s major trading partners to ensure that snakes that hitchhike in goods or on aircraft or ships from Guam are detected before they can establish new populations. They also impact on health - their bites pose a risk especially to children.

Invasive vines like merremia and mikania vines smother forest canopies, reducing the production of flowers and fruits that fruit bats and native birds such as pigeons depend on. They are also close to the top of regional agricultural weed lists.

Invasive species can come from any group of living things like insects such as ants. Rats have some of the biggest impacts. There are also invasive birds such as the mynah and aquatic species, both freshwater and marine species. These are just a few examples.

Effects of invasive species

Invasive species have a range of effects on the environment and on humans: They threaten many species with extinction. They interfere with the species that make up ecosystems and change the way they function. They have negative impacts on the resources people rely on to live – food, clean water, and shelter. They carry diseases and can directly harm humans. They can impact on species we rely on for our livelihoods, or can reduce the tourist potential of the area by reducing the reasons they want to visit and they can impact on Pacific islanders traditional activities.

90% of species that have become extinct since 1800 were island birds, and 90% of these have fallen victim to an invasive species. Many endemic bird species are in trouble in the Pacific, some directly threatened by predators such as rats and stoats, whilst others are threatened by loss of habitat and food due to smothering of their forests by introduced vines.

Ship rats are one of the biggest threats to the survival of birds of the region – they eat eggs and young birds, especially of ground breeding species. They recently arrived in Kiribati’s Christmas Island, which was formerly the largest seabird breeding colony in the world – 18 species of seabird were seen in numbers of up to 6 million.

Meanwhile over in the Indian Ocean’s Christmas Island, which was famous for its red land crabs, the crazy ant developed huge super colonies that covered the ground and killed all the red land crabs in its path, although, millions of dollars later, it is hoped to be under control.

An example of the impact invasives can have on the economic sector. In Samoa a decade ago an outbreak of taro leaf blight, a fungal disease, decimated taro production, which formed a key part of the Samoan economy. It is estimated to have cost Samoa more than the impact of three cyclones, $US 40 million, to replace domestic consumption, lost exports and the cost of measures to control the disease.

Regardless of where we live, invasive species can impact on us all. Every country of the Pacific has invasive species that cause problems and is at risk of getting new ones. Prevention is definitely better than the cure.

How did they get here?

Some invasives were introduced deliberately by people as a food source. Biological control can be an effective method to control certain invasive species, but if not carefully checked first, the biological control agents can become invasive themselves.

Pacific islanders are great gardeners. A large proportion of plant invaders were originally legally introduced for ornamental purposes. Pacific gardeners also often smuggle in garden plants – often as seeds – and produce for their own use. Plant pests, ants and diseases have been introduced as contaminants of fruits, vegetables, soil, plants and commercial feed.

The rate of accidental introductions is increasing as there is more movement of people and more and freer trade around the region. Quarantine often exists at the international borders of countries but not between islands within the country, so increased people movement increases the risk of invasion substantially. Containers and packaging materials also pose a risk. Invasive species can hitchhike to new islands in many ways – they can be transported in cargo and household goods, in cars or timber, in military equipment or used machinery, and in personal effects such as hiking boots and camping equipment.

Shipping is a particular risk as it is more likely to visit uninhabited islands. Yachts pose a risk in the Pacific. Over 2000 yachts visit the Vavau islands of Tonga each year. Invasive species can be found in the ballast water of ships or clinging to the their hulls.

What can we do about them?

There are five steps that can be taken depending on the invasive situation:
Prevent invasives getting to each island
Detect them quickly if they do
Respond rapidly to the incursion
Control the population
Eradicate the species from the island

The Pacific is a leader in collaborating to address invasive species, The regional invasive species strategy, developed collaboratively by countries and endorsed by them all in 2000, was the first regional strategy of its kind in the world and provides a framework for efforts to increase country capacity to take the five steps in relation to invasive species, particularly emphasising prevention.

SPREP's work on invasives

This essay was written by Liz Dovey, Bird Conservation and Invasive Species Officer, SPREP
Go to "Bird Conservation and Invasive Species" page